Transcript Learning to be green: Involving students in the decision

Learning to be green:
Involving students in the
decision making process
Rich Gurney
Department of Chemistry
Simmons College
Boston, MA 02115
[email protected]
Success is a journey, not a destination.
The doing is often more important than
the outcome. - Arthur Ashe
Four stages of greening a process
choices:
– of the reaction
– in performing the reaction
– in isolating and purifying the product
– in characterizing the outcome of the reaction
Four stages of greening a process
choices:
– of the reaction
– in performing the reaction
– in isolating and purifying the product
– in characterizing the outcome of the reaction
[Oxidation]
H
O
OH
When choosing a synthetic path, consider...
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Applicability
Selectivity
Effectiveness
% Yield
Time
$$
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Safety
Hazards
Disposal
Energy
Solvents
[Oxidation]
H
OH
Route 1: Na2Cr2O7 / H2SO4
Route 2: NaOCl / HOAc
O
Hazards of oxidants:
Na2Cr2O7
- Cr (VI)
- Highly carcinogenic (inhalation)
- Target kidney, liver, respiratory system,
eye skin.
- Poison
NaOCl
- Organochlorine formation
- contains traces Hg
Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Engel, R. G. Introduction to Organic Laboratory
Techniques, a Small Scale Approach; Third Edition; Saunders College Publishing: Fort Worth, TX, 1999.
How can we improve the process?
Twelve Principles of Green Chemistry
3. Process should use or generate little or no toxic materials.
5. Auxiliary substances should be eliminated whenever possible
(solvents, separating agents) or be innocuous.
6. Energy requirements should be minimized.
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Solvent (#5)
Heterogeneous/Homogeneous (#3 & #5)
Microwave heat (#6)
Speed (#6)
How can we improve the process?
(0 - 1)
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Oxidant Water soluble,
ground water
contaminant,
not catalytic,
highly toxic or
extreme hazard
Heterogeneous,
not catalytic,
moderate hazard
Heterogeneous,
catalytic,
mild or no hazard
Solvent
Toxic, flammable
Less toxic,
not flammable
No solvent or benign
solvent
Energy
Hot plate: long
Hot plate:
heating time. Heat
shorter heating times,
penetrates one area, less energy expended.
danger of overheating.
Microwave energy:
short heating time.
Or No heat is applied.
Time
> 3 hours
Due to the
constraints of lab
period.
< 1 hr
< 2 hours
[Oxidation]
H
O
OH
Standard Method:
Sodium dichromate (Na2Cr2O7)
Standard Method:
Bleach (NaOCl)
0
Bleach
Traces Hg
1
0
Acetone
1
CH2Cl2 /
Bicarbonate
1
CH2Cl2 /
bicarbonate
1
Temp
Ice-Cold
3
50 min, 50oC
2
Lab Time
>1 hr
3
> 1.5 hours
3
Reaction Oxidant
Dichromate
Solvent
During
Reaction
Ether
Workup
Energy
Time
7
8
http://www.atsdr.cdc.gov/toxprofiles/phs7.html
“small amounts of chromium(VI) that you swallow will not hurt you; however, accidental or
intentional swallowing of larger amounts has caused stomach upsets and ulcers, convulsions,
kidney and liver damage, and even death.”
Solvent-Free, Microwave, Oxidation Reactions
Dr. Rajender Varma, U.S. EPA
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Clayfen
Clay-cop Hydrogen Peroxide
Chromium Trioxide impregnated on wet Alumina
Iodobenzene Diacetate on Alumina
Activated Manganese Dioxide on Silica Gel
[Oxidation]
H
O
OH
Reaction Oxidant
Solvent
MnO2 - SiO2
3
1
1
During
Reaction
Solvent-Free
Workup
Ether /
CH2Cl2
0
5
Energy
Temp
Microwave
5
Time
Lab Time
~ 2 hours
2
2
TIFF (
are
OX
15
http://www.atsdr.cdc.gov/toxprofiles/phs151.html
Manganese is a regular part of the human body; it is a necessary component in order for the
body to work properly. The body normally controls the amount of absorbed manganese. For
example, if large amounts of manganese are eaten in the diet, the body excretes large amounts
in the feces. Therefore, the total amount of manganese in the body tends to stay about the same,
even when exposure rates are higher or lower than usual.
