Chapter Sixteen

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Chapter Sixteen

• Carboxylic Acids, Esters, and Other Acid
  Derivatives

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• Carboxylic acid An organic compound with
  carboxyl functional group
• Carboxyl group A carbonyl group (CO) with a
  hydroxyl group (OH) bonded to the carbonyl
  carbon atom
• A general structural representation for a
  carboxyl group is shown below

Carbonyl group
Carboxylic acid
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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 always contain the carboxyl
  group on __________ ____.
• 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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IUPAC Rules for Naming Monocarboxylic Acids

• Rule 1 Select the longest carbon chain that
  includes the carbon atom of the carboxyl group as
  the parent chain.
• Rule 2 Name the parent chain by changing the
  -e ending of the corresponding alkane to -oic
  acid.
• Rule 3 Number the parent chain by assigning the
  1 to the carboxyl carbon atom.
• Rule 4 Determine the identity and location of
  any substituents in the usual manner, and append
  this information to the front of the parent chain
  name.

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Naming Rules

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

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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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First Six Unbranched Monocarboxylic Acids
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First Six Unbranched Dicarboxylic Acids
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Aromatic Carboxylic Acids

• Benzoic Acid is the ______________ 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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Common Acids

• Acetic Acid CH3COOH
• Vinegar is 4-8 (v/v) acetic acid solution
• Colorless liquid with sharp odor
• Oxalic acid HOOC-COOH - found in spinach and
  cabbage
• Harmful at high concentrations
• Used to remove rust, bleach straw, and leather
  and ink stains

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Polyfunctional Carboxylic Acids

• PCAs contain at least one or more functional
  groups other than carboxyl group
• PCAs are commonly found in living organisms an
  play an important role in human body
• Occur in many fruits
• Used in over the counter skin care products and
  prescription drugs
• Common types of PCAs
• Unsaturated acids
• Hydroxy acids
• Keto acids

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Unsaturated Acids

• Contain at least one carbon-carbon double bond
  (CC)
• Two types of monounsaturated carboxylic acids
• Trans - unsaturated carboxylic acids
• Cis unsaturated carboxylic acids
• Examples
• Propenoic acid (acrylic acid) used in the
  manufacture of polymeric materials.
• Futenedioic acid - has two forms
• Fumaric acid trans-form
• Maleic acid cis-form

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Hydroxy Acids

• Contain at least one hydroxyl group and are
  naturally present in many foods
• Examples
• Glycolic acid present in juice from sugar cane
  and sugar beets
• Lactic acid Present sour milk, sauerkraut, and
  dill pickles
• Malic acid and tartaric acid occur naturally in
  fruits

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Keto Acids

• Contain a carbonyl (CO) group within a carbon
  chain.
• Example
• Pyruvic acid - simplest keto acid with odor
  resembling that of vinegar (acetic acid) and it
  is also a metabolic acid

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• Metabolic acids Polyfunctional acids formed as
  intermediates of ________________ reactions in
  the human body.
• There are eight such acids that will appear
  repeatedly in the biochemistry chapters
• Metabolic acids are derived from
• Propionic acid, (C3 mono acids) lactic,
  glyceric, and pyruvic acids
• Succinic acid (C4 diacid) fumaric, oxaloacetic,
  and malic acids
• Glutaric acid (C5 diacid) a-ketoglutaric and
  citric acids

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At Room Temperature and Pressure

• Straight chain carboxylic acids with 1-9 carbon
  atoms are liquids and strong odors
• Straight chain carboxylic acids with gt10 C atoms
  are waxy solids with no odor.
• Aromatic and dicarboxylic acids Odorless solids

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Properties of Carboxylic Acids

• Like alcohols, carboxylic acids form ___________
  intermolecular hydrogen bonds.
• Most carboxylic acids exist as ___________.
• Boiling points higher than alkanes of similar MW.
• Small carboxylic acids (1-4 carbons) are soluble
  in water

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Boiling Points
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Synthesis of Carboxylic Acids

• Synthesized from aromatic rings, primary
  alcohols and aldehydes.
• Oxidizing Agents
• K2Cr2O7 / H2SO4
• or
• KMnO4

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 ________ acids
• Stronger acids than alcohols
• In water they dissociate to release ___________
  (H) and form carboxylate ion (RCOO-) --
  equilibrium reactions and equilibrium lies
  towards the left indicating that small amount of
  acid is ionized
• CH3COOH H2O CH3COO H3O
• Neutralized by a base
• CH3COOH NaOH CH3COO Na H2O

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• Monocarboxylic acids release ______ H to form
  carboxylate ion with _______ negative charge
• Dicarboxylic acids release ______ H ions to form
  carboxylate ion with _____ negative charges and
  so on

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• Carboxylic acids are obviously _________.
• Stronger acids than alcohols, but __________ than
  mineral acids.
• Will react with _________ 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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Uses of Carboxylic Acid Salts

• Good antimicrobial and antifungal agents
• Benzoate salts Effective (0.1, m/m) against
  yeast and mold in beverages, jams and jellies,
  etc.
• Sodium sorbate Inhibits mold and yeast in dairy
  products, dried fruits, some meat and fish
  products
• Propionate Used in preservation of baked goods
• Benzoate and sorbate cant be used in yeast
  leavened baked goods as they inhibit mold and
  yeast

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Carboxylic Acids
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Esters

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

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Ester

• In an ester, the _______ in the carboxyl group is
  replaced with an ________ 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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• The name for the alcohol part of the ester
  appears _________ and is _____________ by a
  separate word giving the name for the acid part
  of the ester.
• The name for the alcohol part of the ester is
  simply the name of the R group (alkyl,
  cycloalkyl, or aryl) present in the OR portion
  of the ester.
• The name for the acid part of the ester is
  obtained by dropping the -ic acid ending for
  the acids name and adding the suffix -ate.

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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.