骨架镍催化的新反应一乙醇转化制乙酸乙酯和正丁醇

RANEY NICKEL CATALYZED NEW REACTION -ETHANOL TRANSFORMATION TO ETHYL ACATATE AND N-BUTANOL

本文报道了以SbCl_3、AlC1_3、CuCl_2等为改性剂、骨架镍催化的乙醇转化为乙酸乙酯和正丁醇的新反应。发现SbCl_3是最佳改性剂,可以使乙酸乙酯的选择性由46.5％增加至85.4％,收率由3.81％增加至12.3％;在180℃以下,加入SbCl_3可强烈抑制甲烷和CO的生成。此外,还对乙酸乙酯和正丁醇的生成历程进行了讨论,认为经历了中间物乙醛,且经改性剂改性后的骨架镍多功能性加强,即它既有金属催化剂加氢、脱氢性能又具有酸碱催化功能。

Modified Raney nickel used as hydrogenation catalysts has been studied extensively, but little attention was paid to it as catalyst for Cannizarro's reaction and aldol condensation of aldehyde. Up to now, the use of Raney nickel to transform ethanol directly to ethyl acetate and n-butanol has not been reported. This paper aims at the study of SbCl3, A1C13, CuCl2, KOH etc, as modifiers, which make Raney nickel functionalize both as metal ( for dehydrogenation and hydrogenation ) and acid - base ( for Cannizarro's reaction, aldol condensation and esterification ) catalyst in the reaction of ethanol transformation to ethyl acetate and n - butanol. The modified and non-modified Raney nickel were characterized by means of XPS so that the multi-functions could be clarified. The ethanol transformation reaction are carried out in a 100ml stainless steel autoclave,the conditions are: 0.5g of Raney nickel,18 ml of absolute ethanol, 170 ℃, 2.5 h. Raney nickel with SbCl3 as modifier has the selectivity of 85% to ethyl acetate, but the non-modified Raney nickel only has the selectivity of 46.5%.Among the modifiers, such as SbCl3, A1C13, CuCl2, ( NH3 ) 2Mo2O7 and KOH, SbCl3 is the most effective one. The results show that both liquid by-products and gas byproducts were depressed by the modifiers used. The production of ethyl acetate seems to be promoted by stronger acid,but the formation of n-butanol be promoted by the base such as KOH. These results can be explained according to the scheme on p.222. Namely both ethyl acetate and n-butanol form through aldehyde as intermediate with competition (certainly, trace amount of aldehyde was detected in some products by GC).The effects of temperature and amount of SbCl3 on the formation of ethyl acetate were also studied. The optimum conditions for its formation are 170 ℃, SbCl3 / Raney nickel= 1/5. From the results of XPS, it is possible to conclude that a layer of Ni ( OH ) 2 exists on the surface of Raney nickel, which may play the role of base in ethanol transformation to ethyl acetate and n-butanol. However, the amorphous metal nickel behave like a metal catalysts for dehydrogenation of ethanol and hydrogenation of cro-tonaldehyde to n -butanol. No evidences was found for the strong interaction such as coordination of SbCl3 to Raney nickel because the bind energy of Sb 3 d3/2 is the same as that of SbCl3 and there is no change of Ni2p and A12p. Therefore, the promotion effects of SbCl3 can be attributed to increasing acidity of Raney nickel. (One of the major evidences for Raney nickel's acidity increasing after adsorption of acid compounds such as SbCl3, A1C13 and CuCl2 is the formation of very little amount of C2 hydrocarbons from the dehydration of ethanol which is generally accepted as a acid catalyzed reaction and neglected by this paper, but no C2 is found by carefully analysis of gas by-products of the non -modified and KOH modified Raney nickel. ) In spite of the increasing of acidity, the basicity of acid compounds modified Raney nickel seems to be little affected, even more is promoted. So does the function of metal. In summary, the formation of ethyl acetate and n-butanol is the results of multi-function of modified Raney nickel, which not only has the capability of metal catalysts, but also has the capability of acid-base bifunctional catalysts.