Terpenes Proper - Encyclopedia




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TERPENES PROPER The terpenes proper may be subdivided into the simple monocyclic terpenes and the more complex (usually bicyclic) terpenes. The monocyclic terpenes are hydro derivatives of paracymene. A. v. Baeyer proposed the following nomenclature: the dihydroparacymenes are called terpadienes, the tetrahydrocymenes becoming terpenes and the hexahydrocymene terpan, the carbon atoms being numbered as shown in the inset formula: In the more complex terpenes the name camphene is retained, and camphane is /77 (8) (e) used for the dihydrocamphene. G. (7) V6 5 ?C (ro) Wagner (Ber., 1894, 27, p. 1636 Anm.) designates the hexahydrocymenes menthans, the tetrahydrocymenes menthenes, and the dihydrocymenes menthadienes. The position of the double linking in the molecule is shown by the use of the symbol z followed by the number of the carbon atom immediately preceding it.

Monocyclic Terpene Group Limonene, AI :8(9) terpadiene, C10H16, is known in three forms, namely d-limonene, l-limonene, and i-limonene or dipentene. d-Limonene is the chief constituent of oil of orange-rind, and is also found in oil of lemon and oil of bergamot. l-Limonene is found in oil of fir-cones and in Russian peppermint oil. Both are pleasant-smelling liquids, which boil at 175-176° C. They differ from each other only in rotatory power. Dry hydrochloric acid gas converts them into optically active limonene hydrochloride, while in the moist condition it gives dipentene dihydrochloride. When heated to a sufficiently high temperature they are converted into dipentene. Four optically active nitrosochlorides are known, two corresponding to each of the active limonenes, and these on heating with alcoholic potash are converted into d- and l-carvoxime. Dipentene (i-limonene) is found widely distributed in many essential oils, e.g. of camphor, Russian turpentine, cubebs, bergamot, cardamom, &c., and is also a product of the dry distillation of many vegetable resins. It may be produced by heating many terpenes (pinene, camphene, sylvestrene,' limonene) for several hours at 250-270° C.; or by the polymerization of isoprene at 300° C. To obtain pure dipentene it is best to heat dipentene hydrochloride with anhydrous sodium acetate and glacial acetic acid (0. Wallach, Ann. Chem. Pharm., 188 7, 2 39, p. 3). It is a pleasant-smelling liquid, which boils at 175-176° C., and polymerizes on heating to high temperatures. When warmed with alcoholic sulphuric acid it yields terpinene, whilst concentrated sulphuric acid or phosphorus pentasulphide convert it into paracymene. Dipentene dihydrochloride, C 1 oH 16.2HC1, best prepared by passing a current of hydrochloric acid gas over the surface of a glacial acetic acid solution of dipentene, crystallizes in rhombic tables which melt at 50° C. and boil at 118-120° C. (IO mm.). It is apparently a trans-compound, for A. v. Baeyer (Ber., 1893, 26, p. 2863) has obtained a cis-dihydrochloride of melting-point 25° (circa), by the action of hydrochloric acid on cineol.

Terpinolene, AI :4(8) terpadiene, has not as yet been observed in essential oils. It is formed by the action of hot dilute sulphuric acid on terpineol, terpin hydrate and cineol. It is an inactive liquid boiling at 183-185° C., and is readily converted into terpinene by acids.

Terpinene, : 4(8) terpadiene (?), is found in cardamom oil and in oil of marjoram. It is formed by the action of alcoholic sulphuric acid on dipentene, terpin hydrate, cineol phellandrene or terpineol; or by the action of formic acid on linalool.

Phellandrene is a mixture of DI: 5 terpadiene and A2: I (7) terpadiene (pseudo-phellandrene) (F. W. Semmler, Ber., 1903, 36, p. 1749). It is found as d-phellandrene in oil of water-fennel and oil of elemi, and as l-phellandrene in Australian eucalyptus oil and oil of bay. It is an exceedingly unstable compound, and must be extracted from the oils by distillation in vacuo. The hydrocarbons obtained from elemi oil and eucalyptus oil correspond to A1.5 terpadiene. A similar hydrocarbon was obtained by C. Harries and M. Johnson (Ber., 1905, 38, p. 1832) by converting carvone hydrobromide into z6 terpenone-2, then, by phosphorus pentachloride, into chlor-2-phellandrene, which is finally reduced.

Sylvestrene, DI : 8(9) meta-terpadiene, is found in Swedish and Russian oil of turpentine and in various pine oils. It boils at 175-176° C. and is dextro-rotatory. It is one of the most stable of the terpenes and gives a characteristic deep blue colour on the addition of a drop of sulphuric acid to its solution in acetic anhydride. On treating the hydrobromide with bromine in the presence of iodine, a product is obtained which on reduction yields meta-cymene (A. v. Baeyer and V. Villiger, Ber., 1898, 31, p. 2067).

Carvestrene is obtained by the distillation of carylamine or vestrylamine hydrochloride (A. v. Baeyer, Ber., 18 94, 2 7, pp. 34 8 5 seq.). It is regarded by Baeyer as i-sylvestrene. It was synthesized by W. H. Perkin and G. Tattersall (Proc. Chem. Soc., 1907, 22, p. 268) by the application of the Grignard reaction to the ethyl ester of y-ketohexahydrobenzoic acid (1). By the action of magnesium methyl iodide this ester yields the lactone of -y-hydroxy-hexahydrometa-toluic acid, which is transformed by hydrobromic acid into the corresponding -y-bromo-hexahydro-meta-toluic acid. This latter substance by the action of pyridine yields tetrahydro-metatoluic acid, the ester of which by magnesium methyl iodide is converted into 0I-meta menthenol-8 (2). The meta-menthenol on dehydration by potassium bisulphate yields carvestrene (3) of boiling-point 179-180° C.

dioxide yields I-methyl-4-isopropyldiketohexamethylene. This ketone is then reduced to the secondary alcohol, the hydroxyl groups replaced by bromine, and hydrobromic acid is then removed from the bromo-compound by boiling it with quinoline, leaving the terpene. It is a liquid which boils at 174° C. and shows a complete terpene character.

Alcohol And Ketone Derivatives Menthol (terpan-01-3), C10H200. The laevo variety is the chief portion of oil of peppermint; it may be prepared by reducing the menthone obtained by E. Beckmann and M. Pleissner (Ann., 1891, 262, p. 21) from pulegone hydrobromide with sodium and alcohol. It crystallizes in prisms which melt at 43° C. and boil at 212° C. It is readily oxidized by chromic acid to the corresponding ketone menthone. By the action of phosphorus pentoxide, or zinc chloride, it is converted into menthene, C10His, and when heated with anhydrous copper sulphate to 250° C. it yields para-cymene. It is reduced by hydriodic acid and phosphorus to hexahydrocymene. The phosphorus haloids yield haloid esters of composition C10H19C1, which, according to I. L. Kondakow (Jour. prakt. Chem., 1899 [2], 60, p. 257) are to be regarded as tertiary esters; a similar type of reaction is found in the case of carvomenthol. A d-menthol has been prepared from the i-mixture obtained by reducing menthone with sodium. The mixture is benzoylated, and the liquid d-menthol benzoate separated and hydrolysed.

