Mentholisaterpenoid,foundintheessentialoilsofthemintfamily（Menthaspp）,suchaspeppermint,spearmintandothers.Menthol（C10H20O）issolidatroomtemperature,forminglongcrystalsthathaveafattytouch.Severalisomersofmentholexist,somewithamentholsmell,otherswithout.Normallyoccurringmenthol,withthestrongestsmell,is（-）-menthol（lowerleftinfigurebelow）.StructureofmentholandisomersMentholisnotorpoorlysolubleinwater,butreadilysolubleinalcoholoroils.Besidestheuseasanaromainmanydifferentfoodproducts（especiallydentalproducts,suchaschewinggum,coughdropsandconfectionary,suchasmints）,mentholiscontainedinnon-prescriptionproductsforshort-termreliefofminorsorethroatandminormouthorthroatirritation,forexampleinlipbalmsandcoughmedicines.Itisclassedasanantipruritic,whichreducesitching.Mentholisalsocontainedincombinationproductsusedforreliefofmuscleaches,sprains,andsimilarconditions,aswellasindecongestants.Inaddition,itisusedasanadditiveincertaincigarettebrands,bothforflavourandtoreducethethroatandsinusirritationcausedbysmoking.Mentholalsoisacommoningredientinmouthwash.MentholFromWikipedia,thefreeencyclopediaJumpto:navigation,searchNottobeconfusedwithmethanol.MentholGeneralSystematicname2-（2-Propyl）-5-methylcyclohexanolStereochemicalconfiguration（2S,5R,1R）Othernames3-p-Menthanol,Hexahydrothymol,Menthomenthol,peppermintcamphorMolecularformulaC10H20OSMILESCC1CCC（C（C1）O）C（C）CMolarmass156.27 g·mol−1AppearanceWhiteorcolorlesscrystallinesolidCASnumber[89-78-1],racemic[2216-51-5],（−）-isomerPropertiesDensityandphase0.890 g·cm−3,solid（racemicor（−）-isomer）SolubilityinwaterSlightlysoluble,（−）-isomerInethanol,diethylether,acetone,chloroformaceticacid,hexaneSolubleMeltingpoint36-38 °C（311 K）,racemic42-45 °C（318 K）,（−）-form（α）35-33-31 °C,（−）-isomerBoilingpoint212 °C（485 K）Chiralrotation[α]D-50°at18°C,10%inEtOHHazardsMSDSExternalMSDSMainhazardsIrritant,flammableNFPA704210Flashpoint93 °CR/SstatementR37/38,R41S26,S36RTECSnumberOT0350000,racemicOT0700000,（−）-enantiomerSupplementarydatapageStructure&amp;propertiesn,εr,etc.ThermodynamicdataPhasebehaviorSolid,liquid,gasSpectraldataUV,IR,NMR,MSRelatedcompoundsRelatedalcoholsCyclohexanol,Pulegol,Dihydrocarveol,PiperitolRelatedcompoundsMenthone,Menthene,Thymol,p-Cymene,CitronellalExceptwherenotedotherwise,dataaregivenformaterialsintheirstandardstate（at25 °C,100 kPa）InfoboxdisclaimerandreferencesMentholisacovalentorganiccompoundmadesyntheticallyorobtainedfrompeppermintorothermintoils.Itisawaxy,crystallinesubstance,clearorwhiteincolor,whichissolidatroomtemperatureandmeltsslightlyabove.Themainformofmentholoccurringinnatureis（-）-menthol,whichisassignedthe（1R,2S,5R）configuration.Mentholhaslocalanestheticandcounterirritantqualities,anditiswidelyusedtorelieveminorthroatirritation.Contents[hide]1Historyandoccurrence2Structure3Applications4Synthesis5Naturalmenthol6Chemicalproperties7Biologicalproperties8Notes9ReferencesHistoryandoccurrenceThereisevidence[1]thatmentholhasbeenknowninJapanformorethan2000years,butintheWestitwasnotisolateduntil1771,byGambius.[2]（-）-Menthol（alsocalledl-mentholor（1R,2S,5R）-menthol）occursnaturallyinpeppermintoil（alongwithalittlementhone,theestermenthylacetateandothercompounds）,obtainedfrommenthaxpiperita.Japanesementholalsocontainsasmallpercentageofthe1-epimer,（+）-neomenthol.StructureNaturalmentholexistsasonepureenantiomer,nearlyalwaysthe（1R,2S,5R）form（bottomleftofdiagrambelow）.Inthenaturalcompound,theisopropylgroupisorientedtrans-orientationtoboththemethylandalcoholgroups.Inthegroundstateallthreebulkygroupsinthechairareequatorial,making（-）-mentholanditsenantiomerthemoststabletwoisomersoutoftheeight.Therearetwocrystalformsforracemicmenthol;thesehavemeltingpointsof28 °Cand38 °C.Pure（-）-mentholhasfourcrystalforms,ofwhichthemoststableistheαform,thefamiliarbroadneedles.ApplicationsMentholisincludedinmanyproductsforavarietyofreasons.Theseinclude:Innon-prescriptionproductsforshort-termreliefofminorsorethroatandminormouthorthroatirritationExamples:lipbalmsandcoughmedicinesAsanantipruritictoreduceitchingAsatopicalanalgesictorelieveminorachesandpainssuchasmusclecramps,sprains,headachesandsimilarconditions,aloneorcombinedwithproductslikeCamphororCapsaicin.InEuropeittendstoappearasageloracream,whileintheUSpatchesandbodysleevesareveryfrequentlyusedExamples:TigerBalmIcyHotpatchesorknee/elbowsleevesIndecongestantsforchestandsinuses（cream,patchornoseinhaler）Examples:VicksVaporubIncertainmedicationsusedtotreatsunburns,asitprovidesacoolingsensation（thenoftenassociatedwithAloe）Asanadditiveincertaincigarettebrands,forflavor,toreducethethroatandsinusirritationcausedbysmokingandarguablytoreducethebad-breathsmokersexperienceandpossiblyimprovethesmellofsecond-handsmoke.Commonlyusedinoralhygieneproductsandbad-breathremedieslikemouthwash,toothpaste,mouthandtongue-spray,andmoregenerallyasafoodflavoragente.g.inchewing-gum,candyInasodaaswellasinasyruptobemixedwithwatertoobtainaverylowalcoholdrinkor（brandRiclèsinFrance）.Thesyrupis/wasalsousedtoalleviatenausea,inparticularmotionsickness,bypouringafewdropsonalumpofsugar.AsapesticideagainsttrachealmitesofhoneybeesInperfumery,mentholisusedtopreparementhylesterstoemphasisefloralnotes（especiallyrose）Infirstaidproductssuchas"mineralice"toproduceacoolingeffectasasubstituteforrealiceintheabsenceofwaterorelectricity（Pouch,Bodypatch/sleeveorcream）Invariouspatchesrangingfromfever-reducingpatchesappliedtochildren'sforeheadsto"footpatches"torelievenumerousailments（thelatterbeingmuchmorefrequentandelaborateinAsia,esp.Japan:somevarietyuse`functionalprotrusion'i.e.smallbumpstomassageonesfeetaswellassoothingthemandcoolingthemdown）Insomebeautyproductssuchashair-conditioners,basedonnaturalingredients（ex:StIves）Somesupportersofthehomeopathictheoryofpharmacologybelievethatmentholinterfereswiththeeffectsofhomeopathicremedies.Itsuseisstronglydiscouragedforthoseseekinghomeopathiccures,tothepointofprohibitingtheuseofmint-flavoredtoothpaste.Currentlynootherreportednutrientorherbinteractionsinvolvementhol.ItisusedinEasternmedicinetotreatindigestion,nausea,sorethroat,diarrhea,colds,andheadaches.（-）-Mentholhaslowtoxicity:Oral（rat）LD50:3300 mg·kg−1;Skin（rabbit）LD50:15800 mg·kg−1）.Inorganicchemistry,mentholisusedasachiralauxiliaryinasymmetricsynthesis.Forexample,sulfinateestersmadefromsulfinylchloridesandmentholcanbeusedtomakeenantiomericallypuresulfoxidesbyreactionwithorganolithiumreagentsorGrignardreagents.Mentholisalsousedforclassicalresolutionofchiralcarboxylicacids,viathementhylesters.SynthesisAswithmanywidely-usednaturalproducts,thedemandformentholgreatlyexceedsthesupplyfromnaturalsources.Mentholismanufacturedasasingleenantiomer（94%ee）byTakasagoInternationalCo.onascaleof400 000tonnesperyear.TheprocessinvolvesanasymmetricsynthesisdevelopedbyateamledbyRyojiNoyori.Theprocessbeginsbyforminganallylicaminefrommyrcene,whichundergoesasymmetricisomerisationinthepresenceofaBINAPrhodiumcomplextogive（afterhydrolysis）enantiomericallypureR-citronellal.Thisiscyclisedbyacarbonyl-ene-reactioninitiatedbyzincbromidetoisopulegolwhichisthenhydrogenatedtogivepure（1R,2S,5R）-menthol.Racemicmentholcanbepreparedsimplybyhydrogenationofthymol,andmentholisalsoformedbyhydrogenationofpulegone.Forpreparationofotherisomerssuchasneomenthol,seeref.1.NaturalmentholMenthaarvensisistheprimaryspeciesofmintusedtomakenaturalmentholcrystalsandnaturalmentholflakes.ThisspeciesisprimarilygrownintheUttarPradeshregioninIndia.ChemicalpropertiesMentholreactsinmanywayslikeanormalsecondaryalcohol.Itisoxidisedtomenthonebyoxidisingagentssuchaschromicacid,thoughundersomeconditionstheoxidationcangofurtherandbreakopenthering.Mentholiseasilydehydratedtogivemainly3-menthene,bytheactionof2%sulfuricacid.PCl5givesmenthylchloride.BiologicalpropertiesMenthol'sabilitytochemicallytriggercold-sensitivereceptorsintheskinisresponsibleforthewellknowncoolingsensationthatitprovokeswheninhaled,eaten,orappliedtotheskin.Mentholdoesnotcauseanactualdropintemperature.[3]Inthissenseitissimilartocapsaicin,thechemicalresponsibleforthespicinessofhotpeppers（whichstimulatesheatsensors,alsowithoutcausingactualtemperaturerise）.Notes^J.L.Simonsen,TheTerpenesVolumeI（2ndedition）,CambridgeUniversityPress,1947,p230-249.^Adversoriorumvariiargumentii,Liberunus,Leiden,1771,p99.^R.Eccles,MentholandRelatedCoolingCompounds,JournalofPharm.Pharmacol.199446:618-630ReferencesE.E.Turner,M.M.Harris,OrganicChemistry,Longmans,Green&amp;Co.,London,1952.HandbookofChemistryandPhysics,71stedition,CRCPress,AnnArbor,Michigan,1990.TheMerckIndex,7thedition,Merck&amp;Co,Rahway,NewJersey,USA,1960.