This is the second m a series of studies of the production of hydrogen from the degradation of Organic compounds in;sodium hydroxide: solutions. Unsaturated carboxylates, which are,intermediate products in the wet oxidation of the types of monoaromatic compounds typically present in Bayer process liquors, have been found to produce significant amounts of hydrogen during alkaline degradation. The alkaline degradation of nine unsaturated carboxylates was investigated under anaerobic conditions M an autoclave; and the effect of temperature (175-275 degrees C) and NaOH concentration (0-6 M) on the degradation of acrylate, 2-butenoate maleate, and 2-hexenoate was studied in detail for reaction times up to 120 min. All of the compounds investigated decompose to produce about 1 mol of hydrogen gas per mole of organic compound consumed, as well as a range of low molecular weight (LMW) carboxylates. The stoichiometries of the formation of hydrogen and LMW carboxylates from the unsaturated carboxylates Observed here are consistent with the regioselective hydration of the C=C double bond to form the corresponding beta-hydroxycarboxylates, which then undergo further degradation by an ionic mechanism involving base catalyzed oxidation by water. These findings significantly advance the understanding of the production of hydrogen in Bayer process :digestion and have implications for the safe application of wet oxidation of Bayer process. liquors. The results also advance the fundamental understanding Of the alkaline degradation of alpha,beta-unSaturated Carbonyl Compounds in general