Jump to content

Camphor

From Wikipedia, the free encyclopedia

Not to be confused with samphor.
For other uses, see Camphor (disambiguation).
Camphor[1][2]
Structural formula of (R) and (S)-camphor
(+)- and (−)-camphor
Ball and stick model of camphor (both enantiomers).
Names
IUPAC name
1,7,7-Trimethylbicyclo[2.2.1]heptan-2-one
Other names
2-Bornanone; Bornan-2-one; 2-Camphanone; Formosa
Identifiers
3D model (JSmol)
3DMet
1907611
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.860 Edit this at Wikidata
EC Number
  • 200-945-0
83275
KEGG
MeSH Camphor
RTECS number
  • EX1225000
UNII
UN number 2717
  • InChI=1S/C10H16O/c1-9(2)7-4-5-10(9,3)8(11)6-7/h7H,4-6H2,1-3H3 checkY
    Key: DSSYKIVIOFKYAU-UHFFFAOYSA-N checkY
  • InChI=1/C10H16O/c1-9(2)7-4-5-10(9,3)8(11)6-7/h7H,4-6H2,1-3H3
    Key: DSSYKIVIOFKYAU-UHFFFAOYAK
  • CC1(C)C2CCC1(C)C(=O)C2
  • O=C1CC2CCC1(C)C2(C)C
Properties
C10H16O
Molar mass 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)
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)
+44.1°
−103×10−6 cm3/mol
Pharmacology
C01EB02 (WHO)
Hazards
GHS labelling:
GHS02: FlammableGHS07: Exclamation markGHS08: Health hazard
Warning
H228, H302, H332, H371
P210, P240, P241, P260, P261, P264, P270, P271, P280, P301+P312, P304+P312, P304+P340, P309+P311, P312, P330, P370+P378, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
2
0
Flash point 54 °C (129 °F; 327 K)
466 °C (871 °F; 739 K)
Explosive limits 0.6–3.5%[3]
Lethal dose or concentration (LD, LC):
1310 mg/kg (oral, mouse)[4]
800 mg/kg (dog, oral)
2000 mg/kg (rabbit, oral)[4]
400 mg/m3 (mouse, 3 hr)[4]
NIOSH (US health exposure limits):
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 checkY☒N ?)

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, from Tamil: கற்பூரம், romanized: karpooram 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]

(-)-camphor occurs naturally in the essential oil of Matricaria plants. As a result, it's much rarer.[13]

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 anhydride 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.

A biological enzyme has been proposed for producing only the rare (-) or L-camphor. This EstB esterase from Burkholderia gladioli only hydrolyzes (+)-isobornyl acetate.[13]

Reactions

[edit]

The reactions of camphor have been extensively examined. Some representative transformations include


Camphor can also be reduced to isoborneol using sodium borohydride.

Biochemistry

[edit]
Biosynthesis of camphor from geranyl pyrophosphate
Biosynthesis of camphor from geranyl pyrophosphate

Biosynthesis

[edit]
See also: Borneol § Biosynthesis, (+)-borneol dehydrogenase, and (-)-borneol dehydrogenase

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[16]: 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 cubes

Camphor has been used as a folk medicine over centuries, probably most commonly as a decongestant.[17] Camphor was used in ancient Sumatra to treat sprains, swellings, and inflammation.[18] Camphor also was used for centuries in traditional Chinese medicine for various purposes.[17] In Europe, camphor was used after the Black Death era.[19]

In the 20th century, camphor was used as an analeptic by injection,[20] and to induce seizures in schizophrenic people in an attempt to treat psychosis.[21]

Camphor has limited use in veterinary medicine by intramuscular injection to treat breathing difficulties in horses.[22]

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.[23] It is absorbed in the skin epidermis,[23] 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.[17] The action on nerve endings also induces a slight local analgesia.[24]

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.[25] However, the clinical efficacy of these remedies is challenged.[26]

Other niche uses

[edit]

