Chapter 19: Carboxylic Chapter 19: Carboxylic AcidsAcidsCarboxyCarboxy group: group: - -COOH, COOH, - -COCO2 2H, H, Naming: Naming: AlkanoicAlkanoic AcidsAcidsIUPAC: Replace IUPAC: Replace e e of alkane name with of alkane name with oicoic acidacidOOH4 4- -Methylhexanoic acidMethylhexanoic acidC1C1Cyclic: Cyclic: CycloalkanecarboxylicCycloalkanecarboxylic acidsacidsOOHCyclohexanecarboxylicCyclohexanecarboxylic acidacidOHO1 1- -Naphthalenecarboxylic acidNaphthalenecarboxylic acidC1, as in cyclic C1, as in cyclic aldehydesaldehydesCommon NamesCommon NamesCarboxylic acids take Carboxylic acids take precedenceprecedence over other groups:over other groups:Include as many functions as possible in stemInclude as many functions as possible in stem(Better than 4(Better than 4- -acetylheptanoic acid)acetylheptanoic acid)Physical PropertiesPhysical PropertiesPlanarPlanar structure, structure, trigonaltrigonal carbonyl carbonyl carboncarbonThe carboxy group is polar, The carboxy group is polar, undergoes hydrogen bonding, and undergoes hydrogen bonding, and forms forms dimersdimers: :DimerizationDimerization causes relatively causes relatively high melting and boiling pointshigh melting and boiling points1 1H NMR Chemical ShiftsH NMR Chemical ShiftsHOCOH1010- -13 ppm13 ppm2 2- -2.5 2.5 ppmppm cf. cf. aldehydesaldehydes and ketonesand ketonesAldehydeAldehyde likelikeHCOOH1313C NMR Chemical ShiftsC NMR Chemical ShiftsNot quite Not quite as low field as low field as as aldehydealdehyde or ketoneor ketoneIR SpectroscopyIR SpectroscopyTwo important bands: Two important bands: OO- -H H = 2500= 2500- -3300 cm3300 cm- -1 1, , C=OC=O= 1710 cm= 1710 cm- -1 1ResonanceResonance200 200 ppmppm180 180 ppmppmAcidityAcidity The carboxy group is relatively acidic:The carboxy group is relatively acidic:AcetateAcetateReasons: 1. Carbonyl Reasons: 1. Carbonyl carboncarbon is inductively strongly is inductively strongly electron electron withdrawingwithdrawing, 2. , 2. CarboxylateCarboxylate ion is stabilized by ion is stabilized by resonanceresonanceCompare Compare H2 2- -Propenyl (Propenyl (allylallyl) )CH2H2CB BH H + +p pK Ka a 40 40B+ +Electron withdrawingElectron withdrawing groups groups increaseincrease the acidity (decrease the acidity (decrease p pK Ka a): ): CFCF3 3COOH COOH p pK Ka a 0.23 0.23DistanceDistance affects acidity:affects acidity:COOHCOOHClp pK Ka a4.194.19p pK Ka a3.983.98BasicityBasicityProtonated on the Protonated on the carbonyl oxygencarbonyl oxygen: : Allows for Allows for allylicallylic resonanceresonance1. 1. OxidationOxidation of primary alcohols and of primary alcohols and aldehydesaldehydesWith KMnOWith KMnO4 4; or CrO; or CrO3 3, H, H2 2O; or HNOO; or HNO3;3;or Hor H2 2OO2;2;or Cuor Cu2+2+, or Ag, or Ag+ +. . Recall Recall Cr(VICr(VI) oxidation:) oxidation:PreparationPreparationIn H2O: Hydrate, which oxidizes to acid2. 2. CarbonationCarbonation: Organometallic : Organometallic reagents and carbon dioxidereagents and carbon dioxideExample: Example: Synthetic strategy: Synthetic strategy: RH RH RX RX RMgBrRMgBr RCORCO2 2HH3. 3. NitrileNitrile hydrolysishydrolysisMechanism:Mechanism:TautomerizationCOOHClC NCl1.NaOH, H2O 2. H+, H2O90%CyanohydrinCyanohydrin- -hydrolysis: hydrolysis: - -Hydroxy acidsHydroxy acidsReactionsReactionsNucleophilic substitution occurs Nucleophilic substitution occurs by by additionaddition- -eliminationeliminationLead to carboxylic acid derivatives:Lead to carboxylic acid derivatives:General:General: :NuNuLeaving Leaving groupgroupE E+ +EliminationNucleophilic Substitution by Nucleophilic Substitution by AdditionAddition- - EliminationEliminationTetrahedral Tetrahedral intermediateintermediateAddition:Potential problem: AcidityPotential problem: AcidityAcid or base catalyzedAcid or base catalyzedBase Catalyzed MechanismBase Catalyzed MechanismMust not compete with :Must not compete with :NuNu- -Acid Catalyzed MechanismAcid Catalyzed MechanismSynthesis of Carboxylic Acid Synthesis of Carboxylic Acid DerivativesDerivativesA. A. AlkanoylAlkanoyl HalidesHalides: :RCOOHX=X= Cl, BrCl, Br+ -Cl+ -OHRCOClMore More stablestableLess Less stablestablePoor Poor NuNuBad leaving Bad leaving group, strong group, strong base, good base, good NuNuuphilluphillTherefore use other reagents: Therefore use other reagents: SOClSOCl2 2, PCl, PCl5 5, PBr, PBr3 3SOClSOCl2 2: : Mechanism: Mechanism: First step is to convert the First step is to convert the bad leaving group OH into a good onebad leaving group OH into a good oneGood Good leaving leaving groupgroupSame as ROH Same as ROH ? RClRCl, except addition, except addition- -elimination elimination and not Sand not SNN2 2Then it is additionThen it is addition- -elimination:elimination:PClPCl5 5: :90%90%OOHPCl5OClPCl3OHCl+PBrPBr3 3: :PBrPBr3 3Mechanism:Mechanism:1. 1.2.2.ROOHPBr2BrROOPB