Copper-catalyzed dehydroamination of 1-hexanol with dimethylamine: an in situ FTIR study

Abstract

The adsorption of compounds relevant for the copper-catalyzed dehydroamination of 1-hexanol with dimethylamine was investigated on alumina-supported copper and pure alumina in the temperature range 298–540 K. Three types of dynamic FTIR measurements were used; isothermal pulse and step response, temperature-programmed desorption, and temperature-programmed surface reaction. Hexanol was found to form surface-bound aldehyde and hexanoate on copper/alumina. On pure alumina, no hexanoate formation occurred. Hexanal showed hexanoate formation on copper/alumina as well as on alumina. Dimethylhexylamine disproportionated on copper/alumina. When nitrogen was used as the carrier gas, imine and formate surface species were predominant, whereas with hydrogen-containing carrier gas, formate and hexanoate species were identified. Surface-bound aldehyde disappeared when dimethylamine was passed over copper/alumina which previously had been saturated with hexanol. The carboxylate species identified on the surface seem to be of little importance for the dehydroamination reaction. The experimental findings are discussed in the light of the earlier proposed reaction pathway for the dehydroamination of aliphatic alcohols.