The catalytic activity of copper. Part V.—The comparison of the rates of dehydrogenation of various alcohols

Abstract

The study of the dehydrogenation velocity, and the temperature coefficient the dehydrogenation velocity for various alcohols should give valuable formation on the mechanism of the catalytic decomposition. To eliminate possible errors due to continued grain growth in the catalyst, e reaction velocities for all the alcohols used were compared with that of hyl alcohol. These measurements showed that the activity of the catalyst a constant temperature of reduction slowly decreased, as would be expected om the results of Part IV. This decrease does not affect the accuracy of e comparison since the grain growth is slow, and therefore the change in itivity between an experiment with a selected alcohol, and another with hyl alcohol is negligible. The ethyl alcohol behaved in a manner which was ell known from the previous experiments, and moreover, since it could be btained very pure, it afforded an excellent standard of reference. The Purification of the Alcohols . Great care was taken to ensure the purity of the alcohols used. They were ied with lime, often twice, and then subjected to continued fractional dis- llation through a Dufton column till they boiled over a range of not more an 0·1° C. The apparatus was arranged to prevent the absorption of water apour. With normal propyl, normal butyl, and one sample of iso-propyl lcohol, this process resulted in a product which was free from catalyst poisons s shown by the overlapping of the heating and cooling curves. But in the ase of another sample of iso-propyl alcohol, and with iso-butyl and iso-amyl lcohols, though the boiling points were constant to 0·1 C., and the values so btained agreed with the published values for the pure substances, rapid oisoning of the catalyst occurred. In the case of iso-amyl alcohol the velocity became negligibly small in 40 minutes. Since the poison cannot be removed y repeated fractionation, these alcohols provide an excellent opportunity or investigating the mechanism of poisoning with a constant pressure of poison, the composition of the alcohol mixture being unchanged b distillation.