The compound ischiral, existing in two possibleenantiomers 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.
The word camphor derived in the 14th century from Old French:camphre, itself from MedievalLatin:camfora, fromArabic:كافور,romanized: kāfūr, perhaps throughSanskrit:कर्पूर,romanized: karpūra, fromTamil:கற்பூரம்,romanized: karpooram apparently from AustronesianMalay:kapur 'lime' (chalk).[8]
InOld Malay, camphor was calledkapurbarus, meaning "the chalk of Barus", referring to Barus, an ancient port near modernSibolga on the western coast ofSumatra.[9] This port traded in camphor extracted from the Borneo camphor trees (Dryobalanops aromatica) that were abundant in the region.[10]
(+)-camphor has been produced as aforest product for centuries, condensed from the vapor given off by the roasting of wood chips cut fromCamphora 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 inJapan andTaiwan, 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 intoAnping 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]
(-)-camphor occurs naturally in the essential oil ofMatricaria plants. As a result, it's much rarer.[13]
Camphor is produced fromalpha-pinene, which is abundant in the oils of coniferous trees and can be distilled from turpentine produced as a side product ofchemical pulping. With acetic anhydride as the solvent and with catalysis by a strong acid, alpha-pinene is converted toisobornyl acetate. Hydrolysis of this ester givesisoborneol which can be oxidized to giveracemic camphor.
A biological enzyme has been proposed for producing only the rare (-) orL-camphor. ThisEstB esterase fromBurkholderia gladioli hydrolyzes only (+)-isobornyl acetate.[13]
The first significant manmade plastics were low-nitrogen (or "soluble")nitrocellulose (pyroxylin) plastics. In the early decades of theplastics industry, camphor was used in immense quantities[18]: 130 as the plasticizer that createscelluloid from nitrocellulose, innitrocellulose lacquers and other plastics and lacquers.
Camphor is commonly applied as atopical medication as a skin cream or ointment to relieve itching from insect bites, minor skin irritation, or joint pain.[25] It is absorbed in the skinepidermis,[25] 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 acounterirritant.[19] The action on nerve endings also induces a slight localanalgesia.[26]
Camphor is also used via anaerosol, 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.[27] However, the clinical efficacy of these remedies is challenged.[28]
Camphor is used by marksmen to blacken the front and rear sights of rifles to prevent the sights from reflecting.[29] 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 coatbarograph record charts. A barracks-room rumour possibly derived from an older rumour aboutsaltpetre[30][31] holds that soldiers inthe Islamic Republic of Iran are dosed with camphor in their daily meals in order to repress their libido and prevent homosexual incidents.[32]
Camphor is believed to be toxic to insects and is thus sometimes used as a repellent.[33] Camphor is used as an alternative tomothballs. Camphor crystals are sometimes used to prevent damage toinsect collections by other small insects. It is kept in clothes used on special occasions and festivals, and also in cupboard corners as a cockroach repellent. The smoke of camphor crystal or camphor incense sticks can be used as an environmentally-friendly mosquito repellent.[34]
Recent studies have indicated that camphor essential oil can be used as an effectivefumigant againstred fire ants, as it affects the attacking, climbing, and feeding behavior of major and minor workers.[35]
In the ancient Arab world, camphor was a common perfume ingredient.[37] The Chinese referred to the best camphor as "dragon's brain perfume", due to its "pungent and portentous aroma" and "centuries of uncertainty over its provenance and mode of origin".[38]
One of the earliest known recipes for ice cream dating to theTang dynasty includes camphor as an ingredient.[39] It was used to flavor leavened bread in ancient Egypt.[40] In ancient and medieval Europe, camphor was used as an ingredient insweets. It was used in a wide variety of both savory and sweet dishes in medieval Arabic language cookbooks, such asKitab al-Ṭabikh compiled byibn Sayyār al-Warrāq in the 10th century.[41] It also was used in sweet and savory dishes in theNi'matnama, according to a book written in the late 15th century for the sultans ofMandu.[42] It is a main constituent of a spice known as "edible camphor" (orkapur), which may be used in traditional South Indian desserts likePayasam andChakkarai Pongal.[43]
