Kinetics and mechanism of base hydrolysis of chromium(III) complexes with oxalates and quinolinic acid |
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| Authors: | Ewa Kita Hasan Marai |
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| Institution: | (1) Department of Chemistry, Nicolaus Copernicus University, 87-100 Toruń, Poland |
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| Abstract: | Base hydrolysis of Cr(ox)2(quin)]3− (where quin2− is N,O-bonded 2,3-pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to a formation of a
mixture of oligomeric chromium(III) species, known as chromates(III). The reaction proceeds through Cr(ox)(quin)(OH)2]3− and Cr(quin)(OH)4]3− formation. Dissociation of oxalato ligands is preceded by the opening of the Cr-quin chelate-ring at the Cr–N bond. The kinetics
of the chelate-ring opening and the first oxalate dissociation were studied spectrophotometrically, within the lower energy
d–d band region at 0.4–1.0 M NaOH. The pseudo-first-order rate constants (k
obs0 and k
obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of Cr(ox)(quin)(OH)2]3− and cis-Cr(ox)2(OH)2]3− were studied. The determined pseudo-first-order rate constants were independent of OH−]. A mechanism is postulated that the reactive intermediate with the one-end bonded quin ligand, Cr(ox)2(O-quin)(OH)]4−, formed in the first reaction stage, subsequently undergoes oxalates substitution. Kinetic parameters for the chelate-ring
opening and the first oxalate dissociation were determined. |
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