Pulse radiolysis and transient absorption spectra of aqueous solutions of sodium sulfamate

Chemical kinetics for the reactions of sulfamate ions (NH 2 SO 3 - ) with the primary products of water and nitric acid radiolysis were measured in aqueous solutions at ambient temperature. Using time-resolved electron pulse radiolysis techniques with a custom multichannel detection system, we examined the reactivity of NH 2 SO 3 - with the hydroxyl radical ( • OH), hydrogen atom (H • ), and nitrate radical (NO 3 • ). The sulfamate ion was found to react with • OH and H • with second-order rate coefficients of k •OH = (5.60 ± 0.04) × 10 6 M –1 s –1 and k H• = (7.96 ± 0.10) × 10 6 M –1 s –1 , respectively, and with NO 3 • with a rate coefficient of k NO3• = (1.67 ± 0.06) × 10 7 M –1 s –1 . The reactions of NH 2 SO 3 - with • OH and H • resulted in the formation of two transient radical species, one with maximum absorbance at 300 nm and a second with maxima at both 300 nm and 600 nm. These spectra are tentatively assigned to • NH 2 SO 3 and • NHSO 3 – , respectively. By measuring the absorbance of these radicals as a function of pH, the radical p K a was determined to be 9.5 ± 0.1. Overall, this work has implications for the longevity and performance of ferrous sulfamate, Fe(NH 2 SO 3 ) 2 , as a plutonium reductant in the reprocessing of used nuclear fuel. • Pulse radiolysis was used to study sulfamate reactions in water and nitric acid. • Transient spectra reveal two sulfamate radical species: • NH 2 SO 3 / • NHSO 3 - . • The p K a of • NH 2 SO 3 was determined as 9.5 ± 0.1. • Rate constants for sulfamate with • OH, H • , and • NO 3 were determined.