Camphor is widely used in Hindu religious ceremonies.Aarti is performed after placing it on a stand and setting fire to it usually as the last step ofpuja or devotional worship ritual to one or more deities.[44] Camphor is mentioned in theQuran as being the fragrance of wine given to believers in heaven.[45]
Applied on skin, camphor may causeallergic reactions in some people; when ingested by mouth, camphor cream or ointment is poisonous.[25] In high ingested doses, camphor produces symptoms of irritability, disorientation, lethargy,muscle spasms, vomiting, abdominal cramps,convulsions, andseizures.[46] Lethal doses by ingestion in adults are in the range 50–500mg/kg (orally). Generally, ingestion of two grams causes serious toxicity and four grams is potentially lethal.[47]
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).[48]
When its use in the nascentchemical industries (discussed below) greatly increased the volume of demand in the late 19th century, potential forchanges in supply and in price followed. In 1911 Robert Kennedy Duncan, an industrial chemist and educator, related that theImperial 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 thetotal synthesis alternatives,[18] which began in "purely academic and wholly uncommercial"[18] form withGustav Komppa's first report:
This ongoing check on price growth was confirmed in 1942 in a monograph onDuPont's history, where William S. Dutton said, "Indispensable in the manufacture of pyroxylin plastics, natural camphor imported fromFormosa 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."[49]: 293
The background ofGustaf Komppa's synthesis was as follows. In the 19th century, it was known that nitric acid oxidizes camphor intocamphoric acid. Haller and Blanc published a semisynthesis of camphor from camphoric acid. Although they demonstrated its structure, they were unable to prove it. The first completetotal synthesis of camphoric acid was published by Komppa in 1903. Its inputs werediethyl oxalate and3,3-dimethylpentanoic acid, which reacted byClaisen condensation to yield diketocamphoric acid. Methylation withmethyl iodide and a complicated reduction procedure produced camphoric acid.William Perkin published another synthesis a short time later. Previously, some organic compounds (such asurea) had been synthesized in the laboratory as aproof of concept, but camphor was a scarce natural product with a worldwide demand. Komppa realized this, and began industrial production of camphor inTainionkoski, Finland, in 1907 (with plenty of competition, as Kennedy Duncan reported).[citation needed]
A different way of synthesis was developed at the same time by Dr. Karl Stephan fromChemische Fabrik auf Actien. This chemist, who had patented a route to synthesizecamphene in 1902, found out thatborneol orisoborneol could easily be oxidized with permanganate in benzene solution with unprecedentedly high yields of 95+%, and patented it in 1903.[50] The process was efficient enough to compete with natural camphor, and Japan was forced to lower prices in 1907, but the German company still increased its production, reaching 623 tons in 1913, only to be interrupted by the First World War.[51]
^abc"Camphor (synthetic)".cdc.gov. National Institute for Occupational Safety and Health. 4 December 2014.Archived from the original on 13 March 2015. Retrieved19 February 2015.
^White, James D.; Wardrop, Duncan J.; Sundermann, Kurt F. (2002). "Camphorquinone and Camphorquinone Monoxime".Organic Syntheses.79: 125.doi:10.15227/orgsyn.079.0125.
^Bangen, Hans (1992).Geschichte der medikamentösen Therapie der Schizophrenie [History of drug therapy for schizophrenia] (in German). Berlin: Verlag für Wissenschaft und Bildung. pp. 51–55.ISBN3927408824.
^Burrow, A.; Eccles, R; Jones, AS (July 1983). "The effects of camphor, eucalyptus and menthol vapour on nasal resistance to airflow and nasal sensation".Acta Oto-Laryngologica.96 (1–2):157–161.doi:10.3109/00016488309132886.ISSN0001-6489.PMID6613544.
^Chapel, Charles Edward (1948).The Boy's Book of Rifles. New York: Coward-McCann, Inc. p. 96.[some marksmen] always blackened their sights by using a small piece of camphor.
^Muller, H. G. (1986).Baking and bakeries. Shire Publications. p. 7.ISBN9780852638019.
^Nasrallah, Nawal (2007).Annals of the Caliphs' Kitchens: Ibn Sayyâr al-Warrâq's Tenth-century Baghdadi Cookbook. Islamic History and Civilization. Vol. 70. Leiden, The Netherlands: Brill.ISBN978-0-415-35059-4.
^Titley, Norah M. (2004).The Ni'matnama Manuscript of the Sultans of Mandu: The Sultan's Book of Delights. Routledge Studies in South Asia. London: Routledge.ISBN978-0-415-35059-4.
^"Camphor overdose".MedlinePlus. US: National Library of Medicine, National Institutes of Health. 12 January 2019.Archived from the original on 5 July 2016. Retrieved19 February 2020.