Tertiary menthol (terpan-01-4), a liquid boiling at 97-101° C. (20 mm.), has been obtained by the hydrolysis of the ester prepared by heating menthene with trichloracetic acid (A. Reychler and L. Masson, Ber., 1896, 29, p. 1844). It possesses a faint peppermint odour. W. H. Perkin, junr. (Proc. Chem. Soc., 1905, 21, p. 2 55) synthesized it from 1.4 methylcyclohexanone: sodium carbonate converts a-bromhexahydro-para-toluic acid (I) into A I -tetrahydro-para-toluic acid and a-oxyhexahydro-para-toluic acid, and the latter on treatment with dilute sulphuric acid yields I. 4-methylcyclohexanone (2), which by the action of magnesium isopropyl iodide and subsequent hydrolysis is converted into tertiary menthol (3).

Terpin (terpan-diol I. 8), C10H1s(OH)21 is known in two stereoisomeric forms, cis-terpin and trans-terpin. The trans- form is obtained by adding silver acetate to a glacial acetic acid solution of dipentene dihydrochloride, filtering and neutralizing the filtrate by caustic soda. It is then extracted with ether, and the acetyl derivative so obtained is hydrolysed by alcoholic potash. It crystallizes in prisms, which melt at 156-158° C., and boil at 263-265° C. It is converted into terpineol by dilute sulphuric acid. The cis-compound melts at 104-105° C. and may be prepared by heating its hydrate. Terpin hydrate, C10H18(OH)2H20, crystallizes in prisms which melt at 116° C. It is prepared by acting with dilute mineral acids on limonene or dipentene. When boiled with glacial acetic acid it is converted into terpineol, while concentrated hydriodic acid at 210° C. reduces it to hexahydrocymene. When heated with dilute sulphuric acid it gives a number of compounds, which may be considered as arising from the loss of one or two molecules of water from one molecule of terpin.

Cineol, C10H180, is an inner oxide of terpin. It is found in the oils of wormseed, cajaput, eucalyptus, laurel, galanga, camphor and of lavender. It may be prepared by passing a current of dry hydrochloric acid gas into wormseed oil, the precipitated hydrochloride being then distilled in a current of steam (0. Wallach and W. Brass, Ann., 1884, 225, p. 2 97). It is an inactive liquid, which boils at 176° C. The oxygen atom in the molecule does not appear to possess either an alcoholic, ketonic, aldehydic or acid f unction.

Terpineol (M-terpen-01-8), C10Hir(OH). The term "terpineol " has been used to denote what is now known to be a mixture of various isomeric alcohols. Liquid terpineols have been isolated from the oils of Erigeron canadense, of marjoram and of camphor. Liquid terpineol is generally prepared by the action of dilute sulphuric acid on terpin hydrate. It consists of a mixture of various isomers, from which a solid terpineol melting at 35° C. and an isomeric A. 8(9) terpen-ol-I, melting at 32° C., have been isolated (K. Stephan and J. Halle, Ber., 1902, 35, p. 2147. See also G. Bouchardat, Comptes rendus, 1887, 104, p. 99 6; 1895, 121, p. 141; Schimmel & Co., Semi-annual Reports, Oct. 1897, p. I I; J. Godlewsky, Chem. Centralblatt, 1899 (I.), p. 1241). Solid terpineol exists in active and racemic forms. The active form was obtained by F. W. Semmler (Ber., 1895, 28, p. 2190) by replacing the halogen atoms in the active monohydrobromide of limonene by the hydroxyl group; it has also been obtained by the action of acetic acid on linalool. The racemic variety has been prepared by the action of formic acid on geraniol, and was synthesized by the following method (W. H. Perkin, junr., Jour. Chem. Soc., 1904, 85, p. 654). -y -Cyanpentane tricarboxylic ester (I) (prepared by the CH2 CH2 CH2 CH2 CH2 CH2 OH CHa CH< >C Br C02H- -CH3 CH< ?CO --> CH3 CH< >C< CH2 CH2 CHa CHI ? CH2 CH2 C3H7.

(a) (2) (3) H2C< CO-CH2 C(CH3) :CH C(CH3): CH CH3 >CH [[Cooh -3h2c< >Ch C(Ch3)20h -4h2c< >Ch C]]< CH2CH2 CH2 CH2 CH2-CH2 CH2.

(I) (2) (3) A synthetical monocyclic terpene, viz. I-methyl-4-isopropyl dihydrocymene was prepared by A. v. Baeyer (Ber., 1893, 26, p. 232). Succino-succinic ester is converted into the methyl Nso propyl derivative, which on hydrolysis and elimination of carbon H CH2 HCH2 CHs CH2 CH2 CHs C H2 CH2 >CH(CHs)20H CHs C H2 CH2/ CHC02H EHO CH2 CH2' CO 2 H reduction it yields isopulegol and no menthol (4) .0 (cf. pulegone).

