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Acid and metal ion promoted hydrolysis of [N-(o-carboxyphenyl)iminodiacetato](picolinato)chromate(III) complex: a mechanistic study

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Title Acid and metal ion promoted hydrolysis of [N-(o-carboxyphenyl)iminodiacetato](picolinato)chromate(III) complex: a mechanistic study
 
Creator CHATTERJEE, C
STEPHEN, M
 
Subject equilibrium
acid promoted hydrolysis
metal ion promoted hydrolysis
chromium(iii) complexes
resonance interactions
 
Description The sodium salt of the [N-(o-carboxyphenyl)iminodiacetato]picolinatochromate(III) complex has been synthesised and characterised. In acidic media, the complex has been shown to aquate to diaqua[N-(o-carboxyphenyl)imminodiacetato]chromium(III) and picolinic acid as the ultimate products. The enhanced kinetic stability exhibited by the aromatic amino acid (cida) may be attributed to (i) resonance interaction of the carboxyl and tertiary nitrogen group with the phenyl ring resulting in a shortening of the bond distance and thus leading to a closer approach of the chelate donor groups, (ii) the presence of a larger number (two five-membered and one six-membered ring) of chelate rings in the ligated amino acid, in comparison to only one five-membered metal-picolinato ring. The variation of the observed pseudo-first-order rate constants with perchloric acid concentration suggests the operation of two concurrent uncatalysed and acid-catalysed pathways. The reaction exhibits a solvent deuterium isotope effect k(D)/k(H) = 1.5 at 45 degreesC. The solvent deuterium isotope effect is consistent with a rapid pre-equilibrium. protonation followed by rate-determining ring opening and excludes a mechanism involving concerted attack by [H3O+]. The metal ions, Cu2+, Ni2+, and Zn2+, promoted hydrolysis in weakly acidic medium has been studied as a function of metal ion concentration and temperature. The metal ion catalysed aquation is proposed to take place through a rapid pre-equilibrium step to form a binuclear complex with the M2+ ion, followed by the cleavage of the Cr-O bond in a slow rate-determining step. The catalytic efficiency of the metal ion follows the Irving-Williams order of stability and also parallels the logk(M-pic) values. (C) 2001 . .
 
Publisher PERGAMON-ELSEVIER SCIENCE LTD
 
Date 2011-08-23T10:52:15Z
2011-12-26T12:56:25Z
2011-12-27T05:45:09Z
2011-08-23T10:52:15Z
2011-12-26T12:56:25Z
2011-12-27T05:45:09Z
2001
 
Type Article
 
Identifier POLYHEDRON, 20(24-25), 2917-2924
0277-5387
http://dx.doi.org/10.1016/S0277-5387(01)00875-0
http://dspace.library.iitb.ac.in/xmlui/handle/10054/10494
http://hdl.handle.net/10054/10494
 
Language en