Green Chemistry The Green Chemistry Assistant: Expanding the horizons of green chemistry in chemical education Robert M. Hanson, Paul R. Campbell, Elizabeth

Green Chemistry

The Green Chemistry Assistant: Expanding the horizons of green chemistry in chemical education

Robert M. Hanson, Paul R. Campbell, Elizabeth R. Johnson, Gary O. Spessard,

and Marc A. Klingshirn

St. Olaf College

Northfield, MN 55057

[email protected] ACS National Meeting, Atlanta, Georgia

March 27, 2006

Green Chemistry

My Goals Today

• Briefly discuss the important distinction between equations and reactions, and between reactions and processes.

• Introduce a new web-based tool – the Green Chemistry Assistant.

Green Chemistry

My Goals Today

• Share what we have learned about our students from using the GCA.

• Share what we have learned about green chemistry from our students.

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Three Levels of Green Chemistry

Equations

HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l)

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Reactions

http://www.uncw.edu/smec/gk_fellows/askscience.html

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Processes

www.shelldeerpark.com/chemical.htm

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Three Levels of Green ChemistryEquation

Atom Economy = 40%

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Three Levels of Green ChemistryReaction

Atom Economy = 40%

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Atom Economy = 40%

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Atom Economy = 40%

before… …after

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Three Levels of Green ChemistryReaction – Excess, Limiting Reactant

Experimental Atom Economy = 26%

before… …after

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…provides context

Process...

Process MassEfficiency = 1%

unrecovered CH2Cl2

unrecyclablesilica gel

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…can involve more than one step

Process…

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…allows for comparison

Process…Process MassEfficiency = 1%

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Three Levels of Green ChemistryEquation, Reaction, and Process

Wouldn’t it be nice to have access to a tool that would allow us to quickly make comparisons like this?

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Green Chemistry Assistant http://fusion.stolaf.edu/gca

• Based on the EPA “Green Chemistry Expert System”

• User-friendly interface designed to assist students in analyzing the atom economy, and safety of chemical processes

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My Goals Today


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Lessons learned:

• Students need help just writing the balanced chemical equations.

• Process is important, as most real experiments involve more than one process step.

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Lessons learned:

• We need lab manuals that are more explicit in guiding students to an understanding of the overall set of process steps they will be carrying out.

Green Chemistry

My Goals Today


• Share what we have learned about green chemistry from our students.

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Lessons learned:• Introducing green chemistry provides a

rich context for discussing safety, including nomenclature, CAS registry numbers, MSDS sheets, and health and environmental hazards.

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Lessons learned:

• All is not as simple as one might think from what is in the literature in terms of the definitions of green measures.

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Question:

What is the balanced chemical equation for this reaction?

OHTsCl / Et3N

OTs

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Is it this?... (atom economy = 88%)

OH

OTs

+ TsCl

+ HCl

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…or this? (atom economy = 66%)

OH

OTs

+ TsCl + Et3N

+ Et3NHCl

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On assumptions regarding atom economy:

“The process of calculating atom economy may be simplified by only considering key reactants. For example, ‘catalysts’ used in stoichiometric quantities, or the acid or base used in hydrolysis, are considered to be reactