University:
Rutgers University Newark
Course:
CHEM 336 | Organic Chemistry ||
Academic year:

2024
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334

Pages:

60
Author:

Mahitab S.

CHAPTER 17 CARBOXYLIC ACIDS ©2018 Cengage Learning. All Rights Reserved. Chapter Outline • • • • • • • • • (17.1) (17.2) (17.3) (17.4) (17.5) (17.6) (17.7) (17.8) (17.9) Structure Nomenclature Physical properties Acidity Preparation of carboxylic acids Reduction Esterification Conversion to acid chlorides Decarboxylation ©2018 Cengage Learning. All Rights Reserved. Structure of Carboxylic Acids • Functional group: Contains a carbonyl group and a hydroxyl group (-CO2H or -COOH) • General formulas • Aliphatic carboxylic acid – RCOOH • Aromatic carboxylic acid – ArCOOH • α,β-Unsaturated carboxylic acids – RCH2=CH2COOH ©2018 Cengage Learning. All Rights Reserved. Nomenclature of Carboxylic Acids: IUPAC System • Final -e is dropped from the name of the parent alkane, and the suffix -oic acid is added • Chain is numbered beginning with the carbon of the carboxyl group • Common names formic acid and acetic acid are retained ©2018 Cengage Learning. All Rights Reserved. Nomenclature of Carboxylic Acids: IUPAC System • If the compound contains a C=C bond or a C≡C bond, change the infix from -an- to -en- or -yn3 2 I appey I 2 1 3pygmy Eakgicacid • Carboxyl group takes precedence over most other functional groups 65 4 3 2 1 5HydroxyhexonicAcid 65 4 3 2 1 5 oxohetonicAcid ©2018 Cengage Learning. All Rights Reserved. 43 2 I 4 Aminobutonic Aci Nomenclature of Carboxylic Acids: IUPAC System • Dicarboxylic acids are named by adding the suffix -dioic acid to the name of the carbon chain that contains both carboxyl groups ©2018 Cengage Learning. All Rights Reserved. Nomenclature of Carboxylic Acids: IUPAC System 3 2 Cycolohexcycgbdoxylis 2 I dicarboxylic 1,3cyclopentane Acid westartnumb ring from oneposition from cool t carboxylicAcid ©2018 Cengage Learning. All Rights Reserved. Nomenclature of Carboxylic Acids: IUPAC System • Benzoic acid: Simplest aromatic carboxylic acid • Naming derivatives of benzoic acid • Numbers are used to show the location of substituents relative to the carboxyl group h pun Acid 2Hydroxy benzonic µ 1,2Benzenedicarboxylic n 1,4Benzenedicarboxylic Acid • Naming aromatic dicarboxylic acids • The words dicarboxylic acid are added to benzene ©2018 Cengage Learning. All Rights Reserved. Nomenclature of Carboxylic Acids: Common Names • When common names are used, the Greek letters α, β, γ, δ, and so forth are used as prefixes to locate substituents B 4 gI y 4Aminobutonic Acid 3h l za Acid 2 Aminoproponic p • Presence of a ketone carbonyl in a substituted carboxylic acid is indicated by the prefix keto- (Acetyl group: CH3CO- or Ac-) carbonyl and ©2018 Cengage Learning. All Rights Reserved. Group methyl Table 17.1 - Several Aliphatic Carboxylic Acids: Their Common Names and Derivations ©2018 Cengage Learning. All Rights Reserved. Example 17.1 - Naming Carboxylic Acids • Write the IUPAC name for each carboxylic acid 8 7 9 p 65 432 1 I m131 15 p 17 Acid g octadecenoic • Solution a. b. c. d. 2 cyclohexane Hydroxy CarboxylicAcid 3 I 2 2 choloroethanoic 2 Hydroxypropanoic Acid Acid (Z)-9-Octadecenoic acid (oleic acid) trans-2-Hydroxycyclohexanecarboxylic acid (R)-2-Hydroxypropanoic acid [(R)-lactic acid] Chloroacetic acid (IUPAC name: Chloroethanoic acid) ©2018 Cengage Learning. All Rights Reserved. Example • What is the IUPAC name for the following carboxylic acid? so 4 1. x 2. 3. x 4. 