Efficient solvent-free synthesis of N-unsubstituted ketimines from ketones and ammonia on porous solid acids

[Display omitted] •Ketones and ammonia gas condense to NH ketimines on solid acids in high yields.•The best promoter is proton-exchanged zeolite Y (H-Y) among the solid acids.•Not only a diaryl ketone but also a dialkyl ketone with α-hydrogens are applicable. We quantitatively synthesized N-unsubstituted (NH) diphenylketimine from benzophenone and ammonia without solvent under ambient conditions on some solid acids, especially the proton-exchanged Y-type zeolite (H-Y), by a simple procedure. Similarly, other N-unsubstituted ketimines were also obtained in high yields by the reaction of alkyl aryl ketones or a dialkyl ketone having α-acidic hydrogens with a large excess of ammonia gas at 1 atm. without a solvent with the aid of the zeolite’s high dehydration ability and stabilization effects.