General procedure for the synthesis of triazine ring from 2-methylaminothiourea and diethyl oxalate: 2-methylaminothiourea, mixed solvent (1:3 mass ratio of methanol to DMSO), diethyl oxalate and sodium methanolate were added to the reactor in the mass ratio 1:10:4:10. The cyclization reaction was carried out in the temperature range of 0-45°C. Upon completion of the reaction, acidification was carried out with hydrochloric acid in an amount of 30% by mass of 2-methylaminothiourea. Subsequently, the reaction mixture was filtered and dried to give the triazine ring in 91.6% yield. The purity of the product was assayed by HPLC and the by-product content was 0.0005% (5 ppm). The product was calculated as M (triazine ring) / [M (methylaminothiourea) * 159.17 / 105.16].
