Lockhart, Joyce Colquhoun (1957)
Denitration of nitroguanidines.
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The reversible denitration of several nitroguanidines in sulphuric acid media above 67%, in perchloric acid of 59-72% strength and in sulphuric acid-acetic acid media of 49-85% strength, has been investigated. The state of the nitroguanidine molecule in strong acid and the condition of the acid molecules themselves have been discussed.The equilibrium position between the nitroguanidine and corresponding guanidine has been established in all the media used and a correlation of equilibrium position with activity of water in the medium, deduced by Simkins and Williams, has been applied in suitable cases. The rate of denitration over the measurable range has been obtained for several compounds in sulphuric acid-water mixtures, for one in sulphuric acid-acetic acid mixtures and for two in perchloric acid-water mixtures. The rate of guanidine nitration was also measured in sulphuric acid-acetic acid. Rates in perchloric acid are directly proportional to the Hammett acidity function ho. In sulphuric acid this relation does not hold but a relation with ho together with the activities of certain solvent species does apply. The ultra-violet absorption spectra of the nitroguanidines in dilute acid were measured for use in the analysis of reactions. These, together with further spectral data, were used to furnish pKa values for several of the compounds. Certain acidity functions were also investigated, including the H+ function in sulphuric acid-water and perchloric acid-water mixtures, and the Ho function in the higher ranges of perchloric acid.
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Institution: University of London, Royal Holloway College (United Kingdom).