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  • 1990-1994  (290)
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  • 1990  (290)
  • Physical Chemistry  (232)
  • Industrial Chemistry
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  • 1990-1994  (290)
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  • 1
    Electronic Resource
    Electronic Resource
    Sodium compounds as catalysts for methanol dehydrogenation to water-free formaldehydePaper presented at the “DECHEMA-Fachausschuß-Sitzung Technische Reaktionen” February 27 to March 1, 1989. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 145-149 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Formaldehyde is produced industrially from methanol by partial oxidation of oxidative dehydrogenation. In these processes, water is formed as a by-product. Anhydrous formaldehyde is required for many syntheses and, therefore, its production is of potential interest. In the present study, catalysts based on alkali compounds were found to be active in the dehydrogenation of methanol if absence of oxygen. Sodium carbonate doped with indium shows a selective of up to 75% for methanol conversion not exceeding 60%.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130120
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  • 2
    Electronic Resource
    Electronic Resource
    Characterization of Cu and K containing Fe/Mn oxide catalysts for fischer-tropsch synthesisDedicated to Professor Dr. Hansjörg Sinn on the occasion of his 60th birthday (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 156-161 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Copper and potassium containing Fe/Mn oxide catalysts for Fischer-Tropsch synthesis were investigated by X-ray microprobe technique, scanning electron microscopy, low-temperature argon sorption and carbon monoxide and carbon dioxide chemisorption at -80°C. The specific surface areas of the catalysts depend on the preparation method, e.g. addition of K or Cu by coprecipitation leads to an increase while impregnation results in a decrease in surface area. The resulting samples are inhomogeneous, as shown by all method. Mn and especially K accumulated on the surface of the catalysts. Addition of Cu and K considerably altered the selectivity and activity of the Fe/Mn oxide catalyst. High potassium contents produced high olefin to paraffin ratios but these catalysts became rapidly deactivated. Copper and a very small addition of potassium led to a very low olefin to paraffin ratio but showed a high and constant activity.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130122
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of flooding gas velocity and liquid hold-up at flooding in packed columns for gas/liquid systemsPresented in part at the “GVC-Jahrenstreffen der Verfahrens-Ingenieure”, Strasbourg (France), September 17 to 19, 1986. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 184-196 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new model of suspended bed of droplets for describing the vaour or gas the vapour or gas velocity at the flooding point in packed of columns for rectification and absorption under vacuum and normal pressure is presented metallic, ceramic and plastic packings with diameters of 8-90 mm as well on sheet metal and gauze packings, in a wide range of liquid and vapour loads. Approximately 650 literature measurements and own data were evaluated. The mean relative error in determining the gas velocity at flooding point is less than ±5%. On the basis of the double layer model, a new equation was derived for the hold-up at flooding point, which is needed for the calculation of the flooding gas velocity. An example of calculations for sample applications is also included.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130125
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  • 4
    Electronic Resource
    Electronic Resource
    Batch cooling crystallization at constant supersaturation: Technique and experimental results (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 229-237 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new laboratory plant for batch cooling crystallization is described, which allows to maintain the supersaturation at a constant level during an experimental run. A method for continuous supersaturation measurements has been developed, using a density meter and a hydrocyclone. Experimental results obtained from a seeded solution in constant supersaturation cooling mode and at constant cooling rate are compared. In the case of a constant cooling rate, the supersaturation passes through a sharp maximum, whereby effective nucleation is enhanced. As a consequence, a smaller median crystal size is obtained than for cooling at constant supersaturation. Equation for controlled cooling at a constant supersaturation require an accurate description of the effective rate of nucleation. Therefore, the mechanical stress, to which the crystals are subjected, must be included as the main source of new nuclei. This is shown by the influence of stirrer on batch time.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130131
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal decomposition of 2, 3-dimethyl butane: Experiments and mechanistic modelling (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 241-251 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Pyrolysis of 2,3-dimethyl butane (DMB) was carried out in a quartz flow reactor in the temperature range from 740 to 1032 K at normal pressure. The input concentration of DMB was 3.3 × 10-3 mol/1 using argon as diluent. Reaction time ranged between 3.1 and 3.9 s. The following products were analyzed by two-column gas chromatography: hydrogen, methane, ethene, propane, propene, butenes, butadiene, 2-methyl-2-butene, isoprene, benzene and toluene. Compared to thermal decomposition of n-hexane under similar experimental conditions, the main difference concerned the formation of ethylene, ethane and branched alkanes. A reaction model, based on elementary reactions, was developed to predict the experimental results and to verify our data basis of elementary reactions under different conditions. The model gives a quantitative description of the complex chemistry of the process. In addition, an algorithm is presented for model reduction.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130133
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  • 6
    Electronic Resource
    Electronic Resource
    New and overlooked relationships for turbulent flow in channelsPaper base on a poster at the “Jahrestreffen der Verfahrens-In-genieure”, Berlin, September 27 to 29, 1989. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 264-272 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper describes general, asymptotic and speculative relationships which can be deduced directly from the time-averaged form of the basic, partial-differential model for the conservation of mass and momentum in fully developed turbulent flow of constant-property fluids through round and parallel-plate channels. Such relationship are shown to provide insight as well as useful forms for correlation. Several analogies for flow in round tubes and between parallel plates which have generally been overlooked are reexamined and extended. A generally overlooked anomaly which occurs for flow in concentric, circular annuli, for flow between plates of non-identical roughness, and for the combination of forced and wall-Ind.uced flow between parallel plates is also is noted. The data needed to test the above analogies and to quantify the deviations, if any identified, as well as those needed to generalize the anomalous behavior.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130136
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  • 7
    Electronic Resource
    Electronic Resource
    Evaluation of standard thermodynamic parameters for the sorption of n-hexane and methanol in zeolites (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 298-303 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Adsorption isotherms for n-hexane and methanol in mordenite and ZSM5 in the temperature range from 323 K to 473 K were found to be of type 1. The adsorbate-adsorbent interaction (C1) and adsorbate-adsorbate interaction (C2) wee computed according to Bradley and Wilkins model, whereas the Rees and Williams model predicts the adsorption characteristics. Finally, the thermodynamic parameters such as ΔGo, ΔSo, ΔHo, K, K+ have been evaluated for the sorption of n-hexane in mordenite and ZSM5.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130140
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  • 8
    Electronic Resource
    Electronic Resource
    Heavy metal recovery by extraction and permeation in incineration preocessesPaper presented by H.-J. Bart at the “Jahrestreffen der Verfahrens-In-genieure”, Berlin, September 27 to 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 313-318 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Incineration processes are critical for the environment. SO2 and NOX removal with processes is nowadays commonplace. Up to now, heavy metal were recovered via precipitation. The alternative use of liquid ion exchange techniques offers an easy re-use of the heavy metals, which are obtained as concentrates. A separation process is described, starting from laboratory experiments and ending with pilot plant field tests. A cost comparison for extraction, permeation and precipitation gives the scope of the necessary expenses for such environmentally controlled processes.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130142
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  • 9
    Electronic Resource
    Electronic Resource
    Adsorption and catalytic reactions of NO and NH3 on activated carbonPaper presented by E. Richter at the “Jahrestreffen der Verfahrens-In-genieure”, Berlin September 27 to 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 332-340 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In industrial processes, the reduction of nitrogen oxides by ammonia on activated carbons is carried out at temperatures between 90 and 190 °C. Adsorption of NO and NH3 on the catalyst was investigated separately. Reactions models for NO-reduction by carbon and ammonia were derived from experiments carried out in an integral reactor. In each case, the formation of an adsorbed (NO2)-complex is an important step. The kinetics of both reactions was described by modified Langmuir-Hinshelwood equations.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130146
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  • 10
    Electronic Resource
    Electronic Resource
    Computation of plate columns for NOx absorption by a new stage-to-stage method (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 289-297 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new stage-to-stage method has been developed for the calculation of NXx absorption columns. Each stage of the absorption column is simulated as a combination of a bubble column reactor (absorption) and an adiabatic plug for reactor (oxidation). The bubble column reactor is modelled as two single stirred tank reactors, one as a gas-phase and one as a liquid-phase reactor, both coupled by mass and heat transfer. In this hydrodynamic model, a dynamic approach is adopted, in which the gas-phase transport of N2O4 is the limiting step for the absorption. A gas-phasepseudo-enhancement for factor for N2O4 is therefore introduced. The balance equations for a single phase of the bubble column are solved with a Newton-Raphson algorithm. The entire column calculation is divided into a gas and a liquid side. On both sides, the stage-to-stage method is applied in such way that the overall calculation is performed as a loop process. The direction of the loop calculation follows that of the flow: gas-side upwards and liquid-side downwards.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130139
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  • 11
    Electronic Resource
    Electronic Resource
    A reaction model for the electrochemical synthesis of adipontrile (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 376-383 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A theoretical and experimental study of the electrohydrodimerization process to produce adiponitrile is used to determine an appropriate reaction model. From numerical simulations of five proposed reaction schemes and subsequent comparison with experimental data, the most favoured route is via an anion, intermediate of acrylonitrile. This route, a five step reaction involving electrochemical and chemical reaction in a diffusion/reaction layer, gives good predictions of product distributions over a wide range of current densities and acrylonitrile concentrations of product distributions over a wide range of current densities and acrylonitrile concentrations.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130151
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  • 12
    Electronic Resource
    Electronic Resource
    Some strategies for the kinetic study of complex heterogeneous catalytic reactions (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 397-402 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This paper presents a method of transforming the non-liner regression problem in the kinetic study of complex heterogeneous catalytic reactions into a linear regression problem. Application of this method reduced the number of parameters to be estimated by n-1, where n is the number of independent reactions. In addition, a stepwise model discrimination strategy in introduced to reduce the number of equation sets ad equations in the set undergoing parameter estimation. These two new approaches are very advantageous in reducing the computation effort, especially when the number of independent reactions is large. The linear regression method and the stepwise model discrimination strategy are successfully applied in the kinetic study of the methanol synthesis system in which the formation rates of methanol, methane, ethanol and ethane are considered.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130154
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  • 13
    Electronic Resource
    Electronic Resource
    Modern carbon fibres from polyacrylonitrile (PAN)-polyheteroaromatics with preferred orientationDedicated to Professor Hansjörg Sinn on the occasion of his 60th birthday (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 41-49 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This contribution presents the mechanical data of high performance carbon fibres currently available on the market, based on experimental studies on stabilization and pyrolysis of PAN (SAF) from Courtaulds. The effects of stabilization and carbonization temperatures on the properties as well as on the ultra- and crystalline structures of the fibres are shown in more detail.
