The Selective Hydrogenation of Conjugated Dienes with Nickel Complex Catalysts

Abstract

The selective hydrogenation of 1, 3-butadiene (BD), isoprehe (IP), and 2, 3-dimethyl-l, 3-butadiene (DMBD) to the corresponding monoenes. with Ni(acac)2-Al2(C2H5)3Cl3-P(C6H5)3 (catalyst I, Ni: Al2: P=1: 10: 3) and NiBr2 [P(C6H5)3]2 catalyst (catalyst I) was investigated. With catalyst I, which showed a high activity, the hydrogenation proceeded fast in toluene at room temperature under 20atm of H3. The total selectivities of hydrogenation products increased in the order: BD 38% IP 84%>DMBD 40% (Table 2). In all cases, despite the striking differences in selectivity of hydrogenation products, monoenes were obtained in a high proportion (90%~); the percentages of monoenes from BD, IP, and DMBD with catalyst I, for example, were 93.0, 99.0, and 97.5%, respectively, even at 100% conversion. The low selectivities of the hydrogenation products in some reaction systems were due largely to the loss caused by the polymerization of the dienes. Based on the experimental results and available information, a reaction mechanism is proposed for the selective hydrogenation of DMBD with catalyst I. The differences in activity of the catalysts and in reactivity of the dienes used are also discussed. © 1976, The Chemical Society of Japan. All rights reserved.