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-17.1
Carboxylic Acids and Their Derivatives:
Carboxylic acids have an –OH group bonded to the carbonyl C atom.
Esters have an -OR group bonded to the carbonyl C atom. Amides have an
–NH2,
-NHR, or –NR2 group bonded to the carbonyl C atom.
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► Carboxylic acids behave as
weak acids. They surrender
the hydrogen of the carboxyl
group, COOH, to bases and
establish acid–base equilibria
in aqueous solution.
► Like alcohols, carboxylic acids form hydrogen bonds
with each other so that even formic acid (HCOOH),
the simplest carboxylic acid, is a liquid at room
temperature with a boiling point of 101ºC.
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► Acids with saturated straight-chain R groups of up to
9 C’s are volatile liquids with strong, sharp odors;
those with up to 4 C’s are water soluble. Acids with
larger saturated R groups are waxy, odorless solids.
Their water solubility falls off as the size of the
hydrophobic, alkane-like portion increases.
► Carboxylic acids are named in the IUPAC system by
replacing the final -e of the alkane name with -oic
acid. If other functional groups are present, the chain
is numbered beginning at the –COOH end.
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► Dicarboxylic acids, which contain two –COOH groups, are
named systematically by adding the ending -dioic acid to the
alkane name.
► Unsaturated acids are named systematically in the IUPAC
system with the ending -enoic.
► The acyl group that remains when a
carboxylic acid loses its –OH is named by
replacing the -ic at the end of the name with
-oyl. An exception is the acyl group from
acetic acid, which is traditionally called an
acetyl group.
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► When the –OH of the carboxyl group is converted to the –OR
of an ester group the ability of the molecules to hydrogenbond with each other is lost.
► Simple esters are therefore lower boiling than the acids from
which they are derived.
► Esters are colorless, volatile liquids with pleasant odors, and
many of them contribute to the natural fragrance of flowers
and ripe fruits.
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► The nitrogen atom is bonded to a carbonyl-group
carbon in an amide, but not in an amine.
► The positive end of the carbonyl group attracts the
unshared pair of electrons on nitrogen strongly
enough to prevent it from acting as a base by
accepting a hydrogen atom. As a result, amides are
NOT basic like amines.
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► Unsubstituted amides are named by replacing the -ic
acid or -oic acid of the corresponding carboxylic
acid name with -amide.
► If the N atom of the amide has alkyl substituents on
it, the compound is named by first specifying the
N-alkyl group and then identifying the amide name.
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17.2 Some Common Carboxylic Acids
► Formic acid, HCOOH: Chemical that is present in the sting of
ants.
► Acetic acid, CH3COOH: dilute (5%) aqueous acetic acid is
known as vinegar.
► Butyric acid, CH3CH2CH2COOH: Chemical responsible for
odor of rancid butter.
► Caproic acid, CH3CH2CH2CH2CH2COOH: First isolated
from the skin of goats-which has a distinct smell.
► Citric acid: Present in citrus fruits and blood.
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17.3 Acidity of Carboxylic Acids
Carboxylic acids are weak acids that establish
equilibria in aqueous solution with carboxylate ions,
The carboxylate ions are named by replacing the -ic
ending in the carboxylic acid name with –ate.
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17.4 Reactions of Carboxylic Acids:
Ester and Amide Formation
► Ester formation, known as esterification, is carried out by
warming a carboxylic acid with an alcohol in the presence of a
strong-acid catalyst.
► Esterification reactions are reversible. Ester formation is
favored either by using a large excess of the alcohol or by
continuously removing one of the products.
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17.5 Aspirin and Other Over-theCounter Carboxylic Acid Derivatives
Aspirin is a white, crystalline solid.
Chemically, aspirin is
acetylsalicylic acid, an ester formed
between acetic acid and the –OH
group of salicylic acid.
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► An alternative to aspirin for pain relief is
acetaminophen (better known as Tylenol), an amide
that also contains a hydroxyl group.
► Acetaminophen reduces fever, but unlike aspirin it is
not an anti-inflammatory agent. The major advantage
of acetaminophen over aspirin is that it does not
induce internal bleeding.
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17.6 Hydrolysis of Esters and
Amides
Acid-catalyzed hydrolysis is simply the reverse of the
esterification. An ester is treated with water in the
presence of a strong acid and hydrolysis takes place.
An excess of water pushes the equilibrium to the right.
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Ester hydrolysis by reaction with a base such as
NaOH or KOH is known as saponification (after the
Latin word sapo, “soap”). The product of
saponification is a carboxylate anion rather than a
free carboxylic acid.
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17.8 Phosphoric Acid Derivatives
► Phosphoric acid is an inorganic acid with three
ionizable hydrogen atoms (red), allowing it to form
three different anions.
► Just like a carboxylic acid, phosphoric acid reacts
with alcohols to form phosphate esters. It may be
esterified at one, two, or all three of its groups by
reaction with an alcohol.
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