Esters

1
Esters

• C.I. 13.5

2
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

3
Naming
Names of esters end in oate.

• Named after alcohol carboxylic acid from which
  they are derived.

O
lets name some esters!
CH3
C
CH2
O
CH3
ethyl
ethanoate
this part from the acid and is named after it
this part comes from the alcohol is named after
it
4
Structural formulae

• Although the previous structural formula are the
  clearest way of showing esters, they can draw out
  in a shortened form.

In this version the acid part has been written
first
ethyl
ethanoate
Or
O
O
Either
CH3
C
CH2
CH3
O
CH3
C
CH3
CH2
O

• Identify the group attached to the CO this is
  from the acid
• The group attached to the O- is from the alcohol.

5
Wait! Whats 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.

6
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

7
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.

8
Ester hydrolysis

• Breakdown of an ester by water.
• Process sped up by catalysis
• Can use an 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.

9
R
O
H
O
R
C
?

O
R
O
R
C

H
O

• This is why it is a condensation reaction because
  water is produced!

H2O
Definition of a condensation reaction two
molecules reacting to form a larger molecule with
the elimination of a small molecule such as water
10
O
CH
ethyl
methanoate
CH2
O
CH3
O
CH3
CH2
C
methyl
propanoate
CH3
O
O
methyl
methanoate
CH
CH3
O
11
FORWARD REACTION condensation reaction, the
esterification of an alcohol using acid catalyst
under reflux.
R
O
H
O
R
C
?

O
R
O
R
C

H
O
H2O
REVERSE REACTION ester hydrolysis, same
catalyst works for both forward reverse
reactions.
12
ethanol
ethyl
ethanoate
O
OH
CH2
CH3
CH3
C
CH2
O
CH3
?


O
OH-
CH3
C
-O
ethanoate ion
not a reaction that exists in equilibrium (unlike
using acid catalyst)