Theoretical Studies on Mechanism and Rate Constant of Gas Phase Hydrolysis of Glyoxal Catalyzed by Sulfuric Acid

The gas phase hydration of glyoxal (HCOCHO) in the presence of sulfuric acid (H2SO4) were studied by the high-level quantum chemical calculations with M06-2X and CCSD(T) theoretical methods and the conventional transition state theory (CTST). The mechanism and rate constant of the five different reaction paths are considered corresponding to HCOCHO+H2O, HCOCHO+H2O⋯H2O, HCOCHO⋯H2O+H2O, HCOCHO+H2O⋯H2SO4 and HCOCHO⋯H2O+H2SO4. Results show that H2SO4 has a strong catalytic ability, which can significantly reduce the energy barrier for the hydration reaction of glyoxal. The energy barrier of hydrolysis of glyoxal in gas phase is lowered to 7.08 kcal/mol from 37.15 kcal/mol relative to pre-reactive complexes at the CCSD(T)/6-311++G(3df, 3pd)//M06-2X/6-311++G(3df, 3pd) level of theory. The rate constant of the H2SO4 catalyzed hydrolysis of glyoxal is 1.34×10−11 cm3/(molecule·s), about 1013 higher than that involving catalysis by an equal number of water molecules, and is greater than the reaction rate of glyoxal...