Infrared study and quantum calculations of the conversion of methylbutynol into hydroxymethylbutanone on zirconia

The activity and selectivity of metal oxides toward 2-methyl-3-butyn-2-ol (methylbutynol, MBOH) conversion depend on their surface properties. The aim of the present work was to explain the formation of 3-hydroxy-3-methyl-2-butanone (hydroxymethylbutanone, HMB) on zirconia. IR study showed that MBOH and HMB adsorption on ZrO2 was dissociative with the formation of alcoholate species. The transformation of MBOH toward HMB involved residual surface hydroxyl groups or traces of water either contained in the MBOH reactant or formed from MBOH condensation on residual hydroxyl groups and polymerization of acetone, a by-product of the reaction. This polymerization caused a deactivation of the MBOH hydration. Quantum chemistry calculations indicated that pi electrons from the acetylenic MBOH triple bond interacted with a vacant zirconium d orbital polarizing this pi distribution and hence facilitating nucleophilic attack of the carbon 2(-C-C=C-H). This suggested that active sites in the formation of HMB can be acid-base M-O sites, in which M represents a metal with vacant d orbitals. Since the addition of water can noticeably favor HMB formation, it thus appears that the MBOH test should be supported by a systematic study of the effect of adding water to the reactant to evidence possible formation of HMB on the catalyst studied. (C) 1997 Academic Press.