SCH4U - Organic Chemistry
1.6 Carboxylic Acids, Esters and Fats
Carboxylic Acids
A carboxylic acid is an organic compound that contains a carboxyl group, –COOH
These compounds are weak acids.
Citrus fruits, crabapples, rhubarb, and other foods that contain carboxylic acids have a
sour, tangy taste.
Naming Carboxylic Acids
To name organic compounds containing a carboxylic group:
1. Start with the alkane name for the longest chain, including the carbon atom in the
carboxyl group
2. Drop the -e suffix of the root compound and replace it with the suffix -oic, followed by
the word acid.
The simplest aromatic carboxylic acid is benzoic acid, an acid whose common name is
the same as its IUPAC name.
The sodium salt of benzoic acid, sodium benzoate, is used as a preservative in foods
and beverages.
Note that, in a compound that combines an alcohol and a carboxylic acid, the alcohol is
indicated as a substituent group: hydroxy.
Some carboxylic acids have more than one carboxyl group.
When naming an acid with two carboxyl groups, use the suffix dicarboxylic acid.
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Citric acid is an example of a compound with three carboxylic groups.
Draw the structure of 2-methylbutanoic acid.
octanoic acid
3-methylpentanoic acid
ethanedioic acid
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Properties of Carboxylic Acids
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Their molecules are very polar (C=O, O-H)
Hydrogen bonding occurs in carboxylic acids with 5 or fewer carbon atoms making
them very soluble in water
Larger carboxylic acids have decreasing solubility
Soluble in polar organic solvents, such as alcohols
They affect acid–base indicators
React with bases to form ionic compounds and water
Esters
Many plants naturally produce esters, which are responsible for many of the odours
of fruits, flowers, and perfumes. Synthetic esters are often used as flavourings in
processed foods, and as scents in cosmetics and perfumes.
An ester is characterized by a functional group that is similar to a carboxyl group except
that the hydrogen atom is replaced with an alkyl group. The letters R and R in the
formula represent alkyl groups in which a carbon atom attaches to the functional group
Naming Esters
Esters are formed by the condensation reaction of a carboxylic acid and an alcohol.
SCH4U - Organic Chemistry
When naming esters, follow these steps:
1. Identify the two alkyl groups.
2. Determine which group originated from the carboxylic acid and which originated from
the alcohol.
3. Write the name with the alcohol part first and the carboxylic acid part second.
Draw the structural formula of ethyl methanoate.
methyl hexanoate
methyl benzoate
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Properties of Esters
Esters are less polar than carboxylic acids and cannot produce hydrogen bonds.
• Small esters are soluble in water due to the polarity of their carbon–oxygen
bonds
• Esters are less soluble in water than carboxylic acids and have lower boiling
points
• Melting and boiling points of esters are similar to those of the corresponding
aldehydes and ketones
• Smaller, low–molecular mass esters are gases at room temperature, but the
larger, heavier esters are waxy solids
Reactions Involving Carboxylic Acids and Esters
Formation of Carboxylic Acids
Carboxylic acids can be formed by the oxidation of aldehydes in the presence of an
oxidizing agent.
The roadside Breathalyzer test relies on just such a reaction, in which the oxidizing
agent changes colour.
Formation of Esters: Esterification
Esterification is a condensation reaction in which an alcohol and carboxylic acid react
to form an ester and water.
Reaction of Esters: Hydrolysis
When esters are treated with an acid or a base, the esterification process can be
reversed.
The ester splits into the carboxylic acid and alcohol components with the addition of a
molecule of water.
This reaction is called hydrolysis.
SCH4U - Organic Chemistry
Write equations representing the two chemical reactions that result in the formation of
butanoic acid from an alcohol.
Draw the structural formula equation representing the reaction that forms propyl
butanoate. Also write the names of the compounds involved.
Write the structural formula equation for the hydrolysis of ethyl propanoate by sodium
hydroxide solution.
Draw structural formula equations illustrating the following reactions. Give the IUPAC
name for every compound involved. T/I
(a) the production of 2-methylpropanoic acid from an aldehyde
(b) the production of a carboxylic acid from ethanal
(c) the esterification reaction between propanol and hexanoic acid
(d) the hydrolysis of methyl butanoate in the presence of sodium hydroxide solution
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Fats and Oils
Fats and oils are large ester molecules known as lipids.
The long-chain carboxylic acid component is called a fatty acid.
The alcohol component is glycerol.
Glycerol is a 3-carbon alcohol with three hydroxyl groups, so it can bond with three fatty
acids at once.
The ester that is formed is called a triglyceride. So, fats and oils are triglycerides.
Saponification
A triglyceride can be split (hydrolysis) to produce glycerol and the sodium salt of the
fatty acid when sodium hydroxide is added to the triglyceride.
This resulting sodium salt is commonly called soap, so the reaction is called
saponification.
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Structure and Properties of Fats and Oils
Insoluble in water
The hydrocarbon chains in fatty acids affect the physical state of the lipid. This affects
their melting point. Saturated hydrocarbons can “stack” closer to each other increasing
their melting point (solids at room temperature). Unsaturated hydrocarbons cannot
“stack”, as easily, therefore have lower melting points (liquids at room temperature).
Worksheet 1.6: Carboxylic Acids, Esters and Fats
p.55 Q. 1, 2, 4, 6, 8, 10