In a tared 1-l. flask is placed 200 g. (1.5 moles) of 24 per cent aqueous methylamine solution (Note 1), and concentrated hydrochloric acid is added until the solution is acid to methyl red; about 155 cc. of acid is required. Water is added to bring the total weight to 500 g., 300 g. (5 moles) of urea is added, and the solution is boiled gently under reflux for two and three-quarters hours and then vigorously for one-quarter hour. The solution is cooled to room temperature, 110 g. (1.5 moles) of 95 per cent sodium nitrite is dissolved in it, and the whole is cooled to 0°. A mixture of 600 g. of ice and 100 g. (1 mole) of concentrated sulfuric acid in a 3-l. beaker is surrounded by an efficient freezing mixture, and the cold methylurea-nitrite solution is run in slowly with mechanical stirring at such a rate that the temperature does not rise above 0° (Note 2).

The nitrosomethylurea rises to the surface as a crystalline foamy precipitate which is filtered at once with suction and pressed well on the filter. The crystals are stirred to a paste with about 50 cc. of cold water, sucked as dry as possible (Note 3), and dried in a vacuum desiccator to constant weight. The yield is 105–115 g. (66–72 per cent of the theoretical amount) (Note 4).

(A) Acetyl Methylurea.—To a solution (Note 1) of 59 g. (1 mole) of acetamide in 88 g. (0.55 mole) of bromine in a 4-l. beaker is added, dropwise and with hand stirring, a solution of 40 g. (1 mole) of sodium hydroxide in 160 cc. of water. The resulting yellow reaction mixture is heated on a steam bath until effervescence sets in (Note 2), after which heating is continued for an additional two to three minutes. Crystallization of the product from the yellow to red colored solution usually commences immediately (Note 3) and is completed by cooling in an ice bath for one hour. The weight of the white crystalline acetyl methylurea obtained by filtration and air drying is 49–52 g. (84–90 per cent of the theoretical amount) (Note 4)(Note 5). It melts at 169–170°.

(B) Nitrosomethylurea.—A mixture of 49 g. (0.42 mole) of acetyl methylurea (Note 6) and 50 cc. of concentrated hydrochloric acid is heated, with hand stirring, on a steam bath until it is apparent that no more solid (Note 5) is dissolving. Heating is continued for three or four minutes longer (total time on steam bath—eight to twelve minutes), after which the solution is diluted with an equal volume of water and cooled below 10° in an ice bath. A cold saturated solution of 38 g. (0.55 mole) of sodium nitrite in 55 cc. of water is then run in slowly with stirring. The mixture is allowed to remain in the ice bath for several minutes, after which the nitrosomethylurea is filtered and washed with about 8–10 cc. of ice-cold water. Air drying gives 33–36 g. (76–82 per cent of the theoretical amount) of nitrosomethylurea as pale yellow crystals melting at 123–124°.