EFFECTS OF ASSOCIATION COLLOIDS ON ELIMINATION FROM 1,2-DIHALO-1,2-DIPHENYLETHANES - THE ROLE OF SURFACTANT STRUCTURE

Rates of E2 elimination of D,L-1,2-dichloro-1,2-diphenylethane (1) and the analogous dibromide (2) were measured in aqueous cetyltrimethylam monium chloride and hydroxide (CTACl and CTAOH), cetyltripropylammoniu m hydroxide (CTPAOH), didodecyldimethylammonium chloride and hydroxide (DDDACl and DDDAOH), and ,N-dimethyl-N-(2-hydroxyethyl)-n-hexadecylam monium hydroxide (DOH,OH). Micelles or other association colloids of t hese surfactants increase rates in solutions that contain OH-, and DOH ,OH is much more effective than the nonfunctional surfactants. Variati ons of first-order rate constants, k(obs), with [surfactant] or [OH-] are fitted by a pseudophase model with water and micelles as distinct reaction media, to give second-order rate constants in the latter. The se rate constants are in the sequence DOH,OH > CTPAOH approximate to D DDACl > DDDAOH approximate to CTAOH approximate to CTACl. Micelles fav or reactions of 2 over 1, relative to reactivities in water, due to di fferences in amphiphilic interactions with the leaving halide ions.