Kinetics and mechanism of base hydrolysis of chromium(III) complexes with oxalates and quinolinic acid

Wı́sniewska

2011

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Mer-[Cr(pic) 3 ] 0 and [Cr(ox) 2 (pic)] 2-undergo successive base hydrolysis to give chromates(III). Dissociation of the first ligand, pic from [Cr(pic) 3 ] 0 and ox from [Cr(ox) 2 (pic)] 2-, proceeds in two stages, namely initial chelate-ring opening followed by slower liberation of the monodentate ligand. Kinetics of both the stages were studied spectrophotometrically in 0.2-0.9 M NaOH solution, under pseudo-first-order conditions. The calculated values of k obs were independent of [OH -]. A mechanism is proposed, where the formation of intermediates in the hydroxo form prevents the monodentate ligand from undergoing chelate-ring closure. Evidence for the formation of an intermediate with O-bonded picolinate is given. The effects of pH and the complex composition on the reactivity are discussed.

mentioning

confidence: 69%

Kinetics and mechanism of base hydrolysis of mer-[Cr(pic)3]0 and [Cr(ox)2(pic)]2− (pic = picolinate, ox = oxalate)

Marai

Wı́sniewska

2011

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“…Previously, series of complexes with pyridinemonocarboxylato and pyridinedicarboxylato ligands were obtained and kinetic studies on their acid-and base-catalysed aquation were performed [e.g. [6][7][8][9][10]. Additional studies on their effect toward 3T3 fibroblasts revealed that they are not toxic and may be good candidates as biochromium sources [6,10].…”

Section: Introductionmentioning

confidence: 99%

Kinetic studies on chromium-glycinato complexes in acidic and alkaline media

Marai

Muzioł

et al. 2010

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], where k 0 and k 1 are rate constants for the chelate-ring opening via spontaneous and acid-catalysed reaction paths, respectively, and K p1 is the protonation constant. The proposed mechanism assumes formation of the reactive intermediate as a result of proton addition to the coordinated carboxylate group of the didentate ligand. Some kinetic studies on the second reaction stage, the one-end bonded glycine liberation, were also done. The obtained results were analogous to those for stage I. In this case, the proposed reactive species are intermediates, protonated at the carboxylate group of the monodentate glycine.

“…As discussed earlier [6,7], changes within the lower energy d-d band can be attributed to the first ligand dissociation because liberation of the second and third ligands from the appropriate hydroxo complexes has very little effect on this spectral region. Thus, monitoring the base hydrolysis within this spectroscopic range, it is possible to determine the pseudo first-order rate constants for both the reaction stages using a consecutive A ?…”

Section: Resultsmentioning

confidence: 79%

“…Recently, the synthesis of new [Cr(ox) 2 (pdaH)] 2--type complexes (where pdaH 2 = 2,3-, 2,4-or 2,5-pyridinedicarboxylic acid), as well as the kinetics of their aquation in acidic and alkaline solutions and their effect on 3T3 fibroblasts proliferation have been described [5][6][7]. The results of these studies suggest that they may be promising candidates for dietary supplements.…”

Section: Introductionmentioning

confidence: 99%

“…83°), which indicates a high degree of strain in the chelate rings. On the other hand, in the case of [M(ampy) 2 Cl 2 ]X n complexes (M = Co(III), Cr(III), X = Cl -, S 2 O 6 2-), application of XRD revealed that they form cis-isomers with either a-cis (cis-X, trans-py, cis-NH 2 ) or b-cis (cis-X, cis-py, trans-NH 2 ) arrangement [16,18]. Accordingly, both fac-and mer-isomers of [M(ampy) 3 ]Br 3 were obtained, as confirmed by 1 H NMR and XRD methods [15,17].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Potential biochromium sources; kinetic studies on acid- and base-catalyzed aquation of [Cr(ox)2(2-(aminomethyl)pyridine]−

Lisiak

2010

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Acid-and base-catalyzed hydrolysis of [Cr(ampy)(ox) 2 ] -, where ampy = 2-(aminomethyl)pyridine, leads to successive dissociation of the ligands via concurrent reaction paths, whereas at pH 1-9 only ampy is liberated as a result of spontaneous processes. The first ligand dissociation proceeds via aqua intermediates with one-end bonded ampy (1) or ox ligands (2), respectively, which in alkaline media undergo rapid deprotonation to give the appropriate hydroxo-forms. The kinetics of two reaction stages, namely the chelate ring opening and the ligand liberation, were studied spectrophotometrically. In acidic media, the first stage is much faster than the second, whereas in alkaline solutions, both the stages are characterized by similar rate constants. The dependences of k obs on [H ? ] are as follows: k obs1,H = a 1 ? b 1 /[H ? ], k obs2,H = a 2 ? b 2 [H ? ]. At pH [ 13, rate constants k obs1 , OH and k obs2 , OH are [OH -] independent. The effect of pH on the complex reactivity was rationalized based on proposed mechanisms.