Efficient synthesis of 2,3-dimethylbutenes by dimerization of propylene using nickel-phosphine catalyst in the presence of strong sulfonic acids and/or dialkyl sulfates. Remarkable effect of strong sulfonic acids and/or dialkyl sulfates

Abstract

Remarkable catalytic activities as well as high selectivities have been found for dimerization of propylene catalyzed by the nickel-phosphine system composed of nickel naphthenate/P(cyclo-C 6H 11) 3/AlEt 3/2,4,6-trichlorophenol (TCP) especially in the presence of strong sulfonic acids (CF 3SO 3H, MeSO 3H) or dialkyl sulfates (Me 2SO 4 and Et 2SO 4). The catalytic activity was further increased upon the combination of these effective additives. The desired C 6 olefins such as 2,3-dimethylbut-1-ene (DMB-1), 2,3-dimethylbut-2-ene (DMB-2, TMEN) could be obtained in relatively high yields by using these catalysts (selectivity of dimers = 70–80%: selectivity of dimethylbutenes in C 6 olefins = ∼80%). The ratio of DMB-1/TMEN could be controlled without changing the catalytic activities by varying the molar ratios of catalyst precursors. CF 3SO 3H was found to be the most effective additive for increasing the reaction rate, although the selectivity of dimethylbutenes decreased significantly. Addition of a small amount of water enhanced the reaction rate significantly (turnover numbers for 2,3-dimethylbutenes: 7046 → 30358). The importance of these catalyst systems should be emphasized, because the amount of nickel species required can be minimized compared with that required for the conventional process.