Chapter10TheChemistryofAlcoholsandThiols
Organic Chemistry, 5th ed. Marc Loudon
Eric J. Kantorowski California Polytechnic State University San Luis Obispo, CA
Chapter10Overview
• 10.1Dehydra,onofAlcohols• 10.2Reac,onsofAlcoholswithHydrogenHalides• 10.3SulfonateandInorganicEsterDeriva,vesofAlcohols• 10.4ConversionofAlcoholsintoAlkylHalides:Summary• 10.5Oxida,onandReduc,oninOrganicChemistry
• 10.6Oxida,onofAlcohols• 10.7BiologicalOxida,onofEthanol• 10.8ChemicalandStereochemicalGroupRela,onships
• 10.9Oxida,onofThiols• 10.10SynthesisofAlcohols• 10.11DesignofOrganicSynthesis
2
Dehydra2onofAlcohols
• Strongacids(e.g.,H2SO4,H3PO4)catalyzeaβ‐elimina,onreac,oninwhichwaterislost
• HeatandLewisacids(e.g.Al2O3)canalsobeusedtoeffectdehydra,on
310.1Dehydra8onofAlcohols
MechanismofDehydra2on
• Dehydra,ondoesnotfollowtheE2reac,onobservedforalkylhalides
• Hydroxideisapoorleavinggroup• TheO‐HprotonismoreacidicthanHβ
410.1Dehydra8onofAlcohols
MechanismofDehydra2on
510.1Dehydra8onofAlcohols
MechanismofDehydra2on
610.1Dehydra8onofAlcohols
Hydra2onandDehydra2on
• Hydra,onofalkenesanddehydra,onofalcoholsaretheforwardandreverseofthesamereac,on
• Theyhavethesameintermediatesandthesamerate‐limi,ngsteps(theprincipleofmicroscopicreversibility)
• Theacidisacatalystinbothreac,ons• Rateforalcoholdehydra,on:Ter,ary>secondary>primary
710.1Dehydra8onofAlcohols
ProductDistribu2on
• Regiochemistry
• Rearrangements
810.1Dehydra8onofAlcohols
AlkylHalidesfromAlcohols
• Alcoholsreactwithhydrogenhalides(HX)togivealkylhalides
910.2Reac8onsofAlcoholswithHydrogenHalides
AlkylHalidesfromAlcohols
• Keqvaluesforthesereac,onsarenotlarge• Applica,onofLeChâtelier’sprincipleisrequired
• Commonly,thealkylhalideproductisnotsolubleandwillseparateoutasasecondlayer
• AlargeexcessofH‐Xmayalsobeusedtodrivethereac,ontocomple,on
1010.2Reac8onsofAlcoholswithHydrogenHalides
AlkylHalidesfromAlcohols
• Ter,aryalcohols(andmanysecondaryalcohols):
1110.2Reac8onsofAlcoholswithHydrogenHalides
AlkylHalidesfromAlcohols
• Primaryalcohols:
1210.2Reac8onsofAlcoholswithHydrogenHalides
AlkylHalidevsDehydra2on
• Alkylhalideforma,onanddehydra,ontoalkenesarealterna8vebranchesofacommonmechanism
1310.2Reac8onsofAlcoholswithHydrogenHalides
SulfonateEsterDeriva2vesofAlcohols
• Animportantmethodfortheac8va8onofalcoholstowardsubs,tu,onandelimina,onreac,ons
• Sulfonateestersarederiva,vesofsulfonicacids
1410.3SulfonateandInorganicEsterDeriva8vesofAlcohols
SulfonateEsterDeriva2vesofAlcohols
• Theacidichydrogenofasulfonicacidisreplacedbyanalkylorarylgroup
1510.3SulfonateandInorganicEsterDeriva8vesofAlcohols
SulfonateEsterDeriva2vesofAlcohols
• Abbrevia,onsarecommonlyusedbychemists
1610.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Prepara2onofSulfonateEsters
• Alcohols+sulfonylchloridesproducesulfonateesters
• Thisisanucleophilicsubs,tu,onreac,on
1710.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Reac2vityofSulfonateEsters
