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‐α,ω‐dicarboxylic acids (C 18 −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‐α,ω‐dicarboxylic acids and long‐chain unsaturated hydrocarbons by means of this solvent‐free ruthenium‐catalyzed self‐metathesis of readily available monounsaturated FA.