Effect of carbonate ion on the hydrolysis of brilliant green in aqueous solution and in micellar media

Abstract

In an aqueous solution of dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), cetyltrimethylammonium  bromide (CTAB), hexadecylpyridinium bromide (C₁₆PyBr), and hexadecyltriphenylphosphonium bromide (C₁₆TPPBr) at 25 °C, the effect of carbonate ion  on the hydrolysis of 16 brilliant green was studied. The change in pseudo-first order rate constant (k ) with surfactant concentration obs displays a  sigmoid shaped curve which is similar to positive co-operativity in enzymatic reaction. The catalytic factors of the surfactants (k_obs /k_w ) on the reaction are  7.51, 10.14 and 18.50 in aqueous solutions of DTAB, obs w TTAB and CTAB respectively which is consistent with the hydrophobic effect due to change in  the alkyl chain length of the surfactants. In C₁₆PyBr, CTAB and C₁₆TPPBr the catalytic factors are 23.40, 18.50 and 4.02  respectively. This can be  explained to be due to modification in the head groups of the surfactants and the competition between electrostatic and hydrophobic effects of the  carbonate ion and brilliant green for the cationic surfactant. The data obtained fit the pseudophase model of micellar catalyzed reaction.