Download Procedure Notes

Chemistry 2412L
Esterification pre-lab lecture
Properties of Esters
• The purpose of this lab is to study the chemical
properties of esters
• Esters are derivatives of carboxylic acids which
are found in many natural sources. Esters tend
to have a pleasant odor associated with them
and can be found as a key component of the
odor and taste of many fruits and flowers.
Procedure Notes
• You will create eight different known
esters and two unknown esters. You will
identify the unknowns by comparing to
the eight known compounds.
• The eight esters will be created from the
combination of different alcohols and
carboxylic acids.
• Each ester will be reacted in a test tube
and heated to a steady temperature of
40-60 ºC for 15 minutes.
Procedure Notes
• The alcohols are:
1.
2.
3.
4.
5.
6.
Isobutyl alcohol
Amyl alcohol
1-Octanol
1-Propanol
Methanol
Ethanol
• The carboxylic acids are:
1.
2.
3.
4.
5.
Formic acid
Acetic acid
Propanoic acid
Salicylic acid
Cinnamic acid
Procedure Notes
• Fischer esterification is a reaction that involves
refluxing an alcohol and a carboxylic acid in
the presence of an acid catalyst.
• The process is in equilibrium which means that
once equilibrium is reached there could be a
large amount of the starting materials
remaining. This could result in a poor yield of
the desired ester. Adding additional products
could shift the reaction to the right, or adding
additional water could lead to a shift to the left.
O
O
+
+
C
R
OH
R'OH
H
+
C
R
OR'
H2O
Procedure Notes
• Esters are more commonly used as flavoring
rather than scents that are added to the body
due to the fact that the reaction is in equilibrium
and esters are not very stable. The addition of
water and heat from perspiration can cause the
reaction to favor the reactants. Carboxylic acids
tend to be associated with a foul smelling odor
that one would not want to wear on their body.
• Esters also may have biological properties. For
example isoamyl acetate, which smells like
bananas, is also an alarm pheromone released
by bees. This pheromone will attract bees to
any person which is wearing this ester on their
person.
Procedure Notes
• A small amount of acid is needed to act
as a catalyst for the reaction.
• Since a catalyst is never used up in a
reaction, only a small amount of catalyst
is needed.
• Using heat is also a way to accelerate
the reaction.
Procedure Notes
• The esterification process is a slow process
that could take hours to complete.
• If not given time to finish the reaction it is
more likely that the carboxylic acid will still
be left in the reaction and would thus have
a sour smell.
• Producing esters on a small scale in a test
tube, such as the experiment in this lab, will
not produce a lot of the ester.
• The smell of the ester can be masked by
the smell of the carboxylic acid.
Safety Notes
• Concentrated acids such as H2SO4 can
cause burns. Wash immediately with
water if spilled on the skin.
• As always, be careful with the hot
plates!!!!
• Wear Safety Glasses!!!!
• Perform experiment in the hood.