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The title compound was prepared according to: Kister, J.; Assef, G.; Dou, H. J.-M.; Metzger, J. Tetrahedron 1976, 32, 1395. Thus, a solution of N-methylethylenediamine (10.8 g, 146 mmol) in EtOH—H2O (1:1, 90 mL) was preheated to 60° C. and CS2 (9.0 mL, 150 mmol) was added dropwise. The resulting mixture was heated at 60° C. for 3 h and then conc. HCl (4.7 mL) was slowly added. The temperature was raised to 90° C. and stirring was continued for 6 h. After the cooled mixture had been stored at −20° C., it was filtered and the resulting solid dried in vacuo to afford 1-methylimidazolidine-2-thione (8.43 g, 50%) as a beige solid. 1H NMR (400 MHz, CDCl3) δ 5.15 (s, br, 1H), 3.67-3.70 (m, 2H), 3.53-3.58 (m, 2H), 3.11 (s, 3H). To a suspension of 1-methylimidazolidine-2-thione (5.17 g, 44.5 mmol) in acetone (50 mL) was added MeI (2.9 mL, 46.6 mmol). The solution was allowed to stir at room temperature for 4 h and the resulting solid was quickly filtered and then dried in vacuo to give 1-methyl-2-(methylthio)-4,5-dihydro-1H-imidazole hydroiodide (8.79 g, 77%) as beige solid.

1. filtrationthe resulting solid was quickly filtered
2. customdried in vacuo