Catalytic hydrogenation of soybean oil with Rh(l) dihydride complexes as catalysts

Cationic rhodium(I) complexes of the type [NBD Rh L2]+[C1O4]− (NBD = norbornadiene and L = diphenylphosphinoethane or triphenylphosphine) have been studied as catalysts for the hydrogenation of soybean oil. These catalysts give a good yield of products with cis‐configuration. Indeed, hydrogenation could be performed under mild conditions (30 C, 1 atm hydrogen pressure) to an iodine value of 80 with not more than 12% oftrans monoenes and only 5% conjugated isomers formed. The results obtained are interpreted on the basis of the equilibrium H2RhLn+⇌HRhLn+H+. By the addition of acid (HClO4) the bishydrido form of the catalyst could be studied. With this system only small amounts of trans monoenes were formed and no othertrans isomers could be detected. By the addition of a base such as triethylamine, the monohydridic form of the catalyst could be studied. In contrast to the bishydrido complex, this system gave large amounts oftrans monoenes, together withcis‐trans andtrans‐trans forms of the 18:2 acid. With both forms of the catalyst system, conjugated isomers were formed.