In a 250 mL three-neck flask, 95 mL of methanol and 3 mL of tetrahydrofuran were added, followed by 16.7 g of m-nitrobenzoic acid and 0.2 g of 5% palladium carbon catalyst. A constant pressure dropping funnel was installed and 15.2 mL of 37% formaldehyde aqueous solution was added to it. The air in the reaction system was replaced with hydrogen via an air pump. The reaction system was warmed up to 64 °C and the reaction was stirred at this temperature until hydrogen uptake stopped. Subsequently, the hydrogenation reaction was continued by slowly adding the formaldehyde solution through a dropping funnel until the hydrogen uptake stopped again. After stopping stirring, the reaction mixture was filtered to recover the catalyst. The filtrate was concentrated to precipitate the product m-dimethylaminobenzoic acid. The precipitate was collected by filtration, washed with a small amount of water and dried at 100 °C to give 15.3 g of m-dimethylaminobenzoic acid in 93% yield. The recovered catalyst was washed with reaction solvent and could be reused in subsequent reactions.