(6) (5) Carvone (A 6: 8(9)-terpadiene-one-2), C10H14,O, This synthesis determines the constitution of terpin (7) and of is an unsaturated optically active ketone which is found dipentene (8), since the former is produced by the action of 5 per very widely distributed in nature. The dextro-form is the cent. sulphuric acid on terpineol, and the latter by heating terpineol chief constituent of oil of caraway, and is also found in oil with acid sodium sulphate. of dill; the laevo-form is found in oil of spearmint and CHs CH2 CH2 CH CH H2 kuromoji oil. The dextro-form is obtained practically pure >C< >CHC(CHs)20H, CH3 C >CHC by the fractional distillation of caraway oil; the laevo-form HO CH2CH2 CH2CH2' CHs from the oils containing it, by first forming its addition com (7) Terpin (8) Dipentene. pound with sulphuretted hydrogen, decomposing this by alcoholic Terpineol adds on nitrosyl chloride to form a nitrosochloride, potash, and distilling the product in a current of steam. It may which on elimination of hydrochloric acid yields the oxime of an be synthetically prepared from limonene nitrosochloride, alcoholic unsaturated oxyketone; this on boiling with acids is converted potash converting this compound into l-carvoxime, which on boiling into inactive carvone. When reduced by the method of Sabatier with dilute sulphuric acid yields l-carvone; similarly terpineol and Senderens it forms hexahydrocymene (A. Haller, Comptes nitrosochloride by the action of sodium ethylate yields oxydihydro- rendus, 1905, 140, p. 1303); when oxidized with Caro's reagent carvoxime, which on hydrolysis yields i-carvone. On heating with it yields trioxyhexahydrocymene (A. v. Baeyer and V. Villiger, Ber., phosphoric acid carvone is converted into carvacrol (I-methyl-218 99, 3 2, p. 3625). For an isomeric terpineol (0.8(9) terpenol-I) oxy-4-isopropylbenzene). Carvone is closely related to phellandrene, see A. v. Baeyer, Ber., 18 94, 2 7, pp. 443, 815. for C. Harries and M. Johnson (Ber., 1905, 38, p. 1832), by reduction Menthone (terpan-one-3), C10His0, occurs with menthol in oil of of carvone hydrobromide, obtained A 6-terpenone-2, which with peppermint. It was first obtained by M. Moriya (Jour. Chem. Soc., phosphorus pentachloride gives chlor-2-a-phellandrene. 1881, 39, p. 77) by oxidizing menthol with chromic acid mixture at 120° C., and was described as an inactive compound; but R. W. BI-Cyclic Terpene Group Atkinson (ibid., 1882, 41, p. 50) showed that when menthol was A nomenclature for the bicyclic hydrocarbons was devised by oxidized at 135° C. a strongly dextro-rotatory menthone was proA. v. Baeyer (Ber., 1900, 33, p. 377 1). Ac-cording to this system duced. For the preparation of l-menthone and d-isomenthone each hydrocarbon contains two tertiary carbon atoms, which are (Beckmann's d-menthone) see E. Beckmann, Ann., 1889, 250, combined with. each other three times, either directly or by means p. 3 2 5; 1891, 262, pp. 21 seq. The menthone obtained by of other intervening carbon atoms, the combination forming a Beckmann by the reduction of pulegone hydrobromide was shown series of " bridges." These bridges are distinguished by numbers, by C. Martine (Ann. chim. phys., 1904 (8), 3, P. 49) to be not corndenoting the number of carbon atoms contained in them, the pletely identical with l-menthone; it is consequently designated direct union of the two tertiary carbon atoms being designated P-menthone. An inactive menthone has been synthesized as as o; if one carbon atom intervenes, then the number 1 is used, follows. 0-Methyl pimelic ester is converted by sodium ethylate and so on. Thus three numbers serve as the " characteristic " into methyl-I-cyclohexanon-3-carboxylic ester-4, into which the isofor the compound. Hydrocarbons of this class with five atoms of propyl group is introduced (also in position 4) by the action of carbon are termed " bicyclopentanes," with six atoms of carbon isopropyl iodide and sodium ethylate. The ester is then hydrolysed, " bicyclohexanes," &c. Thus, for example, the compound (I) would and carbon dioxide eliminated from the carboxyl group, when be called " bicyclo-(r I 3)- H2C-CH H2C-CH2 inactive menthone is obtained (A. Einhorn and L. Klages, Ber., heptane," and (2) would be I I I 1901, It boils at 20 -206° C. whereas Beckmann's " bic clo o 1 4)-heptane." (x) H2C C H 2 / CH2 (s) H2C CH 9, 34, P3793). 4 C., y ( 4)- P i i L i CH2 menthones boil at 208° C. A. Haller and C. Martine (Comptes Thujene (tanacetene), H2C-CH H2C-CH rendus, 1905, 140, p. 130) synthesized natural menthone from C10H16, is a derivative of bicyclo-(o I 3)-hexane. The name was isopropyl iodide and the sodium derivative of methyl-i-cyclofirst given to the hydrocarbon obtained by F. W. Semmler hexanone-3. It has also been prepared by condensing methyl- (Ber., 1892, 2 5, p. 3345) on the dry distillation of thujylamine hexanone with ethyl acetate, the resulting methyl-I-acetyl-4-cyclohydrochloride. It is a liquid which boils at 60-63° (14 mm.), hexanone-3 being converted into the isopropyl derivative, yielding and has been shown by L. Tschugaeff to be a monocyclic acetylmenthone, which is then hydrolysed to menthone (G. Leser, hydrocarbon, for which he proposes the name " isothujene." The Comptes rendus, 1902, 134, p. 1115). A. Koltz and L. Hesse (Ann., true thujene was prepared by L. Tschugaeff (Ber., 1900, 33, p. 3118) 1905, 34 2, p. 306) convert methylhexanone (I) by means of ethyl by heating the methyl xanthogenic ester obtained from thujyl oxalate and subsequent hydrolysis into methylhexanone oxalic alcohol. It is exceedingly unstable. The isomeric 0-thujene was acid (2), the isopropyl ester of which on treatment with a methyl also obtained by the same investigator by the dry distillation of alcohol solution of caustic potash yields d-menthone (3). trimethylthujyl ammonium hydroxide. It boils at 150-151 ° C., and possesses a different rotatory power.

CH2CO CH2. CO CH2 CO Sabinene, C10His, also a bicyclo-(o I 3)-hexane CHs CH CH2 CH2 >CH2 CHsCH<CH2.CH2>CHCOC02R -.>CHsCH CH2.CH2>CHC3H7. derivative, is found in oil of savine, from which (r) (2) (3) it was first obtained by F. W. Semmler (Ber., 1900, 33, p. 1 455). On shaking with dilute sulphuric 0. Wallach (Ann., 1900, 312, p. 171) showed that the oximes of acid it yields terpinenol (AIterpen-01-4) (0. Wallach, Ber., 1907, cyclic ketones are converted by phosphorus pentoxide into is04 o, p. 592).

oximes, which are readily decomposed by concentrated hydro- Pinene, C15H1s, derived from bicyclo-(i I 3)-heptane, is found chloric acid to yield aliphatic amino-acids; in this way menthone in many essentialoils, and is the chief constituent of oil of tur may be converted into e-amido-decylic acid, pentine; the /-variety is found in French oil of turpentine, the s)2CH CH(NH 2)(C H 2)2 CH(CH s) CH 2 C02H. d-variety in Russian, American and Swedish oil of turpentine. (CH Pinene is also a constituent of the oils of sage, lemon, eucalyptus, Diosphenol, C10H1602, which occurs in the essential oil of bucco olibanum, bay, fennel, sassafras, rosemary and of valerian. The leaves (Borosma betulina) may be synthesized by oxidizing oxyactive varieties are obtained by the fractional distillation of the methylene menthone. Sodium in alcoholic solution reduces it to various oils of turpentine. The inactive variety is obtained by para-terpane-di-ol (2.3). heating pinene nitrosochloride with an excess of aniline (0. Wallach, Pulegone (A 4(8)-terpenone-3), C10H160, is an unsaturated ketone Ann., 1889, 252, p. 132; 1890, 258, p. 243), or better with methylfound in pennyroyal oil, from which it may be obtained by disaniline (W. A. Tilden). The three varieties boil at 155-156° C. tillation in vacuo. It is a dextro-rotatory liquid which boils at Pinene readily absorbs oxygen from the air, resinous products being 221-222° C. F. Tiemann (Ber., 18 97, 30, p. 22) synthesized it formed, together with small quantities of formic and acetic acids.