• Alkyltosylates(R‐OTs)andmesylates(R‐OMs)havenearlythesamereac8vityasR‐Br
• R‐OTs≈R‐OMs≈R‐Br
• Sulfonateanionsaregoodleavinggroups
1810.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Reac2vityofSulfonateEsters
• Subs,tu,onreac,ons:
• Elimina,onreac,ons:
1910.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Reac2vityofSulfonateEsters
• Thetrifluoromethanesulfonateesterishighlyreac,ve
2010.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Alkyla2ngAgents
• Thenucleophileissaidtobealkylatedbythealkylhalide
• Acompoundthatisagoodalkyla2ngagentisonethatreactsrapidlywithanucleophile
2110.3SulfonateandInorganicEsterDeriva8vesofAlcohols
EsterDeriva2vesofStrongInorganicAcids
• Alkylestersofstronginorganicacidsarehighlypotentalkyla,ngagents
2210.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Reac2onsofAlcoholswithSOCl2
• Thereac,onofalcoholswithHClisgenerallynotsa,sfactory
• Abebermethodemploysthionylchloride
• Bestforprimaryandsecondaryalcohols
2310.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Reac2onsofAlcoholswithSOCl2
• SOCl2providesconversiontoagoodleavinggroupandthechloridenucleophiletogether
2410.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Reac2onsofAlcoholswithPBr3
• ArelatedmethodforpreparingR‐Brusesphosphoroustribromide
• Canbeusedwithacid‐sensi,vegroups• Lesschanceofrearrangement(cf.HBr)
2510.3SulfonateandInorganicEsterDeriva8vesofAlcohols
Reac2onsofAlcoholswithPBr3
• PBr3providesconversiontoagoodleavinggroupandthebromidenucleophiletogether
2610.3SulfonateandInorganicEsterDeriva8vesofAlcohols
MethodsforConver2ngR‐OHtoR‐X
• Reac,onwithhydrogenhalides(HX)• Forma,onofsulfonateestersfollowedbySN2withahalideion
• Reac,onwithSOCl2orPBr3
2710.4ConversionofAlcoholsintoAlkylHalides:Summary
PrimaryR‐OH→R‐X
• SOCl2
• HBrorPBr3• UsePBr3toavoidstronglyacidiccondi,onsand/orrearrangements
• HIorKIwithH3PO4
2810.4ConversionofAlcoholsintoAlkylHalides:Summary
SecondaryR‐OH→R‐X
• SOCl2(ifnoβ‐alkylsubs,tu,on)
• HBrorPBr3• UsePBr3toavoidstronglyacidiccondi,onsand/orrearrangements
• Thesulfonateestermethodfollowedbydisplacementwithahalideisalsoeffec,ve
2910.4ConversionofAlcoholsintoAlkylHalides:Summary
Ter2aryR‐OH→R‐X
• Ingeneralforter,aryalcohols,anyofthehydrogenhalides(HCl,HBr,HI)areeffec,ve
• Thesulfonateestermethodwillnotworkaster,aryalcoholscannotundergoSN2reac,ons
3010.4ConversionofAlcoholsintoAlkylHalides:Summary
HalfReac2onsandOxida2onNumbers
• Oxida2on:Atransforma,oninwhichelectronsarelost
• Reduc2on:Atransforma,oninwhichelectronsaregained
• Eachoxida,onmustbeaccompaniedbyareduc,on(andviceversa)
• Halfreac2on:Showseithertheoxida,onorreduc,onbutnotboth
3110.5Oxida8onandReduc8oninOrganicChemistry
HalfReac2ons
1.UseH2Otobalancemissingoxygens
2.Useprotons(i.e.,H+)tobalancemissinghydrogens
3.Useelectronstobalancecharges
• Ethanolhaslostfourelectronsinthisreac,on
3210.5Oxida8onandReduc8oninOrganicChemistry
Oxida2onNumbers
1.Assignanoxida,onleveltoeachcarbonatomthatundergoesachange
2.Determinetheoxida,onnumber(Nox)ofboththereactantandproduct
3.Calculatethedifferencetodetermineifthereac,onisanoxida,on,reduc,on,orneither
• Ethanolhasbeenoxidized(ΔNox=+4)
3310.5Oxida8onandReduc8oninOrganicChemistry
Oxida2onNumbers
• Followingthesamemethod,addi,onofBr2toanalkeneisanoxida,onreac,on
• Notethatanoxida,ondoesnotdependontheintroduc,onofanoxygen
• Moregenerally,considertheelectronega,vityofthenewelement
3410.5Oxida8onandReduc8oninOrganicChemistry
Oxida2onNumbers
3510.5Oxida8onandReduc8oninOrganicChemistry
Oxida2onNumbers
3610.5Oxida8onandReduc8oninOrganicChemistry
OxidizingandReducingAgents
• Whenanorganiccompoundisoxidized,thereagentthateffectsthereac,onisanoxidizingagent
• Whenanorganiccompoundisreduced,thereagentthateffectsthereac,onisanreducingagent
3710.5Oxida8onandReduc8oninOrganicChemistry
OxidizingandReducingAgents
• Considerchromateionasanoxidizingagenttoeffectthereac,onofethanol→ace,cacid
• Whenchromateionoxidizesethanol,Cr3+isformed[hence,Cr(VI)→Cr(III)]
3810.5Oxida8onandReduc8oninOrganicChemistry
Wri2ngaBalanceEqua2on
3910.5Oxida8onandReduc8oninOrganicChemistry
Oxida2ontoAldehydesandKetones
• Chromium‐basedreagentsareeffec,veatconver,ngalcoholstocarbonylcompounds
4010.6Oxida8onofAlcohols
Oxida2ontoAldehydesandKetones
• Primaryalcoholsreacttogivealdehydes,butifH2Oispresenttheyarefurtheroxidized
• H2Ocausesforma,onofaldehydehydrateswhichcanbeoxidizedlikeasecondaryROH
4110.6Oxida8onofAlcohols
Oxida2ontoAldehydesandKetones
• Anhydrousprepara,onscanbeconductedwithpyridiniumchlorochromate(PCC)
• Thesolventtypicallyusedismethylenechloride
4210.6Oxida8onofAlcohols
MechanismofCr(VI)Oxida2ons
• Theα‐carbonmustbearatleastonehydrogen• Hence,ter,aryalcoholsarenotoxidized• Thefirststepsofthereac,oninvolveanacid‐catalyzeddisplacementofwater
4310.6Oxida8onofAlcohols
MechanismofCr(VI)Oxida2ons
• Aoerprotona,on,aβ‐elimina,onoccurs(E2)
4410.6Oxida8onofAlcohols
Oxida2ontoCarboxylicAcids
• Primaryalcoholscanbeoxidizedtocarboxylicacidsusingaqueoussolu,onsofCr(VI)
• Alterna,vely,potassiumpermanganate(KMnO4)inalkalinesolu,onmayalsobeused
4510.6Oxida8onofAlcohols
Oxida2oninLivingSystems
• Oxida,onandreduc,onreac,onsarehighlyimportant
• Atypicalbiologicaloxida,onistheconversionofethanoltoacetaldehyde
• Theoxida,onoccursintheliverwithNAD+servingastheoxidizingagent
4610.7BiologicalOxida8onofEthanol
Oxida2oninLivingSystems
4710.7BiologicalOxida8onofEthanol
Oxida2oninLivingSystems
• NAD+isoneofnature’smostimportantoxidizingagents;itisacoenzyme
• Coenzymesaremoleculesrequired,alongwithenzymes,forcertainbiologicalreac,onstooccur
4810.7BiologicalOxida8onofEthanol
MechanismofNAD+Oxida2on
• NAD+iselectron‐deficient
• Theenzymeholdsthealcohol(specifically,it’sα‐H)incloseproximitytoNAD+
4910.7BiologicalOxida8onofEthanol
MechanismofNAD+Oxida2on
• Thecarboca,oncharacteronNAD+promptsahydridemigra,onfromthealcohol
