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Risk and Green Chemistry 

 27 February 2012 

 Risk = f[hazard,exposure] 

 

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Ways to limit risk 1. Limit exposure –  Wear safety equipment (goggles, lab coat,

gloves, etc) –  Work in a fume hood –  Dispose of toxic chemicals properly –  Command-and-control laws Problems with this approach: –  Safety measures can fail –  Disregards unknown effects of chronic

exposure, along with synergistic affects and bioaccumulation

Ways to limit risk 

2. Limit hazards –  Use less toxic or nontoxic chemicals and

solvents –  Reduce or eliminate use of toxic chemicals Benefits to this approach: –  Safety measures cannot fail

What’s missing: toxicity data on many substances, particularly chronic and synergistic effects.

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Precautionary Principle

•  Ac@ng, even in the absence of complete scien@fic data, before the adverse affects on human health and the environment become significant or irrevocable. 

•  In 2003, San Francisco became the first in the U.S. to adopt a Precau@onary Principle Ordinance.  In 2005, a Precau@onary Purchasing Ordinance was passed. 

•  Precau@on is wriQen into the laws of the E.U. 

Risk management

Green Chemistry seeks to minimize risk by reducing the hazards associated with chemical products and processes.  Two examples: •  Pressure‐treated wood •  CO2 as a blowing agent for polystyrene 

 Risk = f[hazard,exposure] 

 

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Pressure-Treated Wood

•  Untreated wood lasts 3‐12 years (outdoors) •  Treated wood lasts 20‐50 years •  The Southern Forest Products Associa@on es@mated in the early 1990s that pressure‐treated wood saves about 226 million trees each year. 

 •  From the 1930s un@l 2003, wood was treated with chromated copper arsenate (CCA) to prevent rot. 

Cann & Umile (2008) Real‐World Cases in Green Chemistry, Vol. II, pp. 47‐51. 

CCA Type C

•  CCA Type C contains: – CrO3 (47.5%) – CuO (18.5%) – As2O5 (34.0%) 

Photo from ccaresearch.org 

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Chromium(VI) toxicity

•  Hexavalent chromium is toxic – LD50(oral, rat) = 80 mg/kg (5.4 g for a 150‐lb adult, 1.1 g for a 30‐lb toddler) 

– Cr(VI) is a strong oxidizer and damages the kidneys, liver, and blood 

•  Cr(VI) is also a suspected carcinogen •  It can also cause allergic skin reac@ons in some people. 

Arsenic toxicity

•  Arsenic is toxic – LD50(oral, rat) = 48 mg/kg (3.3 g for a 150‐lb adult, 0.7 g for a 30‐lb toddler) 

– As replaces P in many biochemical reac@ons, impairing cell respira@on in the mitochondria 

•  As is also a known carcinogen – Linked to lung, bladder, skin and liver cancer – Perhaps interferes with DNA repair enzymes 

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Department of Ecology, State of Washington 

Pressure-Treated Wood

Ban on CCA

•  The industry agreed to a ban on CCA‐treated lumber for residen@al and playground use star@ng December 31, 2003. 

•  It is s@ll allowed for some commercial uses: – u@lity poles – highway construc@on – marine construc@on – shakes and shingles 

hQp://epa.gov/oppad001/reregistra@on/cca/awpa_table.htm 

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Alternatives to CCA

•  Chemical Special@es, Inc. developed a new treatment protocol (ACQ): 

 •  CuO (67%) •  quaternary alkyl ammonium salts (33%) 

N

H3C CH3

Cl—

didecyl dimethyl ammonium chloride (DDAC) 

benzyl‐C12–18‐alkyldimethylammonium chlorides (BAC) 

N

H3C CH3

Cl—

n

n=10-16

ACQ Toxicity

•  CuO  – LD50(oral,rat) = 470 mg/kg (1/10 as toxic as As)  

•  quaternary alkyl ammonium salts  – LD50(oral,rat) = 730‐800 mg/kg  

•  Neither of these compounds is a known or suspected carcinogen 

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Green Chemistry

•  Presiden@al Green Chemistry Challenge Award (2002) 

•  Es@mated to remove: – 40 million lbs of arsenic (>90% of total used in U.S) – 64 million lbs of chromium(VI) 

•  Avoids risks to workers who make, transport, and use pressure‐treated wood, and to the general public through use and disposal 

•  Generates NO RCRA Hazardous Waste 

hQp://www.epa.gov/greenchemistry/pubs/pgcc/winners/dgca02.html 

 Risk = f[hazard,exposure] 

 

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Polystyrene

•  In 2010, global produc@on and consump@on of polystyrene was nearly 34 billion pounds, used in packaging, construc@on (mainly insula@on), appliances, electronics, and other goods. 

hQp://www.sriconsul@ng.com/WP/Public/Reports/polystyrene/ 

radical polymerizationn

n

Polystyrene properties

Photos from SZ‐wholesale 

crystalline polystyrene: •  hard •  briQle •  transparent 

polystyrene foam: •  som •  insula@ng •  >90% air 

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Foam extrusion

•  hQp://www.youtube.com/watch?v=xyNQ‐oGafik 

Photos from Made‐in‐China.com and supplierlist.com 

Polystyrene Blowing Agents

•  Chlorofluorocarbons 

– Cost‐effec@ve –  Inert – Non‐flammable – Non‐toxic 

•  But – they deplete the ozone layer. 

