After completing this lesson you should be able to :
• Esters can be hydrolysed to produce the parent carboxylic
acid and parent alcohol.
• Given the name of an ester or its structural formula, the
hydrolysis products can be named and their structural
formulae drawn.
• In a hydrolysis reaction, an ester is split apart by a water
molecule.
• Describe the difference between dilute acid catalysed
hydrolysis of an ester and using a strong alkali, such as
NaOH(aq) or KOH(aq).
COPY
• Breakdown of an ester by water.
• Process sped up by catalysis
• Can use a dilute acid to catalyse (H2SO4)
• Alkali catalysts (e.g. sodium hydroxide) can
also be used but instead of producing
carboxylic acid a carboxylate salt is formed.
• Alkaline hydrolysis goes to completion &
hence is usually preferred.
COPY
Hydrolysing Esters
Condensation
Alcohol + Carboxylic Acid  Ester + Water
Hydrolysis
Alcohol + Carboxylic Acid  Ester + Water
The ester is split up by the chemical action of water, hydrolysis.
The hydrolysis and formation of an ester is a reversible reaction.
O
R C
O
R
+
H
Bonds broken
Ester + Water
+
O
O
H
R C
O
O
R
H
H
Bonds formed
Carboxylic Acid + Alcohol
COPY
• Anti-bumping granules ensure even boil and provide uneven surface for bubbles of
gas to form.
• you heat reactants under reflux if the organic compound you are heating is volatile
(that is it goes to the gaseous state very easily under heat).
• When you heat reactants, you turn them back into a liquid so they don’t escape
from your reaction vessel. Reactants are turned back into a liquid by having a
condenser at the top of the apparatus. So you’re 'fluxing' between the two states,
gaseous and liquid.
Alkaline hydrolysis
COPY
Alkaline hydrolysis of an ester has two main advantages over
acid-catalysed hydrolysis.
1) Alkaline hydrolysis is not reversible and hence there should be a
higher yield.
2) It is usually easier to separate the products when alkaline
hydrolysis has been used.
COPY
…After separating your carboxylate salt via distillation you
can displace the sodium using a strong acid to obtain the
parent acid of the ester.
If sodium hydroxide is used a sodium salt of the acid is formed. If this is reacted with a
strong acid (eg. Hydrochloric acid) the acid can be displaced from the salt
RCOO- Na+
+
Carboxylate
Salt
+ hydrochloric
acid
HCl
RCOOH
acid
+
NaCl
+
sodium
chloride
In hydrolysis reactions large molecules are broken down into smaller molecules by water.
Esters can be hydrolysed to produce the parent ................... .......... and the parent
.................... .
ESTER + WATER
⇌
ACID + ALCOHOL
An alkali is often used to catalyse the reaction and the mixture heated under
reflux.
If sodium hydroxide is used a sodium salt of the acid is formed. If this is reacted with a strong acid
(eg. Hydrochloric acid) the acid can be displaced from the salt
HCOO- Na+
Sodium
methanoate
+
+
HCl
hydrochloric
acid
HCOOH
methanoic
acid
+
+
NaCl
sodium
chloride
Past paper question 2015
Esters hydrolysis
COPY
Ester hydrolysis, especially by alkali, is an
important process in the manufacture of soap
from fats and oils. This will be looked at in the
next subtopic (B).
Prevention of ester hydrolysis
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• Prevention of ester hydrolysis is also important in the food, cosmetic
and pharmaceutical industries.
• As esters are found in these products, if they hydrolyse easily then the
property of the products will change.
• Expiry dates are predicted, along with other factors, to take account
how quickly the product is likely to hydrolyse.
• When the acid is produced upon ester hydrolysis it can have an
undesirable smell.
COPY
Extension material - Higher
Properties of Carboxylic Acids
Carboxylate salts are often
used as preservatives and
flavor enhancers in soups
and seasonings.
Sodium propionate, a
preservative, is added to
cheeses, bread, and other
bakery items to inhibit the
spoilage of the food by
microorganisms.
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Polarity of Carboxylic Acids
Carboxylic acids are strongly polar because they
have
two polar groups:
• hydroxyl group (—OH)
• carbonyl group (C O)
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Solubility in Water
Carboxylic acids
• form hydrogen bonds with
many water molecules
• with one to four carbon
atoms are very soluble in
water
As the number of carbons
increases, the solubility of
the carboxylic acid in water
is reduced.
Acetic acid forms hydrogen
bonds with water molecules.
Solubility in Water
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Acidity of Carboxylic Acids
Carboxylic acids
• are weak acids
• ionize in water to produce carboxylate ions
and hydronium ions
• can lose a proton because two oxygen atoms in the
carboxylate ion stabilize negative charge
Study Check
Write the balanced equation for the
ionization of butanoic acid in water and
identify the carboxylate ion.
Solution
Write the balanced equation for the ionization
of butanoic acid in water and identify the
carboxylate ion.
O
O
CH3 —CH2—CH2—C—OH
Butanoic acid
-
CH3 —CH2—CH2—C—Ocarboxylate ion
(butanoate)
+ H3O+
Neutralization of Carboxylic Acids
Carboxylic acid salts
• are a product of the neutralization of a
carboxylic acid with a strong base, such as
NaOH or KOH
(carboxylic acid salt)
• are used as preservatives and flavor
enhancers
Carboxylic Acid Salts
The carboxylate ion is named by replacing the
ic acid ending of the acid name with ate.
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Carboxylic Acid Salts
Carboxylic acid salts
• are ionic compounds with strong attractive
forces between ions
• are solids at room temperature
• have high melting points
• are usually soluble in water
Carboxylic Acid Salts
Carboxylic acid salts are used as preservatives and
flavor enhancers such as
• sodium propionate, which is used in cheese and
breads
• sodium benzoate, which inhibits growth of mold
and bacteria and is added to fruit juices,
margarine, relishes, salads, and jams
• monosodium glutamate, MSG, which is added
to meats, fish, vegetables, and baked goods to
enhance flavor
Study Check
Write the equation for the reaction of propanoic
acid with NaOH.
Solution
Write the equation for the reaction of propanoic
acid with NaOH.