Power Point Presentation (PDF) - Green Chemistry Center

Synthesis of Banana Oil
Using Green Chemistry
Pamela Brown
Simon Dexter
New York City College of Technology
Brooklyn, NY
Green Chemistry: As American
as Apple Pie
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.
AAS in Chemical Technology
Background
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)
Synthesis of esters, especially 3-
methylbutylacetate, banana oil, is a
classic experiment performed in organic
chemistry labs across the country.
Traditionally, the Fisher esterification is
performed:
CH 3 CH 2 OH
CH CH 2 +
CH 3
O
OH
C
=
CH 3
CH CH 2 C CH 3 + H 2 O
CH 3 CH 2 O
isopentanol
acid isopentyl acetate
water
3-methylbutanol + acetic acid= 3-methylbutylacetate+water
CH 3
O
Eq. 1

Background
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.
Microwave Induced Heating
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.
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
CH
CH 3 O
3 CH
CH CH 2 OH + C
== CH 3 CH 2 O CH 3
CH CH 2
O
C
+
CH CH 3
3 C
CH 3 O
O
OH
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
= 2X initial moles of acetic anhydride - moles of acetic acid in
product
= 2X initial moles of acetic anhydride - moles of NaOH to titrate
product

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
Additional Applications
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.
Reactions Studied
3-methylbutanol + acetic anhydride _ 3-methylbutylacetate + acetic acid
CH 3 CH 3 CH 3
O
CH 3 CH
CH CH 2 OH C
== CH 3 CH 2 O CH
CH 2
C
CH 3
O
O
CH 3
+
C
O
OH
O
ethanol + acetic anhydride _ ethylacetate + acetic acid
CH 3 O
CH 3 OH
C
CH
+ ==
3 O
CH 2
CH 3 O O
C
O CH 3
CH 2 C
+
C
CH 3
OH
O
Determination of Rate Equation
A! B
First Order Reaction:-d[A]/dt = k[A]
Plot of ln[A] vs t is a straight line,
slope = -k
Second Order Reaction –d[A]/dt =
k[A] 2
Plot of 1/[A] vs t is a straight line,
slope = k

Procedure
• 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
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
mL 2M NaOH time (min) % Yield time (min) 1/(% reactant)
67.1 0.0123
0 18.7 0
71.6 0 6.5 0 0.010695
74.5 0 -1.6 0 0.009843
70.5 0.5 9.1 0.5 0.011001
64.5 2 25.4 2 0.013405
65.1 4 24.1 4 0.013175
59.6 6 39 6 0.016393
52.5 8 57.9 8 0.023753
51.5 10 60.6 10 0.025381
48.6 12 68.7 12 0.031949
1/% reactant
% Yield
80
70
60
50
40
30
20
10
0
-10
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
1/%reactant vs time(min)-80C microwave
0 5 10 15
time (min)
% Yield vs Time - Microwave Heating - 80C
y = 0.0016x + 0.0099
R 2 = 0.9315
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
E a , Activation
Energy (kJ/mole)
A, Arrhenius
Constant
ln k
0
-1
-2
-3
-4
-5
-6
Determination of Activation Energy and Arrhenius
Constant- Ln k vs 1/T(K)
-7
0.00255 0.0026 0.00265 0.0027 0.00275 0.0028 0.00285
1/T(K)
y = -8026.7x + 16.24
R 2 = 0.9659
Ethylacetate synthesis – conventional heating 185 2.3 x 10 24
Ethylacetate synthesis – microwave heating 110 4.3 x 10 13
Banana oil synthesis– microwave heating and
conventional heating
67 1.1 x 10 7

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