Green Chemistry: As American
as Apple Pie
Synthesis of Banana Oil
Using Green Chemistry
Pamela Brown
Simon Dexter
New York City College of Technology
Brooklyn, NY
AAS in Chemical Technology
General Chemistry I and II (8 credits)
Organic Chemicstry I and II (10 credits)
Analytical Chemistry I and II ( 9 credits)
Introduction to Physical Chemistry (3 credits)
Science Research Skills (3 credits)
Physics I and II ( 8 credits)
Pre-Calculus ( 4 credits)
English I and II ( 6 credits)
Psychology (3 credits)
Liberal Arts Electives ( 6 credits)
As educators we have the opportunity
to influence future generations of
chemists
The laboratory presented today was
developed with an undergraduate,
Simon Dexter, as an honors project in
General Chemistry II.
Background
Synthesis of esters, especially 3methylbutylacetate, banana oil, is a
classic experiment performed in organic
chemistry labs across the country.
Traditionally, the Fisher esterification is
performed:
CH3
CH
CH3
CH2
OH
CH2
OH
+
=
CH CH2
C
O
O
CH3
CH3
CH3
C
CH3
+
H 2O
CH2 O
isopentyl acetate
water
acetic acid acid= 3-methylbutylacetate+water
isopentanol
3-methylbutanol
+ acetic
Eq. 1
Background
Microwave Induced Heating
The reaction uses sulfuric acid as catalyst and
requires about one hour of reflux to reach
equilibrium where:
Keq = 4.2
At equilibrium the yield is only about 67%.
An ether, such as ethyl ether is added to extract the
banana oil. The banana oil is recovered by
fractional distillation.
3-Methylbutylacetate Synthesis with
Microwave Heating
Stoichiometric amounts of acetic anhydride (7.0
mL=0.074 moles) and 3-methylbutanol (8.0 mL = 0.074
moles) are mixed in an HP500 pressure vessel and
heated in a CEM MARS Microwave oven with
temperature control at ambient pressure for 8 minutes at
110C, after a 2 minute ramp to the reaction temperature.
3-methylbutylacetate + acetic anhydride= 3-methylbutylacetate +acetic acid
CH3
CH
CH
CH3
CH3
CH2OH +
O
C
O
==
CH3
CH3
CH
CH3
CH2
O
CH2
C
O
Determination of Yield
The products are titrated using 2.0 M NaOH. The sample
separates into 2 phases, an organic phase containing essentially
pure 3-methylbutylacetate (average yield = 90%), and an
aqueous phase containing sodium acetate. Titration results can
be used to calculate the yield.
Acetic Anhydride + water ! 2 Acetic acid
Acetic Acid + NaOH ! Sodium acetate + water
Moles 3-methylbutylacetate produced
O
C
Microwave radiation rapidly heats
polar substances.
Polar substances try to align
themselves with the electric field.
Since the frequency is 2450 MHz the
molecules don’t have time to line up
one way before they have to line up
the other way. The resulting friction
causes the solution to heat up.
CH3
O
+
OH
= 2X initial moles of acetic anhydride - moles of acetic acid in
product
= 2X initial moles of acetic anhydride - moles of NaOH to titrate
product
Additional Applications
Why is this an example of green chemistry?
Eliminates the need for using sulfuric
acid as a catalyst, and ether for the
extraction
Eliminates the need for fractional
distillation
Reduces energy consumption
Last summer an undergraduate,
Alyse Rich, supported by an NIH
Bridges grant and a high school
student, Vincent Ong, supported by
an ACS SEED grant studied the rates
of reaction using microwave heating
and compared them to conventional
heating.
Determination of Rate Equation
A! B
Reactions Studied
3-methylbutanol + acetic anhydride _ 3-methylbutylacetate + acetic acid
CH3
CH3
CH
CH
CH2OH +
CH3
O
C
O
C
==
CH3
CH3
CH
CH2
O
CH2
C
CH3
O
+
O
CH3
OH
O
ethanol + acetic anhydride _ ethylacetate + acetic acid
CH3
OH
CH2
CH3
+
O
C
O
C
O
==
CH3
CH3
O
CH2
O
C
CH3
First Order Reaction:-d[A]/dt = k[A]
Plot of ln[A] vs t is a straight line,
slope = -k
CH3
+
O
C
OH
Second Order Reaction –d[A]/dt =
k[A]2
Plot of 1/[A] vs t is a straight line,
slope = k
Procedure
Plot of 1/ % ROH vs Time at 80C for
microwave heating – slope = k
Figure 1- Banana oil synthesis- Microwave Heating - 80C
2 min ramp to 80C = 0 time
time (min)
% Yield
time (min)
0
0
0
0.5
2
4
6
8
10
12
18.7
6.5
-1.6
9.1
25.4
24.1
39
57.9
60.6
68.7
0
0
0
0.5
2
4
6
8
10
12
1/(% reactant)
0.0123
0.010695
0.009843
0.011001
0.013405
0.013175
0.016393
0.023753
0.025381
0.031949
1/%reactant vs time(min)-80C microwave
0.035
0.03
1/% reactant
0.025
0.02
y = 0.0016x + 0.0099
0.015
R2 = 0.9315
0.01
0.005
0
0
5
10
15
time (min)
% Yield vs Time - Microwave Heating - 80C
80
70
60
% Yield
• Two equimolar samples of acetic anhydride and
alcohol were prepared (~15 mL total volume)
• One was heated for a given time and temperature
(T=80, 90, 110C with 3-methylbutanol and T=70,
75, 82C with ethanol) in a CEM Microwave reactor
with temperature control. The second was heated in
a constant temperature oil bath.
• The % of unreacted acid = ROH and the % yield of
ester was determined by titration.
• Plots of % ROH vs time, ln (% ROH) vs time and
% ROH-1 vs time were prepared to determine the
reaction order, rate constant and activation energy
mL 2M NaOH
67.1
71.6
74.5
70.5
64.5
65.1
59.6
52.5
51.5
48.6
50
40
30
20
10
0
-10
0
2
4
6
8
10
12
14
Time (minutes)
Arrhenius Equation: k = A exp (-E/RT)
Plot of ln k vs 1/T for microwave heating- slope = -E/R
Figure 5 - ln k vs 1/T(K) - banana oil synthesis - microwave heating
k
Temperature(C)
1/T(K)
ln(k)
0.0016
80
0.002833 -6.43775
0.0042
100
0.002681 -5.47267
0.0102
110
0.002611 -4.58537
Experimental Activation Energies
Reaction
Ea, Activation
Energy (kJ/mole)
A, Arrhenius
Constant
Ethylacetate synthesis – conventional heating
185
2.3 x 1024
Ethylacetate synthesis – microwave heating
110
4.3 x 1013
Banana oil synthesis– microwave heating and
conventional heating
67
1.1 x 107
Determination of Activation Energy and Arrhenius
Constant- Ln k vs 1/T(K)
0
-1
ln k
-2
-3
-4
-5
-6
-7
0.00255
0.0026
0.00265
0.0027
1/T(K)
0.00275
0.0028
0.00285
y = -8026.7x + 16.24
R2 = 0.9659
Discussion
• With ethanol, the rate of reaction was 2-3
times greater with microwave heating
than conventional heating.
• With 3-methylbutanol the rates were
equal.
• This suggests that the alignment of
molecules due to the oscillating electric
field produced by the microwaves may
have a catalytic effect on smaller
alcohols.
Conclusion
Introducing Green Chemistry Labs
into the curriculum reduces waste
generated by the college and creates
a culture of respect for the
environment
Encouraging students to develop
these labs is an opportunity to
develop short-term student projects
with tangible results