“…Indeed, literature reports already highlight the preparation of Nnitroso-hydrochlorothiazide (2, 6-chloro-4-nitroso-3,4-dihydro-2H-benzo[e] [1,2,4]thiadiazine-7-sulfonamide 1,1-dioxide, NO-HCT, Scheme 1); 37,38 however, its reactivity was not explored in a broader context. In this report, we demonstrate that NO-HCT 2 is unstable in aqueous conditions at pH 1 to 8 and readily decomposes to several degradation products among which formaldehyde, aminobenzenesulfonic acid (3, 2-amino-4chloro-5-sulfamoylbenzenesulfonic acid, ABSA, Scheme 1), thiatriazine (4, 6-chloro-2H-benzo[e] [1,2,3,4]thiatriazine-7sulfonamide 1,1-dioxide, Scheme 1), and HCT 1 are the predominant ones. Moreover, independent synthesis of the HCT-diazonium salt (5, 5-chloro-2,4-disulfamoylbenzenediazonium, Scheme 1) and study of its stability and reactivity have demonstrated that it is relatively stable only in highly acidic and anhydrous conditions in aprotic solvents (e.g., acetonitrile), whereas it decomposes rapidly in neutral or acidic aqueous medium to ABSA 3 instead of the typical diazonium salt hydrolysis and reduction products, which were not detected in the NO-HCT 2 degradation pathway.…”