To the reaction vessel, 0.07 mol 4-aminophenol, 0.076 mol salicylamide and 80 mL ethyl acetate were added and the stirring speed was controlled to be 150 rpm. 0.031 mol stannous chloride was added slowly and a gradual darkening of the color of the solution was observed. After the addition was completed, the temperature was slowly raised to 170 °C and the reaction was maintained for 6 h. The reaction was carried out at 2.1 °C. After completion of the reaction, vacuum distillation was carried out at 2.1 kPa to remove some of the ethyl acetate. The solution was cooled to 38 °C and subsequently the reaction mixture was poured into 500 mL of sodium bisulfite solution with a mass fraction of 23%. The pH was adjusted to 4 with 33% oxalic acid solution to induce precipitation of the solid. The solid product was separated by filtration and purified by recrystallization with 87% ethylenediamine solution to give 13.47 g of white solid 2-hydroxy-N-(4-hydroxyphenyl)benzamide in 84% yield.
