[Cl:1][C:2]1[CH:8]=[CH:7][C:5](N)=[CH:4][CH:3]=1.Cl.N([O-])=O.[Na+].[S:14]1[CH:18]=[CH:17][CH:16]=[CH:15]1.[OH-].[Na+]>O.C(Cl)(Cl)(Cl)Cl.C(O)(=O)C>[Cl:1][C:2]1[CH:8]=[CH:7][C:5]([C:15]2[S:14][CH:18]=[CH:17][CH:16]=2)=[CH:4][CH:3]=1
4-Chloroaniline (4.0 g, 31.4 mmol) is added to 4 ml of acetic acid and heated until all solid is dissolved. The solution is cooled to 5° and 5.2 ml of conc. HCl is added, followed by the dropwise addition of sodium nitrite (2.16 g, 31.4 mmol) in 32 ml of water. After addition is complete, the mixture is stirred at 5° for 1 hour. Thiophene (2.64 g, 2.5 ml, 31.4 mmol) in 25 ml of carbon tetrachloride is added to the mixture, followed by the dropwise addition of 25% aq. NaOH (ca. 6.8 ml). After 1 hour, the mixture is poured into water and extracted with chloroform, and the combined extracts are washed with brine, dried and stripped of solvent. The black residue is distilled at ca. 120° 0.35 mm to give 2-(4-chlorophenyl)thiophene, a yellow solid.
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