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Micellar catalysis of organic reactions. 28 . A comparison of the catalytic effects of micelles containing bromide and fluoride counterions on some S N Ar AND B Ac 2 reactions
Author(s) -
Broxton Trevor J.,
Christie John R.,
Wright Sallyanne
Publication year - 1990
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.610031009
Subject(s) - chemistry , micelle , catalysis , counterion , bromide , reaction rate constant , inorganic chemistry , reaction rate , photochemistry , kinetics , organic chemistry , ion , aqueous solution , physics , quantum mechanics
The catalytic effects of micelles of cetyltrimethylammonium bromide (CTAB) and fluoride (CTAF) on several S N Ar and B AC 2 reactions were studied. Rate versus detergent concentration curves predicted by the pseudophase models PPIE (ion exchange) for CTAB studies and PPMA (mass action) for the CTAF studies were fitted to the experimental results to determine the best values of the substrate binding constant ( K s ), the second‐order rate constant for reaction in the micelles ( K 2 M ) and the exchange constant K OH/X (PPIE) or binding constant (PPMA) for the counterions. Better catalysis by micelles of CTAF is shown to be due to the combined effects of a more favourable exchange constant in CTAF than in CTAB, slightly different rates of reaction within the two micelles and different values of β, the fraction of micellar head groups neutralized in CTAF and in CTAB. In both micelles the magnitude of catalysis depends on the charge produced in the intermediate complex and the presence of electron‐withdrawing groups to stabilize that charge. Strongest catalysis was found for a reaction leading to a monoanionic intermediate complex in which the charge was stabilized by two nitro groups, and the weakest catalysis was found for a reaction leading to a dianionic intermediate in which no electron‐withdrawing groups were present.