XXVI. 21 a. action of cyanacetic ester on /-iodopropionic ester) is hydrolysed to from citronellal by converting this compound into isopulegol acetate pentane-aye-tricarboxylic acid (2), which when boiled with acetic by acetic anhydride; this ester is hydrolysed, and the isopulegol anhydride and distilled gives S-ketohexahydrobenzoic acid (3). oxidized to isopulegone, which on treatment with baryta yields The ester of this acid, when treated with the Grignard reagent, pulegone. Pulegone reduces ammoniacal silver nitrate on long yields S-oxyhexahydrotoluic acid (4), which is converted into the boiling. It is reduced by hydrogen to /-menthol. When heated corresponding brom-compound by fuming hydrobromic acid. This with water to 250° C. it yields methyl-I-cyclohexanone-3 and acetone. latter compound on treatment with dilute alkali or pyridine yields When methylcyclohexanone and acetone are condensed together in 0.3-tetrahydro-para-toluic acid (5), the ester of which with magthe presence of sodium methylate, an isomer of pulegone boiling nesium and methyl iodide furnishes terpineol (6) :- at 215-216° C. is obtained. Pulegone combines with hydrobromic CH2 CH2 acid to form a hydrobromide, which on heating (R02C CH2. CH2)2C (CN) C02R -> (H02 C CH2. CH2) 2CH C02HCO< > CHC02H in methyl alcohol solution with basic lead nitrate CH2 CH2 is converted into isopulegone (0 8(9)-terpenone-3) (1) (2) T (3) (C. Harries and G. Roder, Ber., 18 99, 32, p. 3361). It is a laevo-rotatory liquid. A dextro form (a mixture) is also obtained by the oxida- * tion of isopulegol with chromic acid. On Acid oxidizing agents convert it into terephthalic and terebic acids, whilst alkaline potassium permanganate in dilute solution oxidizes it to pinene glycol, C 1 oH 1 s(OH) 2, pinonic acid, Clot-11 6 03, pinic acid, C 9 H 1 404, &c., the products of the reaction varying according to the temperature (G. Wagner, Ber., 1894, 27, p. 2270; F. Tiemann and F. W. Semmler, Ber., 1895, 28, PP. 1 344, 1 77 8). Concentrated sulphuric acid converts it into camphene; and an alcoholic solution of sulphuric acid gives terpinene and terpinolene. When heated to 250-270° C. it yields dipentene; the moist halogen acids at ordinary temperature convert it into the dihalogen halides of dipentene. Dry hydrochloric acid gives pinene hydrochloride (artificial camphor), C 1 oH 17 C1, a white crystalline solid identical with bornyl chloride which melts at 131° C. Elimination of halogen hydride by means of a weak alkali (e.g. soap, silver acetate, &c.) converts it into camphene. Thus the conversion of pinene into its hydrochloride is probably accompanied by an intramolecular rearrangement HzC C11(CH3)-CHC1 --> C(CH2)2 H2C CH CH2 Bomyl chloride.

Nitric acid in aqueous alcoholic solution converts it into terpin hydrate. Pinene nitrosochloride, C 1 oH 16 N0C1, was first obtained in 1874 by W. A. Tilden (Jahresb., 1874 p. 214) from nitrosyl chloride and a mixture of pinene and chloroform. 0. Wallach (Ann., 1889, 253, p. 251) prepared it by the action of acetic acid and ethyl nitrite on oil of turpentine in presence of fuming hydrochloric acid. W. A. Tilden (Jour. Chem. Soc., 1904, 8 5, p. 759) showed that strongly active pinene gives bad yields of the nitrosochloride, since, being bimolecular, its formation is retarded by the inversion of half of the terpene. The nitrosochloride melts at 115° C. (circa) and is a white pleasant-smelling powder. Alcoholic potash converts it into nitrosopinene, C10H16N0.

Bornylene, C 1 oH 16, derived from bicyclo-(i 2 2)-heptane, is prepared by heating bornyl iodide to 170° C. for several hours with a concentrated solution of alcoholic potash (G. Wagner, Ber., 1900, 33, p. 2121), or by decomposition of the methyl esters of the 1- and d-bornyl xanthates, the former yielding d-bornylene and the latter l-bornylene (L. Tschugaeff, Chem. Centralblatt, 1905, i., P. 94).

Camphene, C 1 oH 1 s, also a bicyclo-(i 2 2)-heptane derivative, is a constituent of the oils of citronella, camphor, ginger and of rosemary, and also of French and American oil of turpentine. It may be obtained by the action of sulphuric acid on pinene; by heating pinene hydrobromide or hydrochloride with sodium acetate or glacial acetic acid to 200° C.; or by heating bornyl chloride with aniline (0. Wallach, Ber., 1892, 25, p. 916). According to Konowalow it is best prepared by heating borneol with a diluted sulphuric acid (1 2) for about 6-8 hours, between 60-roe C., with continual shaking, a yield of about 90 per cent. being obtained. The meltingand boiling-points of camphene vary slightly according to the sources from which it is obtained, the former being about 50° C. and the latter about 159-161° C. It is known in d-, 1- and i- forms. It combines with hydrochloric acid to form a hydrochloride, which on reduction with sodium and alcohol yields camphene. Many different oxidation products may be obtained from camphene by varying the conditions of experiment (J. Bredt and W. Jagelki, Ann., 1900, 310, p. 114; G. Wagner, Ber., 1890, 23, p. 2311; S. Moycho and F. Zienkowski, Ann., 1905, 34 o, p. 17 J. E. Marsh and J. A. Gardner, Jour. Chem. Soc., 1891, 59, p. 648 1896, 6 9, P. 74).

Fenchene, C 1 oH 1 s, a bicyclo-(1 2 2)-heptane derivative, is not found in any naturally occurring products. The hydrocarbon may be obtained by the reduction of fenchone and elimination of water from the resulting fenchyl alcohol, or by the elimination of halogen hydride from the fenchyl halogen compounds (0. Wallach, Ann., 1892, 263, p. 145; 1898, 302, pp. 37 1 seq.).

H2C%IHC(CH3)

?G CH2, C3117

. a -Thujene

CH2

C(CH 3)

CH C(CH3)2

CH2 CH Bornylene

x2C? CH(CH3) CH>CH

P-Thujene

CH2CH C:CH2

I (2

CH2 -C(CH3)2 Catnphene

/ CH = CH2 H2C? J CH 2% CH2

C ` ?