    Additional Material: 22 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130107
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  • 14
    Electronic Resource
    Electronic Resource
    Residence time distribution and hold-up in a cocurrent upflow packed bed reactor at elevated pressureDedicated to Professor Ewald Wicke on the occasion of his 75th birthday (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 27-40 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The residence time distribution in liquid phase was measured in a cocurrent upflow packed bed reactor for the system methanol-hydrogen at low Reynolds numbers and at elevated pressure. The plug flow with axial dispersion model was used to describe mixing in the system. The imperfect pulse method was used to measure the system response to a tracer pulse input. The parameters were calculated using the weighted moments method. The influence of the weighting factor was investigated. The experimental and theoretical outputs, as calculated by convolution, agreed very well. Different types of correlations were used for the Bodenstein number and liquid hold-up. From these correlations, the optimal one was selected for each parameter. A comparison was made between the ordinary moments and the weighted moments methods which led to the conclusion that the latter method is superior with respect to the accuracy of the estimated parameters and therefore strongly recommended.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130106
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  • 15
    Electronic Resource
    Electronic Resource
    Modelling of a fluidized bed bioreactor for immobilized enzymes (Part 1)Paper presented by T. Kiesser at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 20-26 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the first part of this paper, a mathematical model is presented for a liquid fluidized bed bioreactor using immobilized enzymes with reversible Michaelis-Menten kinetics. The model is based on the axial dispersion model for the bulk liquid phase. Inter- and intraparticle mass transfer as well as enzyme catalyzed reaction inside the porous beads are considered. The overall efficiency of the biocatalysts is calculated by a numerical routine. For the calculation of the concentration profile inside the reactor, a semi-analytical solution is derived which takes into account the height dependence of the effectiveness factor.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130105
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  • 16
    Electronic Resource
    Electronic Resource
    Influence of feed solids concentration on the performance of hydrocyclonesPaper presented by Th. Braun at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 15-20 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Even though the influence of solids concentration in the feed on the separation efficiency of hydrocyclones has long been recognized, a systematic research on the change in pressure drop across the hydrocyclone and the latter's separation characteristics has thus far been lacking. If all other operating parameters are kept constant, an increase in feed concentration generally leads to a coarser cut size, reduced sharpness of separation and a rise in pressure drop. Apart from the particles hindering one another's radial motion, the limited capacity of the apex valve and the changes in the flow field within the hydrocyclone cause additional particles to be entrained by the overflow. The flow ratio thus becomes an additional parameter in determining the cyclone efficiency. A theoretical model, which takes these effects into account, has been developed and successfully tested against experimental data.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130104
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  • 17
    Electronic Resource
    Electronic Resource
    Effect of nuclei storage and growth rate dispersion on the transient behaviour of continuous crystallizers (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 63-71 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Bench scale experiments and computer simulations of transient crystal size distributions obtained in a 1.4 m3 sucrose crystallizer, which prove the existence of nuclei stock, are presented. This stock represents a large number of non-growing nuclei, which can be activated at increased supersaturations. The nuclei stock attenuates the dynamic behaviour of crystallization process.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130109
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  • 18
    Electronic Resource
    Electronic Resource
    On supersaturation during mass crystallization from solutionPaper presented by M. Kind at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 50-62 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Supersaturation is the driving force for crystallization from solution. For design and operation of crystallization processes, it is necessary to apply a set of criteria for the determination of appropriate or even optimum supersaturation. In this paper we present and discuss the results of our experimental and theoretical investigations on supersaturation during crystallization from solution. While the determination of the metastable zone width of the solution is frequently applied as a fast check on solution behaviour, we demonstrate that the determination of the induction period of the supersaturated solution is a useful aid in ascertaining the maximum allowable supersaturation. Theoretical considerations and experiments confirm that the induction period dependssoley on growth kinetics if secondary nucleation is the predominant mechanism. In order to avoid uncontrollable spontaneous value of between 70 and 130 μm during crystallization. Since growth kinetics turns out to be the only important system property for the determination of maximum possible supersaturation, we conclude the paper with some arguments concerning a closed representation of growth kinetics.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130108
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  • 19
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    Electronic Resource
    Biological treatment of effluents from a coal tar refinery using immobilized biomassPaper presented by P. Hüppe at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 73-79 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An airlift-loop reactor with a fluidized bed was used for the microbiological removal of a complex mixture of aromatic substances originating from coal tar process waters. A specially adapted mixed microbial culture derived from several soil and sludge samples was immobilized on fluidized sand particles and retained in a reactor at high biomas concentrations of 3 to 16 g dry matter per liter, depending on the COD-load. In a two-stage pilot plant, those aromatic substances which passed through the first stage either unaltered or only partially oxidized were effectively eliminated by the immobilized biomass in the second stage. Whereas most of the waste water components such as phenols and quinoline were already degraded by a conventional activated sludge system in the first stage, the majority of nitrogen-containing aromatic bases could be sufficiently eliminated with specially adapted micro-organisms in the second stage. Although the COD-feed load was increased to 12 and 15 kg m-3 d-1 in the first and second stages, respectively, it was removed to the extent of 87% on the average with an overall residence time varying between 11.5 and 29 h.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130110
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  • 20
    Electronic Resource
    Electronic Resource
    Foam breaking by high speed rotors (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 86-96 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The first part of this paper presents a relationship for the minimum velocity of rotating installations for foam breaking. The derivation is based on equilibrium of inertia and surface forces. Inertia forces occur during the acceleration of foam bubbles and act mainly at the plateau borders. High and definite acceleration can be obtained with a deformer composed of a rotor and a stator. The surface force is due to the dynamic surface tension because surface-active solutions react to a rapid change in surface area by altering their surface tension. The theoretical relationship is compared with experimental results of minimum velocities needed to break foams produced from aqueous solutions of detergents. The equation presented here explains why measured minimum velocities often range between 10 and 20 m/s. The second part of the paper deals with condensation of continuously generated foam in a closed system. In the process of condensation, foam is not completely separated into liquid and gas phase but turns into foam with small bubbles and high density. The collapse of this condensed foam must be considered for the control of persistent foams in a closed system. The collapse of foams made of aqueous solutions of different surface-active agents has been investigated. Different highly surface-active agents show small variations in times of coalescence. A relationship for the lifetime is given, which is based on laminar flow along plateau borders. Recommendations are made with respect to the geometry of the foam breaker, scale-up and operating variables such as rotational speed of the foam breaker and gas flow rate.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130112
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  • 21
    Electronic Resource
    Electronic Resource
    Mixing in continuous DTB and FC crystallizers (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 349-356 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Owing to imperfect mixing, the theoretical prediction of CSD for an MSMPR crystallizer deviates from the experimental results. In the present work, different modelling approaches were adopted to account for incomplete mixing in DTB and FC crystallizers. For DTB crystallizers, compartmental model, based on an earlier work of Nyvlt et al. has been proposed. For FC crystallizers, a mixed model comprising perfectly mixed and plug flow regimes has been put forward. This is based on the tracer response studies reported by de Jong. Predicted results were compared with experimental data of Bennett and van Buren for continuous urea crystallizers.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130148
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    Selection and design of aerobic bioreactorsModified version of a paper presented by A. Mersmann at the “Jahrestreffen der Verfahrens-Ingenieure”, Berlin, September 27 to 29, 1989.Dedicated to Professor Kurt Dialer on the occasion of his 70th birthday (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 357-370 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Compared to chemical reactors, there are additional requirements to be considered when selecting and designing a bioreactor. The cultivated organisms and most of the desired products are to a greater or lesser extent sensitive to temperature, pH and Shear stress. Furthermore, sterilization often plays an important role in maintaining a monoseptic process. Many design procedures for chemical reactors can be applied but requirements which are relevant to the biological system are sometimes decisive. Consequently, it is useful to first consider the essential features of the organisms with respect to the selection and design of bioreactors. Attention must be paid to the fermentation medium because its flow behaviour can range from slightly viscous and Newtonian to highly viscous, non-Newtonian. Many papers deal with low viscosity fermentation broths [1-5]. However, little is known about the design of bioreactors for highly viscous non-Newtonian liquids. Fundamentals for the design of bioreactors are presented. It has been attempted to apply theoretical equations suitable for both, low viscosity Newtonian and high viscosity non-Newtonian fermentation broths. Apart from the calculation procedure for the OTR-values, the difference between global and local values within bioreactor is demonstrated by means of velocity and shear stress profiles. Special requirements for bioreactors such as prevention of excessive foaming, shear sensitivity of micro-organisms and cell-lines and effective sterilization are also discussed.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130149
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  • 23
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    Monte carlo simulation of transient CSD in a continuous crystallizer (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 392-397 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A Monte Carlo simulation scheme is proposed for transient crystal size distribution in a continuous crystallizer. The suggested scheme can taken into account dispersion effects of growth rate, shape factor and birth size on crystal size distribution. This method is simple and more versatile than solution of the number balance equation or the finite-state Markov chain model. The proposed algorithm of the process has a very simple structure and can be easily implemented on a personal computer. The present contribution is extension of an earlier work of Sen Gupta and Dutta.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130153
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  • 24
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    Fluid dynamics of pulsed sieve plate extraction columnsPaper presented by M. Lorenz at the “Jahrestreffen der Verfahrens-In-genieure”, Berlin, September 27 to 29, 1989. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 411-422 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The presented contribution reports on comprehensive hydrodynamic investigations in two pulsed sieve-plate extraction columns (PSE) on a pilot scale. The experiments were conducted with three different sieve plate geometries employing test systems recommended by EFCE, under varying pulsation conditions and throughputs. The results of the investigation add to the existing knowledge of relationships between hydrodynamic parameters, drop size, hold-up, flooding throughput and mixing and operating parameters. They also provide useful information for scale up, selection of sieve-plate geometry, most favorable operating range, and constructive design of equipment. On the basis of measurements, analytical methods are recommended for prediction of PSE hydrodynamics.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130156
