Related entries: Geraniol
C10H16O = 152.128.
Citral, C10H16O, is the aldehyde of geraniol, and occurs in the volatile oils of lemon grass, lemon, orange, limetta, and pimento. It may be separated from the oils containing it by fractional distillation, and purified; or it may be obtained by oxidising its alcohol, geraniol, by means of chromic acid mixture, thus:—Add 15 of geraniol to 10 of potassium bichromate dissolved in a mixture of 12.5 of sulphuric acid and 100 of water; keep the liquid cool at first, then allow it to become warm, and shake it well for half an hour. The mixture is next made slightly alkaline and distilled in a current of steam; the distillate is treated with a saturated solution of sodium bisulphite, and allowed to stand for twenty-four hours with occasional shaking. The crystalline body thus formed is separated, pressed between blotting-paper, washed with ether, mixed with sodium carbonate, and distilled in steam. Citral occurs as a mobile, slightly yellowish, oily liquid, having a penetrating odour of lemons. Specific gravity, 0.893 to 0.897. Boiling-point, 228° to 229°, with slight decomposition. Refractive index, 1.4931. It is optically inactive. By condensation with acetone in presence of alkali it yields pseudo-ionone, C13H20O, a ketone which, when heated with diluted sulphuric acid, is converted into ionone, an isomer of the irone of orris root. Ionone has a powerful odour of violets and is extensively used in the preparation of artificial violet perfumes. With dehydrating agents citral yields cymene, C10H14, and on reduction with sodium and alcohol produces the alcohol geraniol.
Uses.—The flavour of oil of lemon is largely due to its citral content, and the pure aldehyde may be used to increase the flavouring power of commercial samples of that oil. Citral is equivalent in this respect to about fifteen times its volume of oil of lemon.