New method for the synthesis of 1,2-diphenyl-2Narylamino- ethanones by irradiation with microwaves in the absence of solvents

Abstract

Several 1,2-diphenyl-2-arylaminoethanones were prepared by the condensation reaction of benzoin with aromatic amines under microwave irradiation, in the absence of solvents. Two cases were considered, with and without the presence of a catalyst (KHSO4). In the firt case, it was necessary 7- 8 min for the reactions to proceed to completion with the elimination of all the water, shifting the equilibrium to the formation of the products, while the temperature reached to 200 oC or higher, which determined some losses,
although the yields were quite good as compared to those obtained with other methods, especially when the aromatic amine, used in a slight excess, resisted such a high temperature. In the second case, when KHSO4 was used as a catalyst, better results were obtained, especially when a very small amount of water was previosly added to the reaction mixture, what aided to get a very fast
and clean reaction. In this way the products were obtained with excellent yields and with a great purity in a very short time. This preparation of diarylaminoethanones using microwave irradiation is reported for the first time.