Decompositions of this nature were first discovered in the naphthalene series, where it was found that derivatives of indene (and of hydrindene and indone) and also of benzene resulted; Zincke then extended his methods to the disintegration of the oxybenzenes and obtained analogous results, R-pentene and aliphatic derivatives being formed (Rsymbolizing a ringed nucleus).
This substance is transformed into hexachlor-R-pentene oxycarboxylic acid (3) when digested with water; and chromic acid oxidizes this substance to hexachlor-R-pentene (4).
Hantzsch (Ber., 1889, 22, p. 1238) succeeded in ob R taining derivatives of o-diketo-R-hexene, which yield R-pentene and aliphatic compounds on decomposition.
When thus chlorinated phenol (I) yields trichlor-o-diketo-R-hexene (2), which may be hydrolysed to an acid (3), which, in turn, suffers rearrangement to trichlor-R-pentene-oxycarboxylic acid (4).
Cyclo-pentene, C 5 H 8, a liquid obtained by the action of alcoholic potash on iodo-cyclo-pentane, boils at 45° C. Cyclopentadiene, C. 1 H 6, is found in the first runnings from crude benzene distillations.
Croconic acid (dioxy - cyclo-pentene-trione), C 5 H 2 0 51 is formed when triquinoyl is boiled with water, or by the oxidation of hexa-oxybenzene or dioxydiquinoyl in alkaline solution (T.
Isolauronolic acid, C 9 H 14 0 2, is trimethyl-2.2.3-cyclo-pentene-3-acid-4.
Stannous chloride reduces it to hexa-oxybenzene, and when boiled with water it yields croconic acid (dioxy-cyclo-pentene-trione).