Preparation of 2-hydroxy-5-(thiocyanato)benzoic acid
5-Aminosalicylic acid (7.65 g) is dissolved in water (600ml) and concentrated hydrochloric acid (14.5 ml) and diazotized in the usual way with sodium nitrite (3.8 g). The greyish-blue diazonium salt is pressed as dry as possible and added in portions to a solution of copper(I) thiocyanate (6.1 g) and potassium thiocyanate (30 g) in water (17 ml) at 65°. Nitrogen is evolved and the solution becomes pale brown. On cooling, 5-thiocyanatosalicylic acid separates and for purification is dissolved in dilute sodium carbonate solution, reprecipitated by hydrochloric acid, and recrystallized from benzene (yield 73 %, m.p. 167-168°).
Ber. Deut. Chem. Ges., 58, 1559 (1925).