Reactions of guanidine and its derivatives

The thesis may he conveniently considered in two sections - a cryoscopic study of the behaviour of guanidine salts in 99.9% H2SO4 and a study of the denitration of methylnitroguanidine in sulphuric acid of strength above 75% H2S04. In the first section it is established that guanidine is diprotonated to the doubly charged cation to the extent of about 28% in 99.9% H2SO4, and hence the concentration of such a cation in media of less than 98% H2SO4 is shown to be very small; a fact of importance in theoretical considerations of the effect of sulphuric acid on nitro-guanidine-guanidine equilibria. In the second section the position of equilibrium between methylnitroguanidine and methylguanidine is established for 0.02 molar solutions in 75-99% H2S04 and the rate of denitration of methylnitroguanidine solutions in 75-81% H2S04 measured. An analytical technique using the ultra violet absorption spectrum of methylnitroguanidine is used. The equilibria are satisfactorily accounted for by theoretical considerations for the media 75-87% H2SO4 but above 88% H2S04 no quantitative agreement is found. The velocity constants for the denitration reactions, initial concentration 0.02 molar methylnitroguanidine, are successfully related to the activities of the sulphuric acid molecules and hydroxonium ions in 75-81% H2S04. The effect of a methyl group on both the forward and back reaction in the equilibrium, nitroguanidine H2SO4 guanidine, is discussed by comparing the present work on methylnitroguanidine with the results of work by Simkins and Williams on nitroguanidine and with the result from an experiment using N,N'-dimethyl-N"-nitro guanidine. This nitroguanidine derivative was prepared, in very small yield, by a new route.