Unconjugated dienes, hydrogenation selective

For hydrogenation in water with an inexpensive catalyst, solutions containing cobalt salts and excess cyanide are useful10,11. The catalysts are selective for conjugated C=C bonds and are relatively unreactive with unconjugated dienes such as 1,5-cyclooctadiene. 

Concerning chemical selectivities in multiple unsaturated acetylenic compounds, conjugated enynes are reduced with modest selectivity. The most difficult case involves the selective reduction of an enyne with a terminal double bond and an internal triple bond, because the difference in the rates of their hydrogenation is minimal. The hydrogenation of nonterminal, unconjugated diynes to (Z,Z)-dienes can be achieved in good yield. 

The use of copper chromite at 40°C and atmospheric pressure was not very effective for selective carbonyl group hydrogenation. Unsaturated alcohols were produced from unsaturated aldehydes in low yields at low conversions and not at all from methyl vinyl ketone. 28 With unconjugated, unsaturated aldehydes, copper chromite is effective as a selective hydrogenation catalyst. Hydrogenation of 46 at 140°-160°C and 200 atmospheres gave better than 70% of the diene diol, 47. Increasing the temperature to 240°C resulted in the complete saturation of 46 (Eqn. 18.28). 29... 

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