Synthesis of Linear Olefins From Fatty Acids: A Comparison of Nickel(i) and Rhodium(i) Catalysts in Liquid Triphenylphosphine

Abstract

Linear α-olefins (LAO) with good selectivity toward linear olefins (LO) can be synthesized from widely available fatty acids (lauric, decanoic, miristic, palmitic and stearic acids) in high yield using a Ni(II) complex: Ni(Ph3P)2Cl2 in liquid triphenylphosphine (TPP). It is shown spectrophotometrically, in liquid triarylphosphine that Ni(Ph3P)2Cl2 assumes an octahedral coordination geometry which is believed to be the active species in the dehydration-decarbonylation reaction of fatty acids. For comparison also the Wilkinson's catalyst, i.e., the Rh(I) complex Rh(Ph3P)3Cl was also studied as a fatty acid decarbonylation catalyst in liquid TPP. The Wilkinson's catalyst gives an extremely smooth >95% selectivity toward LAO. Thus, when high LAO selectivity is requested, Rh(Ph3P)3Cl is the catalyst of choice. On the other hand, when economic LO/LAO mixtures are requested in high yields, for instance as in the case of hydroformylation feedstocks, then Ni(Ph3P)2Cl2 is the recommended catalyst. The LO/LAO products were determined with GC-MS and the LAO selectivity was also determined with Raman spectroscopy.