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  • 1
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The reactions of n-butylamine and piperidine with 1-chloro-2, 4-dinitrobenzene and 4-chloro-3-nitrotrifluoromethylbenzene were studied in n-hexane, benzene and mesitylene. The reactions seem to follow a bimolecular SNAr mechanism for both substrates and amines. However, whereas in n-hexane they are base catalysed, in the aromatic solvents only mild acceleration is observed. The different behaviour of these reactions in the aromatic solvents in comparison with hexane is explained by the specific solvent effect exerted by the aromatic compounds, which solvates the aromatic reactant preferentially in view of its electron-donor properties. These conclusions were confirmed by kinetic studies in hexane-aromatic solvent binary mixtures. It can be concluded that the presence of electron-donor solvents may inhibit SNAr reactions when association constant of the solvent with the substrate is greater than the EDA constants between the reactants. These specific solvent effects could also explain why only mild acceleration is observed in aromatic solvents.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 631-645 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the aromatic nucleophilic substitution (SNAr) reactions of 1,2-dinitrobenzene (1,2-DNB) with butylamine (BA) and piperidine (PIP) were investigated as a function of the amine concentration and temperature, in chloroform, ethyl acetate, tetrahydrofuran (THF), acetonitrile (ACN), dimethylformamide (DMF), dimethyl sulphoxide (DMSO). benzene, toluene, chlorobenzene and diisopropyl ether.In the set of solvents consisting of ethyl acetate, THF, ACN, DMF and DMSO, neither reaction is catalysed (kA = k1). The sequence and range of reactivity for BA and PIP are similar in these solvents. These results indicate that reactions in which nitro in the leaving group behave differently from SNAr reactions with other leaving groups, such as halogens or alkoxy groups, since an intramolecular hydrogen bond may be expected between the leaving nitro group and the ammonium H of the nucleophiles. The correlations of the rate coefficients obtained with Taft and Kamlet's solvatochromic method support these conclusions.On the other hand, these reactions show mild acceleration with relatively non-polar solvents such as the aromatics and diisopropyl ether. The donor properties of these solvents and experiments with solvent mixtures suggest the formation of electron donor-acceptor complexes between them and 1,2-DNB. Hence the preferential solvation of 1,2-DNB by the donor solvent accounts for the mechanism observed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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