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Encyclopedia > Menthol
Menthol
(-)-Menthol
General
Systematic name 2-(2-Propyl)-5-methyl-
1-cyclohexanol
for racemic (−)-isomer (2R)-(2-Propyl)-(5S)-methyl-
(1R)-cyclohexanol
Other names 3-p-Menthanol,
Hexahydrothymol,
Menthomenthol,
peppermint camphor
Molecular formula C10H20O
SMILES CC1CCC(C(C1)O)C(C)C
Molar mass 156.27 g/mol
Appearance White or colorless
crystalline solid
CAS number [89-78-1], racemic
[2216-51-5], (−)-isomer
Properties
Density and phase 0.890 g/cm3, solid
(racemic or (−)-isomer)
Solubility in water Slightly soluble, (−)-isomer
In ethanol, diethyl ether,
acetone, chloroform
acetic acid, hexane
Soluble
Melting point 36-38 °C (311 K), racemic
42-45 °C (318 K), (−)-form (α)
35-33-31 °C, (−)-isomer
Boiling point 212 °C (485 K)
Chiral rotation [α]D -50° at 18 °C, 10% EtOH soln.
Hazards
MSDS External MSDS
Main hazards Irritant, flammable
NFPA 704

Image File history File links Download high resolution version (1100x1488, 20 KB) File links The following pages link to this file: Menthol User:Benjah-bmm27/Gallery ... Image File history File links (-)-menthol-3D-qutemol-ballandstick. ... Image File history File links (-)-menthol-3D-qutemol. ... IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... The simplified molecular input line entry specification or SMILES is a specification for unambiguously describing the structure of chemical molecules using short ASCII strings. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... Density (symbol: ρ - Greek: rho) is a measure of mass per volume. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... It has been suggested that this article or section be merged with Solution. ... This article describes water from a scientific and technical perspective. ... Ethanol, also known as ethyl alcohol or grain alcohol, is a flammable, colorless, mildly toxic chemical compound with a distinctive perfume-like odor, and is the alcohol found in alcoholic beverages. ... Diethyl ether, also known as ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic smell. ... In chemistry, acetone (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and β-ketopropane) is the simplest representative of the ketones. ... Chloroform, also known as trichloromethane and methyl trichloride, is a chemical compound with formula CHCl3. ... Acetic acid, also known as ethanoic acid, is an organic chemical compound best recognized for giving vinegar its sour taste and pungent smell. ... the 3rd ingredient in big mac ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid at a given pressure. ... The specific rotation of a chemical compound [α]D is defined as the observed angle of optical rotation α when light of 589 nanometer wavelength (the sodium D line) is passed through a sample with a path length of 0. ... Ethanol, also known as ethyl alcohol or grain alcohol, is a flammable, colorless, mildly toxic chemical compound with a distinctive perfume-like odor, and is the alcohol found in alcoholic beverages. ... A material safety data sheet or MSDS is a form containing data regarding the properties of a particular substance. ... This page provides supplementary chemical data on Menthol. ... The examples and perspective in this article or section may not represent a worldwide view. ... NFPA 704 is a standard maintained by the U.S. National Fire Protection Association. ... Image File history File links NFPA_704. ...

2
1
0
 
Flash point 93 °C
R/S statement R37/38, R41 S26, S36
RTECS number OT0350000, racemic
OT0700000, (−)-enantiomer
Supplementary data page
Structure & properties n, εr, etc.
Thermodynamic data Phase behavior
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Related alcohols Cyclohexanol, Pulegol,
Dihydrocarveol, Piperitol
Related compounds Menthone, Menthene,
Thymol, p-Cymene,
Citronellal
Except where noted otherwise, data are given for
materials in their standard state (at 25°C, 100 kPa)
Infobox disclaimer and references