5. x 32 Benzoic acid 1-Cyclohexenoic acid 2-Cyclohexenoic acid 1-Cyclohexenecarboxylic acid 2-Cyclohexenecarboxylic acid ©2018 Cengage Learning. All Rights Reserved. COOH Example • What is the IUPAC name for the following carboxylic acid? I 3 4 5 Bromo 4 1. 2. 3. 4. 5. 3 methybenzonic Acid 3-Bromo-4-methylbenzoic acid 4-Methyl-3-bromobenzoic acid Phthalic acid (IUPAC: Benzene-1,2-dicarboxylic acid) 4-Carboxy-2-bromotoluene 5-Carboxy-2-methyl-1-bromobenzene ©2018 Cengage Learning. All Rights Reserved. Example • What is the IUPAC name for the following carboxylic acid? 3 4 g 6 2 1. 2. 3. 4. 5. 2-Propylhexanoic acid hexone propyl 2 Acid 4-Propylhexanoic acid 2-Butylpentanoic acid 4-Carboxyoctane 5-Carboxyoctane ©2018 Cengage Learning. All Rights Reserved. Example • The structure for oleic acid is shown below • What is the IUPAC name of this compound? I 1. 2. 3. 4. 5. x x 2.3 y 6 7 8 9 10 1213 19 cis-Octadecenoic acid (Z)-octadec-9-enoic acid (Z)-octadecyl-9-en-1-oic acid (Z)-octadecen-9-oic acid (Z)-9-octadecylenoic acid ©2018 Cengage Learning. All Rights Reserved. 16 18 Example • Which of the following is not an acyl derivative? 1. 2. 4. 3. 5. IF connected ©2018 Cengage Learning. All Rights Reserved. attached directly Physical Properties of Carboxylic Acids • Carboxylic acids are associated by hydrogen bonding into dimers in liquid and solid states ©2018 Cengage Learning. All Rights Reserved. Physical Properties of Carboxylic Acids • Carboxylic acids have higher boiling points than other types of organic compounds of comparable molecular weight • Result from their polarity and their ability to form very strong intermolecular hydrogen bonds CarboxylicAcids • More soluble in water than alcohols, ethers, aldehydes, and ketones of comparable molecular weight • Result of forming hydrogen bonds with water molecules through both their C=O and OH groups ©2018 Cengage Learning. All Rights Reserved. Table 17.2 - Boiling Points and Solubilities in Water of Selected Carboxylic Acids, Alcohols, and Aldehydes of Comparable Molecular Weight it lesssalable make carbon Adding ©2018 Cengage Learning. All Rights Reserved. Physical Properties of Carboxylic Acids • Solubility in water decreases as molecular weight increases • Hydrophilic carboxyl group increases water solubility • Hydrophobic hydrocarbon chain decreases water solubility • Liquid carboxylic acids from propanoic acid to decanoic acid have extremely foul odors ©2018 Cengage Learning. All Rights Reserved. Example • Why do carboxylic acids boil at higher temperatures than most molecules of the same molecular weight? 1. 2. 3. 4. 5. They have more oxygen atoms than most other molecules They can participate in hydrogen bonding They are polar molecules They have more oxygen atoms than most other molecules, and they can participate in hydrogen bonding They can participate in hydrogen bonding and they are polar molecules ©2018 Cengage Learning. All Rights Reserved. Acidity - Acid Ionization Constants • Carboxylic acids are weak acids • Values of Ka for most unsubstituted aliphatic and aromatic carboxylic acids fall within the range of 10−4 to 10−5 • Greater acidity of carboxylic acids relative to alcohols because of: • Delocalization of the negative charge of the carboxylate anion through resonance • Electron-withdrawing inductive effect of the carbonyl group ©2018 Cengage Learning. All Rights Reserved. Acidity - Acid Ionization Constants EWG ability of electronegative chlorine atoms • Electron-withdrawing stabilizes the anionic charge by electron withdrawal through σ-bonds • Strength of the inductive effect is proportional to the number of chlorine atoms present ©2018 Cengage Learning. All