Eighty grams (1.33 moles) of finely powdered urea is stirred into a mixture of
160 g. (155 cc., 1.23 moles) of ethyl acetoacetate (Note 1), 25 cc. of absolute alcohol (Note
2), and ten drops of concentrated
hydrochloric acid in a
5-in. crystallizing dish. The reagents are mixed well, and the dish is covered loosely with a
watch glass and placed in a
vacuum desiccator over concentrated
sulfuric acid. The desiccator is evacuated continuously with a
water pump until the mixture has gone to dryness (Note
3), which usually requires from five to seven days (Note
4). The crude
β-uraminocrotonic ester when thoroughly dry weighs
200–205 g.
The dry, finely powdered, crude
β-uraminocrotonic ester is stirred into a solution of
80 g. (2 moles) of sodium hydroxide in 1.2 l. of water at 95°. The clear solution is then cooled to 65° and carefully acidified, while stirring, by the slow addition of concentrated
hydrochloric acid. The
6-methyluracil precipitates almost immediately, and after the mixture is cooled the product is collected on a filter, washed with cold water,
alcohol, and
ether, and air-dried. The substance is obtained as a colorless powder of a high degree of purity, and the yield is
110–120 g. (
71–77 per cent of the theoretical amount). For further purification the
pyrimidine may be crystallized from glacial
acetic acid.
6-Methyluracil decomposes above
300°.