This constituent of Eucalyptus oils has the formula C10Hl8O; specific gravity at 150 C. = 0.930; refractive index at 20° C. = 1.4584; boiling point 1760 C.; is optically inactive; crystallises at a low temperature, and melts at - 1° C. The oxygen atom is combined as oxide, and for this reason cineol does not react with either hydroxylamine or phenylhydrazine, nor does sodium act upon it in the ordinary way. Aldehydic, ketonic and alcoholic groupings are thus absent.

The name cineol was given to this oil constituent by Wallach and Brass [Ann. 225 (1884), 291], who first isolated it in a pure condition from the oil of the " Levant Wormseed," and characterised it as a definite chemical substance.

Qualitative Methods For Detection

The presence of cineol in Eucalyptus oils may be determined in several ways.

(a) If the interior of a short test tube is moistened with the oil to be tested and the vapour of bromine passed into it, a crystalline addition product will be formed on the side of the tube, the crystals being very pronounced if the cineol is present in quantity, but indistinct if the reverse. A smear of the oil on a watch glass will answer just as well, and with practice, as little as 10 per cent. of cineol in Eucalyptus oils can be detected in this way.

(b) The reaction with idol, first described by Hirschsohn in 1893, cart also be used for the detection of small amounts of cineol. The determination may be made by dissolving in a small quantity of the oil as much iodol as it will readily take up, gently heating if necessary. After a short time, if cineol be present, a crystalline compound will separate; this addition product consists of equal molecules of the components, and when recrystallised from alcohol or benzene melts at about 1120 C.

(c) A crystalline compound is formed with cineol, when dry hydrobromic acid gas is passed into a mixture of the well-cooled oil, or most suitable fraction, and an equal volume of petroleum ether; the crystals are filtered off and washed with petroleum ether. This hydrobromide melts at 56-570 C. and is readily decomposed into cineol and hydrobromic acid on the addition of water.

(d) Cineol also combines with gaseous hydrochloric acid, with iodine, with a and /3 naphthols, as well as with phosphoric and arsenic acids, and resorcinol.