Thiophen (C4H4S) is a liquid compound which occurs in coal-tar, in which it was discovered by V. Meyer in 1883. It may a1so be readily prepared synthetically, the methods of preparation as well as the reactions of the compound indicating the constitution-
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It is a colourless liquid, which boils at 84° C. and solidifies at low temperatures. It possesses an odour which closely resembles that of benzene, to which latter compound also thiophen exhibits a most remarkable similarity. By replacement of the H atoms in the compound by other elements or radicals a very large number of thiophen derivatives are obtained. These compounds are recognisable by the formation of a dark blue colour when mixed with sulphuric acid and isatin, a test very characteristic of the thiophen group.