Rights Reserved. Acidity - Acid Ionization Constants • The form of carboxylic acid present in an aqueous solution depends on the pH of the solution ©2018 Cengage Learning. All Rights Reserved. Acidity - Reaction with Bases • Carboxylic acids, whether soluble or insoluble in water, react with NaOH, KOH, and other strong bases to give water-soluble salts • Form water-soluble salts with ammonia and amines ©2018 Cengage Learning. All Rights Reserved. Acidity - Reaction with Bases • React with sodium bicarbonate and sodium carbonate to form water-soluble sodium salts and carbonic acid • Carbonic acid breaks down to carbon dioxide and water • Acid-base properties of carboxylic acids allow an easy separation of carboxylic acids from water-insoluble nonacidic compounds (next page) ©2018 Cengage Learning. All Rights Reserved. Figure 17.1 - Flowchart for the Separation of Benzoic Acid from Benzyl Alcohol (PhCO2H from PhCH2OH) ©2018 Cengage Learning. All Rights Reserved. Example 17.3 - Salts of Carboxylic Acids • Complete each acid-base reaction and name the carboxylic salt formed COO Nat H2o cooNat ©2018 Cengage Learning. All Rights Reserved. CoatH2o Example 17.3 - Solution • Each carboxylic acid is converted to its sodium salt • In (b), carbonic acid is formed: It decomposes to carbon dioxide and water ©2018 Cengage Learning. All Rights Reserved. Example • Rank the following molecules in acidity from least acidic to most acidic 1. 2. 3. 4. 5. A, C, B B, A, C C, B, A B, C, A C, A, B BLACC ©2018 Cengage Learning. All Rights Reserved. Example • Rank the following molecules in acidity from most acidic to least acidic 1. 2. 3. 4. 5. A, C, B, D C, B, D, A B, C, A, D A, B, C, D C, B, A, D C B AD ©2018 Cengage Learning. All Rights Reserved. Example • Chloroacetic acid is a stronger acid than acetic acid • Which is the best explanation? ©2018 Cengage Learning. All Rights Reserved. Example 1. 2. 3. 4. 5. More resonance structures can be drawn for chloroacetic acid than for acetic acid More resonance structures can be drawn for chloroacetate ion than for acetate ion Because of its high electronegativity, chlorine is able to donate electrons to the chloroacetate ion by the inductive effect, thereby stabilizing this ion Because of its high electronegativity, chlorine is able to withdraw electrons from the chloroacetate ion by the inductive effect, thereby stabilizing this ion Chlorine is larger than hydrogen and can better hold a negative charge ©2018 Cengage Learning. All Rights Reserved. Example • p-Chlorobenzoic acid is more acidic than pmethylbenzoic acid 1. 2. True False ©2018 Cengage Learning. All Rights Reserved. Preparation of Carboxylic Acids • Carboxylation of Grignard reagents • Overall conversion of an alkyl/aryl halide to a carboxylic acid • (1) Involves treating a Grignard reagent with carbon dioxide to obtain the magnesium salt of a carboxylic acid • (2) Protonation of the magnesium salt with aqueous acid gives a carboxylic acid ©2018 Cengage Learning. All Rights Reserved. Example • What sequence of reagents will accomplish the following transformation? 1. 4. 2. 5. 3. ©2018 Cengage Learning. All Rights Reserved. Example – Nitrile Hydrolysis (Ch.18) • Determine the product of the following sequence of reactions 1. 2. 4. 3. 