Kinetic study of the stability of (NH2)(2)CSSC(NH2)(2)(2+)

The kinetics of the decomposition of formamidine disulfide dihydrochloride, (NH2)(2)CSSC(NH2)2(2+) 2Cl(-), in aqueous solution at 25 degrees C are general base catalysed, and rate constants have been measured over the pH range 1.91-9.03. Analysis of the data yields ionisation constants pK(1) = 5.49, pK(2) = 7.66 and rate constants for deprotonation of the substrate by OH- and H2O. For the doubly charged cation, reaction occurs through a small concentration of a reactive tautomer, (HN=)(NH3+)CSSC+(NH2)(2), which is attacked by H2O. The singly charged cation reacts by parallel pathways involving OH- and H2O as attacking bases.