[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[S:12][C:11]([C:13]([O:15]CC)=[O:14])=[CH:10][CH:9]=2)=[CH:4][CH:3]=1.[OH-].[Na+].Cl>CO>[Cl:1][C:2]1[CH:3]=[CH:4][C:5]([C:8]2[S:12][C:11]([C:13]([OH:15])=[O:14])=[CH:10][CH:9]=2)=[CH:6][CH:7]=1A mixture of ethyl 5-(4-chlorophenyl)thiophene-2-carboxylate (1.05 g, 3.94 mmol), methanol (40 ml) and 1.0 M aq NaOH (15.75 ml, 15.75 mmol) was stirred at reflux for 6 hours. Upon cooling to RT, the reaction was acidified to pH 3 with conc. HCl and extracted with EtOAc (60 ml). The EtOAc layer was dried over Na2SO4 and concentrated to yield 5-(4-chlorophenyl)thiophene-2-carboxylic acid (902 mg, 3.78 mmol, 96% yield) as an off-white solid. LC MS at t=2.44 min. (m+H=240) PHENOMENEX® S5 C18 4.6×30 mm column/water-MeOH-TFA 90:10:0.1 to 10:90:0.1 gradient over 2 min at 5 mL/min with 1 min hold at the end of the gradient. 1H NMR (400 MHz, DMSO) δ ppm 7.36-7.97 (m, 6H), 13.19 (s, 1H).
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