Sulfuric Acid → 1,3-Dihydro-1-oxoisobenzofuran-5-carboxylic acid

Beteiligte Stoffe

Reaktionsschritte

To 153 ml of fuming sulfuric acid, containing about 27% of SO3, 50 g (0.3 m) of terephthalic acid are added, under stirring, at room temperature, then 23 g (0.25 m) of 1,3,5-trioxane are added thereinto in two portions, by cooling to a temperature of 15-18° C. after any addition. At the end of the addition, the mixture is left 30 minutes under stirring at room temperature, then it is heated at 135-145° C. and let under stirring for 2-2.5 hours at this temperature until the end of the reaction. The reaction mixture is cooled to a temperature lower than 3° C., then 100 ml of glacial acetic are added thereto by keeping the temperature at about 25° C. At the end of the addition, the mixture is let to stand 60 minutes under stirring at 20-25° C. and filtered. The wet product is suspended in 1900 ml of water. The suspension is heated up to 25-30° C. under stirring, its pH is adjusted to about 8 by gradual addition of 175 g of sodium bicarbonate. The solid is filtered off on Celite® by washing with hot water (40-45° C.). The pH of the mother liquors is brought to 1.5 by addition of about 125 ml of 37% hydrochloric acid and the obtained precipitate is filtered at 20-25° C. by washing with water until the filtrate reaches a neutral pH. Thus, 32 g of 5-carboxyphthalide with a titer (HPLC)>93% are obtained.

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