The Structure of Cyameluric Acid, Hydromelonic Acid and Related Substances

Over a century ago, in 1835, Leopold Gmelin' prepared the substance tripotassium hydromelonate by heating potassium ferrocyanide with sulfur; he also made other salts of hydromelonic acid, and carried out analyses, which, however, were not sufficiently accurate to lead to correct formulas. He recognized the similarity of the substances to the group of nitrogen compounds discovered and named by Justus Liebig,2 including melon, melam, melamine, etc., and assigned names to them on this basis. Liebig3 then prepared tripotassium hydromelonate by other methods, including, for example, the reaction of fused potassium thiocyanate with antimony trichloride, and, in 1855, after much labor, he succeeded4 in assigning to the acid essentially its correct formula, H3CgNl3 (using the incorrect atomic weight 6 for carbon, he wrote C18N13H3). By decomposing hydromelonates with alkali, Henneberg5 in 1850 prepared salts of another tribasic acid, cyameluric acid, H303C6N7, as well as the acid itself.6