A mixture of 2-methyl-5-oxo-5,6,7,8-tetrahydroimidazo[1,5-c]pyrimidin-2-ium 4-methylbenzenesulfonate (625.1 g), 4-methylbenzenesulfonic acid hydrate (406.6 g), 1,4-dioxan (9.38 litres) and water (625 ml) was heated at reflux (ca. 90° C.) for 2.5 h. when the reaction was complete by nmr. The reaction mixture was concentrated by distillation at atmospheric pressure collecting 7.03 litres. The concentrate was allowed to cool to ca. 77° C., and IMS-G (1.56 litres) was added. The resulting bright solution was allowed to cool and was seeded with [2-(1-methyl-1H-imidazol-4-yl)ethyl]amine bis(4-methylbenzenesulfonate) (0.625 g) at ca. 54° C. The suspension was allowed to cool to ca. 22° C. and aged for 40 min. The solid was filtered off and washed successively with 1,4-dioxan-IMS (3:1, 1.25 litres), and then 1,4-dioxan (2×1.25 litres), pulled dry and dried in vacuo at ca. 50° C. to yield the title compound, 866.3 g.
