A green synthesis of nitrones from diamino glyoxime using aldehydes and ketones

The reaction of diaminoglyoxime with aldehyde and ketone derivatives in the presence of p-toluene sulphonic acid in H₂O–MeOH mixture at room temperature afforded nitrone derivatives in high yields within 10–140 min. The applicability of ketones in this reaction for the preparation of novel nitrones has been verified. The effect of the temperature on the stability of the structural isomers of the products has been studied by NMR as well. The results showed that, at high temperatures only one product could be observed. The nature of solvent and catalyst were evaluated and found that the strong acids H₂SO₄ and CF₃SO₃H in protic solvent CH₃OH work well while neither CH₃SO₃H in protic solvent nor p-toluene sulphonic acid in aprotic solvents toluene and THF perform the same reactions.