Menthol is a covalent organic compound made synthetically or obtained from peppermint or other mint oils. It is a waxy, crystalline substance, clear or white in color, which is solid at room temperature and melts slightly above. The main form of menthol occurring in nature is (-)-menthol, which is assigned the (1R,2S,5R) configuration. Menthol has local anesthetic and counterirritant qualities, and it is widely used to relieve minor throat irritation. The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture with air. ... Risk and Safety Statements, also known as R/S statements, R/S numbers, R/S phrases, and R/S sentences, is a system of hazard codes and phrases for labeling dangerous chemicals and compounds. ... RTECS, also known as Registry of Toxic Effects of Chemical Substances, is a database of toxicity information compiled from the open scientific literature that is available for charge. ... This page provides supplementary chemical data on Menthol. ... This page provides supplementary chemical data on Menthol. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... The dielectric constant εr (represented as or K in some cases) is defined as the ratio: where εs is the static permittivity of the material in question, and ε0 is the vacuum permittivity. ... This page provides supplementary chemical data on Menthol. ... This page provides supplementary chemical data on Menthol. ... Ultraviolet-Visible Spectroscopy or Ultraviolet-Visible Spectrophotometry (UV/ VIS) involves the spectroscopy of photons (spectrophotometry). ... IR spectrum of a thin film of liquid ethanol. ... Nuclear Magnetic Resonance Spectroscopy most commonly known as NMR Spectroscopy is the name given to the technique which exploits the magnetic properties of nuclei. ... Basic schematic of a mass spectrometer Mass spectrometry (also known as mass spectroscopy (deprecated)[1] or in common speech mass-spec) is an analytical technique used to measure the mass-to-charge ratio of ions. ... Functional group of an alcohol molecule. ... Cyclohexanol is a secondary alcohol, formula C6H12O, consisting of a cyclohexane ring with one hydrogen substituent replaced by a hydroxyl group. ... l-Menthone Menthone is a naturally occurring organic compound with a molecular formula C10H18O. l-Menthone (or (5R, 2S)-trans-5-methyl-2-(l-methylethyl)cyclohexanone), shown at right, is the most abundant in nature of the four possible stereoisomers. ... Thymol is a phenol derivative of cymene, C10H13OH, isomeric with carvacrol, found in oil of thyme, and extracted as a white crystalline substance of a pleasant aromatic odor and strong antiseptic properties. ... Cymene, or p-cymene, is a naturally occurring aromatic organic compound. ... Citronellal or rhodinal or 3,7-dimethyloct-6-en-1-al (C10H18O) is is the main component in a mixture of terpene chemical compounds that can be derived from citronella oil. ... In chemistry, the standard state of a material is its state at 1 bar (100 kilopascals) and 25 degrees Celsius (298. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... Benzene An organic compound is any member of a large class of chemical compounds whose molecules contain carbon, with the exception of carbides, carbonates, carbon oxides and elementary carbon. ... Binomial name Mentha × piperita L. Peppermint (Mentha × piperita) is a (usually) sterile hybrid mint, a cross between watermint (Mentha aquatica) and spearmint (Mentha spicata). ... This article is about the herb. ... To meet Wikipedias quality standards, this article may require cleanup. ... For compounds found in organic chemistry, the Cahn Ingold Prelog priority rules are used to determine the orientation of a molecule for purposes of assigning stereochemistry at a stereocenter and for assigning the name of isomers of molecules possessing double bonds such as alkenes. ... A local anesthetic is a drug that reversibly inhibits the propagation of signals along nerves. ...

Contents

History and occurrence

There is evidence[1] that menthol has been known in Japan for more than 2000 years, but in the west it was not isolated until 1771, by Gambius.[2] (-)-Menthol (also called l-menthol or (1R,2S,5R)-menthol) occurs naturally in peppermint oil (along with a little menthone, the ester menthyl acetate and other compounds), obtained from mentha x piperita. Japanese menthol also contains a small percentage of the 1-epimer, (+)-neomenthol. l-Menthone Menthone is a naturally occurring organic compound with a molecular formula C10H18O. l-Menthone (or (5R, 2S)-trans-5-methyl-2-(l-methylethyl)cyclohexanone), shown at right, is the most abundant in nature of the four possible stereoisomers. ... In chemistry, an epimer is a stereoisomer that has a different configuration at only one of several stereogenic centers. ...


Structure

Natural menthol exists as one pure enantiomer, nearly always the (1R,2S,5R) form (bottom left of diagram below). The other seven stereoisomers are: Chemical structure refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. ... In chemistry, enantiomers are stereoisomers that are mirror images of each other. ... ...


