Org Prep Daily

September 22, 2006

5-Cl-Benzodioxole-4-carboxylic acid

Filed under: procedures — milkshake @ 6:41 pm



Butyllithium 70 mmol (28mL of 2.5M solution in hexanes) was added to a diisopropylamine 10mL (70.8mmol) solution in anh.THF (200mL) at –78 C. After 20 minutes, 5-chlorobenzodioxole 7.5mL (64mmol) was added dropwise and the mixture was stirred at –78 C for 1 hour. The reaction mixture was then saturated with a CO2 stream (generated from dry ice in a separate flask) at –78 C for 40 min. Water 10mL was added dropwise, the mixture was removed from the cooling bath and stirred until gas evolution ceased (30 min). The mixture was evaporated to dryness, the residue was dissolved in water 400mL, two small spoons of charcoal were added, the mixture was heated to reflux, cooled and filtered. The filtrates were acidified with conc. HCl (20mL), the resulting slurry was allowed to settle for 15 minutes. The precipitated solids were collected by filtration, washed with a copious amount of water and dried by suction. The crude product (11.77g) was re-crystallized from a mixture of ethanol (100mL) and water (300mL). Y=10.186g (79%) of a white crystalline solid (HPLC purity about 95%).

1-H(d6-DMSO, 400MHz): 13.686(br s, 1H), 7.013(dAB, 8.3Hz, 1H), 6.965(dAB, 8.3Hz, 1H), 6.144(s, 2H)

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