Carboxylic Acid Nomenclature

© 2013 Pearson Education, Inc.Chapter 202 Introduction  The functional group of carboxylic acids consists of a C═O with —OH bonded to the same carbon.  Carboxyl group is usually written —COOH.  Aliphatic acids have an alkyl group bonded to —COOH.  Aromatic acids have an aryl group.  Fatty acids are long-chain aliphatic acids.

Table 18.1 Systematic Name O HCOH O CH 3 COH O CH 3 (CH 2 ) 16 COH methanoic acid ethanoic acid octadecanoic acid Systematic IUPAC names replace "-e" ending of alkane with "oic acid"

Table 18.1 Systematic NameCommon Name methanoic acidformic acid ethanoic acidacetic acid octadecanoic acidstearic acid Common names are based on natural origin rather than structure. O HCOH O CH 3 COH O CH 3 (CH 2 ) 16 COH

Table 18.1 Systematic NameCommon Name 2-hydroxypropanoic acidlactic acid (Z)-9-octadecenoic acid or (Z)-octadec-9-enoic acid oleic acid O CH 3 CHCOH OH O (CH 2 ) 7 COH C C HH CH 3 (CH 2 ) 7

© 2013 Pearson Education, Inc.Chapter 206 Aromatic Acids  Aromatic acids are named as derivatives of benzoic acid.  Ortho-, meta-, and para- prefixes are used to specify the location of a second substituent.  Numbers are used to specify locations when more than two substituents are present.

© 2013 Pearson Education, Inc.Chapter 207 Structure of the Carboxyl Group  The sp 2 hybrid carbonyl carbon atom is planar, with nearly trigonal bond angles.  The O—H bond also lies in this plane, eclipsed with the C═O bond.  The sp 3 oxygen has a C—O—H angle of 106°.

© 2013 Pearson Education, Inc.Chapter 208 Boiling Points  Carboxylic acids boil at considerably higher temperatures than do alcohols, ketones, or aldehydes of similar molecular weights.  The high boiling points of carboxylic acids result from formation of a stable, hydrogen-bonded dimer.

Carboxylic acids are similar to alcohols in respect to their solubility in water. They form hydrogen bonds to water. Solubility in Water H 3 CC OH O O H O H H H

© 2013 Pearson Education, Inc.Chapter 2010 Solubility  Water solubility decreases with the length of the carbon chain.  Acids with more than 10 carbon atoms are nearly insoluble in water.  Very soluble in alcohols.  Also soluble in relatively nonpolar solvents like chloroform because the hydrogen bonds of the dimer are not disrupted by the nonpolar solvent.

Acidity of Carboxylic Acids Most carboxylic acids have a pK a close to 5.

But carboxylic acids are far more acidic than alcohols. Carboxylic Acids are Weak Acids CH 3 COH O CH 3 CH 2 OH pK a = 4.7pK a = 16

© 2013 Pearson Education, Inc.Chapter 2013 Energy Diagram of Carboxylic Acids and Alcohols

© 2013 Pearson Education, Inc.Chapter 2014 Acetate Ion Structure  Each oxygen atom bears half of the negative charge.  The delocalization of the negative charge over the two oxygens makes the acetate ion more stable than an alkoxide ion.

© 2013 Pearson Education, Inc.Chapter 2015 Substituent Effects on Acidity   The magnitude of a substituent effect depends on its distance from the carboxyl group.

© 2013 Pearson Education, Inc.Chapter 2016 Aromatic Carboxylic Acids  Electron-withdrawing groups enhance the acid strength, and electron-donating groups decrease the acid strength.  Effects are strongest for substituents in the ortho and para positions.

Hybridization Effect pKapKa COH O H2CH2C CH COH O O HC C sp 2 -hybridized carbon is more electron- withdrawing than sp 3, and sp is more electron-withdrawing than sp 2.

Salts of Carboxylic Acids Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

© 2013 Pearson Education, Inc.Chapter 2019 Deprotonation of Carboxylic Acids  The hydroxide ion completely deprotonates the acid to form the carboxylate salt.

© 2013 Pearson Education, Inc.Chapter 2020 Protonation of Carboxylic Acids Salts  Adding a strong acid, like HCl, regenerates the carboxylic acid.

© 2013 Pearson Education, Inc.Chapter 2021 Naming Carboxylic Acid Salts  First name the cation.  Then name the anion by replacing the -ic acid with -ate.

© 2013 Pearson Education, Inc.Chapter 2022 Properties of Acid Salts  Usually solids with no odor.  Carboxylate salts of Na +, K +, Li +, and NH 4 + are soluble in water.  Soap is the soluble sodium salt of a long-chain fatty acid.  Salts can be formed by the reaction of an acid with NaHCO 3, releasing CO 2.

© 2013 Pearson Education, Inc.Chapter 2023 Basic Hydrolysis of Fats and Oils The basic hydrolysis of fat and oils produces soap (this reaction is known as saponification).

Unbranched carboxylic acids with carbons give carboxylate salts that form micelles in water. Micelles O ONa sodium stearate (sodium octadecanoate) CH 3 (CH 2 ) 16 CO O Na + –

Micelles O ONa polar nonpolar

Micelles O ONa polar nonpolar Sodium stearate has a polar end (the carboxylate end) and a nonpolar "tail“. The polar end is hydrophilic ("water-loving”). The nonpolar tail is hydrophobic ("water-hating”). In water, many stearate ions cluster together to form spherical aggregates; carboxylate ions are on the outside and nonpolar tails on the inside.

Figure 18.5: A micelle

Micelles The interior of the micelle is nonpolar and has the capacity to dissolve nonpolar substances. Soaps clean because they form micelles, which are dispersed in water. Grease (not ordinarily soluble in water) dissolves in the interior of the micelle and is washed away with the dispersed micelle.

Dicarboxylic Acids

One carboxyl group acts as an electron- withdrawing group toward the other; effect decreases with increasing separation. Oxalic acid Malonic acid Heptanedioic acid COH O HOC O pKapKa HOCCH 2 COH OO HOC(CH 2 ) 5 COH OO

side-chain oxidation of alkylbenzenes (Section 11.12) oxidation of primary alcohols (Section 15.9) oxidation of aldehydes (Section 17.15) Synthesis of Carboxylic Acids: Review

© 2013 Pearson Education, Inc.Chapter 2032 Side Chain Oxidation of Alkylbenzenes

© 2013 Pearson Education, Inc.Chapter 2033 Oxidation of Primary Alcohol to Carboxylic Acids  Primary alcohols and aldehydes are commonly oxidized to acids by chromic acid (H 2 CrO 4 formed from Na 2 Cr 2 O 7 and H 2 SO 4 ).  Potassium permanganate is occasionally used, but the yields are often lower.

© 2013 Pearson Education, Inc. Chapter Oxidation of Aldehydes Aldehydes are easily oxidized to carboxylic acids.

© 2013 Pearson Education, Inc.Chapter 2035 Cleavage of Alkenes Using KMnO 4  Warm, concentrated permanganate solutions oxidize the glycols, cleaving the central C ═ C bond.  Depending on the substitution of the original double bond, ketones or acids may result.

© 2013 Pearson Education, Inc.Chapter 2036 Alkyne Cleavage Using Ozone or KMnO 4  With alkynes, either ozonolysis or a vigorous permanganate oxidation cleaves the triple bond to give carboxylic acids.

Synthesis of Carboxylic Acids by the Carboxylation of Grignard Reagents

© 2013 Pearson Education, Inc.Chapter 2038 Carboxylation of Grignard Reagents  Grignard reagents react with CO 2 to produce, after protonation, a carboxylic acid.  This reaction is sometimes called “CO 2 insertion,” and it increases the number of carbons in the molecule by one.

