Acid-catalysed hydrolysis of cis-[Cr(C2O4)(AaraNH2)(OH2)(OSO2)]− (where AaraNH2 denotes methyl 3-amino-2,3-dideoxy-α,d-arabino-hexopyranoside)

Abstract

The synthesised complex cis-[Cr(C 2 O 4 )(AaraNH 2 )(OH 2 )(OSO 2 )] ) anion with SO 3 2) as a ligand in the inner coordination sphere, where AaraNH 2 denotes methyl 3-amino-2,3-dideoxy-a-D-arabino-hexopyranoside, was hydrolysed in the presence of acid at H + concentrations from 0.01 to 2.7 M (HClO 4 ). The reaction kinetics was studied with the stopped-flow spectrophotometric (u.v.-vis.) technique at temperatures of 5, 10, 15, 18 and 20°C. This hydrolysis turned out to be a single-step process. Determined for this reaction were the rate constant k 1 for the removal of SO 2 from the coordination sphere of the cis-[Cr(C 2 O 4 )(AaraNH 2 )(OH 2 )(OSO 2 )] ) ion and the constant pK 1 of the protonation of this species in the reaction preceding the hydrolysis. The final product of this reactiona new complex of Cr III , cis-[Cr(C 2 O 4 )(AaraNH 2 )(OH 2 ) 2 ] + , was obtained. A mechanism for the acid hydrolysis reaction is put forward based on the analysis of the rate constants obtained.