Abstract
Hydrogenation of cinnamaldehyde (CAL) with a ruthenium-triphenylphosphine complex was carried out under various conditions in several solvents such as N, N-dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP) and ethyl acetate (AcEt). In this reaction, cinnamyl alcohol (COL), hydrocinnamaldehyde (HCAL) and hydrocinnamyl alcohol (HCOL) are formed. Among the solvents used, DMF gives the highest reaction rate and the highest selectivity for COL. The reaction order of the substrate consumption also changes with the solvent. The rate of CAL consumption is of the first order with respect to its concentration in DMF, while those in the other solvents are of the zeroth order. Hydrogenation of COL to HCOL was found to be negligible under the present reaction conditions. By simulation for the concentration–time profiles of the substrate and the products obtained in DMF, rate constants for the elemental reactions involved in the title reaction, i.e. the hydrogenation reactions of CAL to COL, of CAL to HCAL and of HCAL to HCOL, were determined. These rate constants increase linearly with H2 pressure below 4 MPa. Above this pressure, they remain practically constant. Effect of the ligand/metal ratio on these rate constants was also investigated.
