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Ch 17. Outline
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Carboxylic Acids and Their Derivatives: Properties and
Names
Common Carboxylic Acids
Acidity of Carboxylic Acids
Reactions of Carboxylic Acids: Ester and Amide Formation
Aspirin and Other Over-the-Counter Carboxylic Acid
Derivatives
Hydrolysis of Esters and Amides
Polyamides and Polyesters
Phosphoric Acid Derivatives
AMP_Chem 30B
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Carboxylic Acids and Their Derivatives: Properties
and Names
Carboxylic acids: –OH group bonded to the carbonyl C atom.
Esters: -OR group bonded to the carbonyl C atom.
Amides: –NH2, -NHR, or –NR2 group bonded to the carbonyl
C atom. (* R = an alkyl group such as ethyl,methyl etc..)
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• Carboxylic acids and derivatives: polar, higher
boiling than comparable alkanes.
• Carboxylic acids and amides hydrogen bond.
• Carboxylic acids and their derivatives undergo
carbonyl-group substitution reactions, in which
the group bonded to the carbonyl C atom is replaced.
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Carboxylic acids are weak acids.
They give up the hydrogen of the
carboxyl group, COOH, to bases
and establish acid–base equilibria
in aqueous solution.
Write the eqn. for this reaction.
Like alcohols, carboxylic acids form hydrogen bonds with
each other.
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Solubility of carboxylic acids: Solubility decreases with
increasing length of the carbon chain (>4 C’s)
After approximately 9C chain length they are solids.
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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Most of the time, common names are used for carboxylic
acids.
When using common names, the carbon atoms attached to the
–COOH group are identified by Greek letters rather than
numbers. For example,
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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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Esters
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Simple esters have 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 (more on esters in lab…)
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Ester Nomenclature
Naming is in two parts: one originating from the parent acid, the
other part from the parent alcohol.
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Amides
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Unsubstituted amides can form 3 strong hydrogen bonds to
other amide molecules. They are higher melting and higher
boiling than the acids from which they are derived.
Except for the simplest amide (formamide, a liquid), the low
molecular-weight unsubstituted amides are solids that are
soluble in both water and organic solvents.
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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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Amides vs. Amines
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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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Some Common Carboxylic Acids
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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.
Citric acid: Present in citrus fruits and blood.
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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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Reactions of Carboxylic Acids: Ester and
Amide Formation
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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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Unsubstituted amides are formed by the reaction of
carboxylic acids with ammonia.
Substituted amides are produced in reactions between primary
or secondary amines and carboxylic acids.
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Aspirin and Other Over-the-Counter 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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Benzocaine is a local anesthetic used in many over-thecounter topical preparations for such conditions as cold sores,
poison ivy, sore throats, and hemorrhoids. It works by
blocking the transmission of impulses by sensory nerves.
Lidocaine (Xylocaine) is commonly administered by injection
to prevent pain during dental work. Because benzocaine is
less soluble than lidocaine, it cannot be used in this manner.
AMP_Chem 30B
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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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Amides are extremely stable in water but undergo hydrolysis
with heating in the presence of acids or bases.
Under acidic conditions, the carboxylic acid and amine salt
are obtained, using base produces the neutral amine and
carboxylate anion.
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Polyamides and Polyesters
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Nylons are polyamides produced
by reaction of diamines with
diacids. Nylon 66 is made by
heating adipic acid (hexanedioic
acid, a six-carbon dicarboxylic
acid) with hexamethylenediamine
(1,6-hexanediamine, a six-carbon
diamine) at 280°C.
► Nylon being pulled from the interface between
adipoyl chloride and hexamethylenediamine.
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Diacids and dialcohols react to yield polyesters. The most
widely used polyester is made by the reaction of terephthalic
acid with ethylene glycol.
As a clothing fiber, it has the trade name Dacron. Under the
name Mylar it is used in plastic film and recording tape. Its
chemical name, poly(ethylene terephthalate) or PET, is
usually applied when it is used in clear, flexible soft-drink
bottles.
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Phosphoric Acid Derivatives
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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.
AMP_Chem 30B
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Phosphate ester: A compound formed by reaction of an
alcohol with phosphoric acid; may be a monoester, a diester,
or a triester, also may be a di- or triphosphate.
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If two molecules of phosphoric acid combine to lose water,
they form a phosphoric acid anhydride. The resulting acid
(pyrophosphoric acid, or diphosphoric acid) reacts with yet
another phosphoric acid molecule to give triphosphoric acid.
These acids can also form esters, which are known as
diphosphates and triphosphates.
We will look at diphosphates and triphosphate esters in more detail
when looking at DNA structure.
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Phosphoryl group: The –PO3-2 group in organic phosphates.
Transfer of a phosphoryl group from one molecule to another
is known as phosphorylation.
In biochemical reactions, the phosphoryl groups are often
provided by adenosine triphosphate, ATP, which is converted
to adenosine diphosphate, ADP, in a reaction accompanied by
the release of energy.
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