Sabinene

CH2 CH2 C L (CH3)21

l:

CH2 11-CH2 Fenchene

The above bicyclo-terpene hydrocarbons are most probably best represented by the following formulae (pinene is given above): Alcohol And Ketone Derivatives Borneol (Borneo camphor), C 1 oH 17 OH occurs in the pith cavities of Dryobalanops camphora, and in the oils of spike and rosemary; esters are found in many fir and pine oils. It may be prepared by heating camphor with alcoholic potash (M. Berthelot, Ann., 1859, 12, p. 363); or by reducing camphor in alcoholic solution with sodium (0. Wallach, Ann., 1885, 230, p. 225; J. Bertram and H. Walbaum, Jour. prak. Chem. 18 94 (2), 49, p. 12). L. Tschugaeff (Chem. Centralblatt. 1905 i., p. 94) obtains pure d-borneol as follows :-Impure d-borneol (containing isoborneol) obtained in the reduction of camphor is dissolved in xylene and converted into the sodium salt by metallic sodium. This salt is then turned into the xanthate, C 1 oH 17 OCS 2 Na, which with methyl sulphate yields the corresponding methyl ester. The unchanged isoborneol is removed by steam distillation, which also decomposes any methyl xanthate of isoborneol that may have been formed. The residue is crystallized and hydrolysed, when pure borneol is obtained. It behaves as a secondary alcohol. Nitric acid oxidizes it to camphor, and when heated with potassium bisulphate, it gives camphene. With phosphorus pentachloride it forms a bornyl chloride, identical with pinene hydrochloride.

Isoborneol is a tertiary alcohol which may be obtained by dissolving camphene in glacial acetic acid, adding dilute sulphuric acid and heating to 50-60° C. for a few minutes, the isobornyl acetate so formed being then hydrolysed (J. Bertram and H. Walbaum, loc. cit.). It crystallizes in leaflets, which readily sublime. Chromic acid oxidizes it to camphor.

Thujone (tanacetone), C 1 oH 16 0, is found in many essential oils. Oil of thuja contains chiefly a-thujone, and oil of tansy chiefly 1 3-thujone. Oil of artemisia and oil of sage contain a mixture of - the two, whilst oil of absinthe contains principally the 13-variety. The two forms may be obtained by fractional distillation of the oils, followed by a fractional crystallization of their semicarbazones from methyl alcohol. a-Thujone is laevo-rotatory and when warmed with alcoholic potash it is partially converted into 1 3-thujone. Sodium in the presence of alcohol reduces it to thujyl alcohol, which on re-oxidation is converted into 1 3-thujone. The /3-form is dextro-rotatory and is partially converted into the a-variety by alcoholic potash. When heated to 280° thujone is transformed into the isomeric carvotanacetone (z6-terpenone-2). On boiling with ferric chloride it yields carvacrol. Hot dilute sulphuric acid converts it into isothujone (dimethyl-1 2-isopropyl3-cyclopentene-I-one-5). Thujone behaves as a saturated compound and forms a characteristic tribromide. When heated with zinc chloride it yields hydropseudocumene. According to F. W. Semmler (Ber., 1900, 33, p. 275; 1903, 3 6, p. 43 6 7) it is to be considered as a methyl-2-isopropyl-5-bicyclo-(o I 3)-hexanone-3.

Carone, C 1 oH 1E O, is a trimethyl-3 7 7-bicyclo I 4)- heptanone-2, obtained by acting with alcoholic potash on dihydrocarvone hydrobromide (A. v. Baeyer, Ber., 1896, 2 9, pp. 5, 2 79 6; 1898, 31, pp. 1401, 2067). It is a colourless oil, having the odour of camphor and peppermint, and boiling at 210° C. It is known in d-, 1-, and i-forms. It does not combine with sodium bisulphite. When heated it is transformed into carvenone. It is stable to cold potassium permanganate solution, but on heating gives a dibasic acid, caronic acid, C 5 H 8 (CO 2 H) 2, which Baeyer suggested was a gem-dimethyltrimethylene-1 2-dicarboxylic acid. This was confirmed by W. H. Perkin, junr. (Jour. Chem. Soc., 18 99, 75, p. 48) who synthesized the acid from dimethylacylic ethyl ester. This ester with ethyl malonate yields ethyldimethylpropanetricarboxylic ester, which on hydrolysis and subsequent heating is converted into 1316-dimethyl glutaric acid. The a-bromdimethyl ester of this acid when heated with alcoholic potash yields cis-, and trans-caronic acids. Eucarvone, C 1 oH 14 O, is a trimethyl3. 7.7-bicyclo- (0I. 4)-heptene-3-one-2.0. Wallach nn., 1905, 339, P. 94) suggests that the ketone possesses the structure of a trimethyl-1 4 4-cycloheptadiene-5 7-one-2. Phosphorus gentachloride converts it into 2-chiorcymene (A. Klages, Ber., 1899, p. 2558).

Camphor, C 1 oH 16 0, is a trimethyl-i 7 7-bicyclo 2 2)-heptanone-2. The d-variety is found in the camphor tree (Laurus camphora), from which it may be obtained by distillation in steam. The /-variety is found in the oil of Matricaria parthenium. It crystallizes in transparent prisms which possess a characteristic odour, sublimes readily and is easily soluble in the usual organic solvents. It boils at 209° C. and melts at 176° C. (circa). The d-form may also be obtained by the distillation of calcium homocamphorate (A. Haller, Bull. Soc. Claim., 18 9 6 (3), 1 5, p. 324). When heated with phosphorus pentoxide it yields cymene, and with iodine, carvacrol. Nitric acid oxidizes it to camphoric acid, C 8 H 14 (CO 2 H) 2, camphoronic acid, C 9 H 14 O 6, and other products. It forms an oxime with hydroxylamine which on dehydration yields a nitrile, from which by hydrolysis carnpholenic acid, C9H15C02H, is obtained. It combines with aldehydes to form alkylidene compounds, and yields oxymethylene compounds when subjected to the " Claisen " reaction. It does not combine with the alkaline bisulphites. It is readily substituted by chlorine and bromine; and with fuming sulphuric acid forms a camphor sulphonic acid. Sodium reduces it, in alcoholic solution, to borneol. When heated with sodium formate to 120° C. it is converted into bornylamine. Caro's acid converts it into campholid, and a compound C10H1s04 (A. v. Baeyer and V. Villiger, Ber., 1899, 32, p. 3630). When heated with concentrated sulphuric acid to 105-110° C. it yields carvenone and 4-aceto-I 2-xylol (J. Bredt, Ann., 1901, 314, P. 371).

H3C C HC C(CH3)s H 2) 2 Pinene.

(H3C)Cl CH2-? H 2 (CH3)2 CH2 I H2C

a conclusion confirmed by its synthesis (see below). The Bredt formula is also supported by the synthesis of r-camphoric acid by G. Komppa (Ber., 1901, 34, p. 2 47 2; 1903, 36, P. 433 2). In this synthesis ethyl oxalate is, condensed with ($-dimethyl glutaric ester, and the resulting diketoapocamphoric ester (I) is then methylated to diketocamphoric ester (2). The keto groups in (2) are converted in CH 2 groups as follows :- Sodium amalgam converts this ester into dioxycamphoric ester (3), which with hydriodic acid and phosphorus yields r-dihydrocamphoric acid. At 125° C. this compound combines with hydrobromic acid to form fi-bromcamphoric acid, which on reduction with zinc and acetic acid yields r-camphoric acid (4): ROzC CH C(CH3) 2 ' CH C02R, R02C CH C(CH3)2' C(CHa)' C02R CO CO CO CO (I) (2) H02C CH' C(CH3)2' C(CH2) ' C02H ? R02C CH' C(CHa)2' C (CH3) C02R CH2 CHz HC(OH) CH(OH) (4) (3) This series of reactions leads to a complete synthesis of camphor, since A. Haller (Comptes rendus, 1896, 122, p. 446) has shown that camphoric anhydride (I) on reduction yields campholid (2), which by the action of potassium cyanide and subsequent hydrolysis of the nitrite formed is converted into homocamphoric acid (3), the calcium salt of which yields camphor (4) on distillation CsH1 4 "0->CSH1a? CO 2 / O-*CsH1a? COlH OzH?C81114(1 ? (x) (3) (4) Thus camphor and its oxidation products are to be represented as CH2-CH C12 (a) CH2' CH CO 2 H C02H C02H I C (CH3) 2 Pr) I I C(CH2)2 I C(CH3)2 CH2'C(CH3) CO (p), CH 2. C(CH3) C02H, CH2. C(CH3) C02H Camphor, Camphoric acid, Camphoronic acid.

