During the past few years the constitution of essential oils has been studied by a considerable number of chemists, and the composition of many oils has been so fully determined that very good imitations can often be made at cheaper prices than those of the genuine oils, rendering it possible to produce cheap soaps having perfumes which were formerly only possible in the more expensive article.
There is a considerable distinction, however, often lost sight of, between an artificial and a synthetic oil. An artificial oil may be produced by separating various constituents from certain natural oils, and so blending these, with or without the addition of other substances, as to produce a
desired odour, the perfume being, at any rate in part, obtained from natural oils. A synthetic perfume, on the other hand, is entirely the product of the chemical laboratory, no natural oil or substance derived therefrom entering into its composition.
The following are among the most important bodies of this class:—
Amyl salicylate, the ester prepared from amyl alcohol and salicylic acid, sometimes known as
"Orchidée" or "Trèfle". This is much used for the production of a clover-scented soap. It has the specific[Pg 108] gravity at 15° C., 1.052-1.054; optical rotation, +1° 16' to +1° 40'; refractive index at 20° C., 1.5056; and should contain not less than 97 per cent. ester, calculated as amyl salicylate.
Anisic aldehyde, or aubépine, prepared by oxidation of anethol, and possessing a pleasant, hawthorn odour. This has the specific gravity at 15° C., 1.126; refractive index at 20° C., 1.5693; is optically inactive, and dissolves readily in one volume of 70 per cent. alcohol.
Benzyl Acetate, the ester obtained from benzyl alcohol and acetic acid. This has a very strong and somewhat coarse, penetrating odour, distinctly resembling jasmine. Its specific gravity at 15° C. is 1.062-1.065; refractive index at 20° C., 1.5020; and it should contain at least 97-98 per cent. ester, calculated as benzyl acetate.
Citral, the aldehyde occurring largely in lemon-grass and verbena oils, also to a less extent in lemon and orange oils, and possessing an intense lemon-like odour. It has a specific gravity at 15° C., 0.896-0.897, is optically inactive, and should be entirely absorbed by a hot saturated solution of sodium bisulphite.
Citronellal, an aldehyde possessing the characteristic odour of citronella oil, in which it occurs to the extent of about 20 per cent., and constituting considerably over 90 per cent. of eucalyptus citriodora oil. Its specific gravity at 15° C. is 0.862; refractive index at 20° C., 1.447; optical rotation, +8° to +12°; and it should be entirely absorbed by a hot saturated solution of sodium bisulphite.
Coumarin, a white crystalline product found in Tonka beans, and prepared synthetically from salicylic acid. It has an odour resembling new-mown hay, and melts at 67° C.
Geraniol, a cyclic alcohol, occurring largely in geranium, palma-rosa, and citronella oils. Its specific gravity at 15° C. is 0.883-0.885; refractive index at 20° C., 1.4762-1.4770; it is optically inactive, and boils at 218°-225° C.
Heliotropin, which possesses the characteristic odour of heliotrope, is prepared artificially from safrol. It crystallises in small prisms melting at 86° C.
Hyacinth.—Most of the articles sold under this name are secret blends of the different makers.
Styrolene has an odour very much resembling hyacinth, and probably forms the basis of most of these preparations, together with terpineol, and other artificial bodies. The properties of the oil vary considerably for different makes.
Ionone, a ketone first prepared by Tiemann, and having when diluted a pronounced violet odour. It is prepared by treating a mixture of citral and acetone with barium hydrate, and distilling in vacuo.
Two isomeric ketones, α-ionone and β-ionone, are produced, the article of commerce being usually a mixture of both. The two ketones have the following properties:—
Alpha-ionone.—Specific gravity at 15° C., 0.9338; refractive index at 16.5 C., 1.50048 (Chuit);
optically it is inactive.
Beta-ionone.—Specific gravity at 15° C., 0.9488; refractive index at 16.8° C., 1.52070 (Chuit);
optically it is inactive also.[Pg 109]
The product is usually sold in 10 or 20 per cent. alcoholic solution ready for use.
Jasmine.—This is one of the few cases in which the artificial oil is probably superior to that obtained from the natural flowers, possibly due to the extreme delicacy of the odour, and its
consequent slight decomposition during preparation from the flowers. The chemical composition of the floral perfume has been very exhaustively studied, and the artificial article now on the market may be described as a triumph of synthetical chemistry. Among its constituents are benzyl acetate, linalyl acetate, benzyl alcohol, indol, methyl anthranilate, and a ketone jasmone.
