Water → 5-Bromo-2,4-dimethylthiophene-3-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

A solution of bromine (0.73 mL, 2.25 g, 14 mmol) in glacial acetic acid (8 mL) was added to a solution of 2,4-dimethylthiophene-3-carboxylic acid (2.1 g, 13 mmol) in glacial acetic acid (24 mL) at 6° C. Upon completion, the reaction was stirred at 10° C. for an hour, diluted with glacial acetic acid (30 mL), stirred for 14 hours at room temperature, poured into water (400 mL) and extracted with ether (3×40 mL). The combined ethereal extracts were extracted with dilute sodium hydroxide (0.2 N, 3×30 mL). The combined basic extracts were cooled in an ice bath and then acidified to pH 3 using concentrated hydrochloric acid. Precipitated solids were extracted with ether (3×40 mL). Pooled organic extracts were washed with water (50 mL) and brine (50 mL), dried over magnesium sulphate and concentrated under reduced pressure. The residue was recrystallised from ethyl acetate/hexane to give product as an amorphous white solid (2.7 g, 85%): mp 183-184° C.; 1H NMR (CDCl3) δ 2.67 (s, 3H), 2.38 (s, 3H); EI/MS 235 m/e (M+); IR (liq film) 1674 cm−1; Calcd. for C7H7BrO2S: C, 35.8; H, 3.00; S, 13.6; Found: C, 35.8; H, 2.99; N, 13.5.

Provenance & Evidence