Camphor (/ˈkæmfər/) is a waxy, colorless solid with a strong aroma.[5] It is classified as a terpenoid and a cyclic ketone. It is found in the wood of the camphor laurel (Cinnamomum camphora), a large evergreen tree found in East Asia; and in the kapur tree (Dryobalanops sp.), a tall timber tree from South East Asia. It also occurs in some other related trees in the laurel family, notably Ocotea usambarensis. Rosemary leaves (Rosmarinus officinalis) contain 0.05 to 0.5% camphor,[6] while camphorweed (Heterotheca) contains some 5%.[7] A major source of camphor in Asia is camphor basil (the parent of African blue basil). Camphor can also be synthetically produced from oil of turpentine. The compound is chiral, existing in two possible enantiomers as shown in the structural diagrams. The structure on the left is the naturally occurring (+)-camphor ((1R,4R)-bornan-2-one), while its mirror image shown on the right is the (−)-camphor ((1S,4S)-bornan-2-one). Camphor has few uses but is of historic significance as a compound that is readily purified from natural sources. Etymology[edit] The word camphor derived in the 14th century from Old French: camphre, itself from Medieval Latin: camfora, from Arabic: كافور, romanized: kāfūr, perhaps through Sanskrit: कर्पूर, romanized: karpūra, apparently from Austronesian Malay: kapur 'lime' (chalk).[8] In Old Malay, camphor was called kapur barus, meaning "the chalk of Barus", referring to Barus, an ancient port near modern Sibolga on the western coast of Sumatra.[9] This port traded in camphor extracted from the Borneo camphor trees (Dryobalanops aromatica) that were abundant in the region.[10] Production[edit] Natural camphor[edit] Camphor has been produced as a forest product for centuries, condensed from the vapor given off by the roasting of wood chips cut from Camphora officinarum, and later by passing steam through the pulverized wood and condensing the vapors.[11] By the early 19th century most camphor tree reserves had been depleted with the remaining large stands in Japan and Taiwan, with Taiwanese production greatly exceeding Japanese. Camphor was one of the primary resources extracted by Taiwan's colonial powers as well as one of the most lucrative. First the Chinese and then the Japanese established monopolies on Taiwanese camphor. In 1868, a British naval force sailed into Anping harbor and the local British representative demanded the end of the Chinese camphor monopoly. After the local imperial representative refused, the British bombarded the town and took the harbor. The "camphor regulations" negotiated between the two sides subsequently saw a brief end to the camphor monopoly.[12] Synthetic camphor[edit] Camphor is produced from alpha-pinene, which is abundant in the oils of coniferous trees and can be distilled from turpentine produced as a side product of chemical pulping. With acetic acid as the solvent and with catalysis by a strong acid, alpha-pinene is converted to isobornyl acetate. Hydrolysis of this ester gives isoborneol which can be oxidized to give racemic camphor. By contrast, camphor occurs naturally as D-camphor, the (R)-enantiomer.[citation needed] Reactions[edit] The reactions of camphor have been extensively examined. Some representative transformations include sulfonation:[13] oxidation with selenium dioxide to camphorquinone .[14] Camphor can also be reduced to isoborneol using sodium borohydride. Biochemistry[edit] Biosynthesis[edit] In biosynthesis, camphor is produced from geranyl pyrophosphate, via cyclisation of linaloyl pyrophosphate to bornyl pyrophosphate, followed by hydrolysis to borneol and oxidation to camphor. Uses[edit] The first significant manmade plastics were low-nitrogen (or "soluble") nitrocellulose (pyroxylin) plastics. In the early decades of the plastics industry, camphor was used in immense quantities[15]: 130  as the plasticizer that creates celluloid from nitrocellulose, in nitrocellulose lacquers and other plastics and lacquers. Alternative medicine and scent[edit] Camphor has been used for its scent, as an embalming fluid, as topical medication, as a manufacturing chemical, and in religious ceremonies. Camphor has been used for its scent, as an embalming fluid, as topical medication, as a manufacturing chemical, and in religious ceremonies. Camphor cubes Camphor has been used as a folk medicine over centuries, probably most commonly as a decongestant.[16] Camphor was used in ancient Sumatra to treat sprains, swellings, and inflammation.