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  • 25
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    The implications of carboxylic acid propertiesDedicated to Professor, Dr. rer. nat. Wolfgang Hilger on the occasion of his 60th birthday (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 304-312 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Some properties of carboxylic acids are reviewed, with emphasis on recent experimental data, Qualified, consistent latent heat of vaporization data were developed for the series and a two-population viewpoint is suggested. The equation of state formulated by Grenzheuser [1] is also recommended as a practical tool, and its further development is urged.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130141
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  • 26
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    The linear relationship between stoichiometry and dimensional analysis (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 328-332 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The linear algebraic character of the formal representation of chemical species and their reactions is compared with the procedure of searching for dimensionless numbers in a set of physical quantities. A straightforward algorithm is presented to find a finite set of solutions to the relevant system of “balance equations”, the so-called minimal (or simple) solutions. At the third stage of the hierarchy thus established, “mechanisms” among reactions as well as “representations” among dimensionless group can also be defined.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130145
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  • 27
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    A fluid-dynamically based model of bubble column reactorsPaper presented by H.-E. Gasche at the “Jahrestreffen der Verfahrens-Ingenieure”, Berlin, September 27 to 29, 1989. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 341-349 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A heterogeneous fluid dynamic model has been developed to describe the complex flow structure of two-phase in bubble columns. The equation of continuity and momentum balances form the basis of the model. Coupling of the two phases occurs via an interaction force, deduced by a force balance around a single rising bubble. Multiphase flow mixing processes are taken into consideration by introducing turbulent viscosities of the two phases involved. The Simulation program was extended to reactive system, taking into account the mass balances of a second order gas-liquid chemical reaction as well as the different absorption/reaction regimes. The gas phase concentration profiles show pronounced axial and radial dependences, while the liquid phase can be regarded as a CSTR with respect to the liquid component. With reference to the gaseous component, which is being absorbed in the liquid phase, the degree of back mixing does not show CSTR behaviour as the influence of different absorption conditions in different axial and radial reactor positions is superposed on that of turbulent motion of the liquid carrier of the dissolved gaseous component.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130147
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  • 28
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    Masthead (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990) 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130101
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  • 29
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    Study on dynamic behaviour of thermally coupled distillation processes (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 119-125 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A dynamic mathematical model has been developed which is suitable for thermally coupled distillation processes. An algorithm known as the equation-decoupled method was used for simulation. EPISODE software and LU decomposition method were adopted to solve the ordinary differential and algebraic equations of the model, respectively. The initial conditions, viz. a solution for the steady state of the process in dynamics simulation were obtained by means of modified Naphtali-Sandholm algorithm. Research on the dynamic behaviour of thermally coupled distillation processes was carried out on two examples. It was found, via the dynamic simulation, that a disturbance in the distribution of vapour coupled stream has a large effect on the composition of vapour side withdrawal and, similarly, for liquid coupled stream, on that of liquid side withdrawal when the fraction of side withdrawal is fixed, and a smaller effect when the quantity of side withdrawal is fixed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130116
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  • 30
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    Growth rate dispersion in a continuous sucrose crystallizer and its effect on CSD (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 196-202 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A Random Crystal Growth (RCG)model is proposed to predict CSD in a continuous MSMPR crystallizer when the crystals exhibit growth rate dispersion. RCG model links two well-known models of growth rate dispersion, namely the Random Fluctuation (RF) and Constant Crystal Growth (CCG) Models. Monte Carlo simulation has been employed to solve the model equations. Predicted results are compared with experimental CSD data on sucrose reported by Bennett.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130126
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  • 31
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    Simple new formulae for efficiency and mean temperature difference in heat echangersPaper based on a poster presentation at the “Jahrestreffen der Ver-fahrens-Ingenieure”, Berlin, Sept. 26 to 29, 1989 (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 237-241 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The well-known formulae for efficiency and mean temperature difference of a heat exchanger as functions of its numbers of transfer units, or dimensionless lengths, can be written in a more compact form by introducing the auxiliary function ϕ(x) = x/(1 - e-x). The resulting new formulae show a number of advantages: They are shorter, easier to memorize, and in many cases the limiting values can be seen more directly. They may therefore contribute to easier and faster heat exchanger design, and to reduced probability of errors in the relevant calculations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130132
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  • 32
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    Deasphaltization and demetalling of heavy crude oils and distillation residues with CO2 (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 258-264 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Deasphaltization of heavy crude oils and distillation residues may reduce the metal content of these oils to such an extend that the upgrading of deasphaltized oil in a catalytic process becomes economically feasible. Experimental results of deasphaltization of Boscan crude from Venezuela, using subcritical and supercritical carbon dioxide as deasphaltizing agent, are presented. Deasphaltization and demetalling with CO2 in the supercritical state is more effective. Under favorable conditions, the deasphaltized oil contains practically no asphaltenes and the metal content is reduced by 690 wt-%. The influence of n-heptane or n-pentane addition to the crude, which lowers viscosity and promotes flocculation, is also discussed. Furthermore, a multistage deasphaltization process is more efficient than a single stage process.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130135
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  • 33
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    Sensitivity analysis of catalytic conversion of n-C6 (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 277-288 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The present paper is a case study of an application of sensitivity analysis in chemical kinetics. Emphasis is laid upon chemical interpretation of sensitivity information and on identification of the most important model important model parameters. The kinetic model for reforming of C6 hydrocarbons proposed by Mobil [14] is extended to the analysis of the behavior of n-hexane conversion in an adiabatic reactor. The importance of six initial conditions (feed composition and initial temperature) is analyzed by the computation of normalized first order sensitivity gradients (y1o/y) (δyi/δy1o). The relative importance of 21 model parameters αj is estimated by the computation of normalized sensitivity gradients of the type (αj/yi) (δyi/δαj). The influence of the decisive model parameters ΔH6o and ΔH3o (activation enthalpies of benzene hydrogenation and methyl cyclopentane isomerization, respectively) as well as operating parameters is presented. The problem of uncertainly in the value of ΔH6o and its influence on the model solution is also sown. Finally, some advantages of the application of normalized gradients of the explanation of process behavior are discussed.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130138
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  • 34
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    Modeling and simulation of reactions involving bifunctional catalysts (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 319-322 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model based on experimental results is set up for a typical model reaction of hydrocarbon reforming, namely the dehydroisomerization of methyl cyclopentane. Computer simulations shows that the existing theory about the reaction path of hydrocracking reactions involving bifunctional catalysts may be only partly valid.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130143
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  • 35
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    Inertial deposition on front and rear sides of ribbons at intermediate and high reynolds numbers (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 322-327 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Deposition of particles from gas flows on ribbons in normally expected on the front side. Collision efficiencies of ribbons are presented for this case, obtained by means of single particle trajectory computation, which is based on numerically determined flow fields in the Reynolds number range between 2 and 50 and on the potential flow model. Further, it is shown, that deposition of particles on the rear side can be caused by eddylike motion of the fluid in the wake of the ribbon. For this to occur, two conditions must be fulfilled: the free shear layer between the wake and the outer flow must be turbulent to cause lateral transfer of particles into the wake and the Stokes number may not exceed 0.5.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130144
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  • 36
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    Anodic dehalogenation of 1,2-dichloroethane in aqueous electrolytesDedicated to Professor Dr. Karl-Hans Simmrock on the occasion of his 60th birthday (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 371-375 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A solution of 0.1 M 1,2-dichloroethane in 1 M H2SO4 was anodically converted to CO2, Cl2 and HCIO4 as the main products at smooth platinum. The current efficiency for CO2 exceeds 60% at low current densities, while HClO4 is obtained with about 20% current efficiency. Chlorinated products such as 1,2′,2-trichloroethane are formed in negligible amounts. Platinum plays a distinctive role as anode material and shows a reaction limited anodic prewave. Our experimental findings lead to a mechanism, whereby DCE is initially hydroxylated to form chloroacetaldehyde chlorohydrin which releases HCl and becomes rapidly further oxidized to monochloroacetic acid. The cleavage of the C—C bond proceeds via its anodic decarboxylation. Possible practical applications in the field of anodic water purification and in the direct electrosynthesis of vinyl chloride are discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130150
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    Collection of fine adhesive and cohesive dusts with pluse-jet fabric filersPaper presented by E. Schmidt at the “Jahrestreffen der Verfahrens-Ingenieure”, Berlin, September 27 to 29, 1989. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 402-410 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The collection of reactive and therefore extremely adhesive and cohesive fine particles (〈 1 μm) by means of bag filters with pulse-jet cleaning may present problems. The electron-beam dry scrubbing (EBDS) process, used to remove SO2 and Nox in a power plant of the Badenwerk AG, Karlsruhe, serves as an example. To solve the occurring problems and achieve a satisfactory filter performance, extensive know-how of process engineering is necessary. This contribution deal with the following aspects: construction of the cleaning system, selection of filter medium, precoating, and dosage of an auxiliary dust during filtration.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130155
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    Measurement of transient deformations by double-pulsed holographyPaper presented by M. Hajduk at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 1-8 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Holographic interferometry is used for the determination of surface deformation of items of equipment. The material failure which caused the surface deformation can then be identified. Because a double-pulsed laser is used to plot the hologram, non-vibration stabilized holographic equipment is necessary. Thus, non-destructive testing of equipment components is also possible during plant operation. In this report, we present the experimental results of non-destructive testing of composite materials. We examined centrifugally cast pipes and filament wound pipes, which were made from glass fibre reinforced plastic and carbon fibre reinforced graphite. As a rule, the severity of failure is characterized by the apparent perturbation of its holographically stored fringe pattern. In this report, we present the experimental results which yield the relationship between the perturbation of interference fringes and the extent of the specific types of failure. Measurement results were compared with displacements calculated by the finite element method. By using the interferogram, and with the knowledge of tension stress beneath the surface, the size of the crack can be estimated. The size of the smallest detectable flaw was clearly smaller than the critical flaw size. Thus, holographic interferometry is suitable for detecting damage to cylindrical containers.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130102
