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Guanidine is a small, nitrogen-rich organic compound found in nature in plants (e.g., rice hulls and turnip juice) and animals (e.g., mussels and earthworms). Unlike its oxygen analogue, carbonic acid, it exists at ambient conditions (i.e., not in solution nor at cryogenic temperatures). Guanidine should not be confused with guanine, a purine derivative that is found in bat and bird feces.

Many literature sources state that guanine is very soluble in water; but, as shown in the fast facts table, it is only slightly soluble. It is, however, very hygroscopic. Its hydrochloride salt is highly water-soluble and is the usual article of commerce. The free base is extremely toxic, as shown in the hazard information table. 

Guanidine was discovered in nature in the late 19th century. In 1907, a German patent was awarded to Italian chemist Celso Ulpiani for the reaction of dicyanamide with strong acid to produce guanidine (actually, guanidinium) nitrate. Twenty-four years later, G.B.L. Smith, V. J. Sabetta, and O. F. Steinbach, Jr., at the Polytechnic Institute of Brooklyn (now New York University Tandon School of Engineering) published a comprehensive study of the conversion of dicyandiamide (aka 2-cyanoguanidine) to guanidinium nitrate , a powerful explosive.

Guanidine’s hydrothiocyanate salt has an interesting connection to the current COVID-19 pandemic. This past June, the US Food and Drug Administration warned laboratories not to use media that contain the thiocyanate salt or other guanidine-based chemicals to transport COVID-19 samples. The reason: Guanidine compounds can (HCN) gas. The FDA also advised that when personnel do not know the ingredients of a transport medium, they should handle it as though it contained a guanidine product. As of the date of FDA’s warning, no HCN-related injuries had been reported to the agency.