Chapter 20: Carboxylic Acids And Nitriles
Chapter 20: Carboxylic Acids and Nitriles20.1 Naming Carboxylic Acids (please read)In general, the same for alkanes; replace the terminal-e of the alkane name with -oic acidThe carboxyl carbon atom is C1Compounds with -CO2 H group on a ring are namedusing the suffix -carboxylic acidThe -CO2H carbon is not numbered in these casesMany non-systematic names: Table 20.117420.1 Naming Nitriles (please read)If derived from open-chain alkanes, replace the terminal-e of the alkane name -nitrile as a suffixThe nitrile carbon numbered C1Complex nitriles are named as derivatives of carboxylicacids. Replace -ic acid or -oic acid ending with-onitrile17588
20.2 Structure and properties of carboxylic acidsThe carboxylic acid function group contains both ahydrogen bond donor (-OH) and a hydrogen bondacceptor (C O)Carboxylic acids exist as hydrogen bonded dimersH-bondaceptorOH3CCOH-bonddonorHH OOH3C CC CH3OO Hacetic acid17620.3 Dissociation of Carboxylic acidsAcidity Constant and pKaCarboxylic acids react with base to give carboxylate saltsORCOOH NaOHRCNaO H2OBronsted Acidity (Chapter 2.7):Carboxylic acids transfer a proton to water to give H3O andcarboxylate anions, RCO2 ORCKa OOH H2O[RCO2-] [H3O ][RCO2H]typically 10-5for carboxylic acidRCO H3OpKa - log Katypically 5 forcarboxylic acid17789
pKaCH3CH3 50-60CH3CH2OH16PhOH10CH3CO2H4.75HCl-7Increasing acidityThe negative charge of a carboxylate is resonance stabilizedH2OH3C-H2C-OHH2OOH3CCH3C-H2C-O H3OpKa 16OHOH3C COOpKa 4.7CH3CO!O!COOH3CC H3OO4 electron delocalizedover three p-prbitalsC-O bond length of acarboxylates are the same17820.4 Substituent Effects on AciditySubstituents on the α-carbon influence the pKa of carboxylicacids largely through inductive effects. Electronwithdrawing groups increase the acidity (lower pKa) andelectron-donating groups decrease the acidity (higher pKa)also seeTable 20.4Inductive effects work through σ-bonds, and the effect falls offdramatically with distance17990
20.5 Substituent Effects in Substituted Benzoic AcidsAn aromatic or substituted aromatic rings has dramatically lessinfluence on the acidity of benzoic acids, pKa 4.2 (whencompared to acetic acid) than in the case of phenolsOHRpKa 16CO2HH3C-CO2HH3CH2C-OHRR H, pKa 9.9Cl9.4NO27.1CH310.2OCH3 10.2pKa 4.75R H, pKa 4.2Cl4.0NO23.4CH34.3OCH34.5The charge of the carboxylate ion cannot be delocalize intothe aromatic ringElectron-donating groups decrease the acidityElectron-withdrawing groups increase the acidity18020.6 Preparation of carboxylic acids1. Benzoic acids are prepared from the oxidation of alkylbenzene with KMnO4 (Chapter 16.10)CH2CH3CH3CO2HKMnO4O2NO2NAlkyl benzene2. Oxidation of primary alcohols with chromic acid (CrO3/HCl)(Chapter 17.18)3. Oxidation of aldehydes with chromic acid or Ag2O(Chapter 19.3)CrO3/HClOHCO2H1 alcoholCHOAldehydeCrO3/HCl-orAg2OCO2H18191
20.6 Preparation of carboxylic acids4. Acid or basic hydrolysis of a nitrile (mechanism, Fig. 20.4)cyanide ion is an excellent nucleophile and will react with1 and 2 alkyl halides and tosylates to give nitriles. Thisreaction add one 4BrNaC!NC!NDMSOPhO. . . and don’t forgetONaC!NH3O HO CNH3O -orNaOHH3CH2CH2CH2C-CO2HC5H3O CO2H-orNaOH PhOHO CO2H18220.6 Preparation of carboxylic acids5. Carboxylation of Grignard reagentsReaction of a Grignard reagent with CO2 gives a carboxylicacidOBr Mg(0)MgBrCO2CMgBrH3O OOCOHOCO18392
