Reactions of cobalt carbonyl catalysts in methanol under syngas pressure

Abstract

Co 2(CO) 8 1 reacts in methanol at 80 °C with CO/H 2 at 95 bar faster than in hydrocarbon solvents. The HCo(CO) 4 initially formed dissociates largely to H + and Co(CO) 4 − 3'. [Co(MeOH) 6] [Co(CO) 4] 2 reacts with CO/H 2 directly or via the intermediate formation of 1 to yield H + and Co(CO) 4 −. Addition of iodide enhances the rate of formation and also the steady state concentration of 3'. The higher concentrations of H + and Co(CO) 4 − contribute to the increased rate of methanol homologation, in addition to the well-known methyl iodide formation. The hydroformylation of 1-octene is faster in methanol than in nonpolar solvents, yielding mainly dimethylacetals as well as some carboxylic acid esters. Co(CO) 4 − is the only cobalt carbonyl species detectable by IR and UV spectroscopy or polarography during the hydroformylation (HF) in methanol. It is proposed that the HF is started by the addition of H + and Co(CO) 4 − to the olefin to give the alkyl complex. The acyl cobalt tetracarbonyl formed in the next step may react in an acid-catalyzed reaction with Co(CO) 4 − and methanol to give the dimethylacetals, with methanol to give methyl carboxylates, or with H 2 to give aldehydes. The relative importance of these processes depends on the reaction conditions. At high temperatures and high syngas pressure, the acetal formation dominates.