Synthesis of latexes with micelle like surfaces and their use as support for catalyst in the hydrolysis of organophosphate esters

In this study, latexes comprising quaternary ammonium ions were prepared to use as the reaction medium in the catalytic hydrolysis of organophosphate esters by o iodosobenzoate ion (IBA). The effects of the latex medium on the rate of the hydrolysis were investigated. Because the synthesized latexes contained n hexadecyl group on their quaternary ammonium ions, their surfaces mimicked those of the micelles of surfactants. First, a 5.0 mol % crosslinked latex was synthesized by emulsion polymerization of vinylbenzyl chloride and thereafter it was quaternized with varying amounts of N,N?dimethylhexadecylamine. In this way a series of cationic latexes containing 8 67 mol % quaternary ammonium ions were obtained. p Nitrophenyl diphenyl phosphate (PNPDPP) and paraoxon (PO) were used as the model organophosphate ester compounds. The hydrolysis rates of these substrates, especially of PNPDPP, greatly increased in the presence of the cationic latexes and strongly depended on the degree of quaternization and amount of the latex as well as pH, type of buffer. As the quaternization percentage of the latexes increased, the rates of the hydrolysis of PNPDPP increased. The kobserved and kcat of the PNPDPP hydrolysis reactions carried out with different amounts and type of cationic latexes at pH 7.0, 8.0 and 9.0 in different buffer solutions at 25 oC were determined. 1.0×10-5 M IBA in 0.25 mg/mL of KL 67 latex enhanced the rate of the hydrolysis of 1.0×10-5 M PNPDPP about 5670 times in TAPS buffered solution at pH 8.0 compared to the one in buffered solution and about 1590 times in the presence of IBA alone in TAPS buffered solution. In the PO hydrolysis carried out under similar conditions, the rate of hydrolysis increased about 1008 times compared to one obtained in TAPS buffered solution. In the hydrolysis of PNPDPP and PO by latex/IBA catalytic system, the highest values for kobserved were determined as 0.238 s 1 for PNPDPP and 6.85×10 5 s 1 for PO and the highest values for kcat were determined as 21160 M 1s 1 for PNPDPP and 6.95 M 1s 1 for PO.