Acidity effects on light-promoted carbonylation of olefins in the presence of cobalt catalysis

Abstract

Camphene (and other olefins) was photolytically methoxycarbonylated in methanol-acetone solution containing a catalytic amount of bis(acetylacetonato)cobalt(II), Co(acac) 2, at room temperature and atmospheric pressure when the solution was irradiated with UV light through a Pyrex filter. In this photocarbonylation, the presence of an externally added acid, such as chlorinated or fluorinated acetic acids or HCl, retarded the rate of carbonylation and shifted the product distribution in favor of aldehyde from ester. The effects became progressively more pronounced as the acidity of the acid increases. The Co(II) salts of these acids also serve as catalyst precursors to promote the photocarbonylation to give similar trends, i.e. the retardation of rates and higher yields of aldehyde when Co(II) salts of stronger cojugate acids (than acetylacetone) were used. The results are explained by the effect of acid (either added externally or generated in situ) on the ionization equilibrium of cobalt carbonyl species.