Camphor is used by marksmen to blacken the front and rear sights of rifles to prevent the sights from reflecting.[27] 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. A barracks-room rumour possibly derived from an older rumour about saltpetre[28][29] holds that soldiers in the Islamic Republic of Iran are dosed with camphor in their daily meals in order to repress their libido and prevent homosexual incidents.[30]

Pest deterrent and preservative

[edit]

Camphor is believed to be toxic to insects and is thus sometimes used as a repellent.[31] 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.[32]

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.[33]

Camphor is also used as an antimicrobial substance. In embalming, camphor oil was one of the ingredients used by ancient Egyptians for mummification.[34]

Solid camphor releases fumes that form a rust-preventative coating and is therefore stored in tool chests to protect tools against rust.[35]

Perfume

[edit]

In the ancient Arab world, camphor was a common perfume ingredient.[36] 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".[37]

Culinary uses

[edit]

One of the earliest known recipes for ice cream dating to the Tang dynasty includes camphor as an ingredient.[38] It was used to flavor leavened bread in ancient Egypt.[39] 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 Kitab al-Ṭabikh compiled by ibn Sayyār al-Warrāq in the 10th century.[40] It also was used in sweet and savory dishes in the Ni'matnama, according to a book written in the late 15th century for the sultans of Mandu.[41] It is a main constituent of a spice known as "edible camphor" (or kapur), which may be used in traditional South Indian desserts like Payasam and Chakkarai Pongal.[42]

Religious rites

[edit]

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 of puja or devotional worship ritual to one or more deities.[43] Camphor is mentioned in the Quran as being the fragrance of wine given to believers in heaven.[44]

Toxicity

[edit]

Applied on skin, camphor may cause allergic reactions in some people; when ingested by mouth, camphor cream or ointment is poisonous.[23] In high ingested doses, camphor produces symptoms of irritability, disorientation, lethargy, muscle spasms, vomiting, abdominal cramps, convulsions, and seizures.[45] 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.[46]

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).[47]

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,[16] which began in "purely academic and wholly uncommercial"[16] 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."[16]: 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."[48]: 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, and began industrial production of camphor in Tainionkoski, 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 from Chemische Fabrik auf Actien. This chemist, who had patented a route to synthesize camphene in 1902, found out that borneol or isoborneol could easily be oxidized with permanganate in benzene solution with unprecedentedly high yields of 95+%, and patented it in 1903.[49] 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 WWI.[50]

See also

[edit]