Structures of menthol isomers Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...


In the natural compound, the isopropyl group is oriented trans- orientation to both the methyl and alcohol groups. Thus it can be drawn in any of the ways shown: Isopropyl is a term in organic chemistry to refer to a three carbon structure. ... The different types of isomers. ... In chemistry a methyl-group is a hydrophobic Alkyl functional group which is derived from methane (CH4). ... Functional group of an alcohol molecule. ...


Menthol chair conformation Image File history File links Ways of drawing the structure of (-)-menthol. ...


In the ground state all three bulky groups in the chair are equatorial, making (-)-menthol and its enantiomer the most stable two isomers out of the eight. Cyclohexane is a cycloalkane with the molecular formula C6H12. ...


There are two crystal forms for racemic menthol; these have melting points of 28 °C and 38 °C. Pure (-)-menthol has four crystal forms, of which the most stable is the α form, the familiar broad needles.


Applications

Menthol is included in many products for a variety of reasons. These include:

  • In non-prescription products for short-term relief of minor sore throat and minor mouth or throat irritation
  • As an antipruritic to reduce itching
  • As a topical analgesic to relieve minor aches and pains such as muscle cramps, sprains, headaches and similar conditions, alone or combined with products like Camphor or Capsicum. In Europe it tends to appear as a gel or a cream, while in the US patches and body sleeves are very frequently used
  • In decongestants for chest and sinuses (cream, patch or nose inhaler)
  • In certain medications used to treat sunburns, as it provides a cooling sensation (then often associated with Aloe)
  • As an additive in certain cigarette brands, for flavor, to reduce the throat and sinus irritation caused by smoking and arguably to reduce the bad-breath smokers experience and possibly improve the smell of second-hand smoke.
  • Commonly used in oral hygiene products and bad-breath remedies like mouthwash, toothpaste, mouth and tongue-spray, and more generally as a food flavor agent e.g. in chewing-gum, candy
  • In a soda as well as in a syrup to be mixed with water to obtain a very low alcohol drink or (brand Rickles in France). The syrup is/was also used to alleviate nausea, in particular motion sickness, by pouring a few drops on a lump of sugar.
  • As a pesticide against tracheal mites of honeybees
  • In perfumery, menthol is used to prepare menthyl esters to emphasise floral notes (especially rose)
  • In first aid products such as "mineral ice" to produce a cooling effect as a substitute for real ice in the absence of water or electricity (Pouch, Body patch/sleeve or cream)
  • In various patches ranging from fever-reducing patches applied to children's foreheads to "foot patches" to relieve numerous ailments (the latter being much more frequent and elaborate in Asia, esp. Japan: some variety use `functional protrusion' i.e. small bumps to massage ones feet as well as soothing them and cooling them down)
  • In some beauty products such as hair-conditioners, based on natural ingredients (ex: St Ives)