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    Breakthrough behaviour of a binary gas mixture with azeotropic adsorption equilibriumPaper presented by C. Persichini at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 8-14 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This contribution reports on the breakthrough behaviour of binary gas mixtures with ideal and non-ideal multicomponent adsorption equilibria. Investigations were carried out on mixtures CO2/C2H4 and C2H4/C2H6, both adsorbed on molecular sieve 5A (ms5A). The adsorption equilibrium of the system CO2/C2H4/ms5A may exhibit azeotropic behaviour, which subsides with decreasing active pressure (= sum of partial pressures of adsorbable components) or on raising the temperature. In contrast, the system C2H4/C2H6/ms5A maintains its ideal behaviour also at higher active pressures or lower temperatures. Attempts to calculate the non-ideal adsorption equilibrium from measured single component isotherms have failed when known models were applied. The investigation of the effect of azeotropic equilibrium on the fixed bed adsorption led to intersecting breakthrough curves of the two components. This behaviour is due to a displacement of equilibrium caused by the change in the active pressure and partial pressures, and a superposed temperature effect. This can be shown by calculating the breakthrough curves with the equilibrium model.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130103
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  • 40
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    Modelling of a fluidized bed bioreactor for immobilized enzymes (Part 2)Paper presented by T. Kiesser at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 80-85 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In the first part of this contribution, a mathematical model was presented for a liquid fluidized bed using immobilized enzymes, with reversible Michaelis-Menten kinetics. This part is focused on the experimental results. The reaction kinetics of native and immobilized enzymes was determined in continuous stirred tank reactors under comparable conditions. The influence of external mass transfer was investigated in a fixed bed reactor column. The extend of pore diffusional resistance was examined in a continuous stirred tank reactor and with a numerical simulation. Hydrodynamics was measured in different reactor columns (diameter dt = 0.052 - 0.225 m; length L: 1.0-2.0m) and with a static mixer. Further, the concentration profile was determined in a fluidized bed reactor with side stream analysis for different biocatalyst samples, fluid velocities and bed heights. The simulation of experimental results indicates that they are well described by the developed model. Furthermore, the model is well suited to predicting the influence of specific parameters on the effective kinetics of the biocatalyst and the expansion of the fluidized bed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130111
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  • 41
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    Absorption of NO2/N2O4 in nitric acid (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 97-101 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Laboratory-scale measurements were performed on the absorption of NO2 gas into diluted nitric acid. The concentration of NO2 gas, which represents an NO2/N2O4 equilibrium, varied from 1000 to 20000 ppm, the carrier gas being nitrogen. The concentration of nitric acid ranged from 15 to 60 mass-%. The absorption experiments were carried out in a double stirred cell, with a defined gas/liquid interface as the mass transfer area. The liquid phase was conducted periodically and the gas phase continuously. Mass flow rates were determined. The well-known film model of absorption was used for analyzing the experimental results. Only the N2O4 species was considered to pass the gas/liquid interface. The measured data yielded values of HN2O4(k D1)1/2 as well as their variation with temperature and nitric acid concentration.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130113
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  • 42
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    Modelling of thermal desorption of active coke loaded with sulphuric acid and ammonium sulphatePaper presented at the “Jahrestreffen der Verfahrens-Ingenieure”, Hannover, September 21 to 23, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 101-112 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The BF-Uhde-Mitsui Process uses active coke for SO2- and NOx-removal from flue gases in the temperature range between 100 and 190 °C, Experimental methods of thermal regeneration were applied to the evaluation of the state of the adsorbent after use in flue gas cleaning and of the parameters for disrober design. A reaction model was derived from experiments carried out in differential and back-mix reactors. The parameters were evaluated by adaptation of the model to the adsorption spectra. The model was successfully applied to the regeneration of active coke in a fluidized bed reactor.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130114
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  • 43
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    Mass transfer in countercurrent and cocurrent bubble columns (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 113-118 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The hydrodynamic and mass transfer characteristics in countercurrent, cocurrent and liquid batch operations with various Newtonian liquids were studied experimentally using the same bubble column. Taking the effect of gas sparger geometries, operating variables and liquid properties into account, empirical correlations were obtained for the gas hold-up and the volumetric liquid-phase mass transfer coefficient.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130115
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    Critical temperatures and pressures and high temperature vapour pressures of seven alcohols (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 125-130 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Critical temperatures and pressures have been determined experimentally for the four lowest n-alcohols, 2-propanol, 2-butanol, and 2-methyl-1-propanol, and are given in the penultimate line of Table 3. The last line of Table 3 lists the weighted mean critical pressures, with the corresponding critical temperatures obtained from he vapour pressure equation. Comparison with the corresponding data from standard reference books reveals deviations from the experimental data in some [2, 4] and incorrect critical pressure for ethanol in all five reference books quoted in Table 3. In addition, vapour pressure data were obtained for the same alcohols in the temperature range approaching the critical point. The measurements are reproduced by the simplified Clausius-Clapeyron equation with the constants and standard deviation given in Table 2.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130117
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  • 45
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    Influence of geometric and thermophysical properties of reaction layer on sulphur dioxide oxidation in transient conditions (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 131-135 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The sulphur dioxide to sulphur trioxide oxidation process in a fixed bed catalytic reactor is simulated in the case of cyclic change in the direction of the reaction mixture feed. It is shown that, for transient condition, the amount of catalyst in the reactor may be substantially reduced by its partial substitution with inert material of suitable form, dimensions and thermophysical properties, at the end of the layer. This makes the direct regenerative heat transfer process in these zones controllable, producing the same conversion and overall height of the layer. The results are significant for sulphuric acid production from gases poor in sulphur dioxide.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130118
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  • 46
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    Influence of gas flow on heat transfer in film condensation (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 136-143 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For the dimensioning of condensers in film condensation, the heat transfer coefficient between film surface and cooled tube wall must be known. Generally, Nusselt equations are used which have been verified by experiments. When there is no significant gas flow, a large number of equations correlate the experimental. data very well. The description of heat transfer enhancement by a significant gas flow is not sufficiently covered by the available literature. For film wise condensation in a vertical tube, a calculation method is presented which reproduces this phenomenon characterized by the interfacial shear stress at the film surface. This method is based on the assumption that, in the proximity of gas flow, the condensation process also affects the interfacial shear stress. A comparison with known experimental local Nusselt numbers showed a good agreement with water as the fluid. For test fluid MWA, which was used by Blangetti, the measured values show only a moderate agreement with theoretical calculations. Possibly, this is related to entertainment which occurred during measurements at film Reynolds numbers of over 80.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130119
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  • 47
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    Formation of Di-isobutene, main by-product of methyl tertiary butyl ethyl ether synthesis catalyzed by ion exchange resin (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 150-156 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental set-up is presented for the measurement of steady-state reaction rates in the liquid phase methyl tertiary butyl ether (MTBE) synthesis from isobutene and methanol using ion exchange resin as catalyst. This apparatus was used for a separate investigation of the main side reaction, i.e., the formation of isobutene dimers (DIB), in the temperature range between 60 and 90°C. The reaction catalyzed by Amberlyst 15 (A15) showed no steady-state behaviour, but the catalytic activity declined at a rate dependent on the reaction conditions. Time constants for activity loss were determined in the range from 3.5 to 30 h. The deactivated A15 catalyst could be regenerated through MTBE synthesis experiment. Deactivation is assumed to be caused by blocking of the microparticle gel phase by higher isobutene oligomers. The DIB formation, using 1-butene as solvent, was of 2nd order with respect to isobutene and showed an apparent activation energy of about 40 kJ/mol.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130121
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  • 48
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    Evaluation of plug flow assumption in packed beds (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 161-171 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Knowledge of modelling and computer simulation is an essential prerequisite for type design and operation of packed bed systems. Unfortunately, the existing models are based on a number of weak assumptions of which plug flow can be considered as a common deficiency. Such a simplification would inevitably have a noticeable bearing on the accuracy of the final design and consequently calls for the development of a coherent mathematical description of the packed bed systems so that reliable design information can be explored. A two-dimensional heterogeneous transient model has been developed which allows for the radial variations of velocity and void age. The model equations have been solved using numerical approximation. The simulated results reveal significant differences between the present refined data and those established from existing plug flow models.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130123
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    Measurements with multi-point microprobes: Effect of suspended solids on the hydrodynamics of bubble columns for application in chemical and biotechnological processesPaper presented by Chr. Wolff at the “GVC Working Party on Multiphase Flow”, Schliersee, Fed. Rep. Germany, April 13 to 15, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 172-184 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Many experimental studies reveal that suspended solids considerably alter the coalescence behaviour and hydrodynamic functions of wo-phase flow. But no systematic efforts have yet been undertaken to separate the effects of different particle properties on local gas hold-up, bubble size and interfacial area gas/liquid. The aim of this paper is to present the local values of these parameters in three-phase fluidized beds of different solids, using miniaturized optical fiber and conductivity needle probes. It is shown that particle concentration, size and, in particular, density are decisive for the change in coalescence behaviour. Ranges of normal (ϱS 〉 ϱL) and inverse fluidization (ϱS 〈 ϱL) must be distinguished and the flow regime also exerts a strong influence on the interactions between the dispersed phases, the transition point itself being a function of particle properties can be observed, This effect is evaluated for different column diameters, between 0.1 and 0.3 m.
    Additional Material: 13 Ill.
