Cis-2-butene-1,4-diol as probe for studying isomerization versus hydrogenation and hydrogenolysis reactions

The liquid phase hydrogenation of cis-2-butene-1,4-diol over a supported palladium catalyst has been investigated in ethanol at 0.01 ≤ PH2 ≤ 0.5MPa and 273 ≤ T ≤ 303 K. The effect of substrate concentration, catalyst amount, agitation speed and H2 pressure on the reaction rate has also been studied under isothermal conditions. Under reduced H2 pressure, double bond isomerization reaction occurs to a high extent leading to 2-hydroxytetrahydrofuran up to 60% yield. Formation of all reaction products was explained on the basis of a reaction model in which a surface σ-alkyl derivative was postulated and the results were clarified on applying the steady-state approximation to this intermediate. Kinetic rate equations were derived following the Langmuir–Hinshelwood model by assuming a non-competitive adsorption of organic species and hydrogen on the palladium active sites. Rate constants and the adsorption constant for each reaction were determined by a non-linear regression analysis. An excellent agreement between the predicted concentrations versus time profiles and the experimental data was observed. Furthermore, the model predictions of hydrogenated and isomerized compounds formation at different pressures agree well with the experimental results obtained.