5. ©2018 Cengage Learning. All Rights Reserved. Reduction of Carboxylic Acids • Carboxyl group is very resistant to reduction • Not affected by catalytic hydrogenation under conditions that easily reduce (1) aldehydes and ketones to alcohols and (2) alkenes and alkynes to alkanes • Lithium aluminum hydride reduces a carboxyl group to a 1° alcohol: Reduction is carried out in diethyl ether or tetrahydrofuran (Et2O or THF) ©2018 Cengage Learning. All Rights Reserved. Reduction of Carboxylic Acids • Balanced equations for treatment of a carboxylic acid with LiAlH4 to form a tetraalkoxy aluminate ion, followed by its hydrolysis in water • Selective reduction of other functional groups: Carboxyl groups are NOT affected by (1) catalytic hydrogenation under conditions that reduce aldehydes, ketones, alkenes, and alkynes, (2) NaBH4 => one can selectively reduce these functional groups to alcohols or alkanes in the presence of carboxyl groups ©2018 Cengage Learning. All Rights Reserved. Reduction of Carboxylic Acids • Selective catalytic hydrogenation • Selective reduction with NaBH4: aldehyde or ketone carbonyl groups can be reduced selectively in the presence of a carboxyl group using the less reactive NaBH4 ©2018 Cengage Learning. All Rights Reserved. Fischer Esterification • Esters can be prepared by treating a carboxylic acid with an alcohol in the presence of an acid catalyst, commonly H2SO4, ArSO3H, or gaseous HCl • Preparation of an ester in this manner is called Fischer esterification • Acid-catalyzed esterification is reversible Ester • Quantities of both carboxylic acid and alcohol remaining at equilibrium are appreciable ©2018 Cengage Learning. All Rights Reserved. Fischer Esterification • Involves nucleophilic acyl substitution • By careful control of reaction conditions, it is possible to prepare esters in high yield • (1) If the alcohol is inexpensive relative to the carboxylic acid, it can be used in excess to drive the equilibrium to the right • (2) Water can be removed by azeotropic distillation and a Dean-Stark trap (Figure 16.1) ©2018 Cengage Learning. All Rights Reserved. Example 17.4 - Fischer Esterification • Complete the equation for each Fischer esterification reaction one • Solution two Txdot ©2018 Cengage Learning. All Rights Reserved. Synthesis of Methyl Esters Using Diazomethane • Diazomethane (CH2N2) • Potentially explosive, toxic yellow gas • Best represented as a hybrid of two resonance contributing structures • Treating a carboxylic acid with diazomethane in ether solution converts the carboxylic acid to its methyl ester ©2018 Cengage Learning. All Rights Reserved. Synthesis of Methyl Esters Using Diazomethane • Esterification occurs in two steps • Step 1: Deprotonation: Proton transfer to diazomethane gives a carboxylate anion and methyldiazonium cation • Step 2: Bond formation between a nucleophile and an electrophile: Nucleophilic displacement of N2 gives the methyl ester (key step) ©2018 Cengage Learning. All Rights Reserved. Conversion to Acid Chlorides • Acyl halides (acid halides): Functional group containing a carbonyl group bonded to a halogen atom • Among the acyl halides (X = F, Cl, Br), acid chlorides are frequently used in the laboratory and in industrial organic chemistry because of their lower cost and ready availability ©2018 Cengage Learning. All Rights Reserved. Conversion to Acid Chlorides • Acid chlorides are most often prepared by treating a carboxylic acid with thionyl chloride (SOCl2) • Mechanism for this reaction is divided into two steps • Step 1: Reaction with SOCl2 transforms OH, a poor leaving group, into a chlorosulfite group, a good leaving group (key step) ©2018 Cengage Learning. All Rights Reserved. Conversion to Acid Chlorides • Step 2: Nucleophilic attack of chloride ion gives a tetrahedral carbonyl addition intermediate, which collapses to give the acid chloride, SO2, and the chloride ion O R C O O S Cl + Cl - O R C - O O S O Cl Cl A tetrahedral carbonyl addition intermediate ©2018 Cengage Learning. All Rights Reserved. R-C-Cl + SO2 + Cl - Example 17.5 - Making Acid Chlorides • Complete the equation for each reaction MA at Hel 502 mic • Solution ©2018 Cengage Learning. All Rights Reserved. so the Example – Reaction Sequence (incl. Ch.18) • Determine the product of the following sequence of reactions 1. 