20.7 Reactions of carboxylic acids: an overviewObase[H]HDeprotonation(chapters 20.3 - 20.5)OH HHOHReduction(chapters 17.5 & 20.8)OHOHOROHα-Substitution(chapter 22)OHYNucleophilic acylsubstitution (chapter 21)18420.8Reductions of carboxylic acidsCarboxylic acids are reduced to primary alcohols by LiAlH4(Chapter 17.5) and borane (BH3) but not by NaBH4R-CO2Ha. LiAlH4, THFb. H3O RCH2OHLithium aluminium hydride will also reduce ketones, aldehydesesters, nitriles, amides, acid chlorides alkyl halides,epoxides and nitro groupsBorane reacts most rapidly with carboxylic acids to give primaryalcohols and it is possible to reduce carboxylic acids inthe presence of some other functional groupsCO2HO2Na. BH3 , THFb. H3O OHO2N18593
20.9 Chemistry of Nitriles: Preparation of nitriles1. Reaction of cyanide ion with 1 and 2 alkyl halides- this isan SN2 reaction.2. Cyanohydrins- reaction of cyanide ion with ketones andaldehydes (Chapter 19.7)3. Dehydration of primary amides with POCl3 or SOCl2SOCl2 -orPOCl3OCRNH2Rbenzene, 80 CCDehydration: formal lossof H2O from the substrateNnitrilePrimary amideMechanism (p. 751, please read): the carbonyl oxygen of anamide is nucleophilic, and can react with electrophilesORCA very important resonance form of anamide, which contributes significantlyto their properties and ONH2ROO- HClRCSCSClHNHClCl- SO2,- Cl -NHR C N H- HClClR C N20.9 Chemistry of Nitriles: Reactions of NitrilesThe C N bond has a large dipole moment like carbonyls,making the carbon a potential site for nucleophilic attackO! C! aldehydes& ketonesµ 2.8 DOCNuOCH-ANuOHC:NuN!-NNNNCCCCC NuRnitriles! µ 3.9 DR:NuRRNuNHH-ACRNuNu:NuNuRC NuNuOH3O -orHORNH2H-ACRNu18794
1. Hydrolysis of nitriles to carboxylic acids and amides:Nitriles are hydrolyzed in either aqueous acid or aqueousbase to give carboxylic acids. The corresponding primaryamide is an intermediate in the reaction.Mechanism of the base-promoted reaction (Figure 20.4)Please try the acid-promoted mechanism1882. Reduction of nitriles to primary aminesNitriles can be reduced by LiAlH4 or BH3 (but not NaBH4 )to give primary aminesHR CNLiAlH4RetherNC2NC HRHHHNH2C HRHH3O Reduction of a nitrile with Diisobutylaluminium hydride(DIBAH) give an imine, which easily hydrolyzes to thealdehyde (not in book)HR CNAl(iBu)2DIBAHtolueneRNCH3O HNHCRHROCH18995
3. Reaction of nitriles with Grignard reagents: general methodfor the preparation of ketonesH3C MgBrR CMgBrTHFNRNCNHCRCH3H3O CH3ROCCH3Must consider functional group compatibility; there is wideflexibility in the choice of Grignard reagents.Summary:primary aminesCH2NH2CHOaldehydesLiAlH4BrDIBAHOC!NNa -CNMgBrketonesSN2H3O CO2H190carboxylic acids20.10 Spectroscopy of Carboxylic Acids and NitrilesInfrared SpectroscopyCarboxylic acids:Very broad O-H absorption between 2500 - 3300 cm 1Strong C O absorption bond between 1710 - 1760 cm 1Usually broader than the O-H absorption of an alcoholOcarboxylic acidHalcohol19196
Nitriles show an sharp C N absorption near 2250 cm 1 foralkyl nitriles and 2230 cm 1 for aromatic and conjugatednitriles (highly diagnostic)C NH3CH2CH2C C N1921HNMRThe -CO2H proton is a broad singlet near δ 12When D2O is added to the sample the -CO2 H proton is replacedby D causing the resonance to disappear (same foralcohols)-CO2H19397
