Effect of microwave radiation on the solvent-free synthesis of phthaloylamino acids

Abstract

In recent years, microwave radiation has been widely used in organic synthesis, including solvent-free mode. However, the reaction conditions of phthalic anhydride with amino acids under solvent-free microwave activation have not been studied so far. In the present work, the effect of microwave activation on the interaction of phthalic anhydride with amino acids in solvent-free conditions has been studied in detail. The microwave heating dynamics of phthalic anhydride, glycine and their equimolar mixture under microwave conditions have been investigated, and the dependence of the heating rate on the microwave power is defined. The common conditions for the synthesis of phthaloylamino acids have been determined as continuous heating at a power of 200 W at 130 °C for 5-6 min and additional heating for 5-10 min at a temperature close to the melting point of the corresponding amino acid. We apply the developed two-step solvent-free microwave reaction protocol successfully for the synthesis of phthaloyl derivatives of glycine, alanine, β-alanine, 4-aminobenzoic acid, γ-aminobutyric acid, isoleucine, leucine, phenylalanine. Reaction conditions for synthesizing phthaloylamino acids by microwave activation without solvent have been established. The solvent-free microwave reaction between phthalic anhydride and amino acid has been found to proceed in the melted phthalic anhydride.