Abstract: The invention concerns dehydrogenation of carboxylic acids, lactones, esters, nitriles, the carbon skeleton of the feed material being characterized as containing mono-unsaturation or alternatively functional groups such as hydroxyl which convert under process conditions to unsaturation, the dehydrogenation reaction being conducted in the presence of a contact catalyst comprising a carbonaceous layer effective for the dehydrogenation of mono-unsaturated reactants to di-unsaturated products. Another aspect of the invention involves production of the mono-unsaturated reactants. In particular, the invention provides a route to sorbic acid, for example by dehydrogenation of hexenoic acids or esters thereof.