STUDIES ON THE FORMATION AND DECOMPOSITION OF DITHIONATE .4. OXIDATION OF SODIUM-SULFITE WITH NITROGEN-DIOXIDE - WITH SPECIAL REFERENCE TO ANALYTICAL METHODS FOR NITROGEN-SULFUR COMPOUNDS PRODUCED IN THE REACTION SYSTEM

Analytical methods for the determination of nitrogen-sulfur compounds produced by the reaction of aqueous sodium sulfite solution with nitrogen dioxide were developed. The oxidation of sodium sulfite with nitrogen dioxide proceeded by bubbling nitrogen dioxide gas (630 to 2000 ppm) at a flow rate of 2.5l/min through the aqueous sulfite solutions (0.240~0.380mol/l), which ranged 25 to 70°C in temperature and pH 5. 92 to 10.60. More than 99% of nitrogen dioxide was absorbed under all the conditions tested, producing various nitrogen-sulfur compounds such as NO2-, HON(SO3)22-, etc. The reaction products differed remarkably according to the reaction conditions applied. Main products in the pH range 6.60~10.6 at 25°C consisted of SO42-, S2O62-, NO2- and HON (SO3) 22-, and those produced at 70°C in the pH range of 6.60~7.20 consisted of SO42-, S2O62- and HN(SO3)22-. Any appreciable amount of nitrate was not produced in all the cases examined. These results indicated that the reaction between nitrogen dioxide and sulfite solution at the first stage should not be such that but proceeded in the following way : Subsequent reaction of NO2- and HSO3- led to the formation of HON(SO3)22-. The reactions above were competitive, so that the amount of S2O62- produced increased with increasing pH values and temperature. In acid media HON(SO3)22-, N(SO3)33- and HN(SO3)22- became oxidized by NO3- to form sulfate. Also, NO2- partially hydrolyzed to yield NO, NO2 and NO3-. Based on these observations an possible oxidation pathway of sulfite in solution by nitrogen dioxide was suggested. © 1979, The Chemical Society of Japan. All rights reserved.