4. 2. 5. 3. ©2018 Cengage Learning. All Rights Reserved. Decarboxylation (more in Ch.19) • Most carboxylic acids, if heated to a very high temperature, undergo thermal decarboxylation (loss of CO2 from a carboxyl group) • Typical acids are quite resistant to moderate heat and melt or even boil without decarboxylation • Exceptions: Carboxylic acids that have a carbonyl group β to the carboxyl group: undergo decarboxylation readily on mild heating ©2018 Cengage Learning. All Rights Reserved. Decarboxylation: β-Ketoacids • Thermal decarboxylation of a β-ketoacid involves rearrangement of six electrons in a cyclic six-membered transition state • Example: Only one carboxyl group in oxalosuccinic acid, an intermediate in the tricarboxylic acid (TCA) cycle, has a carbonyl in the β-position to it ©2018 Cengage Learning. All Rights Reserved. Decarboxylation: Malonic Acids • Thermal decarboxylation of malonic acid and substituted malonic acids: decarboxylation occurs if there is any carbonyl group at the β-position ©2018 Cengage Learning. All Rights Reserved. Decarboxylation: Malonic Acids • Decarboxylation of malonic acids involves rearrangement of six electrons in a cyclic six-membered transition state • Step 1: Redistribution of six electrons in a cyclic sixmembered transition state gives carbon dioxide and the enol form of a carboxyl group (key step) • Step 2: Keto-enol tautomerism of the enol gives the more stable keto form of the carboxyl group ©2018 Cengage Learning. All Rights Reserved. Example 17.6 - Decarboxylation Reactions • Each of these carboxylic acids undergoes thermal decarboxylation • Draw a structural formula for the enol intermediate and final product formed in each reaction ©2018 Cengage Learning. All Rights Reserved. Example 17.6 - Solution • Carboxylic acids • Enol intermediates and products ©2018 Cengage Learning. All Rights Reserved. Problem 17.24 – Benzil/Benzylic Acid Rearrangement • The reaction of an α-diketone with concentrated NaOH or KOH gives the salt of an α-hydroxyacid • This reaction is given the general name benzil-benzylic acid rearrangement • Propose a mechanism for this reaction ©2018 Cengage Learning. All Rights Reserved. Problem 17.24 – Benzil/Benzylic Acid Rearrangement • Step 1: Addition of hydroxide ion to one of the carbonyl groups forms a tetrahedral carbonyl addition intermediate: Make a bond between a nucleophile and an electrophile (key step) • Step 2: Collapse of the intermediate with simultaneous regeneration of the carbonyl group and migration of a phenyl group gives benzylic acid ©2018 Cengage Learning. All Rights Reserved. Problem 17.24 – Benzil/Benzylic Acid Rearrangement • Step 3: Proton transfer: Take a proton away, or more simply, transfer a proton to form the benzylate anion ©2018 Cengage Learning. All Rights Reserved. Synthesis rt R MI coz 8 R Cor MI EMI Max pka 4 5 Aceticacid R co EM É 3reactions withbases Rcoatt Nant NH R CoENat H2o R CEN Hy R coz not coatH2o Natt coz CarboxylicAcid Reduction g LiAHa i Nasty RAI Helmeted conversionto Acidechloride b mechanism mi In It on rising a rig Son R esterification com Reon E r Rf n r can cane Mechanism m car Hao Decarboxylation Rcare R coat d It d R H rt coz coz a i b a Iko r