Ethanol → 2-Allylamino-5-methylamino-1,3,4-thiadiazole

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A stirred suspension of allyl isothiocyanate (19.8 g, 0.2 mole) and of 4-methyl-3-thiosemicarbazide (21.0 g, 0.2 mole) in 150 ml denatured ethanol (5% methanol) was refluxed for one hour. The crystalline suspension was briefly chilled, and the 1-allyl-6-methyl-2,5-dithiobiurea was collected and vacuum dried. A stirred solution of this biurea (30.6 g, 0.15 mole) in phosphorous oxychloride (150 ml) was refluxed for 11/2 hours. Unreacted phosphorus oxychloride was removed in vacuo, and the residue carefully partitioned between 1.2 M hydrochloric acid (150 ml) and chloroform (150 ml) while maintaining this mixture at 2° C with ice-bath cooling. The chloroform phase was extracted with another portion of 1.2 M hydrochloric acid (100 ml), and the combined acid layer was carefully made alkaline with conc. ammonium hydroxide. The resultant alkaline suspension was extracted with two portions of chloroform, and the combined chloroform extract was washed with a small portion of distilled water. After drying this chloroform extract over magnesium sulfate, the solvent was removed under reduced pressure to yield a colorless solid. Crystallization of the product from ethyl acetate gave 7.3 g (29 percent) of 2-allylamino-5-methylamino-1,3,4-thiadiazole (a colorless solid). Analysis confirmed the desired product.

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