名称:
Oxidation of glyoxylic acid by a mononuclear manganese(IV) complex of 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane: A kinetics and mechanistic study
摘要:
The oxidation of glyoxylic acid (HGI) by (MnL)-L-IV {L4- = tetra deprotonated 1,8-bis(2-hydroxybenzamido)-3,6-diazaoctane) was investigated in the pH range 1.67-10.18, at 25-45 degrees C and 0.5 M ionic strength. The reaction exhibited biphasic kinetics with (MnL-)-L-III as the reactive intermediate. Mn-IV was reduced to Mn-II. The products of oxidation of HGI were identified as formic acid and CO2 in acidic medium, and oxalate in basic medium, consistent with the stoichiometry: -Delta[Mn-IV]/-Delta[HGI] = 1. In acidic medium, both (MnL)-L-IV and (MnL-)-L-III formed outer-sphere adducts with the neutral HGI {HC(OH)(2)COOH} molecule, with an association constant Q(IV) of 28 and 70 M-1, respectively. A similar adduct formation was not observed for the glyoxylate mono anion (Gl(-), CH(OH)(2)(CO2-)) and glyoxylate dianion {Gl(2-), CH(OH)(O-)CO2-}. The rate and activation parameters for the various paths are reported and an outersphere electron transfer mechanism is suggested. (C) 2011 Elsevier Ltd. All rights reserved.