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With potassium carbonate; In N,N-dimethyl-formamide;
Step A 5-Carboxy-2,3-dihydro-1,4-benzodioxin A mixture of 10.8 g (70 mmol) of 2,3-dihydroxybenzoic acid, 38.6 g (280 mmol) of dry potassium carbonate and 24 ml (278 mmol) of 1,2-dibromoethane in 40 ml of N,N-dimethylformamide is heated at 65° C. for 24 hours under an inert atmosphere. After cooling, the reaction mixture is diluted with water and then extracted with ether. The aqueous phase is then acidified with a 3N hydrochloric acid solution and subsequently extracted with dichloromethane. After removal of the solvent by evaporation in vacuo, the residue obtained is recrystallized from toluene to yield the title acid in the form of a white solid. Melting point 193-194° C.
With hydrogenchloride; water; In toluene; at 15 - 35℃; for 0.5h;
Preparation of 2, 3-dihydroxy benzoic acid form 2, 3-dimethoxy benzoic acid To a stirred solution of 2, 3-dimethoxy benzoic acid (lOOg; 0.549 mol) in dichloromethane (500 mL) and catalytic amount of DMF (~2 mL) at a temperature about 30-35°C, thionyl chloride (130.6g ; 1.102 mol) was added and stirred for a period of two hours. Reaction was monitored by TLC for completion of the starting material (NMT- 5percent).If reaction not completed added thionyl chloride (9.8 g; 0.823 mol). Upon completion of reaction, the reaction mass was quenched in to the -5°C chilled aqueous ammonia (580 mL) solution at a temperature below 15°C under stirring. The reaction mass was stirred at temperature 30-35°C over a period of 30 min. The separated organic fraction was concentrated under atmospheric distillation at below 50°C, charged toluene (100 ml) and co-distilled until the reaction mass moisture content become less than 0.5 percent. The obtained benzamide compound was dissolved in toluene (500 mL) at temperature about 30-35°C.To the reaction mass was added POCl3 (126.3 g; 0.824 mol).The temperature of the reaction mass was raised to 80-85°C and maintained over a period of 1 -2 hours for the completion of the reaction (Progress of the reaction was monitored by HPLC until the benzamide NMT 1.0 percent). If the reaction was not completed, added second lot of POCl3 (lO.lg; 0.06 mol) at 30-35°C. The reaction mass was cooled to a temperature about 30-35°C upon completion of the reaction. The reaction mixture was added to cold water (1000 mL) at 0-5°C.The organic fraction was separated and washed with 8percent sodium bicarbonate solution. The organic fraction was separated and azeotropic distilled at 110-115°C (until moisture content NMT 0.2 percent), after reaching moisture content to normal limit cooled the reaction mass temperature to 40°C and distilled reaction mass volume becomes ~3 volumes under vacuum at a temperature 40-50°C.After distillation cooled the reaction mass temperature to 30-35°C. In another RB flask charged toluene (160 ml), triethyl amine (199.7 g; 1.977 mol) at 30-35°C and stirred for 10 min. charged aluminum chloride (52.7 g 5; 1.977 mol) in five lots with the gap of 10 min between each lot addition (addition of aluminum chloride may raise the temperature to 45-50°C). The reaction mass temperature was raised to about 70-75 °C and added above reaction mass (methoxy compound) for 30 min. maintained the reaction mass at 70-75°C for 8 hr. Progress of the reaction was monitored by HPLC (until the 2,3-dimethoxybenzonitrile content 0.25 percent and 3-methoxy-2-hydroxybenzonitrile content 0.2 percent). If reaction was not completed added second lot of triethyl amine (27.7 g; 0.27 mol) and aluminum chloride (36.6 g; 0.27 mol).Upon completion of the reaction, the reaction mixture was cooled to 30-35°C and quenched with chilled aqueous HC1 (prepared by addition of water (500 ml) and Cone. HC1 (500 ml)) at 15°C. Stirred reaction mass at 25-30°C for about 30 min, filtered the obtained solids and separated aqueous and organic layers. Charged MIBK (320 ml) to the solids and charged above aqueous layer, filtered through celite and separated aqueous and organic layers. To the aqueous layer given MIBK (320+160 ml) extractions. To the combined organic layer given 20percent sodium chloride solution washing, organic layer was azeotropic distilled at 110°C to remove the water (moisture content NMT 0.2 percent).Cooled the reaction mass temperature to 30°C and filtered through 0.45 micron / 1 micron filter. To the filterate charged 1percent EDTA (400 ml), stirred for 30 min and filtered through 10 micron cloth. The organic fraction was separated and distilled off to obtain the residue. The residue was treated with dichloromethane (400 ml) and the solid obtained was filtered and dried under vacuum over 6 hr at 60-65°C to obtain the title compound 2, 3-dihydroxy benzonitrile. (56g, yield 75.4percent) Purity by HPLC 99.81 percent; Impurity A: 0.05percent Impurity B: 0.07 percent
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