The Rhodium-Catalyzed Carbonylation of Linear Primary Alcohols

Article abstract of DOI:10.1021/ja00298a027

The results of a comprehensive kinetic, spectroscopic, and analytical study into the rhodium-catalyzed carbonylation of primary linear alcohols (R = Me, Et, and n-Pr) are reported.In all cases, the reaction rate is first order in both and added and independent of CO pressure.The only rhodium species observed under catalytic conditions was RhI2(CO)2^1-.The rates of carbonylation of the alcohols decreased in the order MeOH > EtOH >n-Pr with relative rates at 170 deg C of 21:1:0.47.Apparent activation parameters have been determined.All the data are consistent with the rate-determining step being nucleophilic attack by the rhodium ion on the corresponding alkyl iodide, in agreement with the previous interpretation of the methanol system.Important information was also obatained regarding the stability of the intermediate rhodium alkyl species.Carbonylation of n-PrOH gave a mixture of the two isomeric product butyric acids, the composition of which depended on the CO pressure.The isobutyric acid appears to arise from the isomerization of the initially formed n-alkyl species, and the pressure dependence of this process suggests that loss of CO from the alkyldicarbonylrhodium(III) species is competitive with the migratory insertion reaction which forms the analogous monocarbonyl acyl species observed previously.