Cationic micelle induced reaction kinetic on de-phosphorylation of substituted mono phenyl phosphate ester in borate buffers of pH 8.0 to 10.0

Abstract

Department of Chemistry, Government Raza P. G. College, Rampur-244 901, Uttar Pradesh, India E-mail : bhadanaadesh@ yahoo.co.in Manuscript received 9 November 2006, revised 7 May 2007, accepted 18 July 2007 Hydrolysis of mono 4-methyl phenyl phosphate and 4-ethyl phenyl phosphate ester has been studied with CTAB, a cationic surfactant at 40 ± 1: 1.0°C in borate buffers solutions of pH= 8.0, 9.0 and 10.0. Absorbances of them were mcasurcd spectrophotomdrically and used to calculate rate constant of the hydrolysis, which found to be pseudo-first order. The process was run with and without CTAB with Kψ and K'w as rate constants respectively and the concentration of phosphate was restricted to 5.0 x 10-4 mol dm-3 and CTAB varied in between 0.2 x 10-1 to 2 x 10-3 mol dm-3. Rate constanls increase with concentrations of CTAB, giving as rate maximum Kψ = 67.3 x 105 S-1 at 18 x 103 mol dm-3 CTAB and Kψ = 58.3 X 105 S-1 at 16 x 103 mol dm-3 CTAB respectively at pH= 8.0 and pH= 9.0 for dianions of 4- mpp. But 4-EPP giving as rate maximum Kψ = 69.5 x 105 S-1 at 18 x 103 mol dm-3 CTAB and K'w= 60.8 x 10-3 S-1 at 16 x 10-3 mol dm-3 CTAB respectively at pH= 8.0 and pH= 9.0, it is concluded that the contribution of methylene group towards dcphosphorylation has been found to he 2.2 x 10-5 S-1 and 2.5 x 10-5 S-1 with respect to 18 x 10-3 mol dm-3 CTAB and 16 x 10-3 mol dm-3. The values of ion exchange parameters calculated at pH 8.0 and 9.0 by using various ion exchange equation have been summarized and found mSOH (concentration of reaction ion in Stern layer) 0.14, 0.452. Ks (binding constant) in 103 mol dm-3 is 1.06, 3.64. Kw (second order rate constant of water) in 105 mol dm-3 S-1 is 215,396. [OH-w](ion concentration in water) in 103 mol dm-3 is 3.76, 20.43. [OH-m] (ion concentration in micelle) in 104 mol dm-3 is 1.32, 3.70 at borate buffer 3.9 x 103 mol dm-3 [OH-], 20.3 x JO'l mol dm-3 [OH-]. Activation enerqy is 7.64 kca/mol and entropy is 32.06 [-∆S ± (eu)] at pH = 8 and used borate buffer 3.9 x 103 mol dm-3 [OH-].