Chapter 11 Carboxylic Anhydrides, Esters, and Amides

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Chapter 11 Carboxylic Anhydrides, Esters, and
Amides
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Carboxyl Derivatives

• In this chapter, we study three classes of
  compounds derived from carboxylic acids
  anhydrides, esters, and amides.
• Each is related to a carboxyl group by loss of
  H2O.

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Anhydrides

• The functional group of an anhydride is two
  carbonyl groups bonded to the same oxygen.
• The anhydride may be symmetrical (from two
  identical acyl groups), or mixed (from two
  different acyl groups).
• To name an anhydride, drop the word "acid" from
  the name of the carboxylic acid from which the
  anhydride is derived and add the word "anhydride.

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Examples
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Esters

• The functional group of an ester is a carbonyl
  group bonded to an -OR group. R may be alkyl or
  aryl.
• Both IUPAC and common names of esters are derived
  from the names of the parent carboxylic acids.
• Name the alkyl or aryl group bonded to oxygen
  first, followed by the name of the acid replace
  the suffix -ic acid by -ate.
• A cyclic ester is called a lactone.

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Examples
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Amides

• The functional group of an amide is a carbonyl
  group bonded to a nitrogen atom.
• To name an amide, drop the suffix -oic acid from
  the IUPAC name of the parent acid, or -ic acid
  from its common name, and add -amide.

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Examples

• If the amide nitrogen is also bonded to an alkyl
  or aryl group, name the group and show its
  location on nitrogen by N- two alkyl or aryl
  groups by N,N-di-.

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Amides

• A cyclic amide is called a lactam.

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Amides
The penicillins are referred to as b-lactam
antibiotics
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Amides

• The cephalosporins are also b-lactam antibiotics.

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Fischer Esterification

• Fischer esterification is the most common method
  for the preparation of esters
• In Fischer esterification, a carboxylic acid is
  reacted with an alcohol in the presence of an
  acid catalyst, such as concentrated sulfuric acid.

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Examples
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Preparation of Amides

• In principle, we can form an amide by treating a
  carboxylic acid with an amine and removing -OH
  from the acid and an -H from the amine.
• In practice what occurs if the two are mixed is
  an acid-base reaction to form an ammonium salt.
• If this salt is heated to a high enough
  temperature, water is eliminated and an amide
  forms.

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Examples

• Predict the amide product
• How to synthesize the following compound

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Preparation of Amides

• It is much more common, however, to prepare
  amides by treating an amine with an anhydride.

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Examples
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Hydrolysis of Anhydrides

• Hydrolysis is a chemical decomposition involving
  breaking a bond and the addition of the elements
  of water.
• Carboxylic anhydrides, particularly the
  low-molecular- weight ones, react readily with
  water (hydrolyze) to give two carboxylic acids.

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Example
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Hydrolysis of Esters

• Esters hydrolyze only very slowly, even in
  boiling water.
• Hydrolysis becomes considerably more rapid,
  however, when the ester is heated in aqueous acid
  or base.
• Hydrolysis of esters in aqueous acid is the
  reverse of Fischer esterification.
• A large excess of water drives the equilibrium to
  the right to form the carboxylic acid and alcohol
  (Le Châtelier's principle).

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Examples
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Hydrolysis of Esters

• We can also hydrolyze an ester using a hot
  aqueous base, such as aqueous NaOH.
• This reaction is often called saponification, a
  reference to its use in the manufacture of soaps.
• The carboxylic acid formed in the hydrolysis
  reacts with hydroxide ion to form a carboxylic
  acid anion.
• Each mole of ester hydrolyzed requires one mole
  of base.

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Examples
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Hydrolysis of Amides

• Amides require more vigorous conditions for
  hydrolysis in both acid and base than do esters.
• Hydrolysis in hot aqueous acid gives a carboxylic
  acid and an ammonium ion.
• Hydrolysis is driven to completion by the
  acid-base reaction between ammonia or the amine
  and the acid to form an ammonium ion.
• Each mole of amide hydrolyzed requires one mole
  of acid.

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Hydrolysis of Amides

• Hydrolysis of an amide in aqueous base gives a
  carboxylic acid salt and ammonia or an amine.
• Hydrolysis is driven to completion by the
  acid-base reaction between the carboxylic acid
  and base to form a salt.
• Each mole of amide hydrolyzed requires one mole
  of base.

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Examples
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Reaction with Alcohols

• Anhydrides react with alcohols and phenols to
  give an ester and a carboxylic acid.

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Reaction with Alcohols
Aspirin is prepared by the reaction of salicylic
acid with acetic anhydride.
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Reaction with Amines

• Anhydrides react with ammonia and with 1 and 2
  amines to form amides.
• Two moles of amine are required one to form the
  amide and one to neutralize the carboxylic acid
  by-product.

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Reaction with Amines

• Esters react with ammonia and with 1 and 2
  amines to form amides.
• Thus, an amide can be prepared from a carboxylic
  acid by first converting the carboxylic acid to
  an ester by Fischer esterification and then
  reaction of the ester with an amine.
• Amides do not react with ammonia or with amines

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Phosphoric Anhydrides

• The functional group of a phosphoric anhydride is
  two phosphoryl (PO) groups bonded to the same
  oxygen atom.

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Phosphoric Esters

• Phosphoric acid forms mono-, di-, and
  triphosphoric esters.
• In more complex phosphoric esters, it is common
  to name the organic molecule and then indicate
  the presence of the phosphoric ester by either
  the word "phosphate" or the prefix phospho-.
• Dihydroxyacetone phosphate and pyridoxal
  phosphate are shown as they are ionized at pH
  7.4, the pH of blood plasma.

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Step-Growth Polymerization

• Step-growth polymers are formed by reaction
  between two molecules, each of which contains two
  functional groups. Each new bond is created in a
  separate step.
• in this section, we discuss three types of
  step-growth polymers polyamides, polyesters, and
  polycarbonates.

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Polyamides

• Nylon-66 was the first purely synthetic fiber.
• It is synthesized from two six-carbon monomers.

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Polyamides

• The polyaromatic amide known as Kevlar is made
  from an aromatic dicarboxylic acid and an
  aromatic diamine.

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Polyesters

• The first polyester involved polymerization of
  this diester and diol.

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Polycarbonates

• Lexan, the most familiar polycarbonate, is
  formed by reaction between the disodium salt of
  bisphenol A and phosgene.