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    URL: http://dx.doi.org/10.1002/ceat.270130124
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    Agitation of aerated emulsionsPaper presented by T. Schneider at the internal meeting of the GVC-working party “Mixing” at Breisach, West-Germany, 3 May, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 209-213 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Aerated emulsions are gaining significance in fermentation as well as in inorganic and organic chemistry. In these processes, liquid-liquid mass transfer can be the limiting step. Therefore, the effect of gassing rate on droplet size was investigated as a function of dispersed liquid phase concentration and power input in different vessels. At high power inputs, the droplet size decreased. With increasing dispersed phase concentration and gassing rate, the droplet size increased and its dependence on power input subsided.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130128
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    Motionless mixers for the design of multitubular polymerization reactors (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 214-220 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental investigations of thermal bulk polymerization of styrene in pilot plants of different sizes have been performed. Each pilot plant is composed of a tubular recycle reactor, connected in series with a tubular reactor, both completely filled with Sulzer motionless mixers. Kinetic, reactor and viscosity models have been verified in a wide range of styrene conversions (up to 96%) temperatures (up to 210 °C) and polystyrene molar masses (up to 360 000). Scale-up studies were carried out which confirmed that multitubular reactors of special design can be applied for industrial polymerization process.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130129
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    Large-scale anaerobic/aerobic treatment of complex industrial wastewater using immobilized biomass in fluidized bed and air-lift suspension reactorsPaper presented by J. J. Heijnen at the GVC-VDI Congress “Verfahrenstechnik Abwasserreinigung”, Baden-Baden. October 17 to 19, 1988. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 202-208 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Warm concentrated industrial wastewaters are preferably treated in an anaerobic reactor for reasons of energy generation and low surplus sludge production. Problems to be solved in the practical application concern a low growth rate of the micro-organisms, their low settling rate, process instability and the need for after treatment of the noxious anaerobic effluent which often contains NH4+ and HS-. The use of biomass immobilized on small suspended carriers (〈 0.5 mm) has proven to be a suitable means to overcome most of these problems. Results are presented on pilot and full-scale pretreatment of industrial wastewater in an anaerobic 2-state fluidized bed reactor for CH4-production and laboratory and pilot scale post-treatment of the anaerobic effluent, which contains NH4+ and HS- in an aerobic air-lift suspension reactor for the production of NO3- and SO42-.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130127
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    Contribution to solving the problem of dioxins generated during waste incinerationPaper presented by H. Vogg at the “Jahrestreffen der Verfahrens-In-genieure”, Berlin, Seotember 27 to 29, 1989. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 221-229 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The production of dioxins/furans during waste incineration, and particularly the development of measures for minimizing the amount of generated pollutants, continue to command a considerable scientific as well public interest. Experiments are reported which were performed at the TAMARA municipal solid waste pilot incineration, erected on the premises of the karlsruhe Nuclear Research Centre. These experiments show that the solid waste mass flow rate and moisture content influence the dioxin/furan formation, Good removal efficiencies of dioxins/furans have been In wet cleaning. Hydrogen peroxide added to the crude gas is an interesting “killer” reagent for dioxins/furans.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130130
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    Study on regeneration of diesel particulate filter using a laboratory reactor (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 251-258 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Regeneration of diesel particulate filters can be accomplished by complete combustion of a collected particulate. A reactor has been developed for study of the regeneration in the presence of catalysts, additives and ignition aids. This reactor allows an accurate measurement of soot ignition temperatures and a kinetic study of soot oxidation with an undisturbed soot layer and under a defined gas composition. Results of various investigations carried out with this reactor are presented.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130134
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    Transport effects in catalytic fluidized-bed reactorsPaper presented at the Third National Meeting of Chemists, Dhahran, Saudi Arabia, March 12-14, 1989. (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 273-277 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The majority of the fluidized-bed reactor models are models are rooted in the tacit assumption that transport between the bubble, cloud, and emulsion phases occurs in series with chemical reaction. A more realistic model that anticipates simultaneous transport and reaction is presented in terms of a fluid-bed effectiveness factor which embraces the limits between chemical and mass transport control. Analysis of the predictive capacity of this model vis-a-vis the Kunii-Levenspiel model reveals signal differences in chemical conversion.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130137
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  • 56
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    Search for optimal geometry of a conical turbine agitator for heat transfer in stirred vessels (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 384-392 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Simultaneous measurements of power consumption P and heat transfer coefficient α for a jacketed, baffled, agitated vessel of diameter D = 0.45 m, equipped with a conical turbine, were carried out. The following geometric parameters of the agitator were tested: diameter d, blade width b and number Z, and distance from the bottom of the vessel to the lower edge of the blade h. The results of these investigations were generalized mathematically. On the basis of optimization, the best geometric parameters with respect to heat transfer are proposed for the conical turbine agitator.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130152
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    The Markov process approach to modelling of residence of time distributions in flow systems (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 422-425 
    Details
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The Markov process approach, as used in the modelling of particle residence time distribution in a flow system of interlinked compartments, has been compared with the deterministic model of a complex reaction system of the first order. In the latter model, interfacial reactions take place between flowing phases, corresponding to the compartments in the stochastic model. It has been demonstrated that the two approaches are equivalent. A direct method of calculating the higher moments of the residence time distribution has been verified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130157
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    Effect of dispersions of CSD in continuous MSMPR crystallizers (1990)
    Weinheim : Wiley-Blackwell
    Chemical Engineering & Technology - CET 13 (1990), S. 426-431 
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    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A general model is proposed to predict the crystal size distribution from multistage MSMPR Crystallizers taking into account shape factor, birth size and growth rate dispersions. Two cases, namely nucleation in the first crystallizer and the same process in all crystallizers have been considered. The developed equations can be solved easily by the Monte Carlo technique. The model represents an extension of the earlier work of Sen Gupta and Dutta.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ceat.270130158
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    Structure and stability of 2σ/1σ* three-electron-bonded radical cations from 1,n-bis(alkylthio)alkanes in aqueous solutions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 17-22 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A large number of 1,n-bis(alkylthio)alkanes, R′S(CH2)nSR″, was investigated by pulse radiolysis in aqueous solutions. The sulphur-centred radical cations, which were obtained on oxidation of the dithia compounds by ·OH radicals, are stabilized via 2σ/1σ* three-electron interaction between two sulphur atoms. Intramolecular stabilization is the only process observed for n = 2-4, whereas for longer chain compounds with n 〉 4 some intermolecular sulphur-sulphur interaction is also indicated. The stability and yields of the three-electron-bonded species also depend on the nature of the substituents R′ and R″, and for the intermolecular systems are a function of solute concentration. The results corroborate earlier investigations and demonstrate, in particular, that the optical parameters are a very sensitive measure of changes in electron density and structure of the three-electron-bonded systems.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030105
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    Solvolysis of highly reactive phosphorus-sulphonic anhydrides. Stereochemical and chemical arguments for phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 23-34 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The stereochemistry and mechanism of solvolysis of optically active tert-butylphenylphosphinothioic-O-trifluoromethanesulphonate (1) in solvents of different ionizing power were studied. It was found that in solvents of high ionizing power and low nucleophilicity 1 ionizes with the formation of a phosphathiacylium cation (2) as the reaction intermediate. Product resulting from the reaction of 2 with anisole was isolated and characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030106
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    Stereochemistry of silver-ion-assisted solvolysis of tert-butylphenylphosphinothioic iodidate. Phosphathiacylium cation formation (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 35-37 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the stereochemistry of silver-ion-assisted solvolysis of a new optically active tert-butylphenylphosphinothioic iodidate demonstrated that the reaction proceeds with inversion of configuration at the phosphorus atom. Evidence for phosphathiacylium cation formation as a reactive intermediate is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030107
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    Probing of transient photoenol formation from ortho-methyl-substituted phenyl ketones by hydrogen-tritium exchange (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 38-40 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Studies on the photochemically induced hydrogen-tritium exchange in o-methyl-substituted phenyl ketones are reported. It is shown that the tritium exchange can be beneficial for probing transient photoenol formation, particularly when photochemical side-reactions are occurring.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030108
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    Studies on organophosphorus compounds. XXXVI.For Part XXXV, see S. S. Li, Z. Y. Chen and C. Y. Yuan Scientia Sinica (Series B) 136, (1989).. Substituent effects of alkylphosphonates and -phosphinates in alkaline hydrolysis (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 48-54 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Alkaline hydrolysis of diethyl alkylphosphonates and alkyl diethylphosphinates was studied in aqueous dimethyl sulphoxide. The behaviour of these acyclic phosphorus esters is very similar to that of some cyclic phosphorus esters. Rate constants were measured at three temperatures over a 30°C range, and the activation functions of the reaction were estimated. The basic hydrolytic process was proved to be a bimolecular AE reaction. Multiple regression analyses involving rate constants and substituent parameters gave, as a rule, poor results using steric constants derived from carbon compounds. However, the substituent steric effect on the rate of hydrolysis of phosphonates and phosphinates studied correlated very well with ΔΔE, representing the difference in steric energy calculated by molecular mechanics. It is attributed to the various degrees of susceptibility of carbon and phosphorus atoms to the steric hindrance of the substituents. Moreover, Newman's rule of six for the hydrolytic reaction of carboxylates was completely eliminated in phosphorus ester hydrolysis.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030110
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    The kinetic deuterium isotope effect of proton-transfer reactions in solution. Comparison of the marcus and the quantum-statistical mechanical models (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 62-68 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The free energy dependence of the kinetic deuterium isotope effect of proton-transfer reactions in solution is usually analysed in terms of the Marcus model. By means of modern computer techniques, the more general quantumstatistical mechanical model is also amenable to routine application. The differnces in the basic assumptions of the two approaches concerning the kinetic isotope effect are discussed. Reaction series for which both the Brønsted relation and the free-energy dependence of the kinetic isotope effect are available are analysed by means of the two models using one set of parameters for both free-energy relations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030112
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    Porphyrin-tyrosine interactions: Photo-CIDNP and NMR studies (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 69-76 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Strong 1H and 13C nuclear polarizations are observed when aqueous solutions of synthetic water-soluble porphyrins are irradiated in the presence of tyrosine and some of its derivatives. These polarizations are strongly pH dependent. Evidence is also shown for the formation, in the dark, of a complex between the reactants. The association constants are evaluated from the NMR chemical shifts on the aromatic tyrosine protons induced by the presence of the porphyrins. The nature of the intermediate radical pair generating the CIDNP effects is discussed. An electron-transfer reaction from tyrosine to the excited triplet state of the porphyrin, or within the porphyrin-tyrosine excited complex, is expected to be the primary step in the reaction. It is followed by subsequent proton transfer within the initial ion radical pair. The spin polarizations arise principally from the back-transfer step, as the reactants are the only products which are polarized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030202
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    Brønsted coefficients and the theory of acid-base catalysis of proton transfers from carbon acids (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 95-109 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The intersecting-state model previously used to interpret proton transfers in ground and excited states and enzyme catalysis was applied to the general acid-base catalysis of carbon acids. The results are consistent with the predictions published for these systems and provide a new physical meaning for the Brønsted coefficients. It is shown that in addition to the linear free energy effect, the Brønsted coefficients are also influenced by the tightness of the transition states and by electronic effects. The model suggests that the increased reactivity of carbon acids towards proton transfer in non-hydrogen-bonding solvents is caused by an added electronic effect on the thermodynamics of the reactions. The curvatures of the Brønsted plots are interpreted in terms of an entropic contribution to the position of the transition state.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030206
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    Gas-phase nitration of thiophene and N-methylpyrrole by protonated alkyl nitrates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 110-118 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase nitration of thiophene (1) and N-Methylpyrrole (2) was studied by radiolytic tecniques, supported by chemical ionization mass spectrometry. The substrate and positional selectvities of protonated alkyl nitrtes (CH3NO3H+, CF3CH2NO3H+) were deduced from competitive reactions with bezene performed under different conditions. The apparent kS/kB ratios, which are independent of the pressure and unaffected by the presence of a strong base (NEt3), depend on the nature of the electrophile, passing for 1 and 2 from 7·2 and 6·4, respectively, with CH3NO3H+ to 1·1 and 1·0, respectively, with the more reactive fluorinated caution. Predominant (88%) α-substitution takes place in 1, whereas no appreciable positional discrimination is displaced by 2. The results suggest that the electrophilic attack can also occur a the heteroatom, and point to the same mechanism postulated for gasphase nitration of aromatic substrates, the reactivity being essentially governed by electrostatic interactions within the ‘encounter pair’.
