DE1545614C3 - Process for the preparation of 2-oxo-hexahydropyrimidines - Google Patents

Description

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Cyclic ureas are important intermediate products in the manufacture of leather and lacquer auxiliaries. This application relates to a process for the preparation of 2-oxo-hexahydropyrimidines. In the previously known processes for the preparation of 2-oxo-hexahydropyrimidines, one uses

in which R, and R, a hydrogen atom or a

R ₁ -N NR,

H
/
CC

/ \ / \
HCH

H ₃ C CH ₃

in which R ₁ and R _{2 denote} a hydrogen atom or a methyl group and R denotes a hydrogen atom or an isopropyl radical, obtained in a very simple manner, from easily accessible starting materials and in good yields, if 2-oxo-hexahydropyrimidines of the general formula II

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where R ₁ to R ₃ are as defined above and R _{4 is} a hydrogen atom or an alkyl radical having up to 4 carbon atoms, and is reacted with formic acid at temperatures between 50 and 150 " ¹ ° C.

R ₁ -N

H
\
C.

H ₁ C

NR ₂
OR ₄
C.

CH ₃

RN N — R + HCOOH - ROH -
CHOIR'

in which R ₁ to R _{3 have} the meaning given above and R _{4 is} a hydrogen atom or an alkyl radical having up to 4 carbon atoms, is reacted with formic acid at temperatures between 50 and 150.degree.

The reaction probably takes place as an intermediate via the cyclic a-UreidaIkyl- [carbenium-immonium] -formates. After carbon dioxide has been split off from these formates, the remaining hydride ion can be a-ureidoalkylated. The implementation can be represented by the following reaction equation:

H-COO ^

R-N N-R

It is surprising that practically no hydrolytic splitting of the 2-oxo-hexahydropyrimidine can be observed in the reaction with formic acid. The reduction of the compounds of the general formula II with formic acid is preferably carried out at temperatures between 70 and 100 ⁰ C.

The following 4-hydroxy-2-oxo-hexahydropyrimidines, for example, can be used as starting materials will:

2 - oxo -4 - hydroxy -1,3,5,5 - tetramethyl - hexahydropyrimidine, 2 - oxo - 4 - hydroxy - 5,5 - dimethyl - 6 - isopropyl-hexahydropyrimidine. Furthermore, z. B. the following 4-alkoxy-2-oxo-hexahydropyrimidines suitable as starting materials: 2-oxo-4-methoxy-5,5-dimethylhexahydropyrimidine, 2 - oxo -4 - butoxy -1,3,5,5 - tetramethyl - hexahydropyrimidine and 2 - oxo - 4 - methoxy - 5,5 - dimethyl - 6 - isopropyl - hexahydropyrimidine.

The 4-hydroxy- and 4-alkoxy-2-oxo-hexahydropyrimidines of the general formula II can be z. B. by reacting corresponding acetals or hemiacetals with corresponding ureas in acidic medium. It is also possible to use mono-a-alkylol ureas or their ethers, di-alkylol ureas or their ethers with an α, / 3-unsaturated aldehyde in a molar ratio of about 1: 1 in the presence of acids to the 2-0x0-4-hydroxy- and in the presence of alcohols to the 2-oxo-4-alkoxy-hexahydropyrimidine derivatives cyclize.

It is advantageous to use a higher percentage formic acid, e.g. B. a 60 to 100%. It is appropriate the formic acid at least in a stoichiometric amount, based on the starting material use. An excess of formic acid is preferably used, e.g. B. 1.5 to 20 times stoichiometric excess. When using an excess of formic acid, the formic acid works as a solvent or suspending agent.

The parts mentioned in the examples are parts by weight.

For example

172 parts of 2-oxo-4-hydroxy -1,3,5,5-tetramethyl-hexahydropyrimidine are used in a stirred apparatus mixed with 250 parts of 100% formic acid. The clear solution is heated to 80 ° C. for 3 hours while stirring warmed up. The resulting carbon dioxide is discharged. The water of reaction formed and the excess of formic acid are removed by evaporation under reduced pressure. You get 145 parts of crude 2-oxo-1,3,5,5-tetramethylhexahydropyrimidine. This corresponds to a yield of 93% the theory. The crude product can be purified by fractional high vacuum distillation. at The 2-oxo-1,3,5,5-tetramethylhexahydropyrimidine distills 0.2 torr between 80 and 82 ° C.

Analysis C ₈ H ₁₆ (156):

Calculated ... C 61.6, H 10.25, N 17.95%;
found .... C 61.2, H 10.3, N 17.2%.

Example 2

A mixture of 186 parts of 2-oxo-4-hydroxy-5,5 - dimethyl - 6 - isopropyl - hexahydropyrimidine and 250 parts of 100% formic acid are stirred for 4 hours in a stirred apparatus to 90 to 95 ° C heated. The escaping carbon dioxide is diverted. The excess formic acid as well the water of reaction formed is evaporated off under reduced pressure. The remaining residue is mixed with 200 parts of water, the 2 - oxo - 5,5 - dimethyl - 6 - isopropyl - hexahydropyrimidine begins to crystallize. It is filtered off and used to remove the adhering formic acid washed with dilute sodium hydroxide solution and then with water. There are 161 parts of crude product receive. This corresponds to a yield of 94.7% of theory. The product can be used for cleaning Recrystallized water.

Analysis C ₉ H ₁₈ ON ₂ (170):

Calculated ... C 63.5, H 10.6, N 16.5%;
found .... C 63.4, H 10.5, N 16.2%.

Example3

186 parts 2 - oxo - 4 - methoxy -1,3,5,5 - tetramethylhexahydropyrimidin are mixed with 200 parts of 100% formic acid is heated for 3 hours under vigorous stirring at 8O ⁰ C. The escaping carbon dioxide is discharged. The methanol formed in the reaction and the excess formic acid are then evaporated off under reduced pressure. 150 parts of crude product are obtained, which can be purified by high vacuum distillation.

The pure 2-oxo-1,3,5,5-tetramethylhexahydropyrimidine boils at 0.2 torr between 80 and 82 ° C.

Analysis C ₈ H ₁₆ ON ₂ (156):

Calculated:

C 61.6, H 10.25, O 10.25, N 17.95%;
found:

C 61.4, H 10.2, O 10.0, N 17.8%.

Claims (1)

Palent claim: Process for the preparation of 2-oxo-hexahydropyrimidines of the general formula I. 1,3-Propylenediamines with dialkyl carbonates or with urea. A major disadvantage of this method is that 1,3-propylenediamines can only be produced with difficulty on an industrial scale. It has now been found that 2-oxo-hexahydropyrimidines of the general formula 1 R ₁ -N NR ₂ H (1) H ₃ C CH, Methyl group and R ₃ denotes a hydrogen atom or an isopropyl radical, characterized in that 2-oxo-hexahydropyrimidines of the general formula II R ₁ -N NO, OR ₄ (ID C C H ₃ C CH,