ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The effect of hexadecyltrimethylammonium bromide (CTAB) micelles on the acid dissociation constant of para-substituted benzenethiols, α-toluenethiol and n-heptanethiol was determined. The effect of CTAB on the rate of thiolysis by the thiols was measured using para-substituted p-nitrophenyl benzoates. The effects of micelles were analysed using a pseudophase ion-exchange (PIE) model. The Brønsted plot for ester thiolysis showed discontinuity at the pKa of the leaving group in water and was linear in micelles. Micelles increased the Hammett ρ value for thiolysis of esters by α-toluenethiol from 2·08 to 2·68. The Hammett plot for the rection of benzenethiol with esters in water is linear with σ- and displays a ρ value of 0·87, whereas in micelles the plot is linear with σ and presents a ρ of 2·83. Taken together, these data indicate that micelles produce a change in the rate-limiting step of thiolysis of substituted benzoate esters, leading exclusively to rate-limiting thiolate attack. In micelles thiolysis may be concerted and the effect of the aggregate on the reaction mechanism can be ascribed to the interaction of the thiolate ions, and the transition states, with the head groups as well as a medium effect.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610060103
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