Hexahydro-2-methylpyrimidine was prepared in a good yield and selectively by gas phase reaction of trimethylenediamine with ethylene glycol. The reaction was carried out over 10 kinds of silica-alumina catalysts within the temperature range of 220-440°. They were Neobead (I), 5% K
2O-Neobead (II), 6.8% Cr
2O
3-Neobead (III), synthetic zeo1ite (IV), 5% K
2O-synthetic zeolite (V), natural zeolite (Clinoptilolite, Itaya, Yamagata) (VI), 5% SiO
2+95% Al
2O
3 (VII), 30% SiO
2+70% Al
2O
3 (VIII), 50% SiO
2+50% Al
2O
3 (IX), and 70% SiO
2+30% Al
2O
3 (X). Yield and selectivity of a series of zeolites were higher than that of Neobeads. The yield and selectivity were higher in case of catalysts VII, VIII, IX, and X when SiO
2 content was larger. Among all these catalysts, VI gave the best yield of hexahydro-2-methylpyrimidine, which was 65% under the condition of molar ratio of 1 : 3, for feed rate of materials of 1 ml/min, weight of packed catalyst of 30g, and reaction temperature of 315°.
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