Homogenous catalytic conjugation of polyunsaturated fats by chromium carbonyls

Various arene‐Cr (CO)3 complexes and Cr(CO)6 are effective soluble catalysts for the conjugation of polyunsaturated fats. Methyl benzoate‐Cr(CO)3 is one of the most active catalysts. The following conjugation levels were obtained: methyl linoleate, 65%; methyl linolenate, 45%; the polyunsaturates in soybean and safflower oils, 73%; and in linseed oil 48%. Conjugated dienes from linoleate were predominantlycis,trans in configuration. Their double bonds were distributed between C5 and C16 of the fatty acid chain. Hydrogenation and dehydrogenation are side reactions, which seem to limit the yield of conjugated dienes from methyl linoleate. A conjugation mechanism is proposed that involves allyl‐HCr(CO)3 complexes as intermediates undergoing 1,3‐ and 1,5‐hydrogen shifts.