[Oxidation]
Fall 2003:
EXPERIMENTAL PROCEDURE:
H
MnO2 - SiO2
O
OH
Grind active MnO2, silica gel, and borneol in a mortar and pestle, until a
homogenous mixture is obtained. Transfer this sample into a capped glass
scintillation vial.
Place in the center of a household ($65) microwave.
maximum intensity for 100 s. Remove the hot vial carefully.
Microwave at
Follow the reaction, by TLC (CH2Cl2) of a 1 mL diethyl ether extract of a
spatula of the reaction material. Repeat the microwave heating as
necessary.
Once the reaction is complete by TLC and the reaction material is cooled to
room temperature add 5 mL of CH2Cl2. Separate the organic layer by
vacuum filtration and remove the solvent to obtain crude product. Redissolve
crude product in a minimum amount of diethyl ether to transfer to a
sublimation chamber. Sublime product.
Characterize final product by TLC (CH2Cl2).
Four stages of greening a process
choices:
– of the reaction
– in performing the reaction
– in isolating and purifying the product
– in characterizing the outcome of the reaction
Fall 2003:
Can we find a better TLC solvent system to replace CH2Cl2?
+ (10:1, hexane:EtOAc) works perfectly.
Can the Et2O for TLC extract be replaced with a better solvent?
– hexanes - NO, EtOAc - no, EtOH - no, iPrOH - no.
Can we eliminate the final extraction solvent (CH2Cl2 / Et2O)?
+ place the glass vial in a heated sand bath, product camphor sublimes
directly from the reaction mixture
– product collects in the cap.
– introduction of new heat source, hot plate / sand bath.
Can a test-tube replace the glass vial for final sublimation?
+ camphor sublimes toward the top of the tube, easier to collect
– product falls back onto the reaction materials.
How long is too long? Can we heat the reaction for a longer period and obviate
the need to follow the reaction?
+ 20 sec, 40 sec, 60 sec, 120 sec, camphor to borneol ratio increasing.
– brown/white film climbing the side of the glass vial, top most rim of vessel
– white crystals form.
+ white crystals are product!
– microwave oven can overheat.
Fall 2003:
Can we eliminate the separate sublimation step and thereby eliminate the
energy required for heating the sand?
+ upon further heating in the microwave, the camphor sublimes directly in
the reaction vessel from the reaction mixture.
– yield low due to difficulty in isolating the product from the glass vial.
Can a corked test-tube replace the glass vial?
+ camphor sublimes toward the top of the tube, easier to collect
– product falls back onto the reaction materials.
Can a Petri-Dish replace the corked test-tube?
+ camphor sublimes on top dish, which is easily removed from the bottom,
and product isolation is greatly facilitated.
How green is the characterization of the final product? Is TLC the best method
of analysis?
+ IR Spectroscopy can be used to easily distinguish borneol from camphor,
– the final product is often contaminated with traces of water, which can be
misinterpreted as an alcohol.
[Oxidation]
Fall 2003:
EXPERIMENTAL PROCEDURE:
H
MnO2 - SiO2
OH
Grind active MnO2, silica gel, and borneol in a mortar and pestle, until a homogenous
mixture is obtained. Transfer this sample into a capped glass scintillation vial the
bottom of a Petri-dish.
Replace Petri dish cover and place in the center of a microwave. Microwave at
maximum intensity for 100 s. Remove the hot dish carefully.
Follow the reaction, by TLC (CH2Cl2) of a 1 mL diethyl ether extract of a spatula of
the reaction material. Repeat the microwave heating as necessary.
Once the reaction is complete by TLC and the reaction material is cooled to room
temperature add 5 mL of CH2Cl2. Separate the organic layer by vacuum filtration and
remove the solvent to obtain crude product. Redissolve crude product in a minimum
amount of diethyl ether to transfer to a sublimation chamber.
Sublime product.
Recover the sublimed camphor from the Petri-dish cover with a razor blade.
Characterize final product by TLC (CH2Cl2). Characterize final product by IR
Spectroscopy.
