Hydrochloric Acid → 3-Fluoro-5-(trifluoromethyl)benzeneboronic acid

Temperature

-78 °C

In a second reaction vessel, 40 mL of tetrahydrofuran was cooled to -78° C., and 2.3 mL (0.021 mole) of trimethyl borate was added dropwise as the Grignard reagent of 3-fluoro-5-trifluoromethylphenyl bromide prepared above was transferred into the second reaction vessel using a cannula. The temperature of the reaction mixture was maintained below -60° C. during the additions. Upon completion of the additions, the reaction mixture was again cooled to -78° C., where it was stirred for about 45 minutes. After this time, the reaction mixture was allowed to warm to ambient temperature. The reaction mixture was then poured into about 200 mL of water and was made acidic with aqueous 5% hydrochloric acid. The mixture was extracted with four 100 mL portions of ethyl acetate. The combined extracts were dried with magnesium sulfate and filtered. The filtrate was concentrated under reduced pressure, yielding 3.3 grams of 3-fluoro-5-trifluoromethylphenylboronic acid, mp 167°-168° C. The NMR spectrum was consistent with the proposed structure.

1. customprepared above
2. temperatureThe temperature of the reaction mixture was maintained below -60° C. during the additions
3. temperatureto warm to ambient temperature
4. extractionThe mixture was extracted with four 100 mL portions of ethyl acetate
5. dry with materialThe combined extracts were dried with magnesium sulfate
6. filtrationfiltered
7. concentrationThe filtrate was concentrated under reduced pressure

ORD record

ord-89fce81cff4f4e0f9944221ed549f07d

Source dataset

uspto-grants-1996_07

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US05534518