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Micellar catalysis of organic reactions. Part 34. Nucleophilic aromatic substitution reactions in micelles with bulky head groups
Author(s) -
Broxton Trevor J.,
Christie John R.,
Theodoridis Dorothy
Publication year - 1993
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.610060909
Subject(s) - chemistry , micelle , nucleophilic substitution , catalysis , substitution reaction , nucleophilic aromatic substitution , organic reaction , organic chemistry , electrophilic aromatic substitution , nucleophile , photochemistry , medicinal chemistry , aqueous solution
Observed second‐order rate constants for the hydroxydechlorination of 1‐chloro‐2,4‐dinitrobenzene (2), 2‐chloro‐3,5‐dinitrobenzoate ions (3) and 4‐chloro‐3,5‐dinitrobenzoate ions (4) in micelles of cetyltrialkylammonium bromide (C 16 H 33 NR 3 Br, where R = Me, Et, n ‐Pr and n ‐Bu) are reported. For substrate 2, the observed catalysis increased as the size of the micellar head group was increased. This was shown to be primarily due to an increase in the rate of reaction in the micellar pseudo‐phase ( k 2 M ). For substrates 3 and 4, the observed catalysis decreased as the size of the micellar head group was increased. Much smaller changes in k 2 Mwere observed in these reactions, which lead to a dianionic intermediate which is more sensitive to polarity effects at the micelle surface than is the monoanionic intermediate formed from 2. These results support the contention that as the size of the micellar head group is increased, water is squeezed away from the micelle surface, resulting in a less polar reaction environment.