Systematic studies on mechanochemical synthesis: Schiff bases from solid aromatic primary amines and aldehydes

A versatile and robust mechanochemical route to Aldehyde-Schiff base conversions has been established for a broad range of aldehydes via a simple cogrinding in mortar with a pestle under a solvent-free, as well as solvent-assisted, environment. The extent of amines reactivity under these conditions has also been explored, along with an examination of the possible connection between reactivity and electronic substituent effects. Results obtained demonstrated that the solvent-free mechanochemical conversion of p-toluidine and aromatic aldehydes to the corresponding Schiff bases proceeded more smoothly than the corresponding synthesis with 4-aminobenzonitrile. The present approach not only provides good to excellent yields but also eliminates the disadvantages of the traditional synthesis of Schiff bases, such as the use of hazardous solvents, more or less demand of expensive catalysts, and looking for optimization on reaction conditions.