Electron spin resonance study of the SO2·- formation in the thermal decomposition of sodium dithionite, sodium and potassium metabisulfite, and sodium hydrogen sulfite

Abstract

The thermal decomposition of sodium dithionite (Na2S2O4), sodium and potassium bisulfite (Na2S2O5, K2S2O5), and sodium hydrogen sulfite (NaHSO3) gives sulfur dioxide radical anion (SO2·-) as an esr detectable transient reaction product. The SO2·- present in commercial sodium dithionite samples decays rapidly to a lower "steady state" level at 180-220· The SO2·- radical is detected in sodium and potassium bisulfite as a reaction product which first increases and then decreases in amount as a function of time at temperatures between 200 and 230° for Na2S2O5 and 238 and 280° for K2S2O5. Similar results are found in heating sodium hydrogen sulfite except that the amount of SO2·- detected is less. It is concluded that those compounds which evolve SO2 upon heating may all give detectable amounts of SO2·- as an intermediate reaction product.