The kinetics of the hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyl diphenyl phosphate (PNPDPP) by hydroxamate ions mediated by gemini surfactants with quaternary ammonium bromide (16-n-16,2Br(-), n = , 4, 6, 12) and pyridinium chloride (12py-n-py12,2Cl(-), n = , 4) head group have been investigated at 27 degrees C. The gemini surfactant with the pyridinium head group, 12-py-4-py12,2Cl(-) (tetramethylene-1,4 bis dodecylpyridinium chloride) shows a large rate acceleration effect than that with an ammonium head group, 16-12-16,2Br(-), relative to those in water. The apparent pK(a) of the hydroxamic acids have been determined in the presence of gemini surfactants. Catalytic system N-phenylbenzohydroxamate/12py-4-py12,2Cl(-) demonstrated over similar to 1,590-fold and similar to 255-fold rate enhancement in the hydrolysis of PNPA and PNPDPP, respectively, for the identical reaction performed in buffer aqueous media at 27 degrees C. The second order rate constant and binding constants for reactions were determined employing pseudophase model for micellar catalysis.
Effect of cationic gemini surfactants on the hydrolysis of carboxylate and phosphate esters using hydroxamate ions
QUAGLIOTTO, Pierluigi;
2008-01-01
Abstract
The kinetics of the hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyl diphenyl phosphate (PNPDPP) by hydroxamate ions mediated by gemini surfactants with quaternary ammonium bromide (16-n-16,2Br(-), n = , 4, 6, 12) and pyridinium chloride (12py-n-py12,2Cl(-), n = , 4) head group have been investigated at 27 degrees C. The gemini surfactant with the pyridinium head group, 12-py-4-py12,2Cl(-) (tetramethylene-1,4 bis dodecylpyridinium chloride) shows a large rate acceleration effect than that with an ammonium head group, 16-12-16,2Br(-), relative to those in water. The apparent pK(a) of the hydroxamic acids have been determined in the presence of gemini surfactants. Catalytic system N-phenylbenzohydroxamate/12py-4-py12,2Cl(-) demonstrated over similar to 1,590-fold and similar to 255-fold rate enhancement in the hydrolysis of PNPA and PNPDPP, respectively, for the identical reaction performed in buffer aqueous media at 27 degrees C. The second order rate constant and binding constants for reactions were determined employing pseudophase model for micellar catalysis.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.