FT-IR/NIR Spectroscopic Study of Interactions between Water and Alkylamines

Abstract In the present paper we have studied interactions of the N and NH of alkylamines with water. We analyzed the property from the infrared and near-infrared absorptions that hydration causes to tributylamine (TBA) ((Bu)3N) and dibutylamine (DBA) ((Bu)2NH or (Bu)2HN) in the neat liquid or their solutions in heptane at varying concentrations. It has been found that the amine N of TBA very strongly interacts with water and forms the complex (Bu)3N⋯Hb-O-Hf (OHb: bonded OH, OHf: free OH) which is partly dissociated into (Bu)3NH+ and OH− at equilibrium. DBA retains an NH and may act not only as a proton acceptor but also a proton donor to water. Correspondingly, it has been found, the NH is hydrogen-bonded partly through the N to form the strongly-bound complex (Bu)2HN⋯Hb-O-Hf and partly through the H to form the complex (Bu)2NH⋯OH2. From their associated spectral features we propose that the former is partly dissociated into (Bu)2NH2+ and OH− at equilibrium as in the case of TBA and the latter is rather stabilized to be a larger cluster such as (Bu)2NH⋯OH2·(H2O)m.