Synthesis of 2,3-Dimethylbutenes by Dimerization of Propene Using Highly Active Nickel-Phosphine Catalysts in the Presence of Sulfonic Acids and/or Dialkyl Sulfates

Article abstract of DOI:10.1246/bcsj.70.2671

A nickel-phosphine catalyst system consisting of nickel naphthenate, P(cyclo-C₆H₁₁)₃, AlEt₃, and 2,4,6-trichlorophenol (TCP) in the presence of sulfonic acids (CF₃SO₃H and MeSO₃H) or dialkyl sulfates (Me₂SO₄ and Et₂SO2) exhibits remarkable catalytic activity for the dimerization of propene. The catalytic activity (turnover number (TON) for the formation of C₆, olefins or 2,3-dimethylbutenes) was enhanced when the catalyst was combined with effective additives, such as Et₂SO₄ and MeSO₃H. The reaction products consisted of 2,3-dimethyl-1-butene (DMB-1) and/or 2,3-dimethyl-2-butene (DMB-2) in high yields (selectivity of dimers based on the reacted propene = 70-80%: selectivity of 2,3-dimethylbutenes in C₆ olefins = 78-80%). The ratio of DMB-1/DMB-2 could be controlled by varying the molar ratios of the catalyst ingredients without decreasing in the turnover numbers. Although CF₂SO₃H was found to be the best additive as far as the catalytic activity and the selectivity of dimers (94-99%) are concerned, the selectivity of 2,3-dimethylbutenes in C₆ olefins decreased. The addition of a small amount of water was also effective to enhance the catalytic activity: The turnover number for the formation of 2,3-dimethylbutenes was raised from 7050 to 30360.