Steps for the synthesis of 2-aminobenzothiazole-6-carboxylic acid: (2) Sodium thiocyanate (NaSCN, 65 g, 0.8 mol) was added to a methanol (MeOH) suspension of 4-aminobenzoic acid (1,100 g, 0.73 mol), followed by batch addition of bromine (Br2, 38 mL, 0.73 mol). The reaction mixture was cooled to -10 °C and stirred for 2 hours while keeping the internal temperature below -5 °C. Upon completion of the reaction, the precipitate was collected by filtration and suspended in 350 ml of 1 M hydrochloric acid (HCl). The suspension was heated to reflux and maintained for 30 minutes. After rapid filtration, 150 ml of concentrated hydrochloric acid (HCl) was added to the hot filtrate to give 70 g (42% yield) of 2-aminobenzothiazole-6-carboxylic acid (white solid). The product was dried and used directly without further purification.
