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Structure and reactivity in the hydrolyses of aliphatic carboxylic acid esters and chlorides
Author(s) -
C. Regan Andrew,
Watt C. Ian F.
Publication year - 2007
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1144
Subject(s) - chemistry , steric effects , medicinal chemistry , chloride , organic chemistry , carboxylic acid
For hexanoic acid and its seven isomers, relative rates have been determined for acid catalysed esterification with methanol, and compared with those for saponification of the methyl esters. A good correlation between logarithms of relative rates for the two reactions is obtained, and it is suggested that the eight isomers provide a test set of compounds in which steric effects alone act on reactivity at the acyl carbon. A full set of steric parameters ( $E_{\rm s}^\prime$ values) are presented. Rates of solvolyses of the acid chlorides of the isomers have been determined conductometrically in 3:1 wt:wt acetonitrile water. Logarithms of relative rates show a poor correlation with $E_{\rm s}^\prime$ , and, taking into account the solvent dependence of the rates, the pattern excludes both rate‐limiting formation of a tetrahedral intermediate and rate‐limiting dissociation of chloride to form acylium ions. The remaining possibilities, a concerted process (A N D   N ‡ ) and rapid reversible formation of a hydrate followed by rate‐limiting dissociation of chloride (A N  + D   N ‡ ) are considered. Copyright © 2007 John Wiley & Sons, Ltd.

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