    Additional Material: 2 Ill.
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    Role of 2-carboxyl substituent in the tautomerization between two equivalent enol forms of 3-hydroxyphenalenone (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 485-488 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The interconversion between two equivalent enol forms of 3-hydroxyphenalenone took place predominantly through a diketo form with a free energy of activation of ca 14 kcal mol-1 in DMSO solution determined by 125·8 MHz13C NMR measurement. On the other hand, the corresponding interconversion in 2-carboxy-3-hydroxyphenalenone was not frozen on the time scale of 13C NMR spectroscopy down to -60°C. This acceleration in the interconversion rate of the latter may be interpreted by a double proton switching between the hydrogen-bonded 2-carboxyl and 3-hydroxyenone moieties.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030712
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    Contribution of activity coefficients to the nucleophilicity of solvent components in solvent mixtures. Influence of added acetone on selectivity values, kE/kW, in ethanol-water mixtures (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 503-508 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Literature data on the change in the selectivity values, kE/kw, for several solvolysing systems in ethanol (E)-water (W) on addition of acetone were analysed. It is suggested that acetone acts as a basic cosolvent for both ethanol and water and that the change in the activity coefficients on changing the solvent composition is mainly responsible for the observed effect.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030804
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  • 70
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    Cross-interaction constants as a measure of the transition state structure. Part 8. Mechanism of the reaction of 2-phenylethyl benzenesulphonates with benzylamine in acetonitrile (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 545-549 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of reactions between 2-phenylethyl benzenesulphonates (2-PEB) and benzylamines in acetonitrile at 65·0°C have been studied; the mechanism was examined on the basis of the sign and magnitude of cross-interaction constants ρij and βij. In contrast to the reactions of 2-PEB with anilines in methanol, participation of the aryl-assisted pathway was negligible, with a strong indication that the reaction proceeds largely by an intermolecular SNi mechanism with a four-centre transition state (TS). The effect of substituents on the TS variation was in accord with the predictions of the quantum mechanical model.
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030808
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    Solvent polarity scales. 1. Determination of ET and π* values for phosphonium and ammonium melts (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 534-544 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solvent polarity of a series of organic salts in their molten state has been determined using the solvatochromic dyes: pyridinium N-phenolate betaine, the basis of the ET scale, and N,N-diethyl-4-nitroniline, one of the primary standards for the π* scale. Each of these dyes was dissolved in the following liquids: lithium acetate-sodium acetate-potassium acetate eutectic; ethylammonium chloride; dimethylammonium cloride; diethylammonium nitrate; ammonium trifluoracetate; tetraethylammonium acetate; tetrabutylphosphonium chloride; octyltributylphosphonium chloride; dodecyltributylphosphonium chloride; tetrabutylammonium bromide; tetrabutylphosphonium bromide; octyltributylphosphonium bromide; dodecyltributylphosphonium bromide; octyltributylphosphonium iodide; dodecyltributylphosphonium iodide; tetrahexylammonium benzoate; methyltrioctylphosphonium dimethylphosphate; and methyltrioctylammonium chloride. The ultraviolet and visible spectra were measured for each of these. In addition, data were collected as a function of temperature and in the presence of neutral and ionic additives. In general, these molten salts represent solvent polarities equivalent to moderately polar aprotic solvents such as acetone and acetonitrile. The salts with cations capable of being hydrogen bond donors gave considerably higher values, equivalent to or higher than water, the solvent with the highest value on the ET scale. These and the eutectic mixture are thought to involve specific dye-solvent interactions which cause these anomalously high values.
    Additional Material: 3 Ill.
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    Activation barriers in photosensitized pyrimidine dimer splitting (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 581-586 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Pyrimidine dimers, which form by a symmetry allowed (πs2 + πs2) photocycloaddition reaction, are subject to photosensitized cycloreversion by electron donors, such as indoles. In a linked dimer-indole system, photoinitiated electron transfer occurs intramolecularly from indole to dimer to produce a charge-separated species (dimer-.-indole+.). This species undergoes cycloreversion in competition with back electron transfer. Studies of the temperature dependence and solvent dependence of this competition have allowed the relative values of the activation parameters for the competing processes to be determined. In water (5-65°C) the free energy of activation of splitting minus that of back electron transfer (ΔΔG≠ = ΔGspl≠ - ΔGbet≠) was found to be 1·3 kcal mol-1. The enthalpy of activation difference (ΔΔH≠) was found to be 1·1 kcal mol-1 and the entropy of activation difference (ΔΔS≠) was found to be -0·51 cal mol-1 K-1. In EPA (diethyl ether-isopentane-ethanol, 5:5:2; -85 to 25°C) the value of ΔΔG≠ remained the same, but the entropy and enthalpy contributions were different (ΔΔH≠ = 0·72 kcal mol-1; ΔΔS≠ = -1·8 cal mol-1 K-1). The results have been interpreted in terms of the effect of the polarity of the solvent on the transition states for the two competing processes. Enthalpy effects retard splitting more in water than in EPA, whereas entropy effects favor back electron transfer more in EPA than in water. Potential implications of these results for the mechanism of enzymatic photocycloreversion of pyrimidine dimers in DNA are considered.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030905
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031001
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    Stereochemistry and kinetics of addition of amines to acetylenic ketones (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 627-634 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of a series of 3-(p-substituted phenyl)-1-phenylprop-2-yn-1-ones with piperidine and morpholine in methanol were studied and their rates measured. The products were 3-piperidino- and 3-morpholino-3-(p-substituted phenyl)-1-phenylprop-2-en-1-ones. 1H NMR spectra were used to determine the configurations of the obtained products. A good Hammett correlation was obtained with ρ values of 1·15-1·10 and 1·15-0·53 for piperidine and morpholine, respectively, which suggest a carbanionic character of the transition state. A two-step mechanism is postulated for these nucleophilic additions.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031002
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    The spin delocalization substitutent parameter σJJ. 5. Correlation analysis of 19F chemical shifts of substituted trifluorostyrenes. The unresolved polar substituent parameter σmb (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 643-650 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 19F NMR spectra of 30 substituted α,β,β-trifluorostyrenes (Y-TFSs, 1) covering a diverse range of substituents are reported and discussed. Values (δF1, δF2, Δδ3 - 1 and Δδ3 - 2) derived from the 19F NMR chemical shifts of the fluorine atoms of 1 are found to correlate very well with σI and σR0. The results of the correlations of the 19F chemical shifts with dual (σF and σR) and triple parameter (σF, σR and σα) treatments are compared. An unresolved substituent parameter σmb, is proposed for applications to systems in which the substitutent Y interacts with a multiple bond and is compared with σ+.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031005
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    Direct measurement of the relative rates of C-protonation at unsubstituted and substituted α-and/or β-positions of a pyrrole ring (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 684-686 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Direct kinetic measurements of the C-protonation rates of 1,2,5-trimethyl- and 3,4-dimethyl-pyrroles allow the first comparison of the relative kinetic proton affinities of unsubstituted and substituted positions of the pyrrole ring.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610031010
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    Stereospecificity in anionic 1, 1-addition to isocyanides. A re-examination of the (H- + HN≡C) potential energy surface (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 697-702 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The potential energy surface for the addition of the hydride ion to hydrogen isocynide reported previously was re-examined. An improved energy surface was explored at the MP2/6-31 + + G** level while relative energies were estimated at the MP4SDTQ/6-311 + + G** level and corrected for zero-point vibrational contributions. The calculated results show the existence of transition structures for both cis and trans-additions of H- to the carbon end of HN≡C even though the corresponding barrier heights are small. These transition structures did not exist at a lower level of theory (HF/4-31G) employed previously.The cis addition is calculated to be favoured over the trans addition by 10 kcal mol-1. The overall addition is thus strongly stereoselective, if not purely stereospecific. This result confirms our previous analysis of the stereoelectronic effect in the addition-elimination process involving imidoyl anions as intermediates. Recent experimental work on the addition of OH- to ArN≡C is discussed.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031102
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  • 78
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    Electrochemical reduction of substituted α,α,α-trifluoroacetophenones. Linear relationship between cyclic voltammetric peak potentials and Hammett substituent constants (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 723-731 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The peak potentials of substituted α,α,α-trifluoroacetophenones were measured in acetonitrile with 0·1 M tetrabutylammonium perchlorate. The cyclic voltammograms indicated an irreversible electrochemical process for the first wave (Epc1) and a partially reversible one for the second wave (Epc2) when the scan rate was slower than 100 mV s- 1. Excellent linear correlations were observed for Epc1 with σ constants (ρ = 0·526, r = 0·999) and for Epc2 with σ- constants (ρ = 0·605, r = 0·998), respectively. Therefore, unknown σ values such as -0·36 for 3, 4-ethyleneoxy can be estimated from these correlations. The mechanism of the electrode process probably involves a single electron transfer and the formation of a pinacol.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031105
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  • 79
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    Mechanism of formation of phosphonate carbanions with the use of a lithium salt and 1,8-diazabicyclo[5.4.0] undec-7-ene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 746-750 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The deprotonation reaction mechanism of methyl diethylphosphonoacetate in the presence of lithium salts and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) was examined by infrared spectroscopy. It was found that the intermediate species formed by chelation of the bidentate phosphonate with a lithium cation or an ion pair of the salt deaggregated by DBU takes part in the reaction path. The role of the anion X- is to induce the elimination of a protonated DBUH+X- ion pair and that of the solvent is to compete with the bidentate phosphonate in cation solvation. A similar mechanism via a related intermediate is proposed to interpret the results obtained by other workers on the catalysis by Ba(OH)2 of the Wittig-Horner reaction.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031108