Camphor yields three classes of halogen substitution derivatives known respectively as a, li and r compounds, the positions being shown in the formula above. The a compounds result by direct substitution, the (3 and 7r derivatives being formed in an indirect manner. Cyancamphcr, C10H150CN, is formed by passing cyanogen gas into sodium camphor, or by digesting sodium oxymethylene camphor with hydroxylamine hydrochloride (L. Claisen, Ann., 1894, 281, p. 351).

7-Camphor sulphonic acid results from the action of fuming sulphuric acid on camphor (F. S. Kipping and W. J. Pope, Jour. Chem. Soc., 18 93, 6 3, p. 573). Camphoroxime, C 1 oH 16 0:NOH, was first prepared by E. Nageli (Ber., 1883, 16, P. 497).

/-Camphor is formed by the action of nitric acid on l-borneol (W. J. Pope and A. W. Harvey, Jour. Chem. Soc., 1901, 79, p. 76). r-Camphor melts at 178-179° C. (for its preparation see A. Debierne, Comptes rendus, 1899, 128, p. I110; W. A. Noyes, Amer. Chem. Jour., 1905, 27, p. 430).

Camphoric acid. Four optically active and two inactive forms of this acid are known. The most important is the d-form, which is produced by the oxidation of d-camphor with nitric acid. It crystallizes in plates or prisms which melt at 187° C. Potassium permanganate oxidizes it to oxalic acid and Balbiano's acid, C8H1205, together with small quantities of camphanic, camphoronic and trimethyl succinic acids. It yields two series of acid esters, the alto-esters (I), formed by the partial saponification 'of the neutral esters, and the ortho-esters (2), formed by heating the anhydride with alcohols or sodium alcoholates.

CH2 ' CH. C02H CH2 CH' C02R I go-12)2 I C(CHa)2 CH2' C(CH3) C02R CH2' C(CH3) C02H (I) l-Camphoric acid results on oxidizing l-borneol or matricaria camphor. It melts at 187° C. r-Camphoric acid is formed on mixing alcoholic solutions of equimolecular quantities of the B- and /-acids, or by oxidizing i-camphor. It melts at 202-203° C.

Camphoronic acid, C 9 H 14 0 6. From a study of its distillation products J. Bredt (Ber., 1893, 26, p. 3 0 49) concluded that this acid was an aa 1 3-trimethylcarballylic acid, a conclusion which was confirmed by its synthesis by W. H. Perkin, junr., and J. F. Thorpe (Jour. Chem. Soc., 1897, 71, 1169): Aceto-acetic ester is condensed with a-bromisobutyric ester, the resulting hydroxytrimethyl glutarate (1) converted into the chlorand then into the corresponding cyan-trimethyl glutarate (2), which on hydrolysis with hydrochloric acid yields camphoronic acid (3) and some trimethyl glutaconic acid (3) (2) Fenchone, C10H160, is trimethyl- (2 7 7) - bicyclo- (I 2 2)- heptanone-3. It occurs in d- and /-forms, the former in oil of fennel and the latter in oil of thuja. It may be obtained from these oils by treating the fraction boiling between 190-195° C. with nitric acid and distilling the product in a current of steam. The fenchones are pleasant-smelling oils which boil at 192-193° C., and on solidification melt at 5-6° C. They do not combine with sodium bisulphite. They dissolve unchanged in cold concentrated hydrochloric and sulphuric acids, and are very stable; thus the monobromfenchone is only formed by heating the ketone with bromine to 100° C. under pressure (H. Czerny, Ber., 1900, 33, p. 2287). On oxidation with potassium permanganate it yields acetic and oxalic acids together with dimethylmalonic acid. By the action of hot concentrated sulphuric acid it yields acetyl-orthoxylene, CH3C0(4)C6H3(CH3)2(1.2) (J. E. Marsh, Jour. Chem. Soc., 18 99, 75, p. 1058). When heated with phosphorus pentoxide to 115-130° C. it forms metacymene. Since it does nOt yield any oxymethylene compounds, it cannot contain the grouping-CH 2 -00---in the molecule.

Hydrocarbons, C10h18, Of The Terpene Series Menthene, C 8 H 8 (CH (C 3 H 7), is methylI-isopropyl-4-cyclohexene-3. It is obtained by the action of anhydrous zinc chloride or copper sulphate on menthol (J. W. Bra hl, Ber., 1892, 25, p. 142), by boiling menthyl chloride with aniline (G. Wagner, Ber., 18 94, 27, p. 1636), by heating menthyl chloride with potassium phenolate (L. Masson, Ber., 1896, 29, p. 1843), and by the dry distillation of the methyl ester of menthyl xanthate (L. Tschugaeff, Ber., 18 99, 32, p. 3333). It is a colourless liquid which boils at 167-168° C. When strongly heated with copper sulphate it yields cymene. According to Tschugaeff, the xanthate method alone gives a pure menthene of the above constitution, the menthene obtained from the dehydration of menthol being a cyclohexene-4; and the one obtained by 0. Wallach (Ann., 1898, 300, p. 278) from l-menthylamine being a cyclohexene-2.

Carvomenthene, C 6 H 8 (CH 3)(C3H7), is probably methyl-i-isopropyl4 -cyclohexene-I. It is prepared by heating carvomenthyl bromide with quinoline, or by heating carvomenthol with potassium bisulphate to 200° C. It is a liquid which boils at 175-176° C.

Camphane, C 7 H 9 (CH is I.7.7-trimethyl-bicyclo-(I.2)-heptane. It is prepared by the action of sodium and alcohol on pinene hydriodide, or by reducing the hydriodide with zinc in acetic acid solution. It is a crystalline solid which melts at 153° C. and boils at 160° C.