Example: Alkyl Halide CH 3 CHCH 2 CH 3 (76-86%) 1. Mg, diethyl ether 2. CO 2 3. H 3 O + CH 3 CHCH 2 CH 3 ClCO 2 H 2-methylbutanoic acid

Example: Aryl Halide (82%) 1. Mg, diethyl ether 2. CO 2 3. H 3 O + CH 3 CO2HCO2H Br CH 3

Synthesis of Carboxylic Acids by the Preparation and Hydrolysis of Nitriles

© 2013 Pearson Education, Inc.Chapter 2042 Hydrolysis of Nitriles  Basic or acidic hydrolysis of a nitrile (—CN) produces a carboxylic acid.  The overall reaction, starting from the alkyl halide, adds an extra carbon to the molecule.  A limitation is that the halide must be reactive toward substitution by S N 2 mechanism.

Example NaCN DMSO (92%) CH 2 ClCH 2 CN (77%) H2OH2O H 2 SO 4 heat CH 2 COH O

Example: Dicarboxylic Acid BrCH 2 CH 2 CH 2 Br NaCN H2OH2O (77-86%)NCCH 2 CH 2 CH 2 CN H 2 O, HCl heat (83-85%) HOCCH 2 CH 2 CH 2 COH OO

via Cyanohydrin 1. NaCN 2. H + CH 3 CCH 2 CH 2 CH 3 O OH CN (60% from 2-pentanone) H2OH2O HCl, heat CH 3 CCH 2 CH 2 CH 3 OH CO2HCO2H

Reactions of Carboxylic Acids: A Review and a Preview Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Reduction with LiAlH 4 (Section 15.3) Formation of acyl chlorides (Section 12.7) Esterification (Section 15.8) Reactions already discussed Reactions of Carboxylic Acids

© 2013 Pearson Education, Inc.Chapter 2048 LiAlH 4 Reduction of Carboxylic Acids  LiAlH 4 reduces carboxylic acids to primary alcohols.

© 2013 Pearson Education, Inc.Chapter 2049 Synthesis of Acid Chlorides  The best reagents for converting carboxylic acids to acid chlorides are thionyl chloride (SOCl 2 ) and oxalyl chloride (COCl 2 ).  They form gaseous by-products that do not contaminate the product.

© 2013 Pearson Education, Inc.Chapter 2050 Mechanism of Acid Chloride Formation Step 1 Step 2 Step 3

© 2013 Pearson Education, Inc.Chapter 2051 Fischer Esterification  Reaction of a carboxylic acid with an alcohol under acidic conditions produces an ester.  Reaction is an equilibrium; the yield of ester is not high.  To drive the equilibrium toward the formation of products, use a large excess of alcohol.

© 2013 Pearson Education, Inc.Chapter 2052 Mechanism of the Fischer Esterification  Step 1:  The carbonyl oxygen is protonated to activate the carbon toward nucleophilic attack.  The alcohol attacks the carbonyl carbon.  Deprotonation of the intermediate produces the ester hydrate.

© 2013 Pearson Education, Inc.Chapter 2053 Mechanism of the Fischer Esterification (Continued)  Step 2:  Protonation of one of the hydroxide groups creates a good leaving group.  Water leaves.  Deprotonation of the intermediate produces the ester.

Protonation of carbonyl group activates carbonyl oxygen. Nucleophilic addition of alcohol to carbonyl group forms tetrahedral intermediate. Elimination of water from tetrahedral intermediate restores carbonyl group. Key Features of Mechanism

Intramolecular Ester Formation: Lactones

Lactones are cyclic esters. Formed by intramolecular esterification in a compound that contains a hydroxyl group and a carboxylic acid function Lactones

Examples IUPAC nomenclature: replace the -oic acid ending of the carboxylic acid by –olide. Identify the oxygenated carbon by number. HOCH 2 CH 2 CH 2 COH O O O +H2OH2O 4-hydroxybutanoic acid4-butanolide

Examples HOCH 2 CH 2 CH 2 COH O O O +H2OH2O 4-hydroxybutanoic acid4-butanolide HOCH 2 CH 2 CH 2 CH 2 COH O O O + H2OH2O 5-hydroxypentanoic acid 5-pentanolide

Common names O O O O  -butyrolactone  -valerolactone        Ring size is designated by Greek letter corresponding to oxygenated carbon A  lactone has a five-membered ring. A  lactone has a six-membered ring.

