CAMPHORS occur as components of the essential oils of many plants; and are extracted by distilling the plant material with steam ; separation of the "camphors" is afterwards effected by fractional distillation, freezing or chemical treatment. The camphors are mainly alcohols and ketones of the hydrocarbons known as terpenes. Commercially, the term "camphor" is gener ally applied to any solid product so obtained, and hence includes the solid paraffin "stearoptenes" and sesquiterpene alcohols of essential oils. "Camphors" may thus be divided into two main groups, according to the nature of the corresponding hydrocarbon; chemically, however, the term should be reserved for the oxy genated derivatives of terpenes and sesquiterpenes, liquid as well as solid. The commercial camphors are mostly colourless crystal line solids, with characteristic odours; they are sparingly soluble in water, but dissolve readily in alcohol, ether and organic solvents generally. In this article only the chief camphors of technical interest will be mentioned ; details as to their chemical structure, synthesis, and relations will be found in the article TERPENES.
Camphor, C,OH180, also known as Japan or laurel camphor, which constitutes the bulk of the camphor of commerce, is ob tained from the camphor laurel (Cinnamonum Camphora), a tree flourishing in Japan, Formosa and central China. Camphor occurs also in various other essential oils, e.g., lavender, rosemary, sage and spike. It is obtained by steam-distilling the chopped branches and twigs of the camphor laurel. The crude product, which amounts to about 3% of the wood used, consists of crystalline camphor and camphor oil ; the latter, when distilled, yields cam phor and other products, notably safrol. The crude camphor, which is refined by sublimation with quicklime and charcoal, then forms a translucent mass of hexagonal prisms, m.p. 175° C, b.p. 204° C. It has a characteristic odour, and it sublimes very readily. It is very slightly soluble in water, but it dissolves freely in alco hol, ether, etc. Japan camphor (d-camphor) is dextrorotatory, with in a 20% alcoholic solution. The rare laevo-cam phor, or matricaria camphor, occurs in the oil of Matricaria par thenium; it may also be prepared by oxidizing l-borneol. The so-called "artificial camphor" is pinene hydrochloride (bornyl chloride) ; this substance is an intermediate product in the prep aration of ell-camphor or synthetic camphor, which is optically inactive (m.p. 178.6° C), from pinene of turpentine oil (see TER PENES) . The main use of camphor is in the manufacture of cellu loid; it finds application also in making smokeless powders, and as a disinfectant and medicinal agent. Externally applied it acts as a counter-irritant, and, in some degree, as a local anaesthetic, being also a definite antiseptic. It is therefore used in liniments for the relief of myalgia, sciatica, lumbago, etc.
Borneol, Borneo camphor, or bornyl alcohol, OH, is the dextrorotatory secondary alcohol corresponding to Japan cam phor, from which (in company with l-isoborneol) it is produced by reduction. It occurs in the wood of Dryobalanops aromatics, a majestic East Indian tree, and is known also as Malayan, Barus, or Dryobalanops camphor. d-Borneol melts at 204° and boils at C. It has a camphor-like but somewhat peppery odour. l-Borneol, sometimes called Ngai camphor, or baldrianic camphor, occurs in Blumea balsamif era.
Menthol, or mint camphor, 5-methyl-2-isopropyl hexahydrophenol, is obtained from the essential oils of the so called peppermint (Mentha piperita) and its two varieties, the black mint (M. piperita vulgaris) and the white mint (M. piper ita oficinalis) ; in addition, Japanese and Chinese peppermint oils are distilled from M. arvensis piperascens and M. arvensis gla brata. Crystalline menthol, which was first mentioned by the Dutch botanist Gambius (1771), is obtained by submitting the cooled oil to centrifugalization, preferably after removing the ter penes, etc., by distillation under diminished pressure. Besides unremoved menthol, the residual "dementholized oil" contains l-menthone and many other substances. Peppermint menthol (1 menthol) is laevo-rotatory; it crystallizes in prisms (m.p. 43° C, b.p. C), having the odour and taste of peppermint. It is very slightly soluble in water, but dissolves freely in alcohol, ether, etc. Menthol is used in medicine to relieve pain, as in rheumatism, neuralgia, throat affections and toothache. It acts also as a local anaesthetic, vascular stimulant and disinfectant. Natural 1-menthol has been replaced to some extent by dl-menthol ("syn thetic menthol"), prepared by the catalytic hydrogenation of piperitone (q.v.) and thymol; this substance is optically inactive and melts at 34° C when pure, but otherwise it is practically iden tical with /-menthol in its properties. Other stereoisomeric sub stances are d-menthol (m.p. 43° C), d- and l-neomenthol (oils), dl-neomenthol (m.p. 51° C), d- and l-isomenthol (m.p. 81.5° C), and dl-isomenthol (m.p. 53.5° C).
Thymol, or thyme camphor, 5-methyl-2-isopropyl phenol, occurs in the essential oils of ajowan (Carom ajowan), garden thyme (Thymus vulgaris), wild thyme (T. serpyllum), horse mint (Monarda punctata), etc. It is extracted from such oils by shaking them with an aqueous solution of a caustic alkali ; it may also be prepared synthetically from p-cymene, piperitone, etc. Thymol forms large colourless plates, m.p. 44° C, b.p. 23o° C. It has a strong odour of thyme, and is freely soluble in alcohol, chloroform, ether, olive oil or alkaline solutions. It is a more powerful antiseptic than phenol, but its slight solubility in water prevents its use for the same purposes. A saturated solution (I in 1,000 of warm water), thymol gauze, and an ointment are used. Externally it is antiparasitic, whilst internally it has been used as an intestinal antiseptic in typhoid fever. Its chief use is as an anthelmintic to destroy the Ankylostoma duodenale. With iodine and alkali it yields dithymol di-iodide (aristol), a substi tute for iodoform. Glycothymolin is a proprietary preparation, used in the treatment of catarrhal conditions of mucous mem branes, whilst a mixture of naphthalene, camphor and thymol is sold under the name of thymolin.
Buchzt camphor, or diosplienol, C1oH1602,0 occurs in the leaf-oils of several species of South African Barosma, or "Buchu." It forms crystals (m.p. 83° C, b.p. 232° C) with an odour of mint. (J. RD.)