Preparation of the ethyl analog is as follows (methyl isocyanate is used in
amisometradine manufacture).
To a cooled and stirred solution of 142 parts of methallylamine in 900 parts of
benzene, 156 parts of ethyl isocyanate are added dropwise. Upon
concentration in vacuum N-ethyl-N'-methallylurea is obtained.
260 parts of this urea derivative are dissolved in 500 parts of acetic anhydride
and treated with 157 parts of cyanoacetic acid at 60°C and heated at that
temperature for 2 hours. The solution is then concentrated in vacuum to a
syrup. 100 parts of water are added and the vacuum distillation is repeated.
The remaining syrup contains a mixture of N-cyanoacetyl-N-ethyl-N'-
methallylurea and a small quantity of N-cyanoacetyl-N-methallyl-N'-ethylurea.
This syrup is treated with sufficient 20% sodium hydroxide solution to raise
the pH to 10. A violent reaction occurs. The reaction mixture is diluted with 50
parts of water, stirred, cooled and filtered. The material collected on the filter
is recrystallized from 10% ethanol to yield a mixture of 1-methallyl-3-ethyl-6-
amino-1,2,3,4-tetrahydro-2,4-pyrimidinedione and 1-ethyl-3-methallyl-6-
amino-1,2,3,4-tetrahydro-2,4-pyrimidinedione melting at about 157-159°C.
