Reaktion #574009

Reaktionsgleichung

hexane

N-Butyllithium

m-dibromobenzene

triisopropylborate

→

3-BROMOPHENYLBORONIC ACID

Lösungsmittel

ether

ether

Reaktionsbedingungen

Aufarbeitung

1. 1
   Sonstigeat -78°
2. 2
   SonstigeThe cooling bath was then removed
3. 3
   SonstigeA small amount of solid separated
4. 4
   workup.STIRRINGAfter stirring 15 mins
5. 5
   workup.ADDITIONmore at R.T., 150 mL of ice cold 8% aqueous hydrochloric acid was cautiously added
6. 6
   workup.WAITthe stirring was continued for 15 mins
7. 7
   SonstigeThe organic phase was separated
8. 8
   Waschenwashed with 2×100 mL of saturated sodium chloride solution
9. 9
   Trocknendried over anhydrous magnesium sulfate
10. 10
    SonstigeSolvent removal
11. 11
    Sonstigegave ~30 G of crude product as a semi-solid, which
12. 12
    FiltrationThe solid was filtered
13. 13
    Waschenwashed with 2×25 mL of hexane
14. 14
    SonstigeThe resulting silky solid (mp 178°-9° C. after softening at ~160° C.) (6.5 g)
15. 15
    EinengenThe hexane filtrate was concentrated
16. 16
    workup.STIRRINGthe residue was stirred well with 150 mL of petroleum ether (30°-60°)
17. 17
    FiltrationThe resulting solid was filtered
18. 18
    Waschenwashed with 2×25 mL of petroleum ether

Vorschrift

N-Butyllithium (2.5M; 44 mL; 0.11M) was added dropwise over 15 mins. to a vigorously stirred solution of m-dibromobenzene (25 g; 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 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°). The resulting solid was filtered and washed with 2×25 mL of petroleum ether. This resulting solid (4.4 g) melting at 178.3°-179° C. was the desired 3-bromophenylboronic acid. NMR: 7.38-7.46; 7.70-7.80; 8.1-8.18; 8.31 (aromatic H's) ##STR104##

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