5010.7BiologicalOxida8onofEthanol
ChemicalEquivalenceandNonequivalence
• First,cons2tu2onallyequivalency:
• Ingeneral,cons8tu8onallynonequivalentgroupsarechemicallynonequivalent
• Thisimpliescons,tu,onallynonequivalentgroupsexhibitdifferentchemicalbehavior
5110.8ChemicalandStereochemicalGroupRela8onships
ChemicalEquivalenceandNonequivalence
• Cons8tu8onalequivalentgroupsmaybechemicallynonequivalent
• Chemicalequivalencybetweentwogroupsdependsontheirstereochemicalrela8onship
• Equivalencyisrevealedbyasubs2tu2ontest
5210.8ChemicalandStereochemicalGroupRela8onships
Subs2tu2onTest
• Subs,tuteeachcons,tu,onallyequivalentgroupwithafic,,ousgroupandcompare
• Ifiden,calmoleculesareobtained,thegroupsarehomotopic
5310.8ChemicalandStereochemicalGroupRela8onships
Subs2tu2onTest
• Ifenan,omersareobtained,thegroupsareenan2otopic
• Enan,otopicgroupsarechemicallynonequivalenttowardchiralreagents,butarechemicallyequivalenttoachiralreagents
5410.8ChemicalandStereochemicalGroupRela8onships
Subs2tu2onTest
• Ifdiasteromersareobtained,thegroupsarediastereotopic
• Diastereotopicgroupsarechemicallynonequivalentunderallcondi8ons
5510.8ChemicalandStereochemicalGroupRela8onships
DiastereotopicGroupReac2vity
5610.8ChemicalandStereochemicalGroupRela8onships
RecognizingDiastereotopicGroups
• Diastereotopicgroupsshouldbereadilyiden,fiedintwocases:
5710.8ChemicalandStereochemicalGroupRela8onships
FlowchartforClassifyingGroups
5810.8ChemicalandStereochemicalGroupRela8onships
TheAlcoholDehydrogenaseReac2on
• Theenan8otopichydrogensofethanolarereadilydis,nguishedinthisbiologicalreac,on
• Adeuteriumlabelhelpstrackthereac,on
5910.8ChemicalandStereochemicalGroupRela8onships
TheAlcoholDehydrogenaseReac2on
• Thechiralenvironmentoftheenzymedis,nguishesbetweenthetwoα‐H’s
6010.8ChemicalandStereochemicalGroupRela8onships
Oxida2onofThiols
• Oxida,onofthiolsfollowsadifferentcoursethanthatofalcohols
6110.9Oxida8onofThiols
Oxida2onofThiols
• Avarietyofoxidizingagentsmaybeusedtopreparesulfonicacidsfromthiolsordisulfides
• KMnO4mayalsobeused
6210.9Oxida8onofThiols
Oxida2onofThiols
• DisulfidesmaybepreparedfromthiolswithBr2,I2inbase,ormerelystandinginair(O2)
6310.9Oxida8onofThiols
SynthesisofAlcohols
• Theprepara,onoforganiccompoundsfromotherorganiccompoundsiscalledorganicsynthesis
• Considerthesynthe,cmethodsavailabletopreparealcoholsfromalkenes:
6410.10SynthesisofAlcohols
DesignofOrganicSynthesis
• Commonly,asynthesisofacompoundrequiresmorethanonestep
• Asynthesisinvolvingmorethanonestepiscalledamul2‐stepsynthesis
• Themoleculetobesynthesizedisthetargetmolecule
6510.11DesignofOrganicSynthesis
DesignofOrganicSynthesis
• Toassessthebestroutefromstar,ngmaterialtotargetmolecule…workbackwards!
• Thisprocessiscalledretrosynthe2canalysis• Thispromptsques,onssuchas:
• “Whatisthebestwaytomakeanalkene?”
• “Whatisthebestwaytomakeacarboxylicacid?”
6610.11DesignofOrganicSynthesis