Selectivity to cyclohexene in the gas phase hydrogenation of benzene over ruthenium, as influenced by reaction modifiers: III. FT-IR Study of the Interaction Between the Reaction Modifiers and Cyclohexene

Abstract

The Fourier transform infrared (FT-IR) spectra of mixtures of cyclohexene with methanol, ethanol, trichloroethanol and ε-caprolactam are presented. The occurrence of hydrogen bonding between these reaction modifiers and cyclohexene is clearly demonstrated by these spectra from shifts in the position of the hydroxyl stretching vibration bands by 40-70 cm-1. By measuring the extinction of the OH bands of methanol and of the methanol-cyclohexene adduct as a function of temperature, the enthalpy of formation of the adduct, ΔH°, is found to be −3.75 (±0.40) kJ mol −1. The influence of substitution of the methyl group in cyclohexene on the bond strength is discussed. On the basis of the results, a tentative interpretation of the scavenging action of the modifiers in the catalytic formation of cyclohexene from benzene is presented.