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Esters
What are they? How are they made?
Naming
Structural formulae
Wait! What’s that smell?
Esters from phenols
Slide 7
Ester hydrolysis
Slide 9
Slide 10
Slide 11
Slide 12
Nội dung
Esters
C.I. 13.5
What are they?
How are they made?
Formed when an alcohol reacts with a
carboxylic acid.
Very
slow
reaction, unless! an acid catalyst
used (usually sulphuric acid)
A condensation reaction
The condensation reaction between the
hydroxyl group and the carboxylic acid
known as
esterification
.
Reverse reaction =
ester hydrolysis
Naming
Named after alcohol & carboxylic acid from
which they are derived.
Names of esters
end in –oate.
CH
3
C
CH
2
O
O
CH
3
ethyl ethanoate
this part from the acid
and is named after it
this part comes from the
alcohol & is named after it
let’s name
some esters!
Structural formulae
Although the previous structural formula are the clearest
way of showing esters, they can draw out in a
shortened form.
ethyl ethanoate
CH
3
C
CH
2
O
O
CH
3
Either…
Or…
CH
3
C
CH
2
O
O
CH
3
In this version
the acid part
has been
written first
Identify the group attached to the C=O – this is from
the acid
The group attached to the –O- is from the alcohol.
Wait! What’s that smell?
•
Esters have strong, sweet smells.
•
Their bouquet is often floral or fruity.
•
This means they are used in food flavourings &
perfumes.
•
Also, very good at dissolving organic compounds so
often used as solvents.
ester fragrance
ethyl methanoate raspberries
3-methylbutyl ethanoate pears
ethyl 2-methylbutanoate apples
phenylmethyl ethanoate jasmine
Esters from phenols
•
-OH group in phenol less reactive
to esterification, requires a more
vigourous reagent.
•
Use of ethanoic acid in
esterification is also known as
ethanoylation.
•
Ethanoic anhydride is a more
vigourous ethanoylating agent
OH
Esters from phenols
•
Ethanoic anhydride used as it is reactive
but not too dangerous.
•
Ethanoyl chloride is much more reactive,
but, also toxic and hazardous to
use.
•
Ethanoic anhydride & ethanoyl chloride
are described as acylating agents
using an acylating agent is the only way to esterify a
phenol
alcohols can be esterified using acylating agents or by
reacting with a carboxylic acid.
Ester hydrolysis
Breakdown of an ester by water.
Process sped up by catalysis
Can use an acid to catalyse (H
2
SO
4
)
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.
This is why it is a
condensation reaction
because water is produced!
R
R’C
H
2
O
+
O H
H O
O
R’C
R O
O
+
⇋
Definition of a condensation reaction =
two molecules reacting to form a larger
molecule with the elimination of a
small molecule such as water
CH
3
CH
CH
2
O
O
CH
3
CH
2
C
CH
3
O
O
CH
CH
3
O
O
ethyl methanoate
methyl propanoate
methyl methanoate
.
hydroxyl group and the carboxylic acid
known as
esterification
.
Reverse reaction =
ester hydrolysis
Naming
Named after alcohol & carboxylic acid.
What are they?
How are they made?
Formed when an alcohol reacts with a
carboxylic acid.
Very
slow
reaction, unless! an acid catalyst
used (usually