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Camphor (/ˈkæmfər/) is a waxy, flammable, transparent solid with a strong aroma.^[5] It is a terpenoid with the chemical formula C₁₀H₁₆O. It is found in the wood of the camphor laurel (Cinnamomum camphora), a large evergreen tree found in Asia (particularly in Sumatra and Borneo islands, Indonesia) and also of the unrelated kapur tree, a tall timber tree from the same region. It also occurs in some other related trees in the laurel family, notably Ocotea usambarensis. The oil in rosemary leaves (Rosmarinus officinalis), in the mint family, contains 10 to 20% camphor,^[6] while camphorweed (Heterotheca) only contains some 5%.^[7] Camphor can also be synthetically produced from oil of turpentine. It is used for its scent, as an ingredient in cooking (mainly in India), as an embalming fluid, for medicinal purposes, and in religious ceremonies. A major source of camphor in Asia is camphor basil (the parent of African blue basil).

The molecule has two possible enantiomers as shown in the structural diagrams. The structure on the left is the naturally occurring (R)-form, while its mirror image shown on the right is the (S)-form.

Etymology

The word camphor derives from the French word camphre, itself from Medieval Latin camfora, from Arabic kāfūr, from Sanskrit karpūraḥ (कर्पूरः), from Austroasiatic languages - Khmer kāpōr / kapū, Mon khapuiw, ultimately from an Austronesian source - Malay kapur.^[8] Camphor was not known in India during the Vedic period since there are no references to this product. However, Suśruta and later kāvya literature mention this word. In Old Malay it is known as kapur Barus, which means "the chalk of Barus". Barus was the name of an ancient port located near modern Sibolga city on the western coast of Sumatra island.^[9] This port traded in camphor extracted from laurel trees (Cinnamonum camphora) that were abundant in the region. Even now, the local tribespeople and Indonesians in general refer to aromatic naphthalene balls and moth balls as kapur Barus.

Production

A sample of sublimed camphor

Camphor has been produced as a forest product for centuries by passing steam through the pulverized wood of the relevant trees and condensing the vapors.^[10] When its uses 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,^[11] which began in "purely academic and wholly uncommercial"^[11] 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 […]."^{[11]:133–134} "...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." 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 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."^[12]:293

The background of Gustaf Komppa's synthesis was as follows. In the 19th century, it was known that nitric acid oxidizes camphor into camphoric 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 complete total synthesis of camphoric acid was published by Komppa in 1903. Its inputs were diethyl oxalate and 3,3-dimethylpentanoic acid, which reacted by Claisen condensation to yield diketocamphoric acid. Methylation with methyl iodide and a complicated reduction procedure produced camphoric acid. William Perkin published another synthesis a short time later. Previously, some organic compounds (such as urea) had been synthesized in the laboratory as a proof of concept, but camphor was a scarce natural product with a worldwide demand. Komppa realized this. He began industrial production of camphor in Tainionkoski, Finland, in 1907 (with plenty of competition, as Kennedy Duncan reported).

Camphor can be 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 readily rearranges into camphene, which in turn undergoes Wagner-Meerwein rearrangement into the isobornyl cation, which is captured by acetate to give isobornyl acetate. Hydrolysis into isoborneol followed by oxidation gives racemic camphor. By contrast, camphor occurs naturally as D-camphor, the (R)-enantiomer.

Biosynthesis

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.

Reactions

Typical camphor reactions are

• 
  bromination,

• 
  oxidation with nitric acid,

• conversion to isonitrosocamphor.

Camphor can also be reduced to isoborneol using sodium borohydride.

In 1998, K. Chakrabarti and coworkers from the Indian Association for the Cultivation of Science, Kolkata, prepared diamond thin film using camphor as the precursor for chemical vapor deposition.^[13]

In 2007, carbon nanotubes were successfully synthesized using camphor in chemical vapor deposition process.^[14]

Physical uses

The sublimating capability of camphor gives it several uses.

Plastics

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^[11]:130 as the plasticizer that creates celluloid from nitrocellulose, in nitrocellulose lacquers and other plastics and lacquers.

