The influence of hydrogen bonds upon diffusion of simple amines and binary mixtures of ammonia

Abstract

Self diffusion coefficients of monomethylamine and trimethylamine and intradiffusion coefficients of some model mixtures containing ammonia have been measured up to pressures of 200 MPa at temperatures between the melting pressure curve and 423 K by pulsed field gradient Spin Echo NMR. Compared to water and the lower alcohols the self diffusion coefficients of pure fluid ammonia shows no clear influence from hydrogen bonds in contrast to other thermodynamic properties. Therefore the methylated substance monomethylamine has been studied to see weather a more structured charge distribution on the molecular surface compared to ammonia is needed to hinder fast rearrangements of the hydrogen bonds. For comparison also trimethylamine has been studied where no hydrogen bonds can be formed. Additionally binary mixtures of ammonia with methanol, benzene, trimethylamine and acetonitrile have been studied to see effects of intermolecular interactions.

Key Words:

• Diffusion
• NMR
• ammonia
• mixture
• hydrogen bonds