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Chapter 14
Carboxylic Acids and
Carboxylic Acid Derivatives
1. Carboxylic acids

The carboxyl group consists of carbonyl and hydroxyl
groups attached to the same carbon.

carbonyl + hydroxyl = carboxyl

An aliphatic or aromatic group can be attached to the carboxyl
group.
1. Carboxylic acids

The acyl group is a carboxyl group with either a hydroxyl or
alkoxy group.


If R is a hydroxyl group, the compound is a carboxylic acid.
If R is an alkoxy group, the compound is an ester.
1. Carboxylic acids: boiling points

Intermolecular forces are
strong in carboxylic acids
due to

the high polarity of the
carboxyl group;

the presence of hydrogenbonding between
carboxylic acid molecules.
1. Carboxylic acids: boiling points

When two hydrogen
bonds form between
two carboxylic acid
molecules, the result is
a dimer.

Dimer formation can
cause carboxylic acids
to seem to have double
their actual molecular
mass.
1. Carboxylic acids: boiling points

Compare molecules with similar molar masses and different
functional groups:
1. Carboxylic acids: boiling points

Boiling point (oC) vs. number
of carbons for acids,
alcohols, aldehydes, and
alkanes.
1. Carboxylic acids: solubility

Lower molecular weight carboxylic acids are very soluble in
water.


Vinegar is a solution of ethanoic acid.
Solubility falls off as molecular weight increases.


Why?
Hexadecanoic acid is insoluble in water.
1. Carboxylic acids: solubility

Solubility (g acid/g H2O)
vs. number of carbons for
saturated, unbranchedchain carboxylic acids.
1. Carboxylic acids: nomenclature

Determine the parent compound from the
longest chain that includes the carboxyl
carbon.

Number the chain so that the carboxyl
carbon is carbon 1.

Replace the –e ending with –oic acid.

Assign numbers to any remaining substituents.
1. Carboxylic acids: nomenclature

Additional notes:

If two carboxyl groups are present use –dioic acid.

For cycloalkanes, add carboxylic acid to the name of
the cycloalkane.

For aromatic acids, the simplest acid is benzoic
acid.

If the acid group is attached to the aromatic ring, name after
benzoic acid.

If the acid group is not attached to the aromatic ring, name
after the longest chain, with a –phenyl substituent.
1. Carboxylic acids: nomenclature
pencast
1. Carboxylic acids: nomenclature

Name the following compounds:
pencast
1. Carboxylic acids: nomenclature

Draw structures for the following compounds:

2,5-dimethylhexanoic acid

3-bromo-5-chlorooctanoic acid

2,2-dimethylbutanedioic acid

3-methylcyclohexanecarboxylic acid

2,4-dichlorobenzoic acid

3-phenylpentanoic acid
pencast
1. Carboxylic acids

Is “alpha-hydroxy” an actual substance?

glycolic acid

lactic acid

tartaric acid
1. Carboxylic acids

The last paragraph in the inset box on pages 460-461 of
your textbook states:

"For the time being, biodegradable plastics cannot outcompete their
nonbiodegradable counterparts. Future research and development
will be required to reduce the cost of commercial production and
fulfill the promise of an 'environmentally friendly' garbage bag.”

This statement gives the impression that there are no biodegradable
plastics available to consumers at a reasonable cost.

Compostable plastic bags
1. Carboxylic acids: reactions

Preparation is by complete oxidation of primary alcohols or
oxidation of aldehydes.
1o alcohol
aldehyde
carboxylic acid
1. Carboxylic acids: reactions


Carboxylic acids are proton donors and therefore react as
acids.
Carboxylic acids are weak acids, dissociating only slightly
in solution.
>95%
<5%
1. Carboxylic acids: reactions


When a strong base is added to a carboxylic (weak) acid,
water and salt are formed.
Although the carboxylic acid isn’t initially completely
dissociated, as H+ is removed by reaction with OH-, more
acid dissociates.


Remember le Chatelier’s principle?
When product (H+) is removed, the equilibrium shifts to make more
product (and less undissociated acid).
1. Carboxylic acids: reactions

Acid-base reaction
carboxylic acid + strong base  carboxylic acid salt + water
1. Carboxylic acids: reactions

Naming salts of carboxylic acids




Name the carboxylic acid.
Replace the –ic acid ending with –ate.
Precede this name with the name of the cation.
Name the salts formed in the following reactions:



ethanoic acid + KOH
benzoic acid + LiOH
hexanoic acid + NaOH
pencast
1. Carboxylic acids: reactions

Esterification is the formation of water and an ester from a
carboxylic acid and an alcohol.
More about this in the next section…
2. Esters

Esters are carboxylic acid derivatives, in which the acidic
-H of the acid has been replaced by an alkyl or aryl group –
R.
carboxylic acid
ester derivative
2. Esters: properties

Esters

are slightly polar;

boil at about the same temperature as corresponding aldehydes and
ketones;

are somewhat soluble in water when they are small.

have pleasant aromas.
2. Esters: nomenclature


Recall nomenclature of salts of carboxylic acids.

Name the carboxylic acid.

Replace the –ic acid ending with –ate.

Precede this name with the name of the cation.
Esters are named in the same way, except the alkyl or aryl
portion of the alcohol is used in place of the cation name.

Name the carboxylic acid.

Replace the –ic acid ending with –ate.