The nitrile function group is invisible in the proton NMR.The effect of a nitrile on the chemical shift of the protons onthe α-carbon is similar to that of a ketone.H3CH2CH2C C Nδ 2.3 (2H, t)1.7 (2H, m)1.1 (3H, t)19413CNMRThe chemical shift of the carbonyl carbon in the 13C spectrum isin the range of 165-185. This range is distinct fromthe aldehyde and ketone range ( 190 - 220)The chemical shift of the nitrile carbon in the 13C spectrum isin the range of 115-130 (significant overlap with thearomatic region).133.2129.3128.5127.3Ph-H2C-CO2HH3CH2CH2C C N19.3,19.041.113.3CDCl3178.2CDCl3119.8TMS19598
C10H11N3.72(1H, t, J 7.1)7.3(5H, m)1.92(2H, dt, J 7.4, 7.1)1.06(3H, t, J 9699
Lithium aluminium hydride will also reduce ketones, aldehydes esters, nitriles, amides, acid chlorides alkyl halides, epoxides and nitro groups Borane reacts most rapidly with carboxylic acids to give primary alcohols and it is possible to reduce carboxylic acids in the presence of some oth
hydrogen bonds, their boiling points are usually higher than those of other molecules of the same molecular weight (MW). Low-MW carboxylic acids are generally liquids at room temp. (often, they are somewhat oily); higher-MW carboxylic acids are generally waxy solids. Carboxylic acids
The acylating reagents: carboxylic acid anhydride, acid chlorides, carboxylic acids, esters, thioesters. Classification of poly- and heterofunctional compounds. Polyalcohols, dihydric phenols, dicarboxylic acids, amino alcohols, amino phenols, hy-droxy-acids, oxo-acids (aldehyde and keto acids). Examples. Acid-base prop-erties.
10 tThe carboxyl group is the parent group of a family of compounds called acyl compounds or carboxylic acid derivatives tEsters are named from the corresponding carboxylic acid and alcohol from which the ester would be made lThe alcohol portion is named first and has the ending -yl lThe carboxylic acid is na
UNIT 12 ALDEHYDES KETONES AND CARBOXYLIC ACIDS 1) What are aldehydes ? 1 Aldehydes are the organic compounds containing carbonyl group,linked with one hydrogen and one alkyl /aryl group. 2) What are carboxylic acids? 1 Carboxylic acids are the organic compounds containing carboxyl(-COOH) group/s 3) Between aldehyde and ketones which one is .
Ch21 Carboxylic acid Derivatives(landscape).docx Page 1 Carboxylic acid Derivatives Carboxylic acid derivatives are described as compounds that can be converted to carboxylic acids via simple acidic or basic hydrolysis. The most important acid derivatives are esters, amides and nitriles, although acid halides and anhydrides are also derivatives (really activated forms of a File Size: 2MB
Part One: Heir of Ash Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26 Chapter 27 Chapter 28 Chapter 29 Chapter 30 .
Properties of Acids and Bases Return to the Table of contents Slide 5 / 208 What is an Acid? Acids release hydrogen ions into solutions Acids neutralize bases in a neutralization reaction. Acids corrode active metals. Acids turn blue litmus to red. Acids taste sour. Properties of Acids Slide 6 / 208 Properties
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