In a glass-stoppered, wide-mouthed bottle cooled by ice water are placed 35 g. (0.42 mole) of thiophene (p. 578) and 50 cc. of benzene (Note 1). With constant shaking (Note 2), and cooling when necessary, 75 g. (0.35 mole) of yellow mercuric oxide and 109 g. (0.43 mole) of iodine are added alternately in small amounts during a period of fifteen to twenty minutes. The yellow mercuric oxide changes to crimson mercuric iodide. The mixture is filtered, and the residue is washed with three 25-cc. portions of ether. The ether-benzene filtrate is shaken with a dilute solution of sodium thiosulfate to remove excess iodine and then dried over 5 g. of calcium chloride and filtered. The ether and benzene are removed by distillation on a steam bath (Note 3), and the residue is fractionally distilled under reduced pressure. 2-Iodothiophene distils at 73°/15 mm.; 80–81°/20 mm.; 90–94°/34–38 mm. (Note 4). The yield is 63–66 g. (72–75 per cent of the theoretical amount) (Note 5). If the iodothiophene is still colored by traces of iodine, the color may be removed by shaking with a small amount of mercuric oxide.