Crystalline modifications of salicylidenaminoguanidine

Abstract

The literature provides an infrared spectrum of salicylidenaminoguanidine and several workers have reported m. p. 102° for the free base. Detailed analysis of the base, prepared according to the literature procedure, has however led to the conclusion that it has m. p. 122–124°, and that the published infrared spectrum relates to the hydrogen carbonate derivative and not the free base. In attempting to explain the difference between observed and reported melting points of salicylidenaminoguanidine further studies have suggested that two forms exist (m. p. 122–124° and 139–141°) having identical molecular structure. The precise relationship between the two forms awaits further study.