Carboxylic Acids andCarboxylic Acid Derivatives

Chapter 14

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 hydrogen-bonding 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.

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

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1. Carboxylic acids: solubility

Solubility (g acid/g H2O) vs. number of carbons for saturated, unbranched-chain carboxylic acids.

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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

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1. Carboxylic acids: nomenclature

Name the following compounds:

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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

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1. Carboxylic acids

Is “alpha-hydroxy” an actual substance?

glycolic acid

lactic acid

tartaric acid

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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

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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

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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.

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2. Esters: nomenclature

Draw the structures of the following esters.

propyl ethanoate

octyl decanoate

methyl methanoate

2-methylpropyl propanoate

3-methylbutyl ethanoate

phenyl pentanoate

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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.

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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).

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2. Esters: reactions

Hydrolysis (hydration) of esters, when it is acid-catalyzed, is the reverse of the esterification reaction.

ester carboxylic acid alcohol

H2O

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

+ H2O

+ H2O

+ H2O

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2. Esters: saponification

+ +

(salts of carboxylic acids)

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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.

Draw structures for the following acid chlorides. heptanoyl chloride 2-hydroxypropanoyl chloride

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3. Acid chlorides and acid anhydrides

Preparation of acid chlorides

The reagents PCl3, PCl5, and SOCl2 are inorganic acid chlorides

PCl3 or

+ PCl5 or

SOCl2+ inorganic products

3. Acid chlorides and acid anhydrides

PCl3, PCl5, and SOCl2 replace the hydroxyl group on the acid with a chloride, by the following mechanism!

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3. Acid chlorides and acid anhydrides

Write an equation for the reaction of benzoic acid with SOCl2 and name the organic product.

SOCl2

benzoyl chloride

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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.

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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.

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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?

ethanoic methanoic anhydride?

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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.