High-pressure competitive hydrogenation of aldehydes, ketones, and olefins on copper chromite catalyst

Abstract

Relative reactivities of 4 saturated acyclic aldehydes, 15 saturated acyclic and cyclic ketones, and 11 acyclic and cyclic olefins were determined in the copper chromite-catalyzed vapor-phase hydrogenation of binary and ternary mixtures, at 150–250 °C, under 20–100 bars total pressure, with excess hydrogen, in a continuous-flow reactor. A specific feature of the copper catalyst is the higher reactivity of CO bonds, when compared to CC CO (aldehyde) > CO (ketone) > CC (olefin). Alkyl substituents at the double bond lower the reactivities and cause some overlap between the three groups. The following scale of reactivity R, with methyl isobutyl ketone as reference compound ( R = 1), was found at 185 °C and 80 bars: aldehydes, R = 3–5; cyclic ketones, R = 1–2; acyclic ketones and n-olefins, R = 0.6–1.6; cyclic olefins, R = 0.3–0.6; trisubstituted olefins, R = 0.03–0.2. Phenyl substituents strongly activate both the CC and CO bond hydrogenation; the phenyl ring is not hydrogenated. Changes of R values with temperature and pressure do not modify the reactivity sequence; at higher pressures, all R values become closer to 1. An attempt was made to extend the above scale of reactivity to double bonds included in the same molecule, in the hydrogenation of eight olefinic aldehydes and ketones. A good prediction of selectivity is possible for nonconjugated compounds; unsaturated alcohol formation is therefore frequently favored in copper chromite catalysis. However, the prediction breaks down in conjugated compounds; the CCCO group apparently reacts as a single entity, and the CC reactivity is enhanced.