MICELLAR RATE EFFECTS ON REACTIONS OF HYDROXIDE ION WITH PHOSPHINATE AND THIOPHOSPHINATE ESTERS

Cationic micelles of cetyltrimethylammonium chloride, bromide and mesylate (CTACl, CTABr, CTAOMs) speed reactions of OH- with phosphinate and thiophosphinate esters: Ph2PO.OPh (1a), Ph2PO.OC6H4NO2-p (1b), Ph(i-Pr)PO.OC6H4NO2-p (1c), Ph2PO.SEt (2a), Ph2PO.SPh (2b), (EtO)2PO.SPh (2c) and (EtO)2PS.OC6H4NO2-p (Parathion, 3). First-order rate constants go through maxima with increasing [surfactant]. The rate-surfactant profiles are fitted quantitatively in terms of a kinetic model that treats the distribution of OH- between aqueous and micellar pseudo-phases in terms of coulombic and non-coulombic ion-micelle interactions. Second-order rate constants at the micellar surface are lower than in water by factors that range from 0.035 for 1a to 0.7 for 1c. The thiophenyl derivative (2b) is more reactive than the corresponding phenoxy derivative (1a) and it is more reactive than the corresponding thioethyl derivative (2a). Parathion (3) is the least reactive substrate in both water and micelles.