Kinetics, Mechanism, and Thermodynamics of Glyoxal-S(IV) Adduct Formation

Article abstract of DOI:10.1021/j100313a056

The reversible addition of glyoxal (ethanedial) and S(IV) to form glyoxal monobisulfite (GMBS) was studied spectrophotometrically over the pH range of 0.7-3.3.Far from equilibrium, the rate of GMBS formation is given by d/dt = (k_1,appα₁) + k_2,appα₂), where = <(CH(OH)2)2> + + , = + -> + 2->, α₁ = ->/, and α₂ = 2->/.The apparent rate constants, k_1,app = 0.13 M^-1 s^-1 and k_2,app = 2.08E3 M^-1 s^-1, are pH independent functions of the dehydration equilibrium constants of (CH(OH)2)2 and CHOCH(OH)2, and intrinsic rate constants for the reaction of HSO3^- and SO3^2- with unhydrated and singly hydrated glyoxal.Glyoxal dibisulfite (GDBS) and GMBS were shown to dissociate with a rate given by d/dt = -1 + k"_-1K_D3 + (k'_-2K'_a2 + k"_-2K"_{a2^KD3)/+>>t + -3} + k_-4Ka3^/+>>_t, where k_-1 and k_-2 correspond to the release of bisulfite and sulfite, respectively, from unhydrated and hydrated GMBS species; k_-3 and k_-4 correspond to the release of bisulfite and sulfite from GDBS; KD3 is the dehydration constant for GMBS; K'_a2, K"_a2, and K_a3 are acid dissociation constants.Stability constants for the formation of GMBS and GDBS were determined to be ^cK₁ = ->/(-) = 2.81E4 M^-1 and ^cK₂ = <(CH(OH)SO3^-)2>/(->->) = 1.45E4 M^-1 at 25 deg C and μ = 0.2 M.