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

Hydrolysis of mono 4-methyl phenyl phosphate and 4-ethyl phenyl phosphate ester has been studied with CTAB, a cationic surfactant at 40 ±1.0 °C in borate buffers solutions of pH = 8.0, 9.0 and 10.0. Absorbances of them were measured spectrophotometrically 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 K Ψ 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 -3 to 2 x 10 -3 mol din-3. Rate constants increase with concentrations of CTAB, giving as rate maximum K Ψ = 67.3 x 10 -5 s -1 at 18 x 10 -3 mol dm -3 CTAB and K Ψ = 58.3 x 10 -5 s -1 at 16 x 10 -3 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 K' w = 69.5 x 10 -5 s -1 at 18 × 10 -3 mol dm -3 CTAB and k' Ψ = 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 dephosphorylation has been found to be 2.2 x 10-5 s -1 and 2.5 × 10 -5 s -1 with respect to 18 × 10 -3 mol dm -3 CTAB and 16 × 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 m S OH (concentration of reaction ion in Stern layer) 0.14, 0.452. K S (binding constant) in 10 3 mol dm -3 is 1.06, 3.64. K w (second order rate constant of water) in 10 5 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 × 10 -3 mol dm -3 [OH - ], 20.3 x 10-3 mol dm -3 [OH-]. Activation energy is 7.64 kcal/mol and entropy is 32.06 [-AS ± (eu)] at pH = 8 and used borate buffer 3.9 x 10 -3 mol dm -3 [OH - ].