Experiment 21:
ESTERS:
SYNTHESIS AND FRAGRANCE
O
RCOH
+
H
+ R'OH
O
RCOR'
+
H2O
Objectives:




To synthesize an ester from acetic acid
with isoamyl alcohol under reflux.
To purify your product through acid-base
extraction and simple distillation.
To identify and analyze the purity of your
compound using GC analysis.
To identify your product by analyzing the
NMR and IR spectra.
Before coming to lab…

Review these techniques:

Reflux

Acid-Base Extraction

Simple distillation

Drying over MgSO4

GC Analysis
FISCHER ESTERIFICATION


Fischer esterification is an acid catalyzed nucleophilic
acyl substitution.
Net effect is the replacement of an –OH of a
carboxylic acid with the –OR of an alcohol to produce
an ester.
O
R

O
H
+
H
O
C
O
R'
H
+
R
O
C
R'
+
H
O
It is an equilibrium reaction with an unfavorable Keq,
thus we can improve product yield in several ways:
 Use an excess of the alcohol reactant.
 Use an excess of the carboxylic acid reactant.
 Remove water as it forms.
H
MECHANISM
H
O
C
H3C
CH3
O
+
H
OSO3H
+
C
OH
H3C
acids are not reactive
enough to undergo nucleophilic
addition directly.
H
OH
C
OH
CH3
• Carboxylic
• By using sulfuric acid as a catalyst,
the carbonyl group oxygen is
protonated to give the carboxylic
acid a positive charge. This makes it
more reactive.
• The carboxylic ester is formed
after loss of water from the
tetrahedral intermediate.
H3C
OH
C
H 3C
HO
H
C
O
CH3
H
H
H3C
O
H
C
O
H3C
H
O
H
C
O
H
CH3
H
O
H3C
C
H 3C
H
C
O
CH3
H2O
H2SO4
EXPERIMENTAL PROCEDURE
(SYNTHESIS)
• Combine
acetic acid, isoamyl alcohol
and sulfuric acid in a 25 mL round
bottom flask.
water out
• Clamp flask to ringstand and add
boiling chips.
• Place water cooled condenser on top
of flask, with a CaSO4 drying tube in
the top.
water in
• Heat to reflux. Reflux 30 minutes.
• Cool to room temp.
• Add 10% NaHCO3 slowly to flask.
heating mantle
to voltage regulator
iron ring
EXPERIMENTAL PROCEDURE
(PURIFICATION)
• Transfer
liquid to separatory funnel.
• Rinse reaction flask with ether and
transfer to separatory funnel.
• Wash the organic layer with 10% NaHCO3.
• Transfer the organic layer to a clean
flask.
• Dry over MgSO4.
• Transfer liquid to a preweighed 50 mL
round bottom flask.
• Clamp flask to ringstand.
EXPERIMENTAL PROCEDURE
(PRODUCT ISOLATION)
• Set
up a simple distillation
apparatus, using a 25 mL round
bottom as the receiving flask.
•Collect all distillate that boils under
40oC.
water out
water in
• Record distillation range, Ti-Tf.
Heating Mantle
• Allow reaction flask to cool to room
temperature.
• Reweigh flask to determine final
product mass and calculate % yield.
• Prepare GC sample.
iron ring
to
voltage
regulator
Table 21.1
Determine limiting reagent 1st,
before calculating theoretical
yield!

Theoretical yield (g)
Actual yield (g)
% yield
Record physical state and color
of product!

Product Appearance
Table 21.2
GC Retention Times (min)
Compound
methanol
isoamyl alcohol
isoamyl acetate
Standard
Adjusted Area %
Sample

GC SOLVENT!

REACTANT!

PRODUCT!
EXPERIMENTAL PROCEDURE
(IR ANALYSIS)
CH3
5
CH3CHCH2CH2OH
4
3
CH3
2
1
O
5
CH3CHCH2CH2OCCH3
4
3
2
1
6
7
Table 21.3
Functional
Group
sp3 CH
stretch
Base Values
Acetic acid
Isoamyl
alcohol
Isoamyl
acetate
Frequency
(cm-1)
Frequency
(cm-1)
Frequency
(cm-1)
Frequency
(cm-1)
2800-3000
C-O stretch
1000-1300
OH stretch
3100-3350
C=O stretch
1680-1740
EXPERIMENTAL PROCEDURE
(NMR ANALYSIS)
CH3
5
CH3CHCH2CH2OH
4
3
2
CH3
1
O
5
CH3CHCH2CH2OCCH3
4
3
2
1
6
O
C
H3C
1
2
OH
3
7
SAFETY CONCERNS
CAUTION:
H2SO4
is a
STRONG ACID!
WASTE MANAGEMENT
• All aqueous washes from the extraction
can be flushed down the drain with plenty
of water!
• Ester product and distilled ether should be
placed in the bottle labeled, “ORGANIC
WASTE (Esters)”.
CLEANING



Clean round bottom flasks and distillation
glassware with wash acetone only!
Separatory funnel and all other glassware
should be cleaned with soap, water, and a
brush if necessary, followed by a wash
acetone rinse before returning to lab
drawer.
DO NOT return any glassware to lab
drawer dirty or wet!