Chapter · PDF fileChapter 20 The Chemistry ... • 20.4 Acid‐Base Properes of...

Chapter20TheChemistryofCarboxylicAcids

Organic Chemistry, 5th ed. Marc Loudon

Eric J. Kantorowski California Polytechnic State University San Luis Obispo, CA

Chapter20Overview

•  20.1NomenclatureofCarboxylicAcids

•  20.2StructureandPhysicalProper>esofCarboxylicAcids•  20.3SpectroscopyofCarboxylicAcids•  20.4Acid‐BaseProper>esofCarboxylicAcids•  20.5FaEyAcids,Soaps,andDetergents•  20.6SynthesisofCarboxylicAcids•  20.7Introduc>ontoCarboxylicAcidsReac>ons•  20.8ConversionofCarboxylicAcidsintoEsters•  20.9ConversionofCarboxylicAcidsintoAcidChloridesand

Anhydrides

•  20.10Reduc>onofCarboxylicAcidstoPrimaryAlcohols

•  20.11Decarboxyla>onofCarboxylicAcids2

CarboxylicAcids

•  Thecharacteris>cfunc>onalgroupincarboxylicacidsisthecarboxygroup

•  Thischapterwillalsosurveythechemistryofsulfonicacids

320.1NomenclatureofCarboxylicAcids

CommonNomenclature

•  Dicarboxylicacids


CommonNomenclature


Subs>tu>veNomenclature


StructureandPhysicalProper>es

•  ThecarbonyloxygenistheoxygeninvolvedwiththeC=Odoublebond

•  ThecarboxylateoxygenistheoxygeninvolvedwiththeC‐Osinglebond

820.2StructureandPhysicalProper?esofCarboxylicAcids

StructureandPhysicalProper>es

•  Manyaroma>canddicarboxylicacidsaresolids

•  Simplecarboxylicacidsanddicarboxylicacidsaresolubleinwater(H‐bonding)

920.2StructureandPhysicalProper?esofCarboxylicAcids

IRSpectroscopy

•  C=Ostretch:1710cm‐1(asthedimer)•  O‐Hstretch:2400‐3600cm‐1(verybroad)

1020.3SpectroscopyofCarboxylicAcids

NMRSpectroscopy

•  O‐H:δ9‐13(broad;exchangeswithD2O)

1120.3SpectroscopyofCarboxylicAcids

AcidityofCarboxylicAcids

•  Acidityisoneofthemostimportantproper>esofcarboxylicacids

•  Conjugatebasesofcarboxylicacidsarecalledcarboxylateions

1220.4Acid‐BaseProper?esofCarboxylicAcids

pKaValuesofSomeCarboxylicAcids


AcidityofSulfonicAcids

•  Sulfonicacidsareusefulasacidcatalystsinorganicsolventsbecausetheyaremoresolublethanmostinorganicacids



•  Thealkalimetalsaltsofcarboxylicacidsaresolubleinwater

•  Evena5%NaHCO3solu>onisbasicenough(pH≈8.5)todissolveacarboxylicacid


BasicityofCarboxylicAcids

•  Thecarbonyloxygenisweaklybasic

•  Notethatthecarboxylateoxygenisnotprotonated

•  Thebasicityofcarboxylicacidsplaysanimportantroleinmanyoftheirreac>ons


FaGyAcids

•  Carboxylicacidswithlong,unbranchedcarbonchains

•  Manyareisolatedfromfatsandoilsbythehydroly>cprocessofsaponifica>on

1820.5FaFyAcids,Soaps,andDetergents

SoapsandDetergents

•  Na+andK+saltsoffaEyacidsaresoaps

•  Soapsarepartofalargerclassofcompoundscalleddetergents


Surfactants

•  Soapsanddetergentsarepartofanevenbroaderclassofcompoundscalledsurfactants

•  Surfactantscontainapolarheadgroupandahydrocarbontail

•  Phospholipidsarealsosurfactants


Micelles

•  Micellesformwhenthesurfactantconcentra>onisraisedabovethecri>calmicelleconcentra>on

•  Micellesaresphericalaggregatesof50‐150surfactantmolecules


SynthesisofCarboxylicAcids

•  Oxida>onofprimaryalcohols•  Side‐chainoxida>onofalkylbenzenes•  Grignardororganolithiumwithcarbondioxide

2220.6SynthesisofCarboxylicAcids

CarboxylicAcidReac>ons

•  Therearefourmaintypesofreac>ons:1.Reac>onsatthecarbonylgroup

2.Reac>onsatthecarboxylateoxygen

3.LossofthecarboxygroupasCO2(decarboxyla>on)

4.Reac>onsinvolvingtheα‐carbon(Ch22)

2320.7Introduc?ontoCarboxylicAcidsReac?ons


•  Reac>onsatthecarbonylgroup



•  Reac>onsatthecarboxylgroup



•  LossofthecarboxygroupasCO2(decarboxyla>on)


Acid‐CatalyzedEsterifica>on

•  Estersarecarboxylicacidderiva>ves

•  AlsoreferredtoastheFischeresterifica>on•  Theequilibriumisfavorable,butnotlarge

•  Thealcoholneedstobepresentinlargeexcess(commonlyasthesolvent)

2720.8ConversionofCarboxylicAcidsintoEsters


•  Isotopiclabelingwith18Odeterminedthatthecarboxyloxygenintheesterisfromthealcohol


•  Esterifica>onillustratesaverygeneralmechanis>cpaEern

•  Comparewithaldehydesandketones



Esterifica>onbyAlkyla>on

•  Thecarboxylateoxygenactsasanucleophile


Esterifica>onbyAlkyla>on

•  Carboxylateionsarelessbasic,andthereforelessnucleophilic,thanalkoxides

•  ThisisanSN2reac>onandworksbestwithespeciallyreac>vealkyla>ngagents


SynthesisofAcidChlorides

3420.9ConversionofCarboxylicAcidsintoAcidChloridesandAnhydrides

SynthesisofSulfonylChlorides

•  Sulfonylchloridesaretheacidchloridesofsulfonicacids

•  TypicallytheirsodiumsaltsaretreatedwithPCl5


SynthesisofSulfonylChlorides

•  Aroma>csulfonylchloridesmayalsobeprepared


SynthesisofAnhydrides

•  Anhydride=“withoutwater”



•  Mostanhydridesmaythemselvesbeusedtoformotheranhydrides



•  5‐and6‐memberedringanhydridescancommonlybeformedsimplybyhea>ng


Reduc>onofCarboxylicAcids

•  ThepowerfulreducingagentLiAlH4isrequired

4020.10Reduc?onofCarboxylicAcidstoPrimaryAlcohols

•  Theoverallsequenceforreduc>onissummarizedas:

Reduc>onofCarboxylicAcids

4120.10Reduc?onofCarboxylicAcidstoPrimaryAlcohols

Decarboxyla>onofCarboxylicAcids

•  Decarboxyla>on:ThelossofCO2fromRCO2H

•  Mostordinarycarboxylicacidsdonotpar>cipate,butthefollowingtypesdo:

1.β‐ketoacids

2.Malonicacidderiva>ves

3.Carbonicacidderiva>ves

4220.11Decarboxyla?onofCarboxylicAcids


•  Decarboxyla>onfromβ‐ketoacids

•  Decarboxyla>onoftheβ‐ketoacidoccursmorereadilythanitsconjugatebaseform



•  Decarboxyla>onfrommalonicacidderiva>ves

•  Thisreac>onalsodoesnotoccurinbase•  Notethesimilaritytotheβ‐ketoacid



•  Decarboxyla>onfromcarbonicacidderiva>ves


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