Metathesis of unsaturated fatty acids:: Synthesis of long-chain unsaturated-α,ω-dicarboxylic acids

The self-metathesis of readily available monounsaturated FA has the potential of being an important pathway for the synthesis of symmetrical long-chain unsaturated-alpha,omega-dicarboxylic acids (C-19-C-26). Previous studies on the self-metathesis of monounsaturated FA esters using ruthenium catalysts in solution, however, suffered from low conversions as a result of the thermodynamic control of the reaction. We have found that the second-generation Grubbs catalyst can effectively catalyze the solvent-free self-metathesis of monounsaturated FA of varying purity (from 90 to 99%) to afford two important products-monounsaturated dicarboxylic acids and hydrocarbons-in very high molar conversions (> 80%). This solvent-free self-metathesis reaction also works for monounsaturated FA containing additional functional groups. Reactions were conducted at catalyst loadings as low as 0.005 mol%, and turnover numbers as high as 10,800 could be obtained. This discovery represents an attractive approach to the large-scale production of useful monounsaturated-alpha,omega-dicarboxylic-acids and long-chain unsaturated hydrocarbons by means of this solvent-free ruthenium-catalyzed self-metathesis of readily available monounsaturated FA.