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171.5 g of 2,3-dihydroxy-4-methoxy benzoic acid, 515 cm3 of alcohol, 280 cm3 of soda lye and 175 g of ethylene bromide were introduced into a balloon flask provided with an agitator, a thermometer and an inlet pipe for nitrogen. The mixture was heated under reflux and then cooled and poured into 2.8 liters of water. The solution was filtered and treated with 85 cm3 of concentrated hydrochloric acid. The precipitate was dried off, washed and dried. After recrystallization in dimethylformamide, 110 g of 8-methoxy-1,4-benzodioxane-5-carboxylic acid were obtained (M.P.: 224°-226° C.; yield: 57%).

1. customprovided with an agitator
2. temperatureThe mixture was heated
3. temperatureunder reflux
4. temperaturecooled
5. filtrationThe solution was filtered
6. additiontreated with 85 cm3 of concentrated hydrochloric acid
7. customThe precipitate was dried off
8. washwashed
9. customdried
10. customAfter recrystallization in dimethylformamide