Linalol, the alcohol forming the greater part of linaloe and bois de rose oils, and found also in lavender, neroli, petitgrain, bergamot, and many other oils. The article has the specific gravity at 15°
C., 0.870-0.876; optical rotation, -12° to -14°; refractive index at 20° C., 1.463-1.464; and when estimated by acetylation, yields about 70 per cent. of alcohols.
Linalyl acetate, or artificial bergamot oil, is the ester formed when linalol is treated with acetic anhydride. It possesses a bergamot-like odour, but it is doubtful whether its value is commensurate with its greatly increased price over that of ordinary bergamot oil. It has the specific gravity at 15°
C., 0.912.
Musk (Artificial).—Several forms of this are to be obtained, practically all of which are nitro-derivatives of aromatic hydrocarbons. The original patent of Baur, obtained in 1889, covered the tri-nitro-derivative of tertiary butyl xylene. The melting point of the pure article usually lies between 108° and 112° C., and the solubility in 95 per cent. alcohol ranges from 1 in 120 to 1 in 200, though more soluble forms are also made.
An important adulterant, which should always be tested for, is acetanilide (antifebrin), which may be detected by the characteristic isocyanide odour produced when musk containing this substance is boiled with alcoholic potash, and a few drops of chloroform added. Acetanilide also increases the solubility in 95 per cent. alcohol.
Neroli Oil (Artificial).—Like jasmine oil, the chemistry of neroli oil is now very fully known, and it is therefore possible to prepare an artificial product which is a very good approximation to the natural oil, and many such are now on the market, which, on account of their comparative cheapness, commend themselves to the soap-perfumer. These consist chiefly of linalol, geraniol, linalyl acetate, methyl anthranilate, and citral.
Mirbane Oil or Nitrobenzene.—This is a cheap substitute for oil of bitter almonds, or benzaldehyde, and is a very coarse, irritating perfume, only suitable for use in the very cheapest soaps. It is
prepared by the action of a mixture of nitric and sulphuric acids on benzene at a temperature not exceeding 40° C. Its specific gravity is 1.205-1.206; refractive index at 20° C., 1.550; and boiling point, 206° C.[Pg 110]
Niobe oil, or ethyl benzoate, the ester obtained from ethyl alcohol and benzoic acid, and having the specific gravity at 15° C., 1.094-1.095; refractive index at 20° C., 1.5167; boiling point,
196.5°-198° C.; soluble in 1.5 volumes of 70 per cent. alcohol.
Oeillet is a combination possessed of a sweet carnation-like odour and having as a basis, eugenol or isoeugenol. Its properties vary with the source of supply.
Rose Oil (Artificial).—Several good and fairly cheap artificial rose oils are now obtainable, consisting chiefly of citronellol, geraniol, linalol, phenyl ethyl alcohol, and citral. In some cases stearopten or other wax is added, to render the oil more similar in appearance to the natural article, but as these are inodorous, no advantage is gained in this way, and there is, further, the
inconvenience in cold weather of having to first melt the oil before use.
Safrol, an ether which is the chief constituent of sassafras oil, and also found in considerable quantity in camphor oil. It is sold as an artificial sassafras oil, and is very much used in perfuming cheap toilet or household soaps. Its specific gravity at 15° C. is 1.103-1.106; refractive index at 20°
C., 1.5373; and it dissolves in fifteen volumes of 80 per cent. alcohol.
Santalol, the alcohol or mixture of alcohols obtained from sandalwood oil. Its specific gravity at 15°
C. is 0.9795; optical rotation, -18°; and refractive index at 20° C., 1.507.
Terebene, a mixture of dipentene and other hydrocarbons prepared from turpentine oil by treatment with concentrated sulphuric acid, is used chiefly in medicated soaps. Its specific gravity at 15° C. is 0.862-0.868; the oil is frequently slightly dextro- or lævo-rotatory; the refractive index at 20° C., 1.470-1.478.
Terpineol, an alcohol also prepared from turpentine oil by the action of sulphuric acid, terpene hydrate being formed as an intermediate substance. It has a distinctly characteristic lilac odour, and on account of its cheapness is much used in soap perfumery, especially for a lilac or lily soap. Its specific gravity at 15° C. is 0.936-0.940; refractive index at 20° C., 1.4812-1.4835; and boiling point about 210°-212° C. It is optically inactive, and readily soluble in 1.5 volumes of 70 per cent.
alcohol.
Vanillin, a white crystalline solid, melting at 80°-82° C. and prepared by the oxidation of
isoeugenol. It has a strong characteristic odour, and occurs, associated with traces of benzoic acid and heliotropin, in the vanilla bean. It can only be used in small quantity in light-coloured soaps, as it quickly tends to darken the colour of the soap.
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