Chapter Sixteen

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Chapter Sixteen

• Carboxylic Acids, Esters, and Other Acid
  Derivatives

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Carboxylic Acids

• Fig. 16.1
• The three simplest carboxylic acids methanoic
  acid, ethanoic acid, and propanoic acid.

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Carboxylic Acids

• Fig. 16.2
• Benzoic acid molecule

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Carboxylic Acids

• 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 COH CH3COOH
• carboxyl group

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Naming Carboxylic Acids

• 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

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Naming Rules

• Identify longest chain containing the carboxyl
  group
• (IUPAC) Number carboxyl carbon as 1
• (Common) Assign ?, ?, g to carbon atoms adjacent
  to carboxyl carbon
• CH3
• CH3 CHCH2 COOH
• IUPAC 3-methylbutanoic acid
• Common ?-methylbutryic acid

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Aromatic Carboxylic Acids

• Benzoic Acid is the aromatic carboxylic acid
• Locates substituents by assigning 1 to the carbon
  with the carboxyl group

3-chlorobenzoic acid
Benzoic acid
4-methylbenzoic acid
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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

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Synthesis of Carboxylic Acids

• Synthesized from aromatic rings, primary
  alcohols and aldehydes.

Carboxylic Acid
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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.

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Oxidation of Aromatic Compoundswith KMnO4
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• Oxidation of primary alcohols and aldehydes

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• Oxidation of alcohols to carboxylic acids.

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Properties

• Carboxylic acids are weak acids
• Stronger acids than alcohols
• CH3COOH H2O CH3COO H3O
• Neutralized by a base
• CH3COOH NaOH CH3COO Na H2O

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• 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.

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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

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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

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Carboxylic Acids

• Table 16.3

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Esters

• Fig. 16.12
• Methyl and ethyl esters of acetic acid.

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Ester

• In an ester, the H in the carboxyl group is
  replaced with an alkyl group
• O
• ??
• CH3 CO CH3 CH3COO CH3
• ester group
• Sulfur analogs of esters are called thioesters
  (sulfur replaces the hydroxyl oxygen)

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Naming Esters

• Name the alkyl from the alcohol O-
• Name the acid with the CO with ate
• acid alcohol
• O
• ?? methyl
• CH3 CO CH3
• Ethanoate methyl ethanoate (IUPAC)
• (acetate) methyl acetate (common)

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Esters
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Esterification Preparation of Esters

• Reaction of a carboxylic acid and alcohol
• Acid catalyst
• O
• ?? H
• CH3 COH HOCH2CH3
• O
• ??
• CH3 COCH2CH3 H2O

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Hydrolysis Breaking Up Esters

• Esters react with water and acid catalyst
• Split into carboxylic acid and alcohol
• O
• ?? H
• H COCH2CH3 H2O
• O
• ??
• H COH HOCH2CH3

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Hydrolysis
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Saponification

• Esters react with bases
• Produce the salt of the carboxylic acid and
  alcohol
• O
• ?? H2O
• CH3COCH2CH3 NaOH
• O
• ??
• CH3CO Na HOCH2CH3
• salt of carboxylic acid
• Saponification reactions produce soaps

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Soaps

• Carboxylate salts

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• The following figure represents soap.
• Which end of the anion is hydrophobic?

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• How does soap interact with grease?

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Dicarboxylic Acids
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The C2 dicarboxylic acid, oxalic acid,
contributes to the tart taste of rhubarb stalks.
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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