Pest deterrent and preservative

Camphor is believed to be toxic to insects and is thus sometimes used as a repellent.^[15] Camphor is used as an alternative to mothballs. Camphor crystals are sometimes used to prevent damage to insect 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.^[16]

Recent studies have indicated that camphor essential oil can be used as an effective fumigant against red fire ants, as it affects the attacking, climbing, and feeding behavior of major and minor workers.^[17]

Camphor is also used as an antimicrobial substance. In embalming, camphor oil was one of the ingredients used by ancient Egyptians for mummification.^[18]

Solid camphor releases fumes that form a rust-preventative coating and is therefore stored in tool chests to protect tools against rust.^[19]

Use in Perfumes

In the ancient Arab world, Camphor was one of the most popular perfume ingredients. According to the Perfume Handbook, "[Camphor] features in more than a quarter of al-Kindi's perfume recipes and in many other medieval Arabic works, including the Arabian Nights Tales."^[20] The word camphor or campheer also appears in many translations of the biblical Song of Solomon. However, the original Hebrew word kopher, actually refers to henna, another perfume and dyestuff of the Arabic world.^[21]

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."^[22]

Culinary uses

In ancient and medieval Europe, camphor was used as an ingredient in sweets. It was used in a wide variety of both savory and sweet dishes in medieval Arabic language cookbooks, such as al-Kitab al-Ṭabikh compiled by ibn Sayyâr al-Warrâq in the 10th century,^[23] and an anonymous Andalusian cookbook of the 13th century.^[24]
It also appears in sweet and savory dishes in the Ni'matnama, a book written in the late 15th century for the sultans of Mandu.^[25] An early international trade in it made camphor widely known throughout Arabia in pre-Islamic times, as it is mentioned in the Quran 76:5 as a flavoring for drinks.^[26] By the 13th century, it was used in recipes everywhere in the Muslim world, ranging from main dishes such as tharid and stew to desserts.^[24]

An alcohol analog of camphor also known as isoborneol currently is used in Asia as a flavoring, mostly for sweets. In India it is widely used in cooking, mainly for dessert dishes, and is known as kachha karpooram or "pachha karpoora" ("crude/raw camphor"), in (Telugu:పచ్చ కర్పూరo), (Tamil:பச்சைக் கற்பூரம்), (Kannada:ಪಚ್ಚ ಕರ್ಪೂರ), and is available in Indian grocery stores where it is labeled as "edible camphor".

Medicinal uses

Physiology

Camphor is readily absorbed through the skin, where it stimulates nerve endings sensitive to heat and cold, producing a warm sensation when vigorously applied, or a cool sensation when applied gently.^[27][28][29] These effects are particularly noticeable in the lungs and airways if camphor is inhaled as an aerosol.^[27] The action on nerve endings also induces a slight local analgesia.^[30]

The sensation of heat that camphor produces on the skin is presumably due to activation of the ion channels TRPV3 and TRPV1, while the cool sensation due to activation of TRPM8.^[31][32][33]

The global effects on the body include tachycardia (increased heart rate), vasodilation in skin (flushing), slower breathing, reduced appetite, and increased secretions and excretions such as perspiration and urination.
^[34]

Camphor is toxic in large doses. It produces symptoms of irritability, disorientation, lethargy, muscle spasms, vomiting, abdominal cramps, convulsions, and seizures.^[35][36][37] Lethal doses in adults are in the range 50–500 mg/kg (orally). Generally, two grams cause serious toxicity and four grams are potentially lethal.^[38]

Traditional uses

Camphor has been used in traditional medicine from time immemorial in countries where it was native. It was probably the odor of the substance and its decongestant effect that led to its use in medicine.^[27]

Camphor was used in ancient Sumatra to treat sprains, swellings, and inflammation.^[39]

It has long been used as a medical substance in ancient India, where it generally goes by the name karpūra. It has been described in the 7th-century Āyurvedic work Mādhavacikitsā as being an effective drug used for the treatment of fever. The plant has also been named hima and has been identified with the plant Cinnamomum camphora. According to the Vaidyaka-śabda-sindhu, it is one of the “five flavours” used in betel-chewing, where it is also referred to as candrabhasma (‘moon powder’).

Camphor also was used for centuries in Chinese medicine for a variety of purposes.^[27]

Modern uses

Camphor was a component of paregoric, an opium/camphor tincture developed in the 18th century. Paregoric was used in various formulations for hundreds of years. It was a household remedy in the 18th and 19th centuries when it was widely used to control diarrhea in adults and children, as an expectorant and cough medicine, to calm fretful children, and to rub on the gums to counteract the pain from teething. Its use declined in the 20th century after the regulation of opium.

Also in the 18th century, camphor was used by Auenbrugger in the treatment of mania, paradoxically by inducing seizures.^[40]

Based on Hahnemann's writings, camphor (dissolved in alcohol) was used in the 19th century to treat the 1854-1855 cholera epidemics in Naples.^[41]

In the 20th century, camphor was administered orally in small quantities (50 mg) for minor heart symptoms and fatigue.^[42] This preparation was sold under the trade name Musterole; production ceased in the 1990s.^[why?]

Today the main use of camphor is as a cough suppressant^[43] and as a decongestant.^[43] It is an active ingredient (along with menthol) in vapor-steam decongestant products, such as Vicks VapoRub.

