Infrared study of the adsorption of amines on silica immersed in carbon tetrachloride

Abstract

Infrared spectra of silica immersed in solutions of n-butylamine, di-n-butylamine and tri-n-butylamine in carbon tetrachloride are reported. The predominant surface—adsorbate interactions involved the existence of hydrogen bonds between isolated surface silanol groups and the nitrogen atoms of adsorbed amine molecules. Some proton transfer also occurred, particularly for tri-n-butylamine, and led to the formation of “ion-pair” complexes on the silica surface. For n-butyl-amine chemisorption probably gave a secondary amino surface species. The total relative amounts of amine adsorbed for a particular solution concentration were in the sequence Bu₃N > Bu₂NH > BuNH₂, corresponding to the relative basicities of the amines in the gas phase.