Learning to be green: Involving students in the decision making process Rich Gurney Department of...

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Transcript of Learning to be green: Involving students in the decision making process Rich Gurney Department of...

  • Slide 1
  • Learning to be green: Involving students in the decision making process Rich Gurney Department of Chemistry Simmons College Boston, MA 02115 [email protected]
  • Slide 2
  • Success is a journey, not a destination. The doing is often more important than the outcome. - Arthur Ashe
  • Slide 3
  • 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
  • Slide 4
  • 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
  • Slide 5
  • [Oxidation] When choosing a synthetic path, consider... Applicability Selectivity Effectiveness % Yield Time $$ Safety Hazards Disposal Energy Solvents
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  • [Oxidation] Hazards of oxidants: Na 2 Cr 2 O 7 - Cr (VI) - Highly carcinogenic (inhalation) - Target kidney, liver, respiratory system, eye skin. - Poison Route 1: Na 2 Cr 2 O 7 / H 2 SO 4 Route 2: NaOCl / HOAc 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. NaOCl - Organochlorine formation - contains traces Hg
  • Slide 7
  • 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. How can we improve the process? Solvent (#5) Heterogeneous/Homogeneous (#3 & #5) Microwave heat (#6) Speed (#6)
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  • Solvent vs Solvent-Free Short-term Health Effects dermatitis or skin problems (drying, cracking, reddening or blistering of the affected area) headaches drowsiness poor coordination nausea Long term Heath Effects the brain and the nervous system liver damage blood-forming system kidneys fertility of both M & F carcinogenic (benzene) synergistic effects with other chemicals and drugs death
  • Slide 9
  • Homogeneous vs Heterogeneous Heterogeneous easy and inexpensive removal safe to store, long life time wide range of utility non-toxic, Regenerable easy and safe disposal easy to handle increased stability avoids formation of inorganic salts Homogeneous difficult and expensive to separate from the reaction products and the solvent short life time short range of utility degrades easily not safe to dispose hard to handle
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  • Conventional Heating vs Microwave Energy Larhed M.; Moberg C.; Hallberg A. Microwave-accelerated homogenous catalysis in organic chemistry. Acc. Chem. Res. 2002, 35, 717 - 727. No boundary layer - Internal heating is maximized by direct heating mechanism No temperature gradient, homogenous heating optimizes purity of the reaction Heat source started and ceased instantaneously Shortened reaction times decrease energy requirement Superheating is possible, especially with pressure tube Glass Pressure Tube
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  • OxidantWater soluble, ground water contaminant, not catalytic, highly toxic or extreme hazard Heterogeneous, not catalytic, moderate hazard Heterogeneous, catalytic, mild or no hazard (2 - 3) (0 - 1) (4 - 5) SolventToxic, flammableLess toxic, not flammable No solvent or benign solvent EnergyHot plate: long heating time. Heat penetrates one area, danger of over- heating. Hot plate: shorter heating times, less energy expended. Microwave energy: short heating time. Or No heat is applied. Time> 3 hours Due to the constraints of lab period. < 2 hours< 1 hr How can we improve the process?
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  • [Oxidation] Reaction OxidantDichromate 0 SolventDuring Reaction Ether 0 WorkupCH 2 Cl 2 / Bicarbonate 1 Energy TempIce-Cold 3 TimeLab Time>1 hr 3 Standard Method: Sodium dichromate (Na 2 CrO 7 ) Sodium dichromate (Na 2 Cr 2 O 7 ) 7 Bleach Traces Hg 1 Acetone 1 CH 2 Cl 2 / bicarbonate 1 50 min, 50 o C 2 > 1.5 hours 3 8 Standard Method: Bleach (NaOCl) 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.
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  • Solvent-Free, Microwave, Oxidation Reactions Dr. Rajender Varma, U.S. EPA Clayfen Clay-cop Hydrogen Peroxide Chromium Trioxide impregnated on wet Alumina Iodobenzene Diacetate on Alumina Activated Manganese Dioxide on Silica Gel
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  • [Oxidation] iodosylbenzene - Al 2 O 3 3 Solvent-Free 5 CH 2 Cl 2, NaHCO 3 (aq) 1 Microwave 5 ~ 2 hours 2 Reaction Oxidant SolventDuring Reaction Workup EnergyTemp TimeLab Time 16 2 0 0 OX Clayfen (Emission of NO 2 ) 0 Solvent-Free 5 CH 2 Cl 2 1 Microwave 5 ~ 2 hours 2 3 0 0 OX 13 Claycop - H 2 O 2 1 Solvent-Free 5 CH 2 Cl 2 1 Microwave 5 ~ 2 hours 2 1 0 3 OX 14 Wet CrO 3 - Al 2 O 3 2 distilled H 2 O 5 CH 2 Cl 2 1 Microwave 5 ~ 2 hours 2 3 0 1 OX 15 Class A Poison: causes muscle contractions constricting airways and serious potentially fatal lung damage causing delayed pulmonary edema and a potentially time delayed immune system attack on the lungs. accidental or intentional swallowing of larger amounts of CrO 3 has caused stomach upsets and ulcers, convulsions, kidney and liver damage, and even death.
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  • [Oxidation] Reaction OxidantMnO 2 - SiO 2 3 SolventDuring Reaction Solvent-Free 5 WorkupEther / CH 2 Cl 2 0 EnergyTempMicrowave 5 TimeLab Time~ 2 hours 215 1 1 2 OX 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.
  • Slide 16
  • Fall 2003: EXPERIMENTAL PROCEDURE: Grind active MnO 2, 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. Microwave at maximum intensity for 100 s. Remove the hot vial carefully. Follow the reaction, by TLC (CH 2 Cl 2 ) 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 CH 2 Cl 2. 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 (CH 2 Cl 2 ). [Oxidation] MnO 2 - SiO 2
  • Slide 17
  • 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
  • Slide 18
  • Fall 2003: Can we find a better TLC solvent system to replace CH 2 Cl 2 ? + (10:1, hexane:EtOAc) works perfectly. Can the Et 2 O for TLC extract be replaced with a better solvent? hexanes - NO, EtOAc - no, EtOH - no, iPrOH - no. Can we eliminate the final extraction solvent (CH 2 Cl 2 / Et 2 O)? + 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.
  • Slide 19
  • 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.
  • Slide 20
  • [Oxidation] MnO 2 - SiO 2
  • Slide 21
  • Reaction OxidantMnO 2 - SiO 2 3 Solvent During Reaction Solvent-Free 5 Workup Ether / CH 2 Cl 2 0 EnergyTempMicrowave 5 TimeLab Time~ 2 hours 215 1 1 2 OX [Oxidation] MnO 2 - SiO 2
  • Slide 22
  • Reaction OxidantMnO 2 -