Non-solvent hydrogenation of solid alkenes and alkynes with supported palladium catalysts

The non-solvent hydrogenation of solid alkenes and alkynes was investigated using supported palladium catalysts. trans-Stilbene and carboxylic acids with α,β-CC bonds were employed as the alkene-type substrates for the non-solvent hydrogenation. Their hydrogenation proceeded over a Pd/SiO2 catalyst at room temperature in a hydrogen stream. The hydrogenation rate of the trans-stilbene under the non-solvent conditions was lower than the hydrogenation in tetrahydrofuran (THF). The non-solvent hydrogenation of the CC bond in diphenylacetylene or phenylpropiolic acid proceeded over a Pd/C catalyst more smoothly than their hydrogenation in THF. There was a close relation between the melting points of the substrates or the products and the yields of the non-solvent hydrogenation. This relation suggested that the smooth non-solvent hydrogenation of the substrates with CC or CC bonds proceeded in the fused state.