Synthesis of isobutanol by the Guerbet condensation of methanol with n-propanol in the presence of heterogeneous and homogeneous palladium-based catalytic systems

The catalytic synthesis of isobutanol ((BuOH)-Bu-i), via the Guerbet condensation of methanol with n-propanol is described. In particular, bifunctional catalysts based on either heterogeneous or homogeneous dehydrogenating/hydrogenating palladium species and on sodium methoxide (MeONa) as basic component were investigated. When heterogeneous Pd/C and MeONa was used as catalytic system a high activity was obtained with turnover numbers up to about 110mol of (BuOH)-Bu-i/(mol of Pd h). The increase of the MeONa/Pd molar ratio increased the activity of the catalyst. However, differently from Cu-based/MeONa catalysts, a significant metal leaching was observed; recycle experiments indicated that both heterogeneous and homogeneous palladium species are involved in the catalysis. When homogeneous palladium complexes, such as tetrakis(triphenylphosphine)palladium(0) [Pd(PPh3)(4)], diphenylphosphinoethane(dichloro)palladium(II) [Pd(dppe)Cl-2] and bis(dibenzylideneacetone)palladium(0) [Pd(dba)2], were used in combination with MeONa a remarkable activity was also obtained, independently of the oxidation state of the palladium precursor. During the reaction deposition of a solid was observed and recycle experiments carried out both on the recovered solid and on the liquid phase suggested that also in this case the activity has to be addressed to both heterogeneous and homogeneous (or colloidal) palladium species. (C) 2003 Elsevier Science B.V. All rights reserved.