- Since many 1, 4, 5, 6-tetrahydropyrimidines have become available
and commercially useful in recent years, a study of the chemistry
of certain of these compounds has been undertaken.
2-Hydroxy- and 2-mercapto-1, 4, 5, 6-tetrahydropyrimidine
have been synthesized by the condensation of urea and thiourea, respectively,
with 1, 3-propanediamine, with yields of 30 and 50 percent.
2-Phenyl-1, 4, 5, 6-tetrahydropyrimidine hydrochloride was prepared
in quantitative yield by the addition of hydrogen chloride gas to
the free base in either benzene or absolute ethanol.
A nuclear acylation of 2-phenyl-1, 4, 5, 6-tetrahydropyrimidine
with acetic anhydride produced 1-acetyl-2-phenyl-1, 4, 5, 6-tetrahydropyrimidine
in about 70 percent yield. The same reaction with
2-methyl-1, 4, 5, 6-tetrahydropyrimidine gave an unidentified amorphous
2-Phenyl-1, 4, 5, 6-tetrahydropyrimidine hydrolyzed in an aqueous
solution to only a small extent at room temperature; however, at
100 degrees, the tetrahydropyrimidine ring was completely disrupted
after one hour. Some destruction of the ring was also observed in
boiling xylene and in boiling ethanol. 2-Amino-1, 4, 5, 6-tetrahydropyrimidine
hydrolyzed slowly in neutral and alkaline media at room
temperature; it was found to be less stable in an alkaline solution
than in a neutral one.
Dehydrogenation of 1, 4, 5, 6-tetrahydropyrimidines to the corresponding
pyrimidines was attempted using several different techniques.
Catalytic oxidation with ten percent palladium on charcoal
produced small amounts of 2-phenyl-, 2-methyl-, and 2-aminopyrimidine
from the corresponding tetrahydropyrimidine. Linstead's
catalyst-d was used to dehydrogenate 2-phenyl, 2-methyl-, 2-amino-,
and 2-mercaptopyrimidine, in yields ranging from less than five to
Two quinones, chloranil and phenanthrenequinone, were studied
as dehydrogenation agents. Small amounts of 2-phenyl- and 2-aminopyrimidine
were prepared by treating the appropriate tetrahydropyrimidine
with chloranil. Phenanthrenequinone proved completely unsuccessful.
Sulfur was used to dehydrogenate 2-phenyl-1, 4, 5, 6-tetrahydropyrimidine
and 2-amino-1, 4, 5, 6-tetrahydropyrimidine hydrochloride,
again in only small yields.
In reactions in which only a small amount of pyrimidine was obtained,
ultraviolet spectroscopy was used for the identification of the
pyrimidine. In general, none of the methods of dehydrogenation studied
appeared to be useful as preparative techniques for pyrimidines.