title: Origin of Acid-Base Catalytic Effects on Formaldehyde Hydration.
abstract: The mechanisms of hydronium- and hydroxide-catalyzed formaldehyde hydrations were investigated by quantum mechanical/molecular mechanical molecular dynamics in combination with flexible coordinates. A stepwise bimolecular and a concerted termolecular mechanism were found with a hydronium catalyst. The latter is more favorable and better consistent with experiment. Structurally, a dipole-bound species initially arranges the nucleophile in a favorable configuration for both routes, significantly enhancing the reactive collisions. On the one hand, the hydronium catalyst also plays a role of a reactant in the bimolecular path. On the other hand, only a stepwise mechanism was found with a hydroxide catalyst. Overall, hydroxide is a stronger catalyst than a hydronium when it is in contact distance with formaldehyde.
authors.affiliation: Department of Chemistry and Green-Nano Materials Research Center, College of Natural Sciences, Kyungpook National University , Taegu 702-701, South Korea.
authors.forename: Nizam
authors.initials: N
authors.lastname: Uddin
authors.affiliation: Department of Chemical Engineering Education, Chungnam National University , Daejeon 305-764, South Korea.
authors.forename: Tae Hoon
authors.initials: TH
authors.lastname: Choi
authors.affiliation: Department of Chemistry and Green-Nano Materials Research Center, College of Natural Sciences, Kyungpook National University , Taegu 702-701, South Korea.
authors.forename: Cheol Ho
authors.initials: CH
authors.lastname: Choi