The general procedure for the synthesis of 2-chloro-4-hydroxybenzaldehyde from 3-chlorophenol (CAS 108-43-0) (49.2 g, 0.380 mol) and trichloromethane was as follows: first, 3-chlorophenol, calcium hydroxide (122.0 g) and sodium carbonate (139.4 g) were suspended in water (872 mL). Subsequently, trichloromethane (90.6 g, 0.760 mol) was slowly added over 80 min and the reaction mixture was refluxed for 3 h under vigorous stirring. After completion of the reaction, the mixture was cooled in an ice bath. Next, concentrated hydrochloric acid (385 mL) and trichloromethane (300 mL) were added for extraction and the aqueous layer was discarded. The organic layer was dried with anhydrous sodium sulfate (50 g) followed by evaporation of the solvent under vacuum. The residue was purified by silica gel column chromatography (silica gel 63-100 μm, 600 g, eluents sequentially carbon tetrachloride, chloroform, chloroform/ethyl acetate 93:7). Fractions containing the target product were collected, combined, and the solvents were evaporated and co-evaporated with dioxane to yield 2-chloro-4-hydroxybenzaldehyde (9.77 g, 0.062 mol, 16% yield) as a white powder.1H NMR (DMSO-d6) data were as follows: δ 11.06 (s, 1H, aldehydic hydrogens); 10.14 (s, 1H, hydroxyhydrogens); 7.75 ( d, 1H, J = 8.5 Hz, arylhydrogen); 6.92 (d, 1H, J = 2 Hz, arylhydrogen); 6.85 (dd, 1H, J1 = 8.5 Hz, J2 = 2 Hz, arylhydrogen).
