carboxyl derivatives in this chapter, we study three classes of compounds derived from carboxylic...
DESCRIPTION
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”.TRANSCRIPT
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.
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. Esters The functional group of an ester is a
carbonyl group bonded to an -OR group. R may be alkyl or aryl. A
cyclic ester is called a lactone. Amides The functional group of an
amide is a carbonyl group bonded to a nitrogen atom. 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-. Amides A cyclic amide is called a lactam.
The penicillins are referred to as b-lactam antibiotics. Amides The
cephalosporins are also b-lactam antibiotics. Fischer
Esterification
Fischer esterification is the most common method for the
preparation of esters. In Fischer esterification, a carboxylic acid
condenses with an alcohol in the presence of an acid catalyst, such
as concentrated sulfuric acid. 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. Preparation of
Amides It is much more common, however, to prepare amides by
treating an amine with an anhydride. 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. Hydrolysis of
Esters in Acid
Esters hydrolyze very slowly, even in boiling water. Hydrolysis is
fast with acid or base conditions. 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 Chtelier's principle). Hydrolysis of Esters in
Base
We can also hydrolyze an ester using a hot aqueous base, such as
aqueous NaOH 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 Hydrolysis of Amides in Acid
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. Hydrolysis of Amides in
Base
Hydrolysis of an amide in aqueous base gives a carboxylate 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. Anhydride Reaction with Alcohols
Anhydrides react with alcohols and phenols to give an ester and a
carboxylic acid. Aspirin is prepared by the reaction of salicylic
acid with acetic anhydride. Anhydride 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. Ester 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 Phosphoric
Anhydrides
The functional group of a phosphoric anhydride is two phosphoryl
(P=O) groups bonded to the same oxygen atom. Phosphoric Esters
Phosphoric acid forms mono-, di-, and triphosphoric esters.
Dihydroxyacetone phosphate and pyridoxal phosphate are shown as
they are ionized at pH 7.4, the pH of blood plasma. Synthetic
Polymers 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. Polyamides Nylon-66 was the first purely synthetic
fiber.
It is synthesized from two monomers: A diacid and a diamine
Polyamides The polyaromatic amide known as Kevlar is made from an
aromatic dicarboxylic acid and an aromatic diamine. Polyesters The
first polyester involved polymerization of a diester and a diol.
Polycarbonates Lexan, the most familiar polycarbonate, is formed by
reaction between the disodium salt of bisphenol A and phosgene.
Summary of Reactions Reaction Summary for: Anhydrides Esters
Amides
Hydrolysis Reactions with Alcohols Reactions with Amines Hydrolysis
Reaction with Alcohol Reaction with Amine