December 27, 1900] 



NATURE 



21 



to the extent of 70 to 90 per cent, in foil of cloves ; this is 

 heated with alkali, which converts it into isoeugenol 



CH,0\ JCH:CH.CH„ 



and the latter is then oxidised to vanillin. Synthetic vanillin 

 has practically displaced the vanilla bean for use in perfumery 

 and the manufacture of confectionery, and, in spite of frequent 

 adulteration with sugar, acetanilide and other comparatively 

 valueless materials, the price of the genuine synthetic article is 

 now only a little more than i per cent, of that obtained in 

 1876. The nearly related aldehyde, piperonal. 



CH, 



CHO 



which has a very powerful odour resembling that of the helio- 

 trope, and is consequently used in perfumery under the name of 

 "heliotropin," is largely prepared from safrole 



.Of 



CH, 



\ 



O 



CH„CH:CH, 



a methylenic ether contained in oil of sassafras and oil of 

 camphor ; its price has dropped by about 99 per cent, during 



j^NcHO 

 the last twenty years. Anisic aldehyde, , 



which has an intense odour resembling that of the hawthorn 

 flower, was greatly in use some four or five years ago ; it is 



prepared from anethol. 



CH:CH.CH3 



the 



CH,.0. 



ether constituting 80 or 90 per cent, of oil of anise. Couniarin, 



/\ 



CH : CH 



JO CO 



the 



orthohydroxycinnamic anhydride, 



\/' 

 material to which the tonka bean, sweet woodruff" and 



new-mown hay owe their characteristic odours ; it was syn- 

 thetically prepared by W. H. Perkin, sen., in 1868, by heating 

 sodiosalicylic aldehyde with acetic anhydride, and was obtained 

 commercially by this method until its recent discovery in con- 

 siderable quantities in Liatris odoratissima, a herb indigenous 

 to Florida, provided a cheaper method of preparation. The 

 pleasant smell of cassia oil is due to its containing from 75 to 90 

 per cent, of cinnamic aldehyde, CgHg.CH :CH.CHO, which 

 was first synthesised by Strecker ; the aldehyde is readily 

 obtained by condensing benzaldehyde with acetaldehyde in 

 presence of soda, and has, indeed, been commercially obtained 

 by this method at times when the Chinese cassia oil distillers 

 adulterated the oil to too great an extent with petroleum, 

 resin, &c. 



The greater number of the ethereal oils prized in perfumery 

 owe their pleasant odours, not to one constituent alone, but to 

 several, and the smell of the more valuable, such as lavender 

 oil, rose oil, Ylang-Ylang, &c., is a blend of the odours of a 

 number of odoriferous components ; the determination of these 

 constituents and their preparation in a state of purity with a 

 view to an ultimate successful imitation of particular ethereal 

 oils has long constituted one of the most intrfcate problems of 

 industrial chemistry, one, however, which has been attacked 

 with astonishing success. A few of the more important odori- 

 ferous principles may be briefly discussed. The aldehyde citral 

 or geranial, C(CH3)2:CH.CH2.CH2.C(CH3):CH.CHO, con- 

 stitutes about 6 per cent, of oil of lemons and about 80 per cent, 

 of lemongrass oil, and gives to these oils their lemon-like odour ; 

 it is largely prepared, commercially, from lemongrass oil, and 

 is accompanied in nature by its dihydro-derivative, citronellal, 

 C(CH3)2:CH.CH2.CH2.CH(CH3).CH2.CHO. Citral was syn- 

 thesised from acetoacetic ether by Tiemann in 1898, and is 

 converted by reduction into the alcohol, geraniol, 



C(CH3)2:CH.CH2.CH2.C(CH3):CH.CH2.0H. 