O
[Oxidation]
MnO2 - SiO2
H
O
OH
Reaction Oxidant
Solvent
MnO2 - SiO2
3
1
1
During
Reaction
Solvent-Free
Workup
Ether /
CH2Cl2
0
5
Energy
Temp
Microwave
5
Time
Lab Time
~ 2 hours
2
2
OX
15
Qu
TIFF (Uncom
are neede
[Oxidation]
MnO2 - SiO2
H
O
OH
Reaction Oxidant
Solvent
During
Reaction
MnO2 - SiO2
Solvent-Free
3
1
1
5
Isolation
Solvent-Free
Purification
5
Energy
Temp
Microwave
5
Time
Lab Time
5 mins
5
2
OX
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Qu
TIFF (Uncom
are neede
Fall 2004:
EXPERIMENTAL PROCEDURE:
Grind active MnO2, silica gel, and borneol in a mortar and pestle, until a
homogenous mixture is obtained.
Transfer this sample into the bottom of a Petri-dish. Replace Petri-Dish
cover and place in the center of a microwave. Microwave at maximum
intensity for 100 s. Remove the hot dish carefully.
Recover the sublimed camphor from the Petri-dish cover with a razor
blade.
Characterize final product by IR Spectroscopy.
Fall 2004:
Can we prevent the microwave from overheating?
+ a beaker of water absorbs excess energy in the microwave.
– but increases the -OH stretch in the IR spectrum of the product.
Can we prevent the microwave from overheating?
+ a beaker of alumina absorbs excess energy and does not increase the water
content in the camphor product.
Can we diminish the water signal in the IR of the camphor product?
+ drying the silica gel and the MnO2 before use decreases water in the camphor
product.
Can we maximize the yield of camphor by placing an ice cold Erlenmeyer on top of the
Petri-dish cover?
– ice cold Erlenmeyer does not appear to increase % yield, but increases the –OH
stretch in the IR spectrum of the product.
Can we maximize the yield of camphor by using a Petri-dish with a smaller thickness to
decrease the distance between the reaction medium and the product collection
vessel?
– decreasing the distance increases the amount of MnO2 that is “carried-up” with the
sublimed camphor product.
Can we increase the purity of the sublimed camphor by increasing the distance between
the reaction medium and the product collection vessel?
+ increasing the distance decreases the amount of MnO2 in the product
+ appears to increase the yield.
Fall 2004:
Can we decrease the amount of MnO2 that is “carried-up” with the sublimed camphor
product, by adding a thin layer of pure silica gel over the reaction medium?
+ sublimed material slightly cleaner,
– yield decreases.
Can we minimize the amount of MnO2 that is “carried-up” with the sublimed camphor
product, by increasing the particle size? Can we simply shake the reagents together
instead of grinding them?
– the sublimed material is predominantly borneol instead of camphor when the
reagents are shaken together instead of ground.
Can we create a semi-continuous reaction vessel by layering the MnO2-silica over the
borneol?
– no camphor is isolated.
Can the same reaction be used for the conversion of other alcohols?
+ norborneol can be converted to norcamphor
Does freshly prepared MnO2 “work better” than “store bought” MnO2?
– MnO2 from Aldrich behaves identically to freshly prepared MnO2
Can we increase the yield of camphor by spreading out the reaction medium on the
bottom Petri-dish?
yield improves, yield decreases, yield remained the same?
Can we increase the yield of camphor by piling the reaction medium in the center of the
Petri-dish?
yield improves, yield decreases, yield remained the same?
Fall 2004:
Is the reaction stoichiometric or catalytic?
If the reaction is catalytic, can the reaction medium be used again to produce
more camphor if more borneol is added?
If the reaction is catalytic, can the catalyst be regenerated?
If the reaction is catalytic, how many times can the reaction medium be reused?
What is the optimal heating time to produce camphor, while minimizing the
sublimation of the starting borneol?
Does the particle size of the silica gel matter?
Can the reaction product ratio be followed by GC/MS?
Can the reaction product ratio be determined by 1H NMR?
“Why can’t we cancel the rest of the semester and continue working on this
experiment?”
“Why haven’t we been introduced to green chemistry earlier?”
“Why isn’t every lab a green chemistry lab?”
“Who in their right mind thinks that green chemistry is a bad idea?”
“Why is this (Green Chemistry) a separate concept from regular Chemistry?”
Fall 2005:
+A beaker of dry ice atop the Petri Dishes, increases condensation of product
by cooling the surface without addition of water.
+Reaction is not catalytic.
+Used manganese dioxide silica mixture, can not be reused.
+Many different reactor designs can be used effectively.
+The particle size of the silica gel does not cause a statistically significant
increase in yield or purity of camphor.
+The reaction product ratio can be followed by GC/MS using a standard
GowMac GC using temperature settings typically suited for the separation of
cyclohexane and toluene.
