Hexahydropyrimidines are produced by condensation of aldehydes or ketones with 1,3-diamines (U.S. Pat. No. 4,404,379 to Hajek et al.; Reibsomer, J. L., & Morey, G. H., J. Org. Chem., 1950, 15, 245; Evans, R. F., Aust. J. Chem., 1967, 1967, 20, 1634-61). Water is a by-product in these reactions and must be removed either to favor the imine equilibrium or for product purification. Generally, the condensation is acid or lewis acid catalyzed and run in solvents (DE Patent No. 1,670,093 to BASF). In some cases the open-chain tautomer is produced as a co-product which further contaminates the desired hexahydropyrimidines.
A process has been found to make alkyl-, dialkyl-, and trialkylhexahydropyrimidines in high yield without the formation of water or its open-chain tautomer. The invention is selective to the hexahydropyrimidines with only ammonia as the by-product. Cyclization, ammonia elimination and hydrogenation occur rapidly to produce the hexahydropyrimidine derivative in a single reaction step.
The hexahydropyrimidines have use as catalysts in the production of polyurethanes and epoxies (U.S. Pat. No. 3,787,416), as fungicides (U.S. Pat. No. 3,872,120), emulsifiers (U.S. Pat. No. 4,579,593 to Stanley), pharmaceuticals (J. Pharm. Sci., 1968, 57, 1817-19 and EP 226,511), fuel oil additives (U.S. Pat. No. 3,936,279), antioxidants (U.S. Pat. No. 3,787,416), and light stabilizers for olefins (U.S. Pat. No. 4,404,302 to Gupta et al).