NO. 1626. VOL. 63] 



Similarly, citronellal yields on reduction the corresponding 

 alcohol, citronellol, 



C(CH3)2:CH.CH2.CH2.CH(CH3).CH2.CH2.0H; 



geraniol, further, can be converted into an isomeric alcohol, 

 linalool, C(CH3)2:CH.CH2CH2.C(CH3)(0H).CH:CH2, by 

 heating with water. These three alcohols, geraniol, citronellol 

 and linalool, yield esters with acids, such, for example, as linalyl 



yCH:CH2 

 acetate, C(CH3)2:CH.CH2.CH2.C(CH3)< . These 



^O.CO.CHs 

 aldehydes and alcohols, together with a number of the esters 

 formed with fatty acids, occur in many ethereal oils. French 

 oil of lavender is distilled from wild lavender in the hills of 

 southern France, and contains 30 to 40 per cent, of linalyl 

 acetate and about an equal quantity of linalool and small 

 quantities of geraniol ; English oil of lavender is distilled from 

 the cultivated plant, and contains only 5 to 10 per cent, ot 

 linalyl acetate, but considerable amounts of cineol, 



CH2— CH CH2 



I 

 CH3.C. CH3 



I 

 O 



I 

 CH2— C(CH3).CH2. 



The fact that English oil fetches about ten times the price ot 

 the best French oil is a frequent source of unfavourable com- 

 ment by Continental merchants. Ylang-Ylang oil contains lina- 

 lool and geraniol, and apparently also the acetic and benzoic 

 esters of both alcohols ; the similar, though less valuable, Cananga 

 oil contains smaller quantities of the esters and larger quantities 

 of a sesquiterpene, C15H24. Otto of roses, which has for cen- 

 turies been the most highly prized of all perfume oils, is ob- 

 tained in the East, in Bulgaria, Germany and, to a small 

 extent, in France, by distilling freshly-gathered roses with water; 

 it contains a wax-like hydrocarbon, the so-called stereoptene, 

 and during the last month Walbaum and Stephan have shown 

 that German rose oil owes its odour to geraniol, citral, citron- 

 ellol, linalool, nonylic aldehyde, CgHjg.CHO, and phenyl- 

 ethylic alcohol, C6H5.CH2.CH2.OH. It is interesting to note 

 that Neroli oil, which contains linalool, geraniol and linalyl 

 acetate, owes its odour in part to the presence of a small per- 



/\nH2 

 centage of methyl anthranilate, ! ; this substance, 



' .CO.OCH3 



in an undiluted condition, has a somewhat unpleasant odour, 

 but when highly diluted smells very much like oil of bitter 

 orange. An alcohol termed terpineol, 



/CH2.CH2\ 



1/ \/ 



CH3.C(0H) 



\ 



CH„.CH 



/ 



C:C(CH3)2, 



is found in many essential oils, and is readily and cheaply pre- 

 pared by the action of dehydrating agents upon terpin hydrate, 

 which in turn is easily prepared from turpentine oil ; terpineol 

 has a powerful odour of lilac, and consequently finds extensive 

 application as a basis in the manufacture of perfumes. 



Oil of orris, mainly obtained from Italian orris root, 

 consists, to the extent of about 35 per cent., of the odourless 

 myristic acid. In 1893 Tiemann and Krueger showed that 

 the odour of fresh violets possessed by the oil is due to the 

 presence of a small proportion of a ketone to which they gave 

 the name irone ; as the result of an important piece of experi- 

 mental work, they proved that irone has the constitution 



(CH3)2C— CH.CH rCH.CO.CHs 



HC 



il 

 HC- 



CH.CH3 

 I 

 -CHo, 



and a patent was obtained by Haarmann and Reimer for a 

 method of separating this ketone from oil of orris. Tiemann 

 and Krueger, before actually ascertaining the constitution of 

 irone, conceiving the possibility of preparing a substance of the 

 same molecular composition as irone from citral, endeavoured 

 to do so in order to obtain information as to the constitution of 

 the ketone. They found that, on allowing a mixture of citral 

 and acetone to remain in contact with baryta solution, an 



