Green Chemistry

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Green Chemistry

• Dr. Thomas Wiese
• Associate Professor of Chemistry
• Fort Hays State University

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What is Green Chemistry?

• Not easily definable
• environmentally benign chemistry
• chemistry for sustainable growth
• A way of thinking
• Green chemistry- the design of chemical products
  and processes that reduce or eliminate the use
  and generation of hazardous substances.

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The Good Chemistry Has Done

• Life expectancy in 1900 was 47
• In 2000, life expectancy is 75 (and should be
  more than that)
• Antibiotics, e.g.,
• Better nutrition (pesticides, insecticides, and
  fertilizers)

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Has Not Been Without Cost

• Cuyahoga river, OH caught on fire in 1969
• DDT

Problems cannot be solved by the same level of
thinking that created them. Albert Einstein
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Green Chemistry is Not New

• The terminology is relatively new, and very
  important refinements have been made, but the
  concepts are not new.
• For example, chemical engineers are well known
  for designing chemical plants to use the energy
  generated in one part of the plant for one
  purpose, elsewhere in the plant for another use.

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Green Chemistry is Gaining Much Wider Attention

• Exon-Mobile ad (recycling steam)
• ?bp environment vs. car ad
• Craig Venter starting a company with the goal of
  generating an entirely manmade organism to
  generate hydrogen as a fuel source
• Presidential Green Chemistry Award instituted by
  the Clinton Administration
• A growing willingness to pay more for
  environment-friendly goods

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Twelve Principles of Green Chemistry1

• 1. It is better to prevent waste than to treat or
  clean up waste after it is formed.
• Note the correlation with the principles of
  recycling.
• Example of clock reactions

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
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Clock Reactions

• So named because a sudden, sharp color change
  occurs when a reaction is complete.
• Numerous chemistries many use mercury or
  formaldehyde, e.g.
• IO3(aq) 3 HSO3 (aq) ? I (aq) 3 SO42?(aq)
  3 H (aq)
• Hg2(aq) 2I?(aq) ? HgI2(s)
• IO3(aq) 8 I (aq) 6 H(aq) ? 3 I3?(aq) 3
  H2O(aq)

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Alternative Clock Reaction

• Alternative vitamin C, iodine, and hydrogen
  peroxide (starch indicator)
• 2H(aq) 2I?(aq) H2O2(aq) ? I2(aq) 2H2O(l)
• I2(aq) C6H8O6(aq) ? 2H(aq) 2I?(aq)
  C6H6O6(aq)
• One of the mercury-based clock reactions uses
  approximately 150 mL of 0.01 M HgCl2 solution per
  experiment for each lab group (two students per
  group). As an example, assume that all of the
  approximately two million introductory chemistry
  students in the nation did the safer experiment
  described above rather than the mercury-based
  experiment how much mercury waste would be
  avoided?

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Twelve Principles of Green Chemistry1

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

1Green Chemistry Theory and Practice Oxford
University Press New York 1998
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Twelve Principles of Green Chemistry1

• The principle is simple, but what if you dont
  know all of the products?
• Use percent atom economy instead

1Green Chemistry Theory and Practice Oxford
University Press New York 1998
12
Ibuprofen Synthesis Example
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New Ibuprofen Synthesis Scheme
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Twelve Principles of Green Chemistry1

• 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.
• Clothes washing example
• Soap and water
• Dry cleaning
• Perc

vs scCO2
1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
15
scCO2
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Twelve Principles of Green Chemistry1

• 4. Chemical products should be designed to
  preserve efficacy of function while reducing
  toxicity.
• Marine antifouling example

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
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Tributyltin Oxide (TBTO)

• Leaches from hull plating to prevent fouling
• T½ 5 months in seawater
• T½ 6-9 months in sediment
• Bioaccumulation in marine animals
• Now banned for vessels shorter than 82 feet

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4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOI)

• Like TBTO, leaches from hull plating to prevent
  fouling
• In presence of microorganisms
• T½ lt24 h in seawater
• T½ lt1 h in sediment
• Binds tightly to sediment
• No bioaccumulation
• Must be recoated every three years (TBTO lasts
  five years)

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Twelve Principles of Green Chemistry1

• 5. The use of auxiliary substances (e.g.
  solvents, separation agents, etc.) should be made
  unnecessary whenever possible and, innocuous
  when used.
• Oxygenation of gasoline required when CO gt 2.7
  ppm

• MTBE- methyl t-butyl ether

• Got ethanol?

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
20
Twelve Principles of Green Chemistry1

• 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.
• Compare the reaction time to conduct a reaction
  at room temperature (25C) vs. 100C, assuming it
  follows the Q10 rule.

