1. Grignard reagent was prepared by adding magnesium shavings (2.809 g, 0.12 mol) to anhydrous ether (21.50 ml) under nitrogen protection. 2. Anhydrous ether (33 ml) solution of 1-bromo-2,3,5-trichlorobenzene (8.60 g, 0.033 mol) and ethyl bromide (4.73 ml, 7.31 g, 0.067 mol) was added dropwise to the above mentioned Grignard reagent and reacted at room temperature. 3. The reaction mixture was refluxed for 0.5 hours and then cooled to room temperature. 4. Grignard reagent at room temperature.3. The reaction mixture was refluxed for 0.5 h and cooled to room temperature.4. The above mixture was added dropwise to a solution of trimethyl borate (5.16 ml, 5.16 g, 0.05 mol) in anhydrous ethyl ether (8.60 ml), which had been pre-cooled to below -60°C, under the protection of nitrogen.5. The reaction mixture was slowly warmed to room temperature and stirred overnight.6 . . after completion of the reaction, the mixture was cooled to room temperature and then the reaction was quenched with 2M hydrochloric acid (10 ml) under ice bath conditions.7. The ether layer was separated, washed with water (2 x 20 ml), dried with anhydrous magnesium sulphate, and filtered.8. Vacuum evaporation of the filtrate yielded the crude product.9. The crude product was milled with petroleum ether at 40-60 °C, filtered and dried under vacuum to give 2,3,5-trichlorophenylboronic acid, . Yield 4.57 g (61%), melting point 257-260 °C.