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    The current status of isomer enumeration of useful benzenoids and a new topological paradigm (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 765-783 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The enumeration and development of conceptual tools for understanding the chemical properties of practical benzenoid hydrocarbons is stressed. Currently known isomer numbers for benzenoids having up to 60 carbons are summarized. Although there are well over 2 million isomers in this range, only approximately 500 benzenoid hydrocarbons have been characterized.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031202
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    Reactions of molecules with two equivalent functional groups. 2. Acetylation of the isomers of bis(hydroxymethyl)benzene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 789-798 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The acetylation (with acetic anhydride-pyridine in tetrahydrofuran) of the ortho, meta and para isomers of bis(hydroxymethyl)benzene (1) was studied. Third-order rate constants k1 (formation of monoacetate 2 from 1) and k2 (formation of diacetate 3 from 2) for all three isomers were determined, as were the rate constants for acetylation of benzyl alcohol and its ortho- and para-ethyl derivatives under the same conditions. The compositions of the final product mixtures (comprising 1, 2 and 3) were ascertained as a function of the initial ratio of acetic anhydride to 1. Comparisons were made with predictions based on a previously published independent functional groups model, which assumes that k2/k1 = 0·50. All three isomers gave product mixtures whose compositions were in generally good agreement with predictions based on the model. For the para and meta isomers the ratios k2/k1 were determined experimentally to be 0·548 and 0·521, respectively. The k2/k1 ratio for the ortho isomer was found to be 0·605, and its k1 and k2 values were lower than those for the para and meta isomers. Possible explanations for the anomalous behavior of the ortho isomer are discussed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610031204
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    Radical mechanism of nucleophilic substitution on halocyclohexane systems (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 812-816 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Chlorocyclohexane does not react in the dark with diphenylphosphide ions in liquid ammonia, but it reacts under irradiation to give the substitution product. Bromocyclohexane reacts slowly in the dark, but this reaction is strongly accelerated by light, and inhibited by p-dinitrobenzene. 3-Bromo-2-tetrahydropyranyl allyl ether (used as a radical probe) reacts with diphenylphosphide ions under irradiation to give both the straightforward and the cyclized substitution products. This photostimulated reaction is also inhibited by p-dinitrobenzene. It is suggested that the chlro-bromocyclohexanes and related compounds react under irradiation by the SRN1 mechanism of nucleophilic substitution.
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    URL: http://dx.doi.org/10.1002/poc.610031208
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    Masthead (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990) 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030501
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    β-Secondary deuterium isotope effect and solvent isotope effects in catalysis by subtilisin BPN′ (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 260-265 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Subtilisin BPN′ catalyzes the hydrolysis in protium and deuterium oxides of p-NO2C6H4OCOCL2NHCO2CH2C6H5(L = H, D) in the pH(D) range 5·0-8·5 (H2O) and 5·4-9·0 (D2O), according to simple Michaelis-Menten kinetics. The parameter kcat/Km exhibits pH(D) inflection points of 7·17 ± 0·05 (H2O) and 7·69 ± 0·08 (D2O), and kcat shows 6·88 ± 0·05 (H2O) and 7·50 ± 0·07 (D2O). The ‘normal’ ΔpK values of 0·5-0·6 indicate no unusual effects of D2O on enzyme properties. The solvent isotope effects (H2O/D2O) on the limiting values of the rate constants at high pH(D) are 1·13 ± 0·07 for kcat/Km and 1·29 ± 0·05 for Kcat. These small effects indicate no more than minor contributions of general acid-base catalysis for rate-limiting events for either kcat/Km or kcat. The β-deuterium secondary isotope effects (2H/2D) are roughly estimated by extrapolation as 0·95 ± 0·01 for kcat/Km, corresponding to substantial tetrahedral character in the transition state, and 1·03 ± 0·03 for kcat, consistent with no tetrahedral character. Models consistent with these results have as rate-limiting events for kcat/Km nucleophilic attack by active-site imidazole and for kcat, among other possibilities, the release of carboxylate product from the imidazolium form of the enzyme.
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    URL: http://dx.doi.org/10.1002/poc.610030409
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    Theoretical studies on the gas-phase pyrolysis of acetic anhydride and diacetyl sulphideDetermination of Reactivity by MO Theory, Part 61. For Part 60, see Ref. 1. (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 279-284 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The gas-phase thermal decomposition of diacetyl compounds, (CH3CO)2X with X = O and S, was investigated theoretically using the semiempirical MO methods MNDO and AM1. The initial decomposition of the diacetyl compounds proceeded through a six-membered ring transition state involving the keto form with a slightly lower activation enthalpy for diacetyl sulphide (X = S); the process via an enolic form of the transition state was kinetically unfavourable. In the initial decomposition of the diacetyl compounds and in the subsequent pyrolysis of acetic and thioacetic acid, ketene formation was found to be the most preferred path, where the ease of Cα—X bond cleavage is relatively more important than nucleophilic attack on the β-hydrogen in determining the overall reactivity. In the methane formation process, the reactivity was entirely dependent on the X—H bond strength in CH3COXH where X = S, NH and O.
    Additional Material: 6 Tab.
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    URL: http://dx.doi.org/10.1002/poc.610030502
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    Inhibition of peroxidations of lipids and membranes by estrogens (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 309-315 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The antioxidant activity of 2-hydroxyestradiol was measured quantitatively and compared with those of other estrogens in oxidations of methyl linoleate in homogeneous solution and in aqueous dispersions, oxidations of soybean phosphatidylcholine liposomal membranes and oxidative haemolysis of rabbit erythrocytes, all induced by free radicals generated from a radical initiator. Similar antioxidant activities of estrogens were observed, irrespective of the oxidation system. 2-Hydroxyestradiol was found to be a potent radical scavenger and its antioxidant activity was close to that of α-tocopherol, the strongest natural antioxidant. Other phenolic estrogens such as estrone, estriol and β-estradiol showed a modest antioxidant activity and testosterone did not act as an antioxidant.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/poc.610030507
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    Cycloadditions of 2-diazopropane to bicyclo[2.2.1]hept-2-enes. Direct experimental evidence for an asynchronous mechanism (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 339-345 
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    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 2-Diazopropane, generated by photolysis of 2-methoxy-2,5,5-trimethyl-Δ3-1,3,4-oxadiazoline, was trapped in situ by cycloaddition to norbornene, endo- and exo-5-methylnorbornene, endo- and exo-5-phenylnorbornene, endo- and exo-5-methoxycarbonyl norbornene and endo- and exo-dicyclopentadiene. In all cases, only exo addition was observed. In spite of the exo approach of diazopropane to the norbornene double bond, endo substituents at C-5 and/or C-6 influenced the regiochemistry of addition whereas exo substituents did not. The results are interpreted in terms of a concerted, asynchronous mechanism in which C—C bond formation runs well ahead of N—C bond formation, as predicted from theory. The regiochemical control exercised by apparently remote endo substituents provides a new experimental criterion for asynchrony or synchrony of cycloadditions that are known to be concerted.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030511
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  • 88
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    Electronic Resource
    Gas-phase acidities of acrolein and methyl acrylate (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 346-348 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Gas-phase acidities of acrolein and methyl acrylate were measured by bracketing in a flowing afterglow/SIFT apparatus. For acrolein ΔG°acid = 369 ± 4 kcal mol-1 and for methyl acrylate ΔG°acid = 373 ± 4 kcal mol-1. These acidities are substantially lower than those of the saturated analogs propionaldehyde and methyl acetate, respectively, even though hydrogens attached to sp2-hybridized carbon are intrinsically more acidic than those attached to sp3-hybridized carbon. Resonance stabilization of the neutral form by conjugation of the C=C double bond with the carbonyl group and allenic destabilization of the anionic form of the two acids can account for the relatively low acidities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030512
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  • 89
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    A study of a novel degenerate carbocation rearrangement of the 4,9-dimethyl-9-barbaralyl cation by dynamic 13C and 1H NMR spectroscopy in superacid (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 349-357 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The 4,9-dimethyltricyclo [3.3.1.02,8]nona-3,6-dien-9-yl (4,9-dimethyl-9-barbaralyl) cation (3) was generated from 4,9-dimethyl-9-barbaralol (5) at -135°C in two different superacid mixtures [FSO3H—SO2CIF—SO2F2(1:6:1) and FSO3H—SO2CIF—SO2F2—CHCl2 (2:10:10:1 by volume)]. Its 1H and 13CNMR spectra show a strong temperature dependence in the range -150 to -125°C. The changes in band shapes with temperature show that the following exchanges take place: 4-methyl with 9-methyl, C-4 with C-9, C-1 with C-3 and C-2 with C-8. C-5, C-6 and C-7 are found not to exchange rapidly either with each other or with the other carbons in 3. The mechanism of this novel rearrangement is suggested to involve the bicyclic 2,7-dimethylbicyclo [3.2.2] nona-3,6,8-trienyl cation and the secondary barbaralyl cation 4,6-dimethyltricyclo [3.3.1.02,8] nona-3,6-dien-9-yl as intermediates rather than 7,8-dimethyl bicyclo [3.2.2] nona-3,6,8-trienyl cation, which does not have a methyl group on the allyl cation moiety. Comparisons with rearrangement mechanisms for other barbaralyl cations were also made. The rate constant for the degenerate rearrangement of 3 is 160 s-1 at -140°C, which corresponds to ΔG≠s = 26 kJ mol-1 (6·3 kcal mol-1). At -125°C ion 3 rearranges non-degenerately to the 1,4-bishomotropylium cation 1,8-dimethylbicyclo [4·3·0] nona, 2,4,7-trienyl (4) with k = 3 × 10-4 s-1. A mechanism for this rearrangement and the synthesis and purification of the ion precursor 4 are also reported.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030602
