Green Chemistry: What is it?How do you know it when you see it?
Green Chemistry: What is it? How do you know it when you see it? Chem 253 April 29th Dr. Kellen-Yuen Chemistry as an Industry Chemical manufacturing worldwide value of $1.5 trillion (1998) Value of US chemical shipments $811 billion (2013) 0 100000 200000
2005 610,873 2004 2003 2002 2001 900000 811,571 540,884 487,742 462,499 438,410 Value in million U.S. dollars
Organic Chemistry Plastics, fuels, pharmaceuticals, dyes, fabrics, agricultural and other chemicals Our lifestyles are almost unimaginable without the products of modern industrial production Chemistry can be a problem Atmospheric Pollution VOCs Greenhouse Gasses / Climate Effects Ozone layer depletion
Photochemical smog (NOx and SOx) Aqueous Pollution Industrial and Urban waste Fertilizers, Pesticides, Insecticides Solvents, Detergents, etc Solid Pollution Industrial solids which cant be reused Nuclear and radioactive waste Chemical residues One Specific Example Pesticides (insecticides, herbicides, fungicides) kill unwanted organisms 1 billion kg used in North America alone Both Home and Commercial use Examples: DDT, Metolachlor, Atrazine,
Malathion Persistant Organic Pollutants (POPs) Not water soluble, accumulate in organics/biomass, transfer into fish, people, etc Often not metabolized by fish, just accumulates in fatty tissue (Biomagnification) Growth in regulation laws Whats a Chemist to do? Green Chemistry What is Green Chemistry? The utilization of a set of principles that reduces or eliminates the use or generation of hazardous substances in the design, manufacture, and
application of chemical products Anastas, P.T.; Warner, J.C. Green Chemistry: Theory and Practice, Oxford University Press: Oxford, 1998 EPA focus since 1991 Green Chemistry Institute Founded in 1997 Joined ACS in 2001 12 Principles of Green Chemistry 1. 2. 3. 4. 5. 6.
It is better to prevent waste than to treat or clean it up Synthetic methods should be designed to maximize the incorporation of all materials used in the process into final product Wherever practicable, synthetic methods should be designed to use/generate substances of little or no toxicity to health and environment Chemical products should be designed to preserve efficacy of function while reducing toxicity. Use of auxiliary substances should be avoided Energy requirements should be minimized and reactions carried out at ambient temp and pressure 12 Principles of Green Chemistry A raw material feedstock should be
renewable 8. Unnecessary derivatization should be avoided (protecting/deprotecting, blocking groups, etc) 9. Catalytic reagents are better than stoichiometric 10.Chemical products should be designed so that at the end of their function they do not persist in the environment and instead break down into innocuous degradation products 11.Analytical methods need to be further developed to allow for real-time, in-process monitoring and control 12.Substances used in a chemical process should be chosen to minimize the potential for chemical accidents 7. What is Green Chemistry?
[email protected] Chemical Hazards Many types of hazards Carcinogens, mutagens, teratogens, tumorogens, corrosives, lachrymators, irritants Chronic vs Acute Acute often leads to immediate and dramatic health consequences Chronic is often more problematic in environment Chronic effects often long-lasting LD50
Its all in the Dosage Substance LD50 (mg/kg) Water 180, 000 Sugar 35,000 Sodium Chloride Caffeine 3,750 130 Slightly hazardous
Highly hazardous Sarin (nerve gas) 0.4 Extremely Hazardous Tetanus toxin A 5 x 10-6 Extremely Hazardous Botulinium toxin 3 x 10-8
Extremely Hazardous Sources of Information about Hazards Safety Data Sheets (SDS or MSDS) On-line, for example Sigma Aldrich website Hazardous Chemicals Database Toxnet (toxicology data network) http://toxnet.nlm.nih.gov/ CDC International Chemical Safety Cards (ICSC) http://www.cdc.gov/niosh/ipcs/icstart.html
Hazardous Laboratory Chemicals: Disposal GuideCRC Press So, how can you measure green? Hazard analysis Risk factors Number of Toxic reagents LD50 comparisons So, how can you measure green? Atom Economy
Way to calculate the efficiency of utilization of atoms provided by the starting materials /reagents MWproducts AE = x 100% MWstarting materials Since mass ~ MW, can also use total masses in this calculation So, how can you measure
46.4% Note: since one reagent was used in excess, this lowers overall economy of the reaction So, what do you do to make the Chemistry greener? Use scrubbers to remove VOCs and other gaseous wastes Treat waste water to remove toxins More efficient incinerators to destroy toxins Treat wastes in general to lower toxicity Minimize the generation of toxic waste But all of these are responses--none proactively improve the reactions being conducted First, know your reaction Starting