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
21
Twelve Principles of Green Chemistry1

• 7. A raw material feedstock should be renewable
  rather than depleting whenever technically and
  economically practical.
• Plastic (polyethylene et al.) made from petroleum
• Newer plastic (polylactate) made from glucose

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
22
Twelve Principles of Green Chemistry1

• 8. Unnecessary derivatization (blocking group,
  protection/deprotection, temporary modification
  of physical/chemical processes) should be avoided
  whenever possible.
• This beyond where I think you are at.

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
23
Twelve Principles of Green Chemistry1

• 9. Catalytic reagents (as selective as possible)
  are superior to stoichiometric reagents.
• Stoichiometric reactant driven
• Catalyst- speeds a reaction without taking part
  by lowering the activation energy (Eact)

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Activation Energy
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Twelve Principles of Green Chemistry1

• 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.
• Packing peanuts example.

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
26
Twelve Principles of Green Chemistry1

• 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.
• Excellent principle but beyond what we have time
  for.

1 Green Chemistry Theory and Practice Oxford
University Press New York 1998
27
Twelve Principles of Green Chemistry1

• 12. Substances and the form of a substance used
  in a chemical process should chosen so as to
  minimize the potential for chemical accidents,
  including releases, explosions, and fires.
• Example from my research lab

Hexanes has a flash point of -21C
Cyclohexane has a flash point of -18C
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Why Use Green Chemistry in Teaching?

• Requires the use of interdisciplinary skills
• Students relate well to environmental aspects
• Potential for having multiple classes work
  together
• Green chemistry emphasizes critical thinking

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Six Concepts From Twelve Principles

• 1. Safer Starting Materials
• 2. Renewable Resources
• 3. Safer Solvents
• 4. Avoiding Waste
• 5. Conserving Energy
• 6. Greener Waste

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Safer Starting Materials

• Hands-on clock reaction and effect of
  temperature and concentration

• Materials
• dH2O
• 250-mL containers
• 1000 mg vitamin C tablets
• tincture of iodine (2)
• hydrogen peroxide (3)
• liquid laundry starch
• alcohol thermometer
• ice cubes
• warm water bath

• Procedure
• 1. Make a vitamin C solution by crushing a 1000
  mg vitamin C tablet and dissolving it in 60 mL of
  distilled water. Label as vitamin C stock
  solution.
• 2. Combine 5 mL of the vitamin C stock solution
  with 5 mL of iodine and 60 mL of water. Label
  this solution A.
• 3. Prepare solution B by adding 60 mL of water
  to 15 mL of hydrogen peroxide and 2 mL of liquid
  starch solution.

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Safer Starting Materials Continued

• 4. Pour solution A into solution B, and pour the
  resulting solution back into the empty cup to mix
  them thoroughly. Begin timing as soon as they
  first mix and continue until there is a color
  change. Record the time it takes for the color
  to change.
• 5. Repeat the experiment, but this time use
  either 30 or 90 (instead of 60) mL of water when
  preparing solutions A and B. Time the reaction
  and record the results.
• 6. Using your data and the data of other
  students, prepare a graph of concentration (on
  the x axis) versus time (on the y axis). Is the
  relationship linear?
• 7. Repeat the original experiment using 60 mL of
  water to prepare solutions A and B, but cool the
  solutions before mixing by placing the containers
  in an ice bath. Mix as before, timing the
  reaction and recording the result.
• 8. Repeat again, this time using a warm water
  bath to heat the solutions. Mix as before, timing
  the reaction and recording the result.

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Renewable Resources

• Make and characterize biodiesel
• Procedure
• 1. Measure 100 mL of vegetable oil.
• 2. Carefully add 15 mL of methanol.
• 3. Slowly add 1 mL of 9 M KOH.
• 4. Stir or swirl the mixture for 10 minutes.
• 5. Allow the mixture to sit and separate.
• 6. Carefully remove the top layer using a Beral
  pipette.
• 7. Wash the product using 10 mL of distilled
  water. Mix.
• 8. Allow the mixture to sit and separate.
• 9. Carefully remove the top layer using a Beral
  pipette.
• 10. Measure the amount of biodiesel you have
  collected and compare it to the amount of
  vegetable oil you started with.

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Renewable Resources Continued
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Safer Solvents

• scCO2 example

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Avoiding Waste

• Silver-containing solutions can be treated with
  chloride-containing solutions by the following
  reaction
• Ag (aq) Cl- (aq) ? AgCl (ppt)
• Any chloride can be used, but apply the
  principles of green chemistry to select the best
  choice of HCl, NaCl, or CaCl2.