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  • 90
    Electronic Resource
    Electronic Resource
    Dephosphorylation by peroxyanions in micelles and microemulsions (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 390-396 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dephosphorylation of p-nitrophenyl diphenylphosphate (pNPDPP) by OH- in aqueous cationic micelles of cetyltrimethylammonium hydroxide (CTAOH) is inhibited by tert-butyl hydroperoxide (t-BuO2H), which reduces the binding of OH-, and whose anion is a relatively ineffective nucleophile. Reaction is faster in microemulsions of CTACl, n-octane and OH-, with t-BuO2H as cosurfactant, than in otherwise similar microemulsions with t-butyl alcohol as cosurfactant. Dephosphorylation by m-chloroperoxybenzoate ion is slower in microemulsions of cetyltrimethylammonium mesylate or benzenesulfonate, with n-octane and tert-butyl alcohol, than in cationic micelles, but a wide range of concentrations can be examined. The reaction rates qualitatively follow the concentration of peroxy acid relative to surfactant, and inert anions slow the reaction. Dephosphorylation by peroxyphthalate dianion in micelles of CTACl fits a pseudophase kinetic model, except in very dilute surfactant where reaction is faster than predicted.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030607
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  • 91
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    Electronic Resource
    Synthesis and spectroscopic properties of stereoisomeric 5,7-oxido-6-hydroxyiminocholestane derivatives (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 404-413 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The four possible diastereomeric 5,7-oxido-6-hydroxyiminocholestanes and their O-acetates have been synthesized. The stereochemistry of one of the latter has been proved unequivocally by x-ray diffraction. Their 1H and 13C NMR and also their circular dichroism spectra are discussed. It is now also possible to determine unequivocally the stereochemistry of the ring-junction geometry and the oxime E or Z stereochemistry.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030609
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  • 92
    Electronic Resource
    Electronic Resource
    Role of exciplex and ion pair in the photosensitized oxygenation of 1,4-diphenyl-1,3-butadiene (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 509-518 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: 9,10-Dicyanoanthracene (DCA) sensitized the photooxygenation of 1,4-diphenyl-1,3-butadiene(1a) and its 4,4′-dimethoxy derivative (1b) to afford the corresponding endoperoxides 2 and the other oxidized products such as aldehydes and epoxides. The mechanism of the DCA-sensitized photooxygenation of 1 was diversified by solvent polarity. In non-polar solvents the reaction involves an exciplex intermediate, which leads to formation of triplet DCA (3DCA*) with an efficiency of 0·64 in the case of 1a. The resulting 3DCA* acts as a sensitizer for the generation of singlet oxygen (1O2) and thus 1O2 reaction occurs exclusively to give 2. On the other hand, single electron-transfer quenching of 1DCA* by 1 is feasible in polar acetonitrile and a primary ion pair can be formed. Competing with fast back electron-transfer deactivation, the primary ion pair produces free ions in limited yield to furnish electron transfer oxygenation. In the case of the DCA-1a system, free ions were produced with an efficiency of ca 4%. Thus, in acetonitrile, electron-transfer oxygenation partly took place to give the other oxidized products, whereas the 1O2 pathway was still valid and responsible for the formation of 2. The effect of solvent polarity was apparently less pronounced in the case of 1b because the reactivity of 1b toward 1O2 is about five times higher than tht of 1a. For such 1O2-reactive substrates, the electron-transfer pathway would become dominant only when the substrate concentration is impractically high.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030805
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  • 93
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    Electronic Resource
    Cross-interaction constants as a measure of the transition state structure. Part 9. The degree of bond formation in the SN2 transition state involving anionic nucleophiles (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 550-554 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The second-order rate constants of the reactions between benzenesulphonyl chlorides and anionic nucleophiles, benzoates and cinnamates, in methanol at 30·0°C are reported. A marked increase in rate found with a p-nitro substituent in the substrate indicated the development of an electron-rich centre on the S atom in the transition state. The two types of cross-interaction constants, ρxy and λxy, suggested that bond formation in the SN2 transition state with anionic nucleophiles is greater than that for the corresponding reaction with aniline nucleophiles.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030809
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  • 94
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    Electronic Resource
    Synthesis and chemistry of azolenines.The term ‘azolenines’ refers to the non-aromatic isomers of the azoles. Part 19.For Part 18, see Ref. 1. Basicities of some 2H- and 3H-pyrroles and the remarkably large pKa′ of 2,2,3,5-tetramethyl-2H-pyrrole (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 555-557 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: pKa′ Values are reported for two 2H-pyrroles and their 3H-pyrrole isomers. The latter have basicities of the same order as similarly substituted pyridines, whereas the former are 2-2·5 pK units more basic, 2,2,3,5-tetramethyl-2H-pyrrole having a pKa′ of 8·40, close to that for 2-aminoimidazole. Possible reasons are given.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030810
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  • 95
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    Electronic Resource
    A valence and charge criterion for reactivity of π electron systems (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 599-605 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A new criterion for the reactivity of π electron systems is proposed. The method incorporates and modifies ideas of Coulson and Fukui et al. about free valence. The proposed reactivity index includes covalent and lonic components and is suitable for elctrophilic, radical and nucleophillic attack. The method is tested for a few simple π systems and differences from Coulson and Fukui et al. are discussed. Finally, it is applied to the electrophilic attack of a series of substituted benzenes and to nucleophilic attack of a series of subsituted benzoic acid esters.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610030908
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  • 96
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    Electronic Resource
    Ionization constants of 5-pyridylmethylenehydantoins in 80% (w/w) dimethyl sulphoxide-water at 25 °C (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 703-710 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ionization constants of nine amphoteric 5-pyridylmethylenehydantoins were measured in 80% (w/w) dimethyl sulphoxide-water at 25 °C. The effects of structure and Z/E configuration on both pKaI and pKaII values are discussed. The especially low basicity and acidity of the Z-isomers of the N-unsubstituted and 3-methyl-substituted 5-(2-pyridylmethylene)hydantoin are attributed to the formation of intramolecular N(1)—H…N hydrogen bond in the s-cis conformation of these compounds. The existence of N(1)—CH3…N attraction is also postulated for the Z-isomer of 1-methyl-5-(2-pyridylmethylene)hydantoin.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031103
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  • 97
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    Electronic Resource
    Heats of formation of organic molecules by ab initio calculations. 1. Aliphatic amines (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 732-736 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A bond energy scheme has been developed and two previously existing schemes have been extended for the calculation of heats of formation of aliphatic amines using ab initio 6-31G* energies in place of experimental data. The results are in good agreement with those obtained experimentally and suggest that this method can be used to predict heats of formation of molecules of this class with an accuracy competitive with good quality experiments, and with probable errors of less than 1 kcal mol-1.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031106
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  • 98
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    Electronic Resource
    MO study of the possibility of a concerted mechanism in the pinacol rearrangement (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 737-745 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The ab initio SCF-MO method was employed to examine the possibility of a reaction pathway without a carbocation intermediate in the pinacol rearrangement. The molecular geometries of the transition states were obtained for the 1,2-hydride shift together with H2O elimination, starting from the various methyl-substituted protonated 1,2-diols. It was found that the activation energies depend strongly on the substitutents. A comparison of the relative energies between β-hydroxycarbonium ions and the transition states of the concerted mechanism suggests that the stepwise mechanism is less favourable than the concerted path in each case.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031107
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  • 99
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    Cross interaction constants as a measure of the transition state structure. 13. Steric effects of the N,N-dimethyl group on the transition state structure in aminolysis of alkyl benzenesulphonates (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 751-756 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Kinetic studies on the reactions of methyl (MBS) and ethyl benzenesulphonates (EBS) with N,N-dimethylanilines (DMA) in methanol and acetonitrile are reported. The cross interaction constants ρXZ and βXZ, between the substituents in the nucleophile (X) and the leaving group (Z) indicated that the transition states (TS) are looser than those for the reactions with anilines, but the relative tightness between the two substrates was the same; the TS was tighter for EBS despite the increase in steric effect leading to looser TSs for MBS and EBS alike. The TS variation between two different reaction series expected from the simple Hammett and Brønsted coefficients, ρX, ρZ, βX and βZ, was incompatible with that predicted by the cross interaction constants, demonstrating again the unreliability of the simple parameters.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031109
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  • 100
    Electronic Resource
    Electronic Resource
    Microenvironmental effects in solid-state reactions. Dispersive kinetics of conformation-dependent charge delocalization in aliphatic diamine radical cations (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 757-759 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of conformation-dependent charge delocalization in radical cations generated from a series of α,ω-diaminoalkanes, (CH3)2N(CH2)nN(CH3)2, (n = 1-3) in a 3-methylpentane glassy solution at 90 K are discussed in terms of dispersive kinetics with the use of the time-dependent rate constant in the form k(t) = Btα - 1. It was found that the activation energy distribution function became broader as the number of methylene groups separating the two nitrogen atoms increased, and that this process was accompanied by a substantial increase in the mean value of the activation energy.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031110
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