Description
4-bromo-2-ethylpyridine is an important raw material and intermediate for organic synthesis, pharmaceuticals, agrochemicals and dyes. It can be used as a starting material for the synthesis of crown ester bipyridines and violet essences by sodium or nickel reductive coupling, side chain oxidation and esterification.
Synthesis
The general procedure for the synthesis of 4-bromo-2-ethylpyridine from ethylmagnesium bromide and 4-bromopyridine hydrochloride was as follows: the preparation was carried out according to the method described in Journal of Organic Chemistry, 1985, Vol. 50, No. 22, pp. 4410-4411. First, a THF (100 mL) slurry of 4-bromopyridine hydrochloride (4.17 g, 0.021 mol) was cooled to -78°C under nitrogen protection. Subsequently, ethylmagnesium bromide (15.7 mL, 3.0 M ether solution, 2.2 eq.) was added slowly dropwise via syringe. The reaction mixture was stirred at -78 °C for 10 min before removing the ice bath and allowing it to warm naturally to room temperature. Upon completion of the reaction, it was quenched with 20% aqueous ammonium chloride solution and diluted with ether. The organic phase was washed sequentially with water, 1N HCl aqueous solution and saturated sodium chloride aqueous solution. The organic layer was dried over magnesium sulfate, filtered and concentrated in vacuum. The residue was redissolved in toluene (100 mL) and tetrachloro-1,2-benzoquinone (5.8 g, 1.1 eq.) pre-dissolved in acetic acid (50 mL) was added under nitrogen protection. The reaction mixture was stirred overnight at room temperature. Subsequently, the pH was adjusted to basic with 1N NaOH aqueous solution and extracted with ethyl acetate. The organic phase was acidified with 1N HCl aqueous solution and extracted again with ethyl acetate. The organic phases were combined, washed with saturated aqueous sodium chloride solution, dried over magnesium sulfate, filtered and concentrated in vacuo to give a brown residue (2.64 g, 66% yield).LCMS (ES) analysis showed m/z 188 (M+1, bromide mode).