Olefine Terpenes Myrcene, C10H16, was first isolated by F. B. Power and C. Kleber from oil of bay (Schimmel & Co., Bulletin, April 1895, p. I I); it is also found in oil of sassafras leaves. It is obtained from bay oil by shaking the oil with a 5 per cent. solution of caustic soda, followed by fractionation in vacuo. It boils at 67-68° C. (20 mm.), and polymerizes when heated for some time. When oxidized by potassium permanganate it yields succinic acid. By the action of glacial acetic acid in the presence of dilute sulphuric acid, a liquid is produced, which on hydrolysis yields myrcenol, C10H180, an alcohol which is probably an isomer of linalool (P. Barbier, Comptes rendus, 1901, 132, p. 1048). The hydrocarbon is probably to be considered as being (CH 3) 2 C: CH (CH 2) 2 C(: CH 2) CH: CH 2 (Enklaar, Bulletin of Rouse-Bertrand fits, Nov., 1906, p. 92). Ocymene is an isomer which can be extracted from the leaves of the basil. Enklaar (loc. cit.) represents it as (CH 3) 2 C: CH CH 2 CH: C(CH 3) CH: CH2. Anhydro-geraniol, C10H16, the first olefine terpene isolated, was prepared in 1891 by F. W. Semmler; it is formed when geraniol is heated with potassium bisulphate to 170° C.

Alcohols, Aldehydes And Ketones d-Citronellol, C10H190H or CH. 0 (:CH2) (CH 2). CH (CH (CH2)20H, or 2.6 dimethyl-octene-t-01-8 occurs in Reunion geranium oil and was first prepared by F. D. Dodge (Amer. Chem. Jour., 1889, 11, p. 463) by reducing the corresponding aldehyde (d-citronellal). It is an odorous oil which boils at 117-118° C. (17 mm.). Oxidation by chromic acid mixture converts it into citronellal, whilst A vast amount of work has been done on the constitution of the camphor molecule. The earlier investigations on the ready formation of benzene derivatives by the breaking down of camphor led to the view that the molecule was a simple six-membered carbon ring. Subsequent research, however, showed that the formula proposed by J. Bredt (Ber., 1893, 26, p. 3047), in which camphor is to be regarded as a bicyclo-heptane derivative, is correct. This formula is based on the fact that camphoronic acid yields trimethylsuccinic, isobutyric, and carbonic acids, and carbon on dry distillation, and Bredt suggested that it was an aa(3 (CH3)203r C02R+CH3COCH2' C02R ->(CHa)2C(C02R) C(OH)(CH3) CH2' C02R trimethylcarballylic acid, (I) HO 2 CCH 2 C(CH 3)(CO 2 H)C(CH 3 2CO 2 H,) (CHa)2C(C02H) C(COzH)(CH3) ' C?iz' COzH E- (CH3)2C(C02R) C(CN)(CHa) ' CH2' C02R a more drastic oxidation with potassium permanganate yields acetone and l -methyladipic acid.

1-Rhodinol,C 1 oH 19 0H or(CH 3) 2 C: CH (CH2)2CH(CH3)(CH2)2.OH, or 2.6 dimethyl-octene-2-01-8, occurs in the essence of geranium and of rose. It is a structural isomer of citronellol (P. Barbier and L. Bouveault, Comptes rendus, 1896, 122, pp. 529, 673; Bull. Soc. Chim., 1900, [3], 2 3, p. 459), and its inactive form has been synthesized from ethyl heptenone. It is an oil of strong rose odour, which boils at I 10° C. (TO mm.). Chromic acid mixture oxidizes it to rhodinal and rhodinic acid, whilst by drastic oxidation it yields acetone and (-methyladipic acid.

Geraniol, C10H170H, or (CH3)2C :CH (CH 2) 2. C(CH 3) :CH CH20H, 2.6 dimethyl-octadiene-2, 6-01-8, is found in the oils of geranium, citronella, neroli, petit-grain, spike, citronella, and in Turkish and German rose oil. It is prepared from the oils by treating them with alcoholic potash and then fractionating in vacuo. The geraniol fraction is then mixed with freshly dried calcium chloride and the mixture allowed to stand in vacuo at a low temperature, when the compound C10H180 CaCl2 separates out. This is washed with absolute ether and finally decomposed by water, when pure geraniol is liberated (0. Jacobsen, Ann., 1871, 157, p. 232; J. Bertram and E. Gildemeister, Jour. prak. Chem., 1897 (2), 56, p. 507). It may also be prepared by reducing the corresponding aldehyde (citral) with sodium amalgam. It is a colourless, pleasant-smelling oil, which boils at 230° C. Oxidation converts it into citral and geranic acid, (CH 3) 2 C:CH(CH 2) 2 C(CH 3) :CHCO 2 H. By shaking it with 5 per cent. sulphuric acid it yields terpin hydrate, and when heated with concentrated alcoholic potash to 150° C. it is converted into dimethylheptenol (P. Barbier, Comptes rendus, 1899, 128, p. IIo). Geraniol may be converted into linalool by distilling a faintly alkaline solution of acid geranyl phthalate with steam.

Nerol, C10H170H, was obtained in 1902 from neroli oil by A. Hesse and 0. Zeitschel (Jour. prak. Chem., 1902 (2), 66,, p. 481); it also is found in petit-grain oil. It boils at 226-227° C. (755 mm.), and has a distinctive rose odour. It is inactive and is to be regarded as a stereo-isomer of geraniol. It does not form a compound with calcium chloride. It combines with four atoms of bromine to form a characteristic tetrabromide. It is formed (along with other products) by the action of acetic acid on linalool (0. Zeitschel, Ber., 1906, 39, p. 1780) and also by the reduction of citral-b.

Linalool,C10H170H,or(CH3)2C:CH(CH2)2C(CHs)(OH)CH: CH2, is 2.6-dimethyloctadiene-2, 7-01-6. d-Linalool was first found in coriander oil, and l-linalool in oil of linaloe. It is also found in oil of bergamot, petit-grain, lavender, neroli, spike, sassafras leaves and lemon, either in the free condition or as esters. It is a pleasantsmelling liquid which boils at 197-199° C. (according to its source). The inactive variety can be prepared from geraniol, this alcohol on treatment with hydrochloric acid yielding a mixture of chlorides, which when digested with alcoholic potash are transformed into i-linalool (F. Tiemann and F. W. Semmler, Ber., 1898, 31, p. 832). It is oxidized by chromic acid to citral. When shaken for some time with dilute sulphuric acid it yields terpin hydrate.

Citronellal, C10H180, is the aldehyde of citronellol. It is a constituent of many essential oils, and was first discovered in citronella oil by F. D. Dodge (Amer. Chem. Jour., 1889, I I, p. 456); it is also found hi eucalyptus oil and in lemon-grass oil. It is a dextrorotatory liquid which boils at 203-204° C. It is readily reduced by sodium amalgam to citronellol, and oxidized by ammoniacal silver oxide to citronellic acid. Potassium permanganate oxidizes it to acetone and /-methyladipic acid. It forms a dimethyl acetal, C10H1s(OCH3)21 which on oxidation with potassium permanganate yields a dioxydihydro-citronellaldimethyl acetal, CH3C(CH20H)(OH)(CH2)3CH(CH3)CH2.CHO, which must possess the above composition, since on further oxidation by chromic acid it yields a keto-aldehyde of the constitution CH 3 CO(CH 2) 3 CH(CH3)CH2CHO (C. D. Harries and-O. Schauwecker, Ber., 1901, 34, p. 2981); this reaction leads to the formulation of citronellal as a dimethyl-2.6-octene-I-al-8. Citronellal is readily converted into an isomeric cyclic alcohol isopulegol 08(9)- terpenol-3) by acids or acetic anhydride (F. Tiemann, Ber., 1896, 29, p. 913). It combines with sodium bisulphite, giving a normal bisulphite and also a monoand dihydrosulphonic acid.

Geranial (citral), C11H160, is the aldehyde corresponding to geraniol. It occurs in the oils of lemon, orange, lemon-grass, citronella, bay, verbena, and in various eucalyptus oils. It may be obtained from the oils by means of its bisulphite compound, provided the operation is carried out at low temperature, otherwise loss occurs owing to the formation of sulphonic acids. Synthetically it may be produced by the oxidation of geraniol with chromic acid mixture, or by distilling a mixture of calcium formate and calcium geraniate. Its aldehydic nature is shown by the facts that it forms an alcohol on reduction, and that on oxidation it yields an acid (geranic acid) of the same carbon content. The position of the ethylene linkages in the molecule is proved by the formation of addition compounds, by its products of oxidation (acetone, laevulinic acid), and by the fact that on warming with potassium carbonate solution it yields methyl heptenone and acetaldehyde (F. Tiemann, Ber., 1899, 32, p. 107). On fusion with potassium bisulphate it forms para-cymene. It combines with /-naphthylamine and pyruric acid, in alcoholic solution, to form the characteristic citryl-0-naphthocinchonic acid, C23H23N02.2H20, which is useful for identifying citral. The crude citral obtained from essential oils is a mixture of two ethylene stereoisomers which are designated as citral-a and citral-b (F. Tiemann and M. Kerschbaum, Ber., 1900, 33, p. 8 77). Citral-a boils at 110-112° C. (12 mm.) and citral-b at 102-104° C. The structural identity of the two forms has been confirmed by C. Harries (Ber., 1907, 40, p. 2823), who has shown that their ozonides (prepared from the citrals by the action of ozone on their solution in carbon tetrachloride) are quantitatively decomposed in both cases into acetone, laevulinic aldehyde and glyoxal. Lemon-grass oil contains 73 per cent. of citral-a and 8 per cent. of citral-b. Citral combines with sodium bisulphite to form a normal bisulphite compound, a stable dihydrosulphonate, an unstable dihydrosulphonate and a hydromonosulphonate (F. Tiemann, Revue gen. de chim. pure et appl., 1, 16, p. 150). Citral condenses readily with acetone, in the presence of alkalis, to form pseudo-ionone (see Ionone, below).

The compounds of the citral series are readily converted into cyclic isomers by acids, the ring closing between he first and sixth carbon atoms in the chain. Two series of such compounds exist, namely the a and f3 series, differing from each other in the position of the double linkage in the molecule. The constitution of the a-series is determined by the fact that on oxidation they yield isogeronic acid, which can be further oxidized to 00-dimethyladipic acid; the 0-series in the same way yielding geronic acid and aa-dimethyladipic acid. The cyclocitrals themselves cannot be obtained direct from citral by the action of acids, since under these conditions para-cymene results, but they are prepared by boiling citrylidenecyanacetic ester with dilute sulphuric acid and subsequent hydrolysis of the cyclic ester with caustic potash (F. Tiemann, Ber., 1900, 33, p. 3719), or citral may be condensed with primary amines to the corresponding aldehydeimino compounds, which are then isomerized by concentrated acids, the amine group being hydrolysed at the same time (German Patent, 12 3747 (1901)).

Ionone, C13N200. By condensing citral with acetone F. Tiemann (Ber., 1893, 26, p. 2691) obtained pseudo-ionone (I), an oil of boiling-point 143-145° C. (12 mm.), which on boiling with sulphuric acid is converted into a mixture of the isomeric aand 0-ionones (2 and 3) (I) (CH3)2C: CH (CH2)2 C(CH3): CH CH: CH CO CHa C(CH3)2 C(CHa)2 H2C/CH CH:CHCOCH 3 H2C/CCH:CHCOCH3 (2) (3) H2C H/ C CHa H2C C /C CH3 C a-Ionone is an oil which boils at 127-128° C. (12 mm.) and possesses a characteristic violet odour. The 0-compound boils at 128-129° C. (to mm.). and possesses a similar odour. They are largely used in perfumery. An isomer of ionone is irone, the odoriferous principle of the iris root. It boils at 144° C. (16 mm.). When heated with hydriodic acid and phosphorus it yields the hydrocarbon irene, C13H1s (F. Tiemann, loc. cit.). Sesquiterpenes Cadinene, C15H24, is found in the oils of cade (from the wood of Juniperus oxyeldrus), cubeb, patchouli, galbanum, cedar-wood and juniper. It may be obtained by fractionating oil of cade, converting the crude hydrocarbon into its dihydrochloride and decomposing this by boiling with aniline. It is an oil which boils at 2 742 75° C. and decomposes on exposure. Caryophyllene is found in oil of cloves and in oil of copaiba balsam. Various other sesquiterpenes have been described, e.g. zingiberene (from essence of ginger), cedrene (from oil of cedar-wood), santalene (from oil of sandal-wood), humulene and clovene.

Of the sesquiterpene alcohols pure santalol, C16H260, has been obtained from essence of sandal-wood by conversion into the acid phthalic esters and saponification of these by potash (Schimmel &Co., Bulletin, April 18 99, p 41). A mixture of two alcohols is thus obtained, one boiling at 165-167° C. (13 mm.) and the other at 173° C. They are distinguished by their different optical activities, one being practically inactive, the other strongly laevo-rotatory (see also M. Guerbet, Comptes rendus, 1900, 130, p. 417; Bull. Soc. Chim., 1900 (3), 2 3, p. 54 0). Caryophyllene alcohol is obtained from oil of cloves; by elimination of water it yields clovene, Ci 5H24, a liquid which boils at 261-263° C.

Many diand tri-terpenes have been described, but as yet are not thoroughly characterized.

References.-Gildemeister and Hoffman, The Volatile Oils (Milwaukee, 1900); R. Meldola, The Chemical Synthesis of Vital Products (London, 1904); F. W. Semmler, Die aetherischen Oele (Leipzig, 1906); G. Cohn, Die Riechstoffe (Brunswick, 1904); J. M. Klimont, Die synthetischen and isolirten Aromatica (Leipzig, 1899); and F. Heusler, Die Terpene (Brunswick, 1896). For camphor see A. Lapworth, Brit. Assoc. Rep. for 1900, and 0. Aschan, Die Konstitution des Kamphers (Brunswick, 1903). (F. G. P.*)

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