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.