esters. what are they? how are they made? formed when an alcohol reacts with a carboxylic acid. very...
TRANSCRIPT
Esters
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 reactionThe condensation reaction between
the hydroxyl group and the carboxylic acid known as esterification.
Reverse reaction = ester hydrolysis
NamingNamed after alcohol & carboxylic acid
from which they are derived.
Names of esters end in –oate.
CH3C
CH2 O
O
CH3
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 formulaeAlthough the previous structural formula are the clearest way of showing esters, they can draw out in a shortened form.
ethyl ethanoate
CH3CCH2 O
O
CH3
Either…Or…
CH3C CH2O
O
CH3
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
Ester hydrolysis
Breakdown of an ester by water.Process sped up by catalysisCan 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.
This is why it is a condensation reaction because water is produced!
R
R’C
H2O
+
O H
H O
OR’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
CH3
CH
CH2 O
O
CH3
CH2C
CH3 O
O
CH
CH3 O
O
ethyl methanoate
methyl propanoate
methyl methanoate
R
R’C
H2O
+
O H
H O
OR’C
R O
O
+⇌
FORWARD REACTION = condensation reaction, the esterification of an alcohol using acid catalyst under reflux.
REVERSE REACTION = ester hydrolysis, same catalyst works for both forward & reverse reactions.
+
OH
OH- →CH3C
CH2 O
O
CH3
ethyl ethanoate
+
CH2CH3
CH3C-O
O
ethanol
ethanoate ionnot a reaction that exists in equilibrium (unlike using acid catalyst)