Premium
A linear Brönsted‐type behavior in the aminolysis of substituted naphthyl acetates
Author(s) -
Rajarathnam D.,
Nadar P. Ananthakrishna
Publication year - 2001
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/1097-4601(200103)33:3<157::aid-kin1009>3.0.co;2-y
Subject(s) - aminolysis , chemistry , morpholine , piperidine , ethanolamine , medicinal chemistry , amine gas treating , ionic strength , tetrahedral carbonyl addition compound , aqueous solution , reactivity (psychology) , nucleophile , nucleophilic substitution , protonation , imidazole , reaction rate constant , hydroxylamine , ethylamine , organic chemistry , kinetics , catalysis , medicine , ion , physics , alternative medicine , pathology , quantum mechanics
The reactions of 4‐acetyl‐1‐naphthyl acetate ( 1 ) and 6‐acetyl‐2‐naphthyl acetate ( 2 ) with a series of amines of varying pK a ,viz. morpholine, ammonia, ethanolamine, glycine, n ‐butylamine, piperidine, hydrazine, imidazole, and hydroxylamine, are subjected to a kinetic investigation in aqueous medium, 30°C, ionic strength 0.1 M (KCl ). Pseudo‐first‐order rate coefficients ( k obs ) are found under amine excess. The plots of ( k obs − k H ) against free amine concentration are linear at constant pH. The macroscopic nucleophilic substitution rate coefficients ( k N ) are obtained as the slopes of these plots and found to be pH‐independent for all the amines employed. The Brönsted‐type plots obtained (log k N against amine p K a ) for the aminolysis of both esters 1 and 2 are linear with slope values of β = 0.74 and β = 0.94, respectively. From these values, the kinetic law and the analysis of products, it is deduced that for both esters aminolysis proceed through a zwitterionic tetrahedral addition intermediate ( T ± ) whereby its dissociation into products is rate‐limiting ( k 2 step). Comparison of k N values among them shows that both esters follow an identical mechanistic pathway with 1 having higher reactivity than 2, the reasons for which are discussed. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 157–164, 2001