Decarboxylation and Dephosphorilation in new Gemini Surfactants: Changes in Aggregate Structures

Dicationic gemini surfactants, [CH3-(CH2)m-Me2N+CH2ArCH2N+Me2-(CH2)m-CH3]2Br-, where CH2ArCH2 is the spacer, with Ar ) 2,5-(MeO)-C6H2, have been prepared with bromide as counterion and with m ) 11, 13, and 15, pXMo(DDA)2, pXMo(MDA)2, and pXMo(CDA)2, respectively; their physical properties have been compared with those of bis-(2,5-n-dodecyloxy)bis(trimethylammonium)benzene, pXDo(TA)2, and a surfactant with an unsubstituted spacer, m ) 11 and ArdC6H4, pX(DDA)2. Solubilities of pXMo- (DDA)2, pXMo(MDA)2, pXMo(CDA)2, and pXDo(TA)2 are much higher than that of pX(DDA)2 in water, and critical micelle concentrations, cmc’s, are lower than those of the corresponding monocationic surfactants. Micelles of pXMo(DDA)2, pXMo(MDA)2, pXMo(CDA)2, and pXDo(TA)2 significantly accelerate decarboxy- lation of 6-nitrobenzisoxazole-3-carboxylate ion and dephosphorylation of 2,4-dinitrophenyl phosphate dianion. Rate constants increase and become constant as substrates become fully micellar bound and then increase at surfactant concentrations which are greater than the cmc’s by factors of ca. 25. These subsequent increases are ascribed to changes in micellar morphologies, consistent with changes in 1H NMR line widths.