Ammonia → 2-Amino-4,6-dimethoxybenzamide

Participants

Reaction Steps

A solution of 3,5-dimethoxyaniline (199 g, 1.30 mol) in ether (5.0 L) in a 5 L 3-necked flask was cooled to 0° C. HCl gas (227 g) was bubbled through the solution over 45 min. After 45 min at 10° C., the mixture was filtered, washed with isopropylacetate (4 L), and dried overnight on high vacuum at 45° C. to give the hydrochloride (242.3 g, 98%), as a white solid. A mixture of the hydrochloride above (20 g, 0.105 mol) and oxalyl chloride (33 mL) in a 3-necked flask equipped with a reflux condenser was heated for 2 h with stirring (170° C. external temperature), and the oxalyl chloride was distilled from the reaction mixture. The flask was cooled to 0° C. and methanol (40 mL) was added. The reaction mixture was heated to reflux for 45 min, filtered while hot, and washed with methanol (80 mL) to give the 4,6-dimethoxyisatin (17.2 g, 79%) as a yellow-green solid. To a heated solution (external temp 70° C.) of the isatin (162 g, 0.78 mol) in aqueous NaOH (40%, 1.5 L) was added H2O2 (35%, 405 mL) slowly over 2 h: After the addition of each portion of H2O2, the internal reaction temperature (initially 64° C.) increased (to a maximum temp of 80° C.). After the addition was complete, the foaming reaction mixture was then stirred for an additional 2 h at 70° C., and the mixture was allowed to stir overnight while cooling to room temperature. The mixture was heated to 70° C. Additional H2O2 (75 mL) was added, and the mixture was stirred at 70° C. for a further 2 h until the reaction was complete. After cooling to 10° C. (bath temperature), aqueous Na2S2O3 (150 mL, saturated) was added. The mixture was brought to pH 8 with HCl (37%, 1.6 L) and pH 6 with acetic acid (glacial, 75 mL), without allowing the reaction mixture to warm to greater than 40° C. Filtration of the reaction mixture and washing with water (4 L) gave the expected amino acid as a tan solid (83.7 g, 55%). To a solution of the amino acid (82.7 g, 0.42 mol) in anhydrous THF (4.2 L) was added EDCl (89.2 g, 0.48 mol), HOBT (65 g, 0.48 mol), and NMM (51.3 mL), and the mixture was allowed to stir at room temperature for 3 h. Aqueous NH3 (83 mL, 50%) was added, and the mixture was stirred at room temperature for 16 h. Water (1.25 L) was added, and the mixture was extracted with DCM (2×250 mL). The combined extracts were then washed with water (2×500 mL). Concentration, formation of a slurry with ether (550 mL), filtration, and drying under high vacuum gave 2-amino-4,6-dimethoxybenzamide (46.7 g, 57%) as a brown solid.

Provenance & Evidence