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Effect of hexadecyltrimethylammonium bromide micelles on the rate of oximolysis of esters
Author(s) -
Zanette Dino,
Chaimovich Hernan
Publication year - 1992
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.610050610
Subject(s) - chemistry , micelle , oxime , reaction rate constant , bromide , aqueous solution , nucleophile , aqueous two phase system , medicinal chemistry , micellar solutions , organic chemistry , inorganic chemistry , kinetics , catalysis , physics , quantum mechanics
Two amphiphilic oximes, 10‐phenyl‐10‐hydroxyiminodecanoic acid (oxime II) and 4‐(9‐carboxynonanyl)‐1‐(9‐carboxy‐1‐hydroxyimino nonanyl)benzene (oxime III) were synthesized. The p K a values of oximes II and III and acetophenoxime (oxime I) and the rates of oximolysis of p ‐nitrophenyl acetate (NPA) and p ‐nitrophenyl octanoate (NPO) were determined in the presence and absence of micellar hexadecyltrimethylammonium bromide (CTAB). The rates of oximolysis increased by up to 3 × 10 4 ‐fold in the presence of CTAB. Quantitative analysis of micellar effects, using an ion‐exchange pseudo‐phase model, allowed the determination of the second‐order rate constants for the reactions of oximes I‐III with NPA and NPO in the micellar pseudo‐phase. The calculated rate constants in the micellar pseudo‐phase were lower than those in water, demonstrating that the rate enhancements were due to substrate concentration in the micelles. Comparison of the rate constants in micelles and water suggests that the sites of reaction of oximes I‐III with NPO and NPA are similar to those in bulk aqueous solution. Micellar incorporation of the hydrophobic oximes II and III does not lead to a major change in the nucleophilicity of the oximate anion.