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Conserving Energy

• In this module, the most efficient heating method
  (Bunsen burner, hotplate or microwave) is
  determined.
• For the Bunsen burner, the essential steps are
• Using the balanced equation, calculate the ?Hr
  for the combustion of CH4 by looking up ??fs
• Determine how much natural gas is delivered over
  time.
• Set up a beaker containing a carefully measured
  amount of water and measure the initial
  temperature
• Timing how long it takes, heat the water until
  the temperature rises by 3050C and measure the
  final temperature to the nearest 0.1C.
• Calculate the amount of heat absorbed by the
  water, the amount of heat released by combustion,
  and the percent efficiency of the heating
  process. Equations are provided.
• For the hot plate and microwave, power
  consumption (specified on equipment is used).

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Conserving Energy continued

• Typical results
• Bunsen burner efficiency typically 1020.
• Hot plate significantly higher, ca. 50
• Microwave typically 80.

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Greener Waste

• Packing peanuts (styrofoam and starch) vs paper
  and bubblewrap
• Suggested activity would be to have students
  design a procedure to show time of degradation
  under various conditions
• Also, how are each of these materials made?

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Plastics and Recycling
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Plastics and Their Recycle Numbers

• Recycle code name
• 1 PET(E) poly(ethylene terephthalate)
• 2 HDPE high density polyethylene
• 3 V vinyl, polyvinyl chloride
• 4 LDPE low density polyethylene
• 5 PP polypropylene
• 6 PS polystyrene
• 7 Other
• The lower the number, the easier it is to recycle.

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Uses of Virgin and Recycled Plastics

• Plastic Use Recycle Use
• 1 PET(E) pop bottles pop bottles
• 2 HDPE milk jugs molded containers
• 3 V pipes plastic floor mats
• 4 LDPE plastic wrap trash bags
• 5 PP toys mix
• 6 PS coffee cups molded things (VCR tapes,
  e.g.)
• 7 various plastic lumber

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Properties of Plastics

• Different shapes (subsequent slide)
• Molecular weight
• Domains either crystalline or amorphous
• Tm
• Amorphous dont scatter light (glassy)
• Amorphous weaker
• Ex PET crystallinity 0-55 depending on rate of
  cooling

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Properties of Plastics
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Properties of PE As a Function of Crystallinity
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Types of Plastic

• Thermoplastic- polymers that can be melted to
  become sufficiently fluid that they can be molded
  into shapes that are retained when they are
  cooled.
• Thermoset plastics- can be molded when first
  prepared, but harden irreversibly when cool.

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Nylon Synthesis

• Step growth or condensation reaction

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Hexanedioic Acid Production (Traditional and
Biotech)

• In the study of amino acid metabolism, an
  organism was (genetically engineered) discovered
  to convert glucose to adipic acid

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Addition Polymerization

• Polythylene, polypropylene, polystyrene, and
  polyvinyl chloride synthesized in this way.
• They have in common double bond as part of their
  structure.

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Polylactic Acid Production

• I have drawn this reaction incompletely- what
  else has gone on?

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Recycling Process (PET)

• Most common is hand sorting on conveyor belt
• Shred into small chips
• Air cyclone to separate light paper
• Detergent wash (adhesive)
• Dry
• Aluminum caps removed electrostatically
• 99.9 pure, worth 50 of virgin

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Recycling

• Depolymerization yields the most effective means
  of recycling
• Best case is PET (30 of bottles are recycled)

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Recycling of Other Plastics

• Often just heat-molded into plastic lumber, e.g.
• McDonalds is making shingles for new franchises
  from used PS burger boxes

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Other Recycling

• Glass is being recycled by grinding and used to
  replace Florida beaches washed away by last years
  hurricanes
• Steel and aluminum melted, use 10 of energy to
  recycle than mine originally

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The Fourth R

• Reduce
• Reuse
• Recycle
• Respond
• Educate others on source reduction and recycling
  practices
• Make your preference known to manufacturers,
  merchants, and community leaders
• Be creativefind new ways to reduce waste
  quantity and toxicity

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Resources

• American Chemical Society Green Chemistry
  Institute
• http//www.chemistry.org/greenchemistryinstitute
• They also have a listserve that might be of value
• U.S. Presidential Green Chemistry Challenge
  Awards
• http//www.epa.gov/greenchemistry/past.html
• J.Chem.Ed. Feature column Topics in Green
  Chemistry
• http//www.fhsu.edu/twiese/green.htm