85 parts of monoallylurea are dissolved in 105 parts of acetic anhydride, and
85 parts of cyanoacetic acid are added gradually and the mixture is
maintained at 65°C for 2.5 hours. The mixture is distilled at 20 mm until a
syrup remains. 50 parts of water are added to this syrup and distillation is
resumed. The resulting syrup is dissolved in 96% ethanol at 60°C, stirred with
charcoal and filtered. One to one and one-half volumes of ether are added to
the filtrate at 40°C. Upon cooling the N-cyanoacetyl-N'-allylurea precipitates.
It is collected on a filter and washed with ether. The white crystals melt at
about 142-143°C. The N-cyanoacetyl-N'-allylurea is dissolved by warming with
10% sodium hydroxide. Sufficient 70% sodium hydroxide is added to raise the
pH to 10. The solution is maintained at 60°C for five minutes. After cooling
the crystals are collected on a filter and recrystallized from water. 1-Allyl-6-
amino-1,2,3,4-tetrahydro-2,4-pyrimidinedione is obtained in the form of white
crystals melting at 270-272°C.
334 parts of 1-allyl-6-amino-1,2,3,4-tetrahydro-2,4-pyrirnidinedione are
dissolved in a solution of 88 parts of sodium hydroxide in 1,100 parts of
water. While this mixture is stirred rapidly at 50°C, 430 parts of diethyl sulfate
are added in the course of 30 minutes. Stirring is continued at 50-55°C for
one hour longer, and an alkaline reaction is maintained by occasional additions
of small portions of 20% aqueous sodium hydroxide solution, about 300 parts
in all being required. On cooling, the 1-allyl-3-ethyl-6-amino-1,2,3,4-
tetrahydro-2,4-pyrimidinedione separates as the monohydrate; it is filtered
off, washed with cold water, and recrystallized from water containing a small
amount of sodium hydroxide to hold in solution any unreacted 1-allyl-6-
amino-1,2,3,4-tetrahydro-2,4-pyrimidinedione. The air dried product thus
obtained contains 1 mol of crystal water and melts over a wide range with
dehydration at 75-115°C. After dehydration by treatment with anhydrous
ether, the anhydrous 1-allyl-3-ethyl-6-amino-1,2,3,4-tetrahydro-2,4-
pyrimidinedione melts sharply at about 143-144°C.
