The starting material 2-bromo-4-methylaniline (51.4 g, 0.276 mol) was dissolved in 5N HCl (150 ml), and an aqueous solution of NaNO2 (14.2 g, 0.203 mol) was added while stirring at 0-5 °C for 2 h. The reaction mixture was neutralized with Na2CO3, and then a suspension of copper cyanide (83.3 g, 0.522 mol) with water (70 ml) and toluene (200 ml) was added at 0-5 °C. The reaction mixture was stirred for another 30 min, then brought to room temperature and stirred for another 2 h. The toluene layer was separated and then steam distilled. After removing the toluene, the remaining substance was recrystallized from ethanol to give 2-bromo-4-methylbenzonitrile (26.0 g, 48%).
2-Bromo-4-methylbenzonitrile (22.5 g, 0.115 mol) was dissolved in 150 mL of ethanol, and 50 mL of KOH (9.05 g, 0.115 mol) aqueous solution was added. The mixture was refluxed and heated for 8 h. The reaction mixture was evaporated, and the remaining aqueous solution was acidified with concentrated hydrochloric acid. A white solid precipitated, and the precipitate was collected by filtration. The precipitate was recrystallized from water-ethanol (2:5) to give 2-bromo-4-methylbenzoic acid (19.9 g, 81%).