+The presence of borneol in the camphor product down to a 5% can be
observed by 1H NMR (90 MHz, EFT Anasazi).
+The yield of camphor can increase from 12 - 15% to 85 - 92% while still
maintaining a 90 - 95% purity level by heating the reactor directly on a
hotplate, by carefully monitoring the temperature.
(Best temperature “program”: 25oC to 165oC over ~5 min.; hold at 165oC for
10 min.; ramp up to 200oC over 5 min. and hold at 200oC for 10 min.).
+Better reactor can be designed for hotplate reaction.
Alternative “Jetsons’” Probe
By: Tayaba Naz
4” Watch Glass
1” Watch Glass
Wide-mouth Powder Glass Funnel
Hotplate
0.350g MnO2
0.70g Silica Gel
0.40g Borneol
Step 1: Weigh the small watch glass and the funnel.
Step 2: Mix the reagents in a small 50-mL beaker with a metal spatula for 5 minutes and pour
the regents in a pile on the large watch glass.
Step 3: Cover the reagents with the cut-off or wide-mouth powder funnel as shown in the
figure above. Place the small watch glass on the mouth of the funnel.
Step 4: Carefully put the setup on the hotplate and gradually raise the temperature of the
hotplate to 165oC over ~5 minutes. Monitor the temperature with a thermocouple.
Step 5: Hold the temperature of the hotplate at 165oC for 10 minutes.
Step 6: Gradually raise the temperature of the hotplate to 200oC over ~5 minutes and hold the
temperature of the hotplate at 200oC for 10 minutes.
Step 7: Carefully remove the setup from the hotplate and allow it to cool for about 5 minutes.
Ensure the temperature is below 45oC
Step 8: Weigh the funnel and the small watch glass with the sublimed camphor product and
determine the isolated weight and percent yield of your product.
Step 9: Run TLC/IR/NMR/GC on your product to check the purity.
Key Concepts introduced: solid-phase green oxidation
• Synthesis: Solid phase oxidation chemistry
• Work-up techniques: heterogeneous extraction
• Purification techniques: sublimation
• Characterization methods:
• sealed capillary tube melting point determination
• thin layer chromatography (ethyl acetate/hexanes)
Value Added: solid-phase green oxidation
Added Characterization methods due to extra time:
• 1H NMR (CDCl3)
• GC (traces of diethyl ether)
• IR (KBr)
Contextualized discussion of:
• heterogeneous reactions
• solvent free reactions
• MSDS, safety, disposal, environmental consequences
• alternative energy sources (reaction can be done in microwave)
• choosing from multiple synthetic procedures
Spare lab time to allow students to apply and test green chemical principles
Unanticipated outcomes: solid-phase green oxidation
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high level of student engagement with content
high level of student personal accountability
engagement within research and scientific method
increased enthusiasm for chemistry and chemical research
true concern and appreciate for disposal and safety
every student became a critical evaluator
every student became a contributing member of my research group
“We don’t receive wisdom, we must discover it ourselves after a journey
that no one can take for us, or spare us.” Marcer Proust
“Who would venture upon the journey of life, if compelled to begin it at the
end.” Madame de Maintenon.
“Am I going to be an author on the paper?” Brandi Watts, Simmons ‘05
“Maybe I should consider a career in chemical research instead of
medical school because I can bring about greater good, by championing
green chemistry.” Tayaba Naz ‘08
Qui ckTi me™ and a
TIFF (Uncompressed) decompressor
are needed to see this pictur e.
Acknowledgements
Tayaba Naz, Simmons College (‘08)
Shauna Tracy, Simmons College (‘08)
YinYin Lin, Simmons College (‘05)
Craig Schwartz, Northwestern University (‘04) (UC Berkeley)
Marc Sala, Northwestern University (‘04) (Northwestern Medical)
Students in CHEM 225, Fall 2003, 2004, 2005
Henry and Camille Dreyfus Foundation Postdoctoral Fellowship in Environmental
Chemistry
Simmons College Faculty Start-Up Funds.
Procedures? Slides? Technical help? Questions? Contact me:
Rich Gurney
Department of Chemistry
Simmons College
Boston, MA 02115
[email protected]
(617) 521 - 2729
QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
Procedures? Slides? Technical help? Questions? Contact me:
Rich Gurney
Department of Chemistry
Simmons College
Boston, MA 02115
[email protected]
(617) 521 - 2729