ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Reaction curves for the simplest of cellulose acetylation systems; namely, the homogeneous reaction of secondary cellulose acetates with acetic acid and water, were studied. These reactions were found to be slow and complex, consisting of two interdependent simultaneous reversible second-order processes. The faster process represented the reaction of primary hydroxyl and acetyl groups, while the slower process represented the reaction of the two secondary hydroxyl and acetyl groups. Equilibrium and rate constants and initial and final concentrations of hydroxyl and acetyl groups were calculated for the two simultaneous reactions. Equilibrium constants for the primary groups favored acetylation, while equilibrium constants for the secondary groups favored deacetylation. Final equilibrium was not affected by the presence of sulfuric acid. On the other hand, rate of reaction was increased in the presence of sulfuric acid, indicating catalysis by this reagent. The reaction mechnanism outlined above was confirmed by comparing primary hydroxyl group contents calculated from acetylation results with primary hydroxyl group contents measured by means of the tritylation reaction. Energies of reaction and energies of activation were calculated. Energies of reaction were low, indicating that equilibrium for this process is very nearly temperature independent. Energies of activation were in agreement with energies of activation for esterifications of simple alcohols, from which it was concluded that the acetylation and deacetylation of secondary cellulose acetates in homogeneous solution is but another example of general acid catalyzed esterification with carboxylic acids and general acid catalyzed hydrolysis of fatty acid esters. Degradation of the cellulose chain molecule was followed throughout these studies and energies of activation for this reaction were calculated. These energies of activation were higher than those for the acetylation reactions. It was concluded that degradation is more severe at higher temperatures for a given change in acetyl group substitution. Initial determination of equilibrium and rate constants for acetic acid acetylation of cellulose acetate has been carried out. It is suggested that through use of such procedures as tritylation analysis, which isolates the reaction of the primary groups from the secondary groups, improved values for these constants may be achieved.
Additional Material:
19 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1953.120100404
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