Kinetic analysis of the disproportionation of aqueous glyoxal

Rates of disproportionation of 0.015–0.4 mM aqueous glyoxal toglycolic acid were measured at 0.24–75 mM NaOH and constant ionic strength, leading to the empirical rate expression r = ( a 1 [OH − ] + a 2 [OH − ] 2 ) [ G T ]/(1 + a 3 [OH − ]), where [ G T ] is the total glyoxal concentration. These results were confirmed in bicarbonate/carbonate buffer and at 2–20 mM [ G T ]. The rate form is in contradiction to earlier work on glyoxal, which suggested a second‐order dependence on [OH − ], but agrees with the rate equation for phenylglyoxal disproportionation. The kinetic data can be explained by a mechanism postulating the presence of monohydrated and dihydrated forms of glyoxal in equilibrium, with the rate‐limiting steps being intramolecular hydride ion transfers to the unhydrated carbonyl carbon of the mono‐ and divalent anions of glyoxal monohydrate.