ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The aqueous cleavage of methyl salicylate has been studied in the buffer solutions of various primary mono- and di-amines as well as secondary amines at 30°C. Both ionized (MS-) and nonionized (MSH) methyl salicylate are reactive toward primary mono- and di-amines. The second-order rate constants for the reactions of MS- with primary mono- and di-amines of pKa 〉 9.4 exhibit Bronsted plot of slope (βnuc) of 0.82. This high value of βnuc is attributed to an intramolecular proton transfer in a thermodynamically unfavorable direction in the rate-determining step in a stepwise process for the formation of monoanionic tetrahedral intermediate. However, a concerted process for the formation of a monoanionic tetrahedral intermediate in the reactions of MS- with amine nucleophiles wherein expulsion of leaving group is a rate-determining step is not completely ruled out. The α-effect nitrogen nucleophiles hydroxylamine and hydrazine reveal, respectively, ca. 104- and 103-fold higher reactivity compared to other amine nucleophiles of comparable basicity. The value of βnuc of 1.03 obtained for the reactions of primary monoamines with MSH is ascribed to the expulsion of leaving group as the rate-determining step. The significantly lower value of βnuc of 0.60 obtained in the reactions of MSH with both monoprotonated and unprotonated diamines is explained in terms of possible occurrence of intramolecular general acid-base catalysis. Intramolecular general base catalysis is responsible for the enhanced nucleophilic reactivity of primary amines toward MS-. Dimethylamine, piperidine, morpholine, and piperazine have no detectable nucleophilic reactivity toward MS-.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550190504