Precede this name with the name of the alkyl or aryl portion of the
alcohol.
2. Esters: nomenclature

Name the following esters.
pencast
2. Esters: nomenclature

Draw the structures of the following esters.

propyl ethanoate

octyl decanoate

methyl methanoate

2-methylpropyl propanoate

3-methylbutyl ethanoate

phenyl pentanoate
pencast
2. Esters: reactions

Preparation of esters is by reaction of a carboxylic acid and
an alcohol to produce an ester and water.



This is a dehydration reaction. [water is lost]
Heat and a trace of acid catalyst (H+) are required.
The reaction produces an equilibrium mixture.
heat
2. Esters: reactions

Show the esterification reaction that would produce butyl
propanoate.
pencast
2. Esters: reactions

Esters can be synthesized starting from alcohols only.



An alcohol can be oxidized to an aldehyde, and further oxidized to a
carboxylic acid.
This carboxylic acid can undergo an esterification reaction with
another alcohol.
Name the required alcohols and show the necessary
reactions to produce


pentyl butanoate (apricots).
octyl ethanoate (oranges).
pencast
2. Esters: reactions

Hydrolysis (hydration) of esters, when it is acid-catalyzed,
is the reverse of the esterification reaction.
H2O
ester
carboxylic acid
alcohol
2. Esters: reactions

Hydrolysis of esters, when it is base-catalyzed, is called
saponification.
ester
carboxylic acid salt
alcohol
2. Esters: reactions

The carboxylic acid that forms when the ester breaks up
reacts immediately with the base, forming the carboxylate
anion, associated with the cation of the base.
2. Esters: reactions

What are the products of the following reactions?
+ H2O
pencast
+ H2O
+ H2O
+ H2O
2. Esters: saponification
(salts of carboxylic acids)
+
+
2. Esters: saponification

A soap (carboxylic acid salt)

has a nonpolar end that dissolves in nonpolar fats and oils, and a
polar end that dissolves in water.

forms groups of soap molecules called micelles that dissolve in
water and are washed away.
2. Esters: saponification
EXTRA CREDIT QUESTION

Radioactive isotopes of an element behave chemically in exactly
the same manner as the nonradioactive isotopes. As a result,
they can be used as tracers to investigate the details of chemical
reactions. A scientist is curious about the origin of the bridging
oxygen atom in an ester molecule. She has chosen to use the
radioactive isotope 18O to study the following reaction:

Design experiments using 18O that will demonstrate whether the
oxygen in the water molecule came from the –OH of the alcohol
or the –OH of the carboxylic acid.
Post your answer in the Journal for this module with tag = XC.

3. Acid chlorides and acid anhydrides

Acid chlorides are carboxylic acid derivatives in which the
hydroxyl group, -OH, has been replaced by –Cl.

Naming

Name the corresponding carboxylic acid.

Replace the -oic acid ending with –oyl chloride.
3. Acid chlorides and acid anhydrides

Examples
ethanoic acid
ethanoyl chloride
benzoic acid
benzoyl chloride
3. Acid chlorides and acid anhydrides

Name the following acid chlorides.
pencast

Draw structures for the following acid chlorides.


heptanoyl chloride
2-hydroxypropanoyl chloride
3. Acid chlorides and acid anhydrides

Preparation of acid chlorides
+

PCl3 or
PCl5 or
SOCl2
+ inorganic products
The reagents PCl3, PCl5, and SOCl2 are inorganic acid chlorides
3. Acid chlorides and acid anhydrides

PCl3, PCl5, and SOCl2 replace the hydroxyl group on the
acid with a chloride, by the following mechanism!
3. Acid chlorides and acid anhydrides

Write an equation for the reaction of benzoic acid with
SOCl2 and name the organic product.
pencast
SOCl2
benzoyl chloride
3. Acid chlorides and acid anhydrides

Acid anhydrides are two carboxylic acid molecules with a
water molecule removed.
+ H2O
3. Acid chlorides and acid anhydrides

Acid anhydrides with identical acyl groups are symmetrical.

Symmetrical acid anhydrides are named after the acid from
which they are made, with the acid ending replaced with
anhydride.

The molecule above, made from two molecules of ethanoic acid, is
called ethanoic anhydride.
3. Acid chlorides and acid anhydrides

Unsymmetrical anhydrides have two different acyl groups.

Unsymmetrical anhydrides are named using both parent
carboxylic acid names, in alphabetical order, followed by the
word anhydride.

The molecule above is called butanoic ethanoic anhydride.
3. Acid chlorides and acid anhydrides

Name the following acid anhydrides.
pencast
3. Acid chlorides and acid anhydrides

Acid anhydrides can be prepared from an acid chloride and
a carboxylate anion.

Direct reaction of the two parent carboxylic acids is usually not
possible.
acid chloride
carboxylate anion
acid anhydride
3. Acid chlorides and acid anhydrides

Write equations for the synthesis of butanoic anhydride,
beginning with butanoic acid.
pencast
3. Acid chlorides and acid anhydrides

Acid anhydrides react with water, if it is present, to produce
two carboxylic acids.
+ H2O
3. Acid chlorides and acid anhydrides

What are the products of the hydrolysis of

ethanoic anhydride?
pencast

ethanoic methanoic anhydride?
3. Acid chlorides and acid anhydrides

An acid anhydride can also react with an alcohol, in a
reaction analogous to hydrolysis.

Hydrolysis: products are two carboxylic acids.

Reaction with alcohol: products are an ester and an acid.