Complexes of acetic anhydride and Lewis acids and bases

Acetic anhydride forms compounds of 1 : 1 composition with trihalides of boron, aluminium, with antimony pentachloride, and with the trioxides of sulphur and selenium, of 1 : 2 composition with tetrahalides of tin and titanium. From molar conductance, molecular weight determinations and i.r. spectral studies, these are found to be simple donor-acceptor complexes. However, in the case of antimony pentachloride and aluminium tribromide, the presence of acetylium ion is indicated.A number of bases also form 1 : 1 compounds with acetic anhydride. From molar conductance and i.r. spectral studies, their structures have also been elucidated.