chapter sixteen carboxylic acids, esters, and other acid derivatives
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Chapter 16 | Slide 2 of 39
Fig. 16.1 The three simplest carboxylic acids: methanoic acid, ethanoic acid, and propanoic acid.
Carboxylic Acids
Chapter 16 | Slide 4 of 39
Carboxylic acids contain the carboxyl group on carbon 1.• A carboxyl group is a carbonyl attached to a hydroxyl
• Acts differently than an alcohol or a carbonyl compound
O
CH3 — C—OH = CH3—COOH
carboxyl group
Carboxylic Acids
Chapter 16 | Slide 5 of 39
Formula IUPAC Common alkan -oic acid prefix – ic acid
HCOOH methanoic acid formic acid
CH3COOH ethanoic acid acetic acid
CH3CH2COOH propanoic acid propionic acid
CH3CH2CH2COOH butanoic acid butyric acid
Naming Carboxylic Acids
Chapter 16 | Slide 6 of 39
• Identify longest chain containing the carboxyl group• (IUPAC) Number carboxyl carbon as 1• (Common) Assign , , to carbon atoms adjacent to
carboxyl carbon
CH3
|
CH3 — CH—CH2 —COOHIUPAC 3-methylbutanoic acidCommon -methylbutryic acid
Naming Rules
Chapter 16 | Slide 7 of 39
Aromatic Carboxylic Acids
• Benzoic Acid is the aromatic carboxylic acid• Locates substituents by assigning 1 to the carbon with the
carboxyl group
C
O OH
C
O OH
Cl
C
O OH
CH3
Benzoic acid 3-chlorobenzoic acid
4-methylbenzoic acid
Chapter 16 | Slide 10 of 39
Properties of Carboxylic Acids
• Like alcohols, carboxylic acids form strong intermolecular hydrogen bonds.
• Most carboxylic acids exist as dimers.– Boiling points higher than alkanes of similar MW.– Small carboxylic acids (1-4 carbons) are soluble in
water
H3C
O
O H
H
O
O
CH3
Chapter 16 | Slide 12 of 39
Synthesis of Carboxylic Acids
• Synthesized from aromatic rings, primary alcohols and aldehydes.
Oxidizing agent
R
R OH
R
O
CarboxylicAcid
Chapter 16 | Slide 13 of 39
Oxidation of Aromatic Compounds
• Benzene does not react with KMnO4.
• Alkyl groups on the ring (-R) are readily oxidized though.
• One product for all reactions.
R
+ KMnO4
O
OH
Chapter 16 | Slide 15 of 39
• Oxidation of primary alcohols and aldehydes:
R
OH
CrO3, H3O+
or Na2Cr2O7, H2O, CH3CO2HR
O
OH
R
O
AgNO3NH4OH
H R
O
OH
Chapter 16 | Slide 16 of 39
• Oxidation of alcohols to carboxylic acids.
OH
CrO3, H3O+
O
HO
OH
CrO3, H3O+
O
OH
Chapter 16 | Slide 17 of 39
• Carboxylic acids are weak acids– Stronger acids than alcohols
CH3COOH + H2O CH3COO– + H3O+
• Neutralized by a base
CH3COOH + NaOH CH3COO– Na+ + H2O
Properties
Chapter 16 | Slide 18 of 39
• Carboxylic acids are obviously acidic.• Stronger acids than alcohols, but weaker than mineral
acids.• Will react with NaOH to give metal carboxylates.• There is a large range of acidities depending on the
substituents on a carboxylic acid.
O
R OH
+ NaOH
O
R O-Na+
+ H2O
Chapter 16 | Slide 19 of 39
Carboxylate Ions
• The conjugate base of a carboxylic acid– Formed when a carboxylic acid loses a proton– Named by dropping the -ic acid ending and replacing it
with –ate
• CH3CH2COO- Propionate
• CH3COO- Ethanoate (Acetate)
• CH3CH2CH2COO- Butanoate
Chapter 16 | Slide 20 of 39
Carboxylate Salts
• An ionic compound in which the negative ion is a carboxylate ion– Naming: the positive ion is named first, followed by a
separate word giving the name of the negative ion– Converted back to a carboxylic acid by the addition of a
strong acid
• CH3CH2COO-Na+ Sodium Propionate• CH3COO-K+ Potassium Ethanoate• CH3CH2CH2COO-Li+ Lithium Butanoate
Chapter 16 | Slide 23 of 39
In an ester, the H in the carboxyl group is replaced with an alkyl group
O
CH3 — C—O —CH3 = CH3—COO —CH3
ester group
Sulfur analogs of esters are called thioesters (sulfur replaces the hydroxyl oxygen)
Ester
Chapter 16 | Slide 24 of 39
• Name the alkyl from the alcohol –O-• Name the acid with the C=O with –ate
acid alcohol
O
methyl
CH3 — C—O —CH3
Ethanoate methyl ethanoate (IUPAC)
(acetate) methyl acetate (common)
Naming Esters
Chapter 16 | Slide 27 of 39
• Reaction of a carboxylic acid and alcohol• Acid catalyst
O H+
CH3 — C—OH + HO—CH2CH3
O
CH3 — C—O—CH2CH3 + H2O
Esterification: Preparation of Esters
Chapter 16 | Slide 28 of 39
• Esters react with water and acid catalyst• Split into carboxylic acid and alcohol
O H+
H — C—O—CH2CH3 + H2O
O H — C—OH + HO—CH2CH3
Hydrolysis: Breaking Up Esters
Chapter 16 | Slide 30 of 39
• Esters react with bases • Produce the salt of the carboxylic acid and alcohol
O H2O
CH3C—OCH2CH3 + NaOH
O
CH3C—O– Na+ + HOCH2CH3
salt of carboxylic acid
• Saponification reactions produce soaps
Saponification
Chapter 16 | Slide 32 of 39
• The following figure represents soap.
• Which end of the anion is hydrophobic?
Chapter 16 | Slide 38 of 39
The C2 dicarboxylic acid, oxalic acid, contributes to the tart taste of rhubarb stalks.
Chapter 16 | Slide 39 of 39
Polyfunctional Carboxylic Acids
• Carboxylic acids that contain one or more additional functional groups– Unsaturated acids
• Contain a multiple bond
– Hydroxy acids• Contains an additional hydroxyl group
– Keto acids• Contains an additional carbonyl group
• Many monoacids and polyfunctional carboxylic acids are intermediates in metabolic reactions