References

[edit]
  1. ^ The Merck Index, 7th edition, Merck & Co., Rahway, New Jersey, 1960
  2. ^ Handbook of Chemistry and Physics, CRC Press, Ann Arbor, Michigan, USA
  3. ^ a b c d NIOSH Pocket Guide to Chemical Hazards. "#0096". National Institute for Occupational Safety and Health (NIOSH).
  4. ^ a b c "Camphor (synthetic)". National Institute for Occupational Safety and Health (NIOSH). 4 December 2014. Archived from the original on 13 March 2015. Retrieved 19 February 2015.
  5. ^ Mann JC, Hobbs JB, Banthorpe DV, Harborne JB (1994). Natural products: their chemistry and biological significance. Harlow, Essex, England: Longman Scientific & Technical. pp. 309–11. ISBN 978-0-582-06009-8.
  6. ^ "Rosemary". Drugs.com. Archived from the original on 14 September 2016. Retrieved 23 July 2016.
  7. ^ Lincoln, D.E.; Lawrence, B.M. (1984). "The volatile constituents of camphorweed, Heterotheca subaxillaris". Phytochemistry. 23 (4): 933–934. Bibcode:1984PChem..23..933L. doi:10.1016/S0031-9422(00)85073-6.
  8. ^ "Camphor". Online Etymology Dictionary. Douglas Harper. Archived from the original on 23 May 2021. Retrieved 23 May 2021.
  9. ^ Drakard, Jane (1989). "An Indian Ocean Port: Sources for the Earlier History of Barus". Archipel. 37: 53–82. doi:10.3406/arch.1989.2562.
  10. ^ Laufer, Berthold (1919). "SINO-IRANICA: Chinese Contributions to the History of Civilization in Ancient Iran". Publications of the Field Museum of Natural History. Anthropological Series. Publication. Field Museum of Natural History. 15 (3): 478–479. doi:10.5962/bhl.title.3538. ISSN 0894-8380. JSTOR 29782155. Archived from the original on 17 November 2020. Retrieved 22 January 2022.
  11. ^ "Camphor". britannica.com. Archived from the original on 13 December 2018. Retrieved 12 December 2018.
  12. ^ Cheung, Han. "Taiwan in Time: The camphor dispute". Taipei Times. Archived from the original on 15 November 2020. Retrieved 14 November 2020.
  13. ^ a b Calderini, Elia; Drienovská, Ivana; Myrtollari, Kamela; Pressnig, Michaela; Sieber, Volker; Schwab, Helmut; Hofer, Michael; Kourist, Robert (13 October 2021). "Simple Plug-In Synthetic Step for the Synthesis of (−)-Camphor from Renewable Starting Materials". ChemBioChem. 22 (20): 2951–2956. doi:10.1002/cbic.202100187. PMC 8596451. PMID 34033201.
  14. ^ Bartlett, Paul D.; Knox, L. H. (1965). "D,L-10-Camphorsulfonic acid (Reychler's Acid)". Organic Syntheses. 45: 12. doi:10.15227/orgsyn.045.0012.
  15. ^ White, James D.; Wardrop, Duncan J.; Sundermann, Kurt F. (2002). "Camphorquinone and Camphorquinone Monoxime". Organic Syntheses. 79: 125. doi:10.15227/orgsyn.079.0125.
  16. ^ a b c d Kennedy Duncan, Robert (1911), "Camphor: An Industry Revolutionized", Some Chemical Problems of Today, Harper and Brothers, LCCN 11026192, archived from the original on 27 July 2020, retrieved 17 January 2018.
  17. ^ a b c Parker, Keith; Brunton, Laurence; Lazo, John; Buxton, Iain; Blumenthal, Donald (September 2005). Goodman and Gilman, Pharmacological Basis of Therapeutics, Macmillan 1965, p. 982-983. McGraw-Hill Professional. ISBN 9780071468046.
  18. ^ Miller, Charles. History of Sumatra : An account of Sumatra. p. 121.
  19. ^ Chen, Weiyang; Vermaak, Ilze; Viljoen, Alvaro (10 May 2013). "Camphor—a fumigant during the Black Death and a coveted fragrant wood in ancient Egypt and Babylon—a review". Molecules (Basel, Switzerland). 18 (5): 5434–5454. doi:10.3390/molecules18055434. ISSN 1420-3049. PMC 6270224. PMID 23666009.
  20. ^ Wax, P. M. (1997). "Analeptic use in clinical toxicology: a historical appraisal". Journal of Toxicology. Clinical Toxicology. 35 (2): 203–209. doi:10.3109/15563659709001195. ISSN 0731-3810. PMID 9120893.
  21. ^ Bangen, Hans: Geschichte der medikamentösen Therapie der Schizophrenie. Berlin 1992, Page 51-55 ISBN 3-927408-82-4