[17] Camphor also was used for centuries in traditional Chinese medicine for various purposes.[16] In Europe, camphor was used after the Black Death era.[18] In the 20th century, camphor was used as an analeptic by injection,[19] and to induce seizures in schizophrenic people in an attempt to treat psychosis.[20] Camphor has limited use in veterinary medicine by intramuscular injection to treat breathing difficulties in horses.[21] Topical medication[edit] Camphor is commonly applied as a topical medication as a skin cream or ointment to relieve itching from insect bites, minor skin irritation, or joint pain.[22] It is absorbed in the skin epidermis,[22] where it stimulates nerve endings sensitive to heat and cold, producing a warm sensation when vigorously applied, or a cool sensation when applied gently, indicating its properties as a counterirritant.[16] The action on nerve endings also induces a slight local analgesia.[23] Respiratory aerosol[edit] Camphor is also used via an aerosol, typically by steam inhalation, sometimes in the form of branded nasal inhaler sticks, to inhibit coughing and relieve upper airway congestion due to the common cold.[24] However, the clinical efficiency of these remedies is challenged.[25] Other niche uses[edit] Camphor is used by marksmen to blacken the front and rear sights of rifles to prevent the sights from reflecting.[26] This is done by setting light to a small amount of camphor, which burns at a relatively low temperature, and using the soot rising from the flame to deposit a coating on a surface held above it. Historically, this soot blackening was also used to coat Barograph record charts. Toxicity[edit] Applied on skin, camphor may cause allergic reactions in some people; when ingested by mouth, camphor cream or ointment is poisonous.[22] In high ingested doses, camphor produces symptoms of irritability, disorientation, lethargy, muscle spasms, vomiting, abdominal cramps, convulsions, and seizures.[41] Lethal doses by ingestion in adults are in the range 50–500 mg/kg (orally). Generally, ingestion of two grams causes serious toxicity and four grams is potentially lethal.[42] Airborne camphor may be toxic if respired by humans. The Permissible Exposure Limit (PEL) for camphor in ambient air is 2 mg/m3 at exposure time (TWA) not more than 8 hours. 200 mg/m3 is considered a very dangerous concentration (IDLH).[43] History of synthetic camphor[edit] When its use in the nascent chemical industries (discussed below) greatly increased the volume of demand in the late 19th century, potential for changes in supply and in price followed. In 1911 Robert Kennedy Duncan, an industrial chemist and educator, related that the Imperial Japanese government had recently (1907–1908) tried to monopolize the production of natural camphor as a forest product in Asia but that the monopoly was prevented by the development of the total synthesis alternatives,[15] which began in "purely academic and wholly uncommercial"[15] form with Gustav Komppa's first report: "... but it sealed the fate of the Japanese monopoly ... For no sooner was it accomplished than it excited the attention of a new army of investigators—the industrial chemists. The patent offices of the world were soon crowded with alleged commercial syntheses of camphor, and of the favored processes companies were formed to exploit them, factories resulted, and in the incredibly short time of two years after its academic synthesis artificial camphor, every whit as good as the natural product, entered the markets of the world ... And yet artificial camphor does not—and cannot—displace the natural product to an extent sufficient to ruin the camphor-growing industry. Its sole present and probable future function is to act as a permanent check to monopolization, to act as a balance-wheel to regulate prices within reasonable limits."[15]: 133–134  This ongoing check on price growth was confirmed in 1942 in a monograph on DuPont's history, where William S. Dutton said, "Indispensable in the manufacture of pyroxylin plastics, natural camphor imported from Formosa and selling normally for about 50 cents a pound, reached the high price of $3.75 in 1918 [amid the global trade disruption and high explosives demand that World War I created]. The organic chemists at DuPont replied by synthesizing camphor from the turpentine of southern US pine stumps, with the result that the price of industrial camphor sold in carload lots in 1939 was between 32 cents and 35 cents a pound."[44]: 293