Thus benzene, (CH) gives thiophene, (CH) S, from which it is difficultly distinguished; pyridine, (CH) N, gives thiazole, (CH) N S, which is a very similar substance; naphthalene gives thionaphthen, C 11 S, with which it shows great analogies, especially in the derivatives.
The three primary members are furfurane, thiophene and pyrrol, each of which contains four methine or CH groups, and an oxygen, sulphur and imido (NH) member respectively; a series of compounds containing selenium is also known.
Thiophene yields a similar series: isothiazole (only known as the condensed ring, isobenzothiazole), thiazole, diazosulphides, piazthioles, azosulphimes and thiobiazole (the formulae are easily derived from the preceding series by replacing oxygen by sulphur).
Thiophene also gives rise to triazsulphole, three nitrogen atoms being introduced.
One or two benzene nuclei may suffer condensation with the furfurane, thiophene and pyrrol rings, the common carbon atoms being vicinal to the hetero-atom.
The -y-diketones are characterized by the readiness with which they yield furfurane, pyrrol and thiophene derivatives, the furfurane derivatives being formed by heating the ketones with a dehydrating agent, the thiophenes, by heating with phosphorus pentasulphide, and the pyrrols by the action of alcoholic ammonia or amines.
It separates from benzene and thiophene with one molecule of the "solvent of crystallization."
The thiophen homologues are best prepared by heating the 1.4 diketones with phosphorus pentasulphide, the diketones reacting in the enolic form: Thiotenol, or oxymethyl thiophene, is prepared by heating laevulinic acid with phosphorus pentasulphide (W.