MICELLAR CATALYSIS OF ORGANIC-REACTIONS .28. A COMPARISON OF THE CATALYTIC EFFECTS OF MICELLES CONTAINING BROMIDE AND FLUORIDE COUNTERIONS ON SOME SNAR-REACTION AND BAC2-REACTION

The catalytic effects of micelles of cetyltrimethylammonium bromide (CTAB) and fluoride (CTAF) on several SNAr and BAC2 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 (Ks), the second‐order rate constant for reaction in the micelles (K 2M) and the exchange constant KOH/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. Copyright © 1990 John Wiley & Sons Ltd.