Aluminium-27 and hydrogen-1 nuclear magnetic resonance studies of solutions of aluminium salts in alcohol–chloroform mixtures

Abstract

The nature of the ionic species formed when AlCl₃ or Al(ClO₄)₃ is dissolved in various anhydrous alcohols and diluted with CDCl₃ has been investigated using ²⁷Al n.m.r. Spectroscopy. The alcohols MeOH, PrOH, BuOH, and BuⁱOH show similar behaviour, although the resonances in the higher alcohols are much broader than in MeOH. Ethanol is anomalous, but if this alcohol is diluted with CDCl₃ its behaviour becomes normal. The resonances in the diluted alcohols become generally less broad with increasing dilution, and at the highest dilutions evidence is obtained for the presence of the hexasolvate, with a weak, narrow resonance. Addition of water to AlCl₃–EtOH solutions produces mixed solvates as already observed for methanol solutions. However, the aluminium resonances are too broad in EtOH to allow adequate analysis of the system and it was found necessary to use low-temperature ¹H n.m.r. spectroscopy. All the mixed solvates could be recognised, although the chemical shift progression of the HOH and EtOH protons across the series of complexes formed was somewhat irregular.