Some supporters of the homeopathic theory of pharmacology believe that menthol interferes with the effects of homeopathic remedies. Its use is strongly discouraged for those seeking homeopathic cures, to the point of prohibiting the use of mint-flavored toothpaste. Currently no other reported nutrient or herb interactions involve menthol. Menthol is available as a dietary supplement or natural medicine in the form of peppermint oil. It is used in Eastern medicine to treat indigestion, nausea, sore throat, diarrhoea, colds, and headaches. (-)-Menthol has low toxicity: Oral (rat) LD50: 3300 mg/kg; Skin (rabbit) LD50: 15800 mg/kg). A tube of ChapStick. ... A cough medicine is a drug used to treat coughing and related conditions. ... Antipruritic is a drug which reduces pruritis, or itching. ... R-phrases 11-20/21/22-36/37/38 S-phrases 16-26-36 RTECS number EX1260000 (R) EX1250000 (S) Supplementary data page Structure and properties n, εr, etc. ... Species C. annuum (incl. ... Wikipedia does not have an article with this exact name. ... A box of the cream version of IcyHot. ... A Patch can refer to several different things: A piece of fabric. ... Sleeve (O. Eng. ... A decongestant is a broad class of drugs designed to symptomatically treat ailments affecting the respiratory system. ... Vicks (VapoRub) In Germany, the brand name is written Wick, as Wichs(pronounced vicks) is German slang for semen. ... Species See Species The words aloe or aloes sometimes denotes an aromatic wood better known as aloeswood. ... A lit cigarette will burn to ash from one end. ... Mouth rinse or mouthwash is a product used for oral hygiene. ... Modern toothpaste gel Toothpaste is a paste or gel used to clean and improve the aesthetic appearance and health of teeth. ... Chewing gum Chewing gum is a type of confectionery which is designed to be chewed instead of swallowed. ... A wide range of candies on display on a market in Barcelona, Spain. ... Look up soda in Wiktionary, the free dictionary. ... In cooking, a syrup (from Arabic شراب sharab, beverage, via Latin siropus) is a thick, viscous liquid, containing a large amount of dissolved sugars, but showing little tendency to deposit crystals. ... For other uses, see Nausea (disambiguation). ... Motion sickness is a condition in which the endolymph (the fluid found in the semicircular canals of the inner ears) becomes stirred up, causing confusion between the difference between apparent perceived movement (none or very little), and actual movement. ... For the book Perfume by Patrick Süskind, see Perfume (book). ... World map showing the location of Asia. ... Homeopathy (also spelled homœopathy or homoeopathy), from the Greek words homoios (similar) and pathos (suffering), is a controversial system of alternative medicine involving the use of remedies without chemically active ingredients. ... Pharmacology (in Greek: pharmacon (φάρμακον) meaning drug, and logos (λόγος) meaning science) is the study of how substances interact with living organisms to produce a change in function. ... An LD50 test being administered In toxicology, the LD50 or colloquially semilethal dose of a particular substance is a measure of how much constitutes a lethal dose. ... An LD50 test being administered In toxicology, the LD50 or colloquially semilethal dose of a particular substance is a measure of how much constitutes a lethal dose. ...


In organic chemistry, menthol is used as a chiral auxiliary in asymmetric synthesis. For example, sulfinate esters made from sulfinyl chlorides and menthol can be used to make enantiomerically pure sulfoxides by reaction with organolithium reagents or Grignard reagents. Menthol is also used for classical resolution of chiral carboxylic acids, via the menthyl esters. Organic chemistry is a specific discipline within the subject of chemistry. ... A chiral auxiliary is a chemical compound or unit that is temporarily incorporated into a organic synthesis so that it can be carried out asymmetrically with the selective formation of one of twoenantiomers. ... The two optical isomers of bromochlorofluoromethane Chiral synthesis (also called asymmetric synthesis) is organic synthesis which preserves or introduces a desired chirality. ... A sulfinate is a sulfur compound and a SO2- anion. ... General formula of a carboxylate ester. ... In chemistry, enantiomers are stereoisomers that are mirror images of each other. ... Sulfinyl group A sulfoxide is a chemical compound containing a sulfinyl functional group attached to two carbon atoms. ... An organolithium reagent is an organometallic compound with a direct bond between a carbon and a lithium atom. ... The Grignard reaction is an organometallic chemical reaction involving alkyl- or aryl-magnesium halides, also called Grignard reagents, with electrophiles. ...


Synthesis

As with many widely-used natural products, the demand for menthol greatly exceeds the supply from natural sources. Menthol is manufactured as a single enantiomer (94% ee) by Takasago International Co. on a scale of 400 000 tonnes per year. The process involves an asymmetric synthesis developed by a team led by Ryoji Noyori: In chemistry, enantiomers are stereoisomers that are mirror images of each other. ... In chemistry two stereoisomers are said to be enantiomers if one can be superimposed on the mirror image of the other. ... A tonne (also called metric ton) is a non-SI unit of mass, accepted for use with SI, defined as: 1 tonne = 103 kg (= 106 g). ... The two optical isomers of bromochlorofluoromethane Chiral synthesis (also called asymmetric synthesis) is organic synthesis which preserves or introduces a desired chirality. ... Ryoji Noyori (野依良治) (born September 3, 1938) won the Nobel Prize in Chemistry in 2001. ...


