反应详情

2'-hydroxyacetophenone (25.7 g) and diethyl oxalate (33.1 g) were added to a solution of sodium ethoxide in ethanol (prepared from 13.0 g of sodium and 375 ml of ethanol), and the mixture was heated for 1 hour while refluxing. After the reaction mixture was cooled to room temperature, ethyl ether (500 ml) was added, and the separating crystals were collected by filtration. To this crystal, 2N hydrochloric acid (600 ml) was added, followed by ethyl ether extraction. The ethyl ether layer was washed with water and dried (MgSO4), after which it was concentrated under reduced pressure. The residual oily substance was dissolved in acetic acid-concentrated hydrochloric acid (1:1,200 ml) and heated for 1 hour while refluxing. The reaction mixture was poured over water (1 liter); the separated crystals were collected by filtration and then washed by sequential additions of water, ethanol and ethyl ether in that order, to yield 4-oxo-4H-1-benzopyran-2-carboxylic acid (83.5%), which was then recrystallized from ethanol to yield colorless needles having a melting point of 240° to 241° C. (decomposed).

1. temperaturethe mixture was heated for 1 hour
2. temperaturewhile refluxing
3. filtrationthe separating crystals were collected by filtration
4. additionTo this crystal, 2N hydrochloric acid (600 ml) was added
5. extractionfollowed by ethyl ether extraction
6. washThe ethyl ether layer was washed with water
7. dry with materialdried (MgSO4)
8. concentrationafter which it was concentrated under reduced pressure
9. dissolutionThe residual oily substance was dissolved in acetic acid-concentrated hydrochloric acid (1:1,200 ml)
10. temperatureheated for 1 hour
11. temperaturewhile refluxing
12. additionThe reaction mixture was poured over water (1 liter)
13. filtrationthe separated crystals were collected by filtration
14. washwashed by sequential additions of water, ethanol and ethyl ether in that order