Materials Reagents Solvent(s) Energy Products + By-products What can you do? Existing Procedure Assess: starting materials, reagents, products, byproducts, solvent, reaction conditions, efficienct, etc Modify the process
Identify hazards or inefficiencies Greener Alternatives Test efficacy of new process Change the Reagents--Pesticides Natural insecticides Pyrethrins from chrysanthemum flowers Harpin Technology Bacterial protein which causes plants natural defense mechanisms to kick in Causes a response which kills cells at the point of attack
Creates a physical barrier to further entry of a pathogen Wont cause immunity response in pest. Made from modified E coli through fermentationno chemical synthesis Requires 70 % less than typical pesticide Change the Reagents--Pesticides Targeted insectides Diacylhydrazins Cause insects in their larval stage to think they are still shedding their cuticle Caterpillars stop eating GMOs Change the Reagents-New Routes Biological
Petroleum Feedstocks Catalysis / Reagents Chemical transf ormations HO HO OH HO HO O NH2 CO2H H3CO
Gallic OH Acid H3CO N N NH2 OCH3 Microbe Catalysis Trimethoprin (an antibiotic) OH OH
H3CO HO CHO Vanillin Change the Solvents Typical issues with organic solvents Volatility (exposure and release issues) Flammability Explosion Hazard / Flash points (particularly ethers) Toxicity Ozone depletion (halogenated solvents like CFCs) Storage / Handling /Disposal A
favorite target for greening a reaction Change the Solvents-Existing Options Use the greenest of the conventional solvents Low toxicity / environmental hazards Less volatile liquids Recycle Popular choices: Ethanol, Isopropyl Alcohol, Polyethers (diglyme), Ethyl Acetate WATER
Change the Solvents-New Approaches Fluorous Phase Supercritical fluids Ionic Liquids No Solvent Change the Solvents-Fluorous Phase Hydrofluorocarbons (HFCs) Designed to replace CFCs No Chlorines, therefore no damage to ozone layer Change the SolventsSupercritical fluids
CO2 liquefies under pressure replaces PERC for dry cleaning (Cl2C=CCl2) VOC, carcinogen, ground water contaminant Supercritical CO2 (73 atm, 31oC) Decaffeination of coffee Low viscosity and polarity Penetrates like a gas Dissolves small organics Use of surfactants can help (micelles) Change the Solvents-Ionic Liquids Ions tend to have high MP (ex: Na Cl, 801
C) ILs are made of bulky ions with dispersed charges and large non-polar regions low vapor pressure (unlike VOC solvents) Cheap, recyclable, non-flammable, and heat tolerant good for microwave heating o Change the Energy Requirements Microwave heating Speed (lower energy costs) Directly heat sample (less energy required) Efficient Heating of Smaller Samples High Temperatures (in sealed vials)
Microwave Effect Two methods of heating Dipolar polarization polar molecules oscillate with electric field; collisions produce heat Conduction ions/conductive molecules move in field causing polarization; resistance produces heat The Three Rs Recovery Solvents, spent reagents, catalysts Reuse /Recycle Reuse = useable without further purification
(catalysts) Recycle = processing or purification needed before using (solvents) Regenerate Most commonly when reagent is attached to a solid support Chemically treated to regenerate the reagent AmPAC Fine Chemicals: racemization of undesired enantiomer Examples of Green Chemistry: Sertraline Examples of Green Chemistry Click ChemistryTriazole Synthesis
C C CC C CO CO22Me Me MeO22C (-) (-) (+) (+) N=N=N-CH N=N=N-CH22RR MeO2C C N CH2R MeO2C C N N
Examples of Green Chemistry H CHR2 N N N >95% (+) (-) RCH2 C C H R2CH-N=N=N, 1.5 eq CuSO4, Ascorbate RCH2
DMF/H2O, mw 20 min., 80oC Joosten, et. al. Eur. J. Org. Chem 2005, 3182-3185. (+) (-) MeO2C C C CO2Me PhCH2-N=N=N mw 30 sec, 30% MeO2C MeO2C N N N
CH2Ph ~98% Examples of Green Chemistry Polymers 60 billion kg of oil-based feedstocks are used to make 27 billion kg of plastics/polymers each year PET (polyethylene terephthalate)plastic bottles and cloth Polyethylenetrash/grocery bags polystyrenepacking foam, drink cups to appliances and furniture Recycling of PET (only ~25%) generally cant go back into bottles, but is often used for fibers (carpets and clothing)
Examples of Green Chemistry Polylactic acid (PLA) Examples of Green Chemistry Polylactic acid (PLA) Made from corn and sugar beets Goal is to use waste biomass for this fuel Renewable source, less fossil fuel required in production, natural fermentation requires no organic solvent, high yields, recyclable,
compostable Green Chemistry-Conclusions Synthesis should be done in an environmentally friendly and sustainable manner Many approaches to improving syntheses: Reagents, catalysts, solvents, procedures, energy, Recovery, Recycle, Regenerate
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