The Hydrogenation of 2-butyne-1,4-diol over a Carbon-supported Palladium Catalyst
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Catalysis Letters Vol. 103, Nos. 3–4, October 2005 ( 2005) DOI: 10.1007/s10562-005-7154-6
The hydrogenation of 2-butyne-1,4-diol over a carbon-supported palladium catalyst Iain T. Duncanson, Iain W. Sutherland, Bernard Cullen, S. David Jackson, and David Lennon* Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
Received 7 May 2005; accepted 2 June 2005
The hydrogenation of 2-butyne-1,4-diol in propan-2-ol over a carbon-supported palladium catalyst has been investigated in a batch reactor. At low conversions complete selectivity to cis-but-2-ene-1,4-diol is observed. However, further hydrogenation leads to a wide variety of products, most notably 2-isopropoxy-tetrahydrofuran and butane, neither of which have previously been associated with this reaction system. The former is thought to occur as a result of a surface-mediated process, involving the insertion of dissociatively adsorbed solvent molecules. Butane formation is attributed to the double condensation and hydrogenation of a chemisorbed cis-but-2-ene-1,4-diol intermediate. The alkane preferentially partitions in the gaseous phase, which results in an marked mass imbalance for the liquid phase. A reaction scheme is presented to rationalise these observations. KEY WORDS: 2-butyne-1,4-diol; hydrogenation; Pd/C; cis-but-2-ene-1,4-diol; liquid phase hydrogenation.
1. Introduction Butane-1,4-diol (global production capacity ca. 910 kilotonnes p.a.) is an important chemical feedstock, which is used in the production of tetrahyrdofuran, polybutenepthalate and polyurethanes [1]. The manufacturing process typically involves the conversion of ethyne to 2-butyne-1,4-diol, which is then hydrogenated to butane-1,4-diol. Partial hydrogenation to 2-butene1,4-diol is also beneficial, as this trifunctional molecule can be used to form a precursor of the Thiodan insecticide [1] and in the production of vitamin B6[2]. The hydrogenation of 2-butyne-1,4-diol has been studied over a variety of different catalysts including nickel and nickel–copper based systems, which require severe conditions [3,4]. The use of milder conditions is desirable, as it can improve the selectivity towards cis-2butene-1,4-diol. This has been achieved through the use of precious metal catalysts such as palladium. Winterbottom et al. [3] have established a general reaction scheme for the reaction, using a 5% Pd/C catalyst. Their scheme consists of two stages: (i) adsorption and reduction of 2-butyne-1,4-diol to form cis-2-butene-1,4diol via a consecutive mechanism; and (ii) further reduction of cis-2-butene-1,4-diol to form butane1,4-diol, along with a variety of side products. The side products observed were cis- and trans-crotyl alcohol and n-butanal, the latter formed via isomerisation of a crotyl alcohol intermediate [3]. Telkar et al. [5], investigating the hydrogenation of 2-butyne-1,4-diol over a range of supported palladium catalysts, proposed a second scheme * To whom correspondence should be addressed. E-mail: [email protected]
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