Acid-catalyzed Hydrolysis of the cis-[Cr(1,10-phenanthroline)2(O2CO)]+ Ion Studied by the u.v.–vis Stopped Flow Method

Abstract

Acid-catalyzed hydrolysis of the cis-[Cr(1,10-phenanthroline) 2 (O 2 CO)] + ion studied by the u.v.-vis stopped flow method Abstract The cis-½Cr(phen) 2 ðO 2 COÞ þ ion was prepared through the displacement of two molecules of water from the cis-½Cr(phen) 2 ðOH 2 Þ 2 3þ by the bidentate carbonate anion. It underwent two-phase hydrolysis reactions under acidic conditions (0:1 < ½H þ < 2:7 M) at 5, 10, 15, 20 and 25°C. Via slow carbonato chelate ring opening (first step k slow 1 ) and a second fast decarboxylation (k fast 2 value). The first step was preceded by protonation of the coordinate bidentate carbonate ligand. The second step exhibited no pH dependence, while k slow 1 values increased with acid concentration that suggested the presence of both protonated and deprotonated reactant species. Based on these observations we have proposed a hydrolysis mechanism featuring H 2 O-induced ring-opening of the coordinate CO 2À 3 group in the first step ðk slow 1 Þ followed by loss of CO 2À 3 from two intermediates, ½Cr(phen) 2 ðO 2 COHÞ 2þ ðk slow 1 Þ and ½Cr(phen) 2 ðOH 2 ÞðO 2 COHÞ 2þ ðk fast 2 Þ.

Kinetic studies of acid-catalyzed hydrolysis of the cis-[Cr(oxalate)(pyridoxamine)CO3]−coordination anion

“…The increase in the rate constants with an increase of the ionic strength indicates that two protolytic forms (Scheme 1) are involved in the rate determining step. A similar observation was made in our previous papers [15,16]. In the present report, we describe the study of the reaction of acid-catalyzed hydrolysis of cis-[Cr(oxalate)(pyridoxamine)CO 3 ] -.…”

“…In the present report, we describe the study of the reaction of acid-catalyzed hydrolysis of cis-[Cr(oxalate)(pyridoxamine)CO 3 ] -. In our previous works [15,16] but one cannot find data on the acid hydrolysis of chromium(III) complexes. This can be attributed to different factors in the case of both types of complexes: steric hindrance, geometric arrangement of the ligands and electronic effects.…”

“…This paper is a continuation of kinetic studies on CO 2 uptake and acid-catalyzed hydrolysis reactions with coordination compounds of some chosen transition metal centers such as chromium(III) or cobalt(III) [15,16].…”

Reaction mechanisms in solution

“…[67][68][69] Acid-catalysed hydrolysis of cis-[Cr(phen) 2 (O 2 CO)] + exhibits biphasic kinetics, the first step being slow carbonato chelate ring-opening, the second being fast decarboxylation. 70 ). 71…”