General procedure for the synthesis of 2,1,3-benzoxadiazole-5-carboxylic acid from benzoxafurazan-5-carboxylic acid: 2,1,3-benzoxadiazole-5-carboxylic acid N-oxide (80 g) was dissolved in anhydrous ethanol (800 ml) in a 2 L reactor fitted with a mechanical stirrer, a thermometer, a dosing funnel, a reflux condenser and a nitrogen inlet. Triethyl phosphite (114.05 g) was slowly added to this solution over a period of 10 minutes at a temperature range of 62°C to 70°C. The reaction mixture was heated to reflux temperature (76-78°C) and maintained for 2 hours. The progress of the reaction was monitored by thin layer chromatography (TLC, unfolding reagent ratio of CHCl3:acetone:acetic acid = 100:2:1) to confirm that the reaction was complete. Subsequently, the solvent was evaporated under reduced pressure conditions (30 mbar, 40 °C) to give a black oily product (180 g). To this oily product, water (400 ml) was added and subsequently extracted with ethyl acetate (first 400 ml, second 160 ml). The organic phases were combined and washed with 850 ml of aqueous sodium hydroxide (9.5 μl).