Manufacturing process for menthol Image File history File links Process for the manufacture of (-)-menthol from myrcene. ...


The process begins by forming an allylic amine from myrcene, which undergoes asymmetric isomerisation in the presence of a BINAP rhodium complex to give (after hydrolysis) enantiomerically pure R-citronellal. This is cyclised by a carbonyl-ene-reaction initiated by zinc bromide to isopulegol which is then hydrogenated to give pure (1R,2S,5R)-menthol. An allyl group is an alkene hydrocarbon group with the formula H2C=CH-CH2-. It is made up of a vinyl group, CH2=CH-, attached to a methylene -CH2. ... Myrcene, or β-myrcene, is an olefinic natural organic compound. ... In chemistry, isomerization is the transformation of a molecule into a different isomer. ... Figure 1 (S)- and (R)-BINAP In organic chemistry, BINAP, an acronym used for 2,2-bis(diphenylphosphino)-1,1-binaphthyl, is an important chiral ligand widely used in asymmetric synthesis. ... Rh redirects here. ... Hydrolysis is a chemical reaction or process in which a molecule is split into two parts by reacting with a molecule of water, which has the chemical formula H2O. One of the parts gets an OH- from the water molecule and the other part gets an H+ from the water. ... Citronellal or rhodinal or 3,7-dimethyloct-6-en-1-al (C10H18O) is is the main component in a mixture of terpene chemical compounds that can be derived from citronella oil. ... Zinc Bromide is a white ionic solid which is used in organic chemistry as a lewis acid. ...


Racemic menthol can be prepared simply by hydrogenation of thymol, and menthol is also formed by hydrogenation of pulegone. For preparation of other isomers such as neomenthol, see ref. 1. In chemistry, a racemate is a mixture of equal amounts of left- and right-handed stereoisomers of a chiral molecule. ... Thymol is a phenol derivative of cymene, C10H13OH, isomeric with carvacrol, found in oil of thyme, and extracted as a white crystalline substance of a pleasant aromatic odor and strong antiseptic properties. ... Pulegone is a naturally occurring organic compound obtained from essential oils. ...


Chemical properties

Menthol reacts in many ways like a normal secondary alcohol. It is oxidised to menthone by oxidising agents such as chromic acid, though under some conditions the oxidation can go further and break open the ring. Menthol is easily dehydrated to give mainly 3-menthene, by the action of 2% sulfuric acid. PCl5 gives menthyl chloride. In chemistry, chromic acid is a hypothetical chromium (Cr) compound, yet to be isolated, that would have the formula H2CrO4. ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... Phosphorus pentachloride is the chemical compound with the formula PCl5. ...


Reactions of menthol Image File history File links Reactions of (-)-menthol. ...


Biological properties

Menthol's ability to chemically trigger cold-sensitive receptors in the skin is responsible for the well known cooling sensation that it provokes when inhalated, eaten, or applied to the skin. It should be noted that Menthol does not cause an actual drop in temperature. [3]. In this sense it is similar to capsaicin, the chemical responsible for the spiciness of hot peppers (which stimulates heat sensors, also without causing actual temperature rise). The chemical compound capsaicin (8-methyl-N-vanillyl-6-nonenamide) is the active component of chili peppers, which are plants belonging to the genus Capsicum. ...


Notes

  1. ^ J. L. Simonsen, The Terpenes Volume I (2nd edition), Cambridge University Press, 1947, p230-249.
  2. ^ Adversoriorum varii argumentii, Liber unus, Leiden, 1771, p99.
  3. ^ R. Eccles, Menthol and Related Cooling Compounds, Journal of Pharm. Pharmacol. 1994 46: 618-630

References

  • E. E. Turner, M. M. Harris, Organic Chemistry, Longmans, Green & Co., London, 1952.
  • Handbook of Chemistry and Physics, 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
  • The Merck Index, 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.

External links

  • Link page to external chemical sources.
  • Colacot T. J. Platinum Metals Review 2002, 46(2), 82-83.
  • Ryoji Noyori Nobel lecture (2001)
  • Menthol Information
  • Cooler than Menthol
  • A review of menthol from the Science Creative Quarterly

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