  22. ^ "Camphor injection (Canada)". Drugs.com. 6 February 2020. Archived from the original on 27 July 2020. Retrieved 19 February 2020.
  23. ^ a b c "Camphor cream and ointment". Drugs.com. 25 August 2019. Archived from the original on 3 May 2021. Retrieved 19 February 2020.
  24. ^ Bonica's Management of Pain (4th ed.). Philadelphia, Baltimore: Wolters Kluwer - Lippincott Williams & Wilkins. 2009. p. 29. ISBN 9780781768276.
  25. ^ "Camphor Inhalation Liquid: Indications, Side Effects, Warnings". Drugs.com. Retrieved 28 October 2022.
  26. ^ 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. ISSN 0001-6489. PMID 6613544.
  27. ^ [some marksmen] "always blackened their sights by using a small piece of camphor."Chapel, Charles Edward, "The Boy's Book of Rifles, " Coward-McCann, Inc., New York, Copyright 1948, page 96.
  28. ^ "Does saltpeter suppress male ardor?". 16 June 1989.
  29. ^ "Saltpeter for sex drives, and the urban legend of the military's libido manipulation". 22 September 2021.
  30. ^ "Camphor during military service". سرباز مشاور (in Persian). May 2024.
  31. ^ The Housekeeper's Almanac, or, the Young Wife's Oracle! for 1840!. No. 134. New-York: Elton, 1840. Print.
  32. ^ Ghosh, G.K. (2000). Biopesticide and Integrated Pest Management. APH Publishing. ISBN 978-8-176-48135-9.
  33. ^ Fu JT, Tang L, Li WS, Wang K, Cheng DM, Zhang ZX (2015). "Carbon Nanotubes from Camphor: An Environment-Friendly Nanotechnology". J Insect Sci. 15 (1): 129. doi:10.1093/jisesa/iev112. PMC 4664941. PMID 26392574.
  34. ^ "Mummy-making complexity revealed". Archived from the original on 18 May 2015. Retrieved 3 July 2018.
  35. ^ "Remove rust from tools". www.naturalhandyman.com. Retrieved 28 April 2022.
  36. ^ Groom, N. (2012). The Perfume Handbook. Springer Netherlands. ISBN 978-9-401-12296-2.
  37. ^ Donkin, R. A. (1999). Dragon's Brain Perfume: An Historical Geography of Camphor. Brill. ISBN 978-9-004-10983-4.
  38. ^ Clarke, Chris (2004). Science of Ice Cream. Royal Society of chemistry. p. 4.
  39. ^ Muller, H. G. (1986). Baking and bakeries. Shire Publications. p. 7. ISBN 9780852638019.
  40. ^ Nasrallah, Nawal (2007). Annals of the Caliphs' Kitchens: Ibn Sayyâr al-Warrâq's Tenth-century Baghdadi Cookbook. Islamic History and Civilization, 70. Leiden, The Netherlands: Brill. ISBN 978-0-415-35059-4.
  41. ^ 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, UK: Routledge. ISBN 978-0-415-35059-4.
  42. ^ "5 Unique Culinary Uses Of Edible Camphor To Add To Your Diet". NDTV Food. Retrieved 1 January 2023.
  43. ^ Bahadur, Om Lata (1996). The book of Hindu festivals and ceremonies (3rd ed.). New Delhi: UBS Publishers Distributors ltd. pp. 172–3. ISBN 978-81-86112-23-6.[dead link‍]
  44. ^ Quran 76:5 pg 578
  45. ^ "Camphor overdose". MedlinePlus, National Library of Medicine, US National Institutes of Health. 12 January 2019. Archived from the original on 5 July 2016. Retrieved 19 February 2020.
  46. ^ "Poisons Information Monograph: Camphor". International Programme on Chemical Safety. Archived from the original on 11 February 2021. Retrieved 12 December 2008.
  47. ^ "CAMPHOR | Occupational Safety and Health Administration". www.osha.gov. Retrieved 29 November 2022.
  48. ^ Dutton, William S. (1942), Du Pont: One Hundred and Forty Years, Charles Scribner's Sons, LCCN 42011897, archived from the original on 4 August 2020, retrieved 17 January 2018.
  49. ^ CA 84302A, "Process of making camphor" ; AT 21683B, "Verfahren zur Darstellung von Kampfer" 
  50. ^ "The Raw Materials of Celluloid Film: Wartime Economy, Educational Animation, and Film's Plasticity". film-history.org. Retrieved 10 June 2024.
[edit]
Wikisource has the text of the 1911 Encyclopædia Britannica article "Camphors".
Retrieved from "https://en.wikipedia.org/w/index.php?title=Camphor&oldid=1264628792"