Abstract
Disproportionation of methyl abietate by metal complex catalysts was studied. The catalysts used were RhCI (PPh3) 3, PdCl2 (PPh3) 2, PtCl2 (PPh3) 2, Fe (CO) 5, Cr (CO) 5, Fe (acac) 3, Co (acac) 3, Pd/C, and I2. Among these Fe (CO) 5 was the most effective catalyst at 250°C. The effects of reaction temperature and catalyst amount on the product composition were investigated, and it was found that, with 10% Fe (CO) 5 at 250°C, almost all of methyl abietate entered into the reaction in 4 hr affording methyl dehydroabietate (66%) and methyl dihydroabietates (27%). Methyl dihydroabietates were separated by chromatography and their structures were determined by NMR and mass spectrometry. From the relative amounts of two isomers of methyl dihydroabietates, selectivity in hydrogenation was recognized. In the case of I2 catalyst, 13 α- (RtDeAb 0.46) and 13 β-abiet-8-enoate (RtDeAb 0.49) were obtained in 15.0% and 22.2% yield, respectively, while in the case of Fe (CO) 5 catalyst, the yields were 6.0% and 18.1%, respectively. Further, it was found that Fe (CO) 5 was effective for the disproportionation between methyl abietate and methyl linolate.