Reactions designed to give hydroxy acids often yield the corresponding lactone, especially if the resulting ring is 5- or 6-membered. Lactones

Example 5-hexanolide (78%) O H3CH3C O CH 3 CCH 2 CH 2 CH 2 COH OO 1. NaBH 4 2. H 2 O, H + via: CH 3 CHCH 2 CH 2 CH 2 COH O OHOHOHOH

Decarboxylation of Malonic Acid and Related Compounds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Decarboxylation of Carboxylic Acids Simple carboxylic acids do not decarboxylate readily. RH + CO 2 RCOH O But malonic acid does. 150°C CH 3 COH O + CO 2 HOCCH 2 COH OO

O HO O O HH H Mechanism of Decarboxylation of Malonic Acid This compound is the enol form of acetic acid. O O OHHO HH H H OH HO + C O O One carboxyl group assists the loss of the other.

Mechanism of Decarboxylation of Malonic Acid One carboxyl group assists the loss of the other. HOCCH 3 O These hydrogens play no role. H H OH HO + C O O O O O HH H O O OHHO HH

R Mechanism of Decarboxylation of Malonic Acid One carboxyl group assists the loss of the other. HOCCHR' O Groups other than H may be present. R R’ OH HO + C O O O O O RR’ H O O OHHO RR’

185°C Decarboxylation is a general reaction for 1,3-dicarboxylic acids 160°C CO 2 H H (74%) CH(CO 2 H) 2 (96-99%) CH 2 CO 2 H

Mechanism of Decarboxylation of Malonic Acid One carboxyl group assists the loss of the other. This OH group plays no role. R R’ OH HO + C O O O O O RR’ H O O OHHO RR’ R HOCCHR' O

Mechanism of Decarboxylation of Malonic Acid O O OHR" RR' R C O O One carboxyl group assists the loss of the other. Groups other than OH may be present. R"CCHR' O R O O O RR' H R" R' OH + R"

Mechanism of Decarboxylation of Malonic Acid O O OHR" RR' This kind of compound is called a  -keto acid.   R"CCHR' O R Decarboxylation of a  -keto acid gives a ketone.

Decarboxylation of a  -Keto Acid C CH 3 C O CH 3 CO 2 H 25°C CO 2 C CH 3 C O CH 3 H +

© 2013 Pearson Education, Inc.Chapter 2072 Some Important Acids  Acetic acid is in vinegar and other foods, used industrially as a solvent, catalyst, and reagent for synthesis.  Fatty acids from fats and oils.  Benzoic acid is found in drugs and preservatives.  Adipic acid is used to make nylon 66.  Phthalic acid is used to make polyesters.

Spectroscopic Analysis of Carboxylic Acids

© 2013 Pearson Education, Inc.Chapter 2074 IR Bands of Carboxylic Acids  There will be two features in the IR spectrum of a carboxylic acid: the intense carbonyl stretching absorption (1710 cm –1 ) and the OH absorption (2500–3500 cm –1 ).  Conjugation lowers the frequency of the C═O band.

© 2013 Pearson Education, Inc.Chapter 2075 IR Spectroscopy

© 2013 Pearson Education, Inc.Chapter 2076 NMR of Carboxylic Acids  Carboxylic acid protons are the most deshielded protons we have encountered, absorbing between  10 and  13.  The protons on the  carbon atom absorb between  2.0 and  2.5.

© 2013 Pearson Education, Inc.Chapter 2077 NMR Spectroscopy

13 C NMR Carbonyl carbon is at low field (  ppm), but not as deshielded as the carbonyl carbon of an aldehyde or ketone (  ppm).

Aliphatic carboxylic acids undergo a variety of fragmentations. Aromatic carboxylic acids first form acylium ions, which then lose CO. Mass Spectrometry ArCOH O ArCOH + O ArC O + Ar +