1,3-Dibromobenzene → (3-Bromophenyl)boronic acid

Participants

Reaction Steps

N-butyllithium (2.5M) (44 mL; 0.11M) was added dropwise over 15 mins. to a vigorously stirred solution of m-dibromobenzene (25G; 0.106M) in 500 mL of anhydrous ether at -78° under nitrogen. After stirring 10 mins. more, a solution of triisopropylborate (25.3 mL; 0.11M) in anhydrous ether (200 mL) was added over 20 mins. The cooling bath was then removed and the stirring solution was allowed to warm to R.T. over ~2 hrs. A small amount of solid separated. After stirring 15 mins. more at R.T., 150 mL of ice cold 8% aqueous hydrochloric acid was cautiously added, and the stirring was continued for 15 mins. The organic phase was separated, washed with 2×100 mL of a saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. Solvent removal gave ~30 G of crude product as a semi-solid, which was shaken well with 150 mL of hexane. The solid was filtered and washed with 2×25 mL of hexane. The resulting silky solid (mp 178°-9° C. after softening at ~160° C.) (6.5 G) was used as 3-bromophenylboronic acid with a small amount of contamination. The hexane filtrate was concentrated and the residue was stirred well with 150 mL of petroleum ether (30°-60° C.). The resulting solid was filtered and washed with 2×25 mL of petroleum ether. This resulting solid (4.4G) melting at 178.3°-179° C. was the desired 3bromophenylboronic acid.

Provenance & Evidence