Cyclizations of 2-(omega-bromoalkyloxy)phenoxide ions in dicationic surfactants

Cyclization of 2-(3-bromopropyloxy)phenoxide ion (PhBr7) in micelles is a m odel for S(N)2 reactions of nucleophilic anions at micelle-water interfaces . In this paper we report observed rate constants (k(obs)) in aqueous micel les of dimeric surfactants. k(obs) in 1,4-bis(N-hexadecyl-N,N-dimethylammon ium)butane dibromide (1) is constant in a range of concentration, then incr eases at high [1], suggesting a transition to a different type of aggregate . A H-1 NMR investigation confirms a phase transition at the [1] which corr esponds to the reactivity change. (2S,3S)-2,3-Dimethoxy-1,4-bis(N-hexadecy, N-dimethylammonium)- butane dibromide (2) forms very large aggregates and s hows a modest catalytic effect. Cyclization of 2-(12-bromododecyloxy)phenox ide ion (PhBr16) in 1 under preparative conditions yields the intramolecula r cyclic product only despite a low effective molarity and a relative high substrate concentration This result reveals the presence of a well-organize d substrate-surfactant aggregate.