Regulation

In 1980, the US Food and Drug Administration set a limit of 11% allowable camphor in consumer products, and banned products labeled as camphorated oil, camphor oil, camphor liniment, and camphorated liniment (except "white camphor essential oil", which contains no significant amount of camphor^{[citation needed]}). Since alternative treatments exist, medicinal use of camphor is discouraged by the FDA, except for skin-related uses, such as medicated powders, which contain only small amounts of camphor.

Hindu religious ceremonies

Camphor is widely used in Hindu religious ceremonies. It is put on a stand called 'karpur dāni' in India. Aarti is performed after setting fire to it usually as the last step of puja.^[44]

See also

• 1,4-Dichlorobenzene


• Citral


• Eucalyptol


• Lavender


• Vaporizer

References

External links

Camphor^[1][2]

(R)- (left) and (S)-camphor
Names
IUPAC name 1,7,7-Trimethylbicyclo[2.2.1]heptan-2-one
Other names 2-Bornanone; Bornan-2-one; 2-Camphanone; Formosa
Identifiers
CAS Number	76-22-2 Y 21368-68-3 N 464-49-3 (R) N 464-48-2 (S) N
3D model (JSmol)	Interactive image Interactive image
3DMet	B04902
Beilstein Reference	1907611
ChEBI	CHEBI:36773 Y
ChEMBL	ChEMBL504760 N
ChemSpider	2441 Y 7822160 (R) Y 9655 (S) Y
DrugBank	DB01744 Y
ECHA InfoCard	100.000.860
EC Number	200-945-0
Gmelin Reference	83275
IUPHAR/BPS	2422
KEGG	D00098 Y
MeSH	Camphor
PubChem CID	2537 9543187 (R) 10050 (S)
RTECS number	EX1225000
UNII	5TJD82A1ET Y
UN number	2717
InChI InChI=1S/C10H16O/c1-9(2)7-4-5-10(9,3)8(11)6-7/h7H,4-6H2,1-3H3 Y Key: DSSYKIVIOFKYAU-UHFFFAOYSA-N Y InChI=1/C10H16O/c1-9(2)7-4-5-10(9,3)8(11)6-7/h7H,4-6H2,1-3H3 Key: DSSYKIVIOFKYAU-UHFFFAOYAK
SMILES CC1(C)C2CCC1(C)C(=O)C2 O=C1CC2CCC1(C)C2(C)C
Properties
Chemical formula	C10H16O
Molar mass	7002152237000000000♠152.237 g·mol−1
Appearance	White, translucent crystals
Odor	Fragrant and penetrating
Density	0.992 g·cm−3
Melting point	175–177 °C (347–351 °F; 448–450 K)
Boiling point	209 °C (408 °F; 482 K)
Solubility in water	1.2 g·dm−3
Solubility in acetone	~2500 g·dm−3
Solubility in acetic acid	~2000 g·dm−3
Solubility in diethyl ether	~2000 g·dm−3
Solubility in chloroform	~1000 g·dm−3
Solubility in ethanol	~1000 g·dm−3
log P	2.089
Vapor pressure	4 mmHg (at 70 °C)
Chiral rotation ([α]D)	+44.1°
Magnetic susceptibility (χ)	−103×10−6 cm3/mol
Pharmacology
ATC code	C01EB02 (WHO)
Hazards
EU classification (DSD) (outdated)	FXn
R-phrases (outdated)	R11 R22 R36/37/38
S-phrases (outdated)	S16 S26
NFPA 704
Flash point	54 °C (129 °F; 327 K)
Autoignition temperature	466 °C (871 °F; 739 K)
Explosive limits	0.6–3.5%[3]
Lethal dose or concentration (LD, LC):
LD50 (median dose)	1310 mg/kg (oral, mouse)[4]
LDLo (lowest published)	800 mg/kg (dog, oral) 2000 mg/kg (rabbit, oral)[4]
LCLo (lowest published)	400 mg/m3 (mouse, 3 hr)[4]
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 2 mg/m3[3]
REL (Recommended)	TWA 2 mg/m3[3]
IDLH (Immediate danger)	200 mg/m3[3]
Related compounds
Related Ketones	Fenchone, Thujone
Related compounds	Camphene, Pinene, Borneol, Isoborneol, Camphorsulfonic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Wikimedia Commons has media related to Camphor.

Wikisource has the text of the 1911 Encyclopædia Britannica article Camphors.

• 
  INCHEM at IPCS (International Programme on Chemical Safety)


• 
  NIOSH Pocket Guide to Chemical Hazards - Camphor at Centers for Disease Control and Prevention