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Trends in Organic Chemistry   Volumes    Volume 4  Issue 2
Abstract
Mechanisms of hydrolysis of 2- and 4-halo-N-heteroarenes
Oliver J. Muscio Jr.
Pages: 493 - 504
Number of pages: 12
Trends in Organic Chemistry
Volume 4  Issue 2

Copyright © 1993 Research Trends. All rights reserved

ABSTRACT
 
Analysis of kinetic data for the hydrolysis of 2-fluoropyridine and several related compounds in 0.5-6.0 M hydrochloric acid suggests that the reaction is subject to water catalysis, in which nucleophilic attack by water is assisted by concerted proton transfer to a second water molecule functioning as general base. In contrast, the data for hydrolysis of 2-fluoropyrimidines indicate that nucleophilic attack by water on these compounds is unassisted. Proton inventories of the hydrolyses of 2-chloro-1-methylpyrimidinium ion, 2-fluoro-1-methylpyridinium ion, and 4-fluoroquinaldine indicate that all three react by a proton-transfer mechanism. The hydrolyses of the latter two compounds were also examined in carboxylic acid buffer solutions and were found to be catalyzed by the buffer bases, with Brønsted slopes of 0.66 ± 0.03 and 0.57 ± 0.01, respectively. The kinetic results were consistent with general base catalysis. However, 18O-labeling studies in which the two compounds were hydrolyzed either in 18O-enriched water with unenriched acetate buffer or in unenriched water with enriched acetate demonstrated that the oxygen in the hydrolysis products was incorporated from the acetate buffer, not from the water.  Thus, the buffer bases enhanced the hydrolyses by nucleophilic catalysis, not by functioning as general bases.
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