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In the production of biofuels from plant or animal raw materials, a by-product is formed — glycerol, the simplest trihydric alcohol. Glycerin is harmless and even useful in many areas, however, from the point of view of the chemical industry, it is almost useless. The principles of green chemistry require that even by-products be put to use. If the resulting substance is of little value, it is necessary to carry out valorization — to find a way to convert it into a more valuable product. Therefore, chemists are looking for ways to valorize glycerol, which was formed during the synthesis of biofuels. A RUDN University chemist, together with colleagues from Spain, Italy and Saudi Arabia, proposed converting glycerol into benzoxazine derivatives, which are used in medicine.

“The depletion of fossil fuels, together with the increase in energy consumption, is prompting the development of more sustainable protocols for the production of biofuels in accordance with the principles of green chemistry. Many protocols result in the formation of glycerol. Now this product is practically useless. However, benzoxazine derivatives can be made from it. They are necessary for the manufacture of antidepressants, antidiabetic, and anticancer drugs. In addition, such compounds have antiplatelet activity,” Rafael Luque, Head of the Research Center “Molecular Design and Synthesis of Innovative Compounds for Medicine”, RUDN University.

Chemists have proposed converting glycerol into benzoxazine derivatives using a two-step process. During the reaction, glycerin combines with aminephenol, an aromatic organic compound. The first stage of the process is mechanochemical activation, the second is the actual reaction under the action of microwave radiation. The essence of mechanochemical activation is the grinding of a substance in a special mill with steel balls. The second key “ingredient” of the process — microwave radiation — makes the reaction more efficient.

Chemists experimentally managed to obtain two derivatives of benzoxazine. The reaction proceeded by heating to 110°C for one hour. Prior to this, also within an hour, the reagents were ground in a mill with a rotation speed of 350 rpm. “Mill” and “microwave” were able to give 93% selectivity (that is, in the end, only 7% of by-products were formed).

“Mechanochemical activation prior to the microwave process increases the likelihood of contact between the reactants and greatly contributes to the higher conversion of the amine phenol. A consistent mechanochemical-microwave approach improves the selectivity towards the formation of a benzoxazine derivative, which can be used in a wide range of biomedical fields,” Rafael Luque, Head of the Research Center “Molecular Design and Synthesis of Innovative Compounds for Medicine”, RUDN University.

The results in the journal Molecules.