Pyridine → N-Acetyl-3-(3,5-di-t-butyl-4-hydroxyanilino)benzoic Acid

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A mixture of 5.6 g of 3-(3,5-di-t-butyl-4-hydroxyanilino)benzoic acid (from Example 13) and 15 ml of acetic anhydride was heated under a nitrogen atmosphere at 70°-120° C. for about 90 minutes. The mixture was cooled to 80° C., 5 drops of pyridine were added and the reaction was reheated to 120° C. for 10 minutes. An additional 0.25 ml of pyridine was added at about 80° C., followed by the gradual addition of 10 ml of water to hydrolyze the excess acetic anhydride and the mixed anhydride of the product. Heating was continued until a precipitate formed. The reaction mixture was allowed to cool to room temperature, and the precipitate was then collected, rinsed with a cold mixture of methanol and water, and dried to give 4.3 g of off-white solid m.p. 204°-205.5° C. This material was recrystallized first from a mixture of 30 ml of ethanol and 5 ml of water, and then from a mixture of 30 ml of isopropanol and 5 ml of hexane to give 3.3 g of white solid N-acetyl-3-(3,5-di-t-butyl-4-hydroxyanilino)benzoic acid m.p. 214.5°-215.5° C. Analysis: Calculated for: C23H29NO4 ·1/2(CH3)2CHOH: % C, 71.2; % H, 8.0; % N 3.4. Found: % C, 71.4; % H, 8.1; % N, 3.2.

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