Cann & Connelly (2000) Real‐World Cases in Green Chemistry, pp. 49‐54. 

Cl

CCl

FF

CFC‐12 

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Ozone Depletion

Cl

CCl

FF

CCl

FF

UV light (! ! 220 nm)+ Cl•

2 Cl• + 2 O3 2 ClO• + 2 O2

2 ClO• ClOOCl

2 O3 3 O2 NET REACTION:

ClOOCl ClOO• + Cl•

ClOO• Cl• + O2

UV light 

Ozone Depletion

•  Hydrochlorofluorocarbons were used next – These are mostly destroyed in the troposphere. 

– Reduced ozone‐deple@ng poten@al compared to CFCs. 

•  Later, hydrocarbons were used  – These are flammable and contribute to smog 

Cl

CH

FF

HCFC‐22 

Chemistry in Context, 7th edi@on, 2012, p. 66.  

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CFCs and Global Warming

Chemistry in Context, 7th edi@on, 2012, p. 99.  

Poten@al rela@ve to CO2 (value = 1) 

CO2 as a blowing agent

•  Dow Chemical developed a process using CO2 (Presiden@al Green Chemistry Award 1996) – Not ozone‐deple@ng – Not smog‐forming – Non‐flammable –  Economical – No new CO2 is produced, so no net global warming effect 

•  CO2‐blown polystyrene is more duc@le – less likely to break than that blown with CFCs or HCFCs. 

Cann & Connelly (2000) Real‐World Cases in Green Chemistry, pp. 49‐54. 

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Still… polystyrene?

•  Styrene is extremely hazardous –  Irritant to skin and eye – Known carcinogen – Chronic exposure can cause nerve and respiratory damage 

•  Derived from petroleum (non‐renewable) •  Requires a lot of energy to produce •  Not easy to recycle •  Next green chemistry challenge –    Replace Polystyrene 

Fungal packaging •  Ecova@ve has developed a new process to make packaging from fungus and waste agricultural materials. – Use local waste materials – Growth at room temperature and in the dark 

– Growth mixture poured into molds and dried 

– Not scaled up yet 

hQp://green.blogs.ny@mes.com/2009/04/13/using‐fungi‐to‐replace‐styrofoam/ hQp://www.mushroompackaging.com/ 

hQp://www.ted.com/talks/eben_bayer_are_mushrooms_the_new_plas@c.html 

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A Vision for Sustainable Chemistry

•  The Future We Create – Sustainable Chemistry – www.futurewecreate.com –  John Warner: hQp://www.youtube.com/user/thefuturewecreate#p/u/12/W0_ey‐se2Aw 

 

Green Chemistry

•  “The enemy of the excellent is the perfect.” 

•  Green chemistry offers a set of principles to guide chemists, engineers and managers toward more sustainable processes, in order to minimize hazards to human health and the environment. 

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12 Principles of Green Chemistry 

1.  It is better to prevent waste than to treat or clean up waste after it is formed.

2.  Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.

12 Principles of Green Chemistry 

3.  Wherever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

4.  Chemical products should be designed

to preserve efficacy of function while reducing toxicity.

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12 Principles of Green Chemistry 5.  The use of auxiliary substances (e.g.

solvents, separation agents, etc.) should be made unnecessary wherever possible, and innocuous when used.

6.  Energy requirements should be recognized for their environmental and economic impacts and should be minimized. Synthetic methods should be conducted at ambient temperature and pressure.

12 Principles of Green Chemistry 

7.  A raw material of feedstock should be renewable rather than depleting wherever technically and economically practicable.

8.  Unnecessary derivatization (blocking group, protection/deprotection, temporary modification of physical/chemical processes) should be avoided whenever possible.

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12 Principles of Green Chemistry 

9.  Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.

10. Chemical products should be designed so that at the end of their function they do not persist in the environment and break down into innocuous degradation products.

12 Principles of Green Chemistry 11. Analytical methodologies need to be

further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.

12.  Substances and the form of a substance used in a chemical process should be chosen so as to minimize the potential for chemical accidents, including releases, explosions, and fires.

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Homework •  WriQen assignment: Ch. 1, #5; Ch. 2, #2‐5 •  Read Ch. 3 & 4 •  Think about which Principles best apply to the examples discussed today 

•  Before leaving today: Select one ar@cle from the Real‐World Cases books for your presenta@on in Week 4.  I’ll copy it and bring it to you next week.