2-Chloro-4-hydroxybenzonitrile

20925-27-3

3336-16-1

Step 5: 2-Chloro-4-aminobenzonitrile (25 g, 0.187 mol) was added to a stirred mixture of concentrated sulfuric acid (58 g) and water (570 mL) and heated between 49 °C and 61 °C for about 30 minutes. The suspension was cooled to about 0°C and a cold solution of sodium nitrite (13.2 g, 0.187 mol) dissolved in water (125 mL) was slowly added dropwise over a temperature range of 0°C to 6°C. After the dropwise addition was completed, stirring of the reaction mixture was continued for about 3 hours. Subsequently, urea (1.5 g) was added to the mixture to quench the excess sodium nitrite. Insoluble impurities were removed by filtration. To the filtrate was added a 50% aqueous sulfuric acid solution (600 mL) while the reaction mixture was heated to between 74 °C and 81 °C with continuous stirring until the nitrogen stopped escaping. Upon completion of the reaction, the product was separated by filtration and purified with recrystallized water to give 2-chloro-4-hydroxybenzonitrile (17.9 g, 62.5% yield, melting point 160 °C).