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Kinetics and mechanism of the cobalt(III) tetraammine complex-promoted hydrolysis of 4-nitrophenyl glycinate

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Title Kinetics and mechanism of the cobalt(III) tetraammine complex-promoted hydrolysis of 4-nitrophenyl glycinate
 
Creator PHULAMBRIKAR, AA
CHATTERJEE, C
 
Subject amino-acid esters
phosphate diesters
nickel(ii)
copper(ii)
reactivity
 
Description The kinetics of the hydrolysis of 4-nitrophenyl glycine ester (PNPG) catalysed by [Co(OH)(trien)(OH2)](2+), [Co(OH)(tren)(OH2)](2+) and [Co(OH)(en)(2)(OH2)](2+) complexes has been studied spectrophotometrically in weakly basic aqueous media (pH = 6.5 to 7.4). Kinetic experiments were carried out as a function of the pH, complex concentration and temperature. The rate of hydrolysis increases linearly with the complex concentration with a trend to wards rate saturation, suggesting the formation of associative species in a pre-equilibrium step. The pseudo-first order rate constant, k(obs), increases rapidly with a decrease in the hydrogen-ion concentration. The complexes promote the hydrolysis of 4-nitrophenyl glycinate significantly, and the acceleration rate is about 400-600. An attack of external OH- on the chelated ester is suggested as a probable mechanism for the hydrolysis. The lower rate enhancements observed in the present study could probably be ascribed to a weaker cobalt(III) alkoxy carbonyl interaction in the chelate, owing to a decreased nucleophilicity of the carbonyl oxygen in the p-nitrophenyl ester. The activation parameters for all three complex-promoted reactions are found to be comparable, thus suggesting a common mechanism operative in all complex catalysed reactions.
 
Publisher CHEMICAL SOC JAPAN
 
Date 2011-07-20T08:26:42Z
2011-12-26T12:51:23Z
2011-12-27T05:35:17Z
2011-07-20T08:26:42Z
2011-12-26T12:51:23Z
2011-12-27T05:35:17Z
2002
 
Type Article
 
Identifier BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 75(7), 1515-1519
0009-2673
http://dx.doi.org/10.1246/bcsj.75.1515
http://dspace.library.iitb.ac.in/xmlui/handle/10054/5409
http://hdl.handle.net/10054/5409
 
Language en