Frank George Pope

“ 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. ”

“ 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) . ”

“ Cineol, C10H18O, 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 (O. Wallach and W. Brass, Ann., 1884, 225, p. 297) . 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, aldehyde or acid function.
Terpineol (Δ1-terpen-ol-8) , C10H17 (OH) . ”

“ This salt is then turned into the xanthate, C10H17OCS2Na, 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. ”

“ It may be synthetically prepared from limonene nitrosochloride, alcoholic potash converting this compound into l-carvoxime, which on boiling with dilute sulphuric acid yields l-carvone; similarly terpineol nitrosochloride by the action of sodium ethylate yields oxydihydrocarvoxime, which on hydrolysis yields i-carvone. On heating with phosphoric acid carvone is converted into carvacrol (1-methyl-2-oxy-4-isopropylbenzene) . ”

“ When shaken for some time with dilute sulphuric acid it yields terpin hydrate.
Citronellal, C10H18O, 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, 11, p. 456) ; it is also found in eucalyptus oil and in lemon-grass oil. It is a dextro-rotatory 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 β-methyladipic acid. ”

“ 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. ”

“ 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-ol-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) . ”

“ These bridges are distinguished by numbers, denoting the number of carbon atoms contained in them, the direct union of the two tertiary carbon atoms being designated as 0; if one carbon atom intervenes, then the number 1 is used, and so on. ”

“ This latter substance by the action of pyridine yields tetrahydro-meta-toluic acid, the ester of which by magnesium methyl iodide is converted into Δ·1-meta menthenol-8 (2) . The meta-menthenol on dehydration by potassium bisulphate yields carvestrene (3) of boiling-point 179–180° C.
A synthetical monocyclic terpene, viz. 1-methyl-4-isopropyl dihydrocymene was prepared by A. v. Baeyer (Ber., 1893, 26, p. 232) . Succino-succinic ester is converted into the methyl isopropyl derivative, which on hydrolysis and elimination of carbon dioxide yields 1-methyl-4-isopropyldiketohexamethylene. ”

“ It has also been prepared by condensing methylhexanone with ethyl acetate, the resulting methyl-1-acetyl-4-cyclohexanone-3 being converted into the isopropyl derivative, yielding acetylmenthone, which is then hydrolysed to menthone (G. Leser, Comptes rendus, 1902, 134, p. 1115) . A. Koltz and L. Hesse (Ann., 1905, 342, p. 306) convert methylhexanone (1) by means of ethyl oxalate and subsequent hydrolysis into methylhexanone oxalic acid (2) , the isopropyl ester of which on treatment with a methyl alcohol solution of caustic potash yields d-menthone (3) . ”

“ The hydrocarbon is probably to be considered as being (CH3) 2C:CH· (CH2) 2·C (:CH2) ·CH:CH2 (Enklaar, Bulletin of Rouse-Bertrand fils, Nov., 1906, p. 92) . Ocymene is an isomer which can be extracted from the leaves of the basil. Enklaar (loc. cit.) represents it as (CH3) 2C:CH·CH2·CH:C (CH3) ·CH:CH2. Anhydro-geraniol, C10H16, the first olefine terpene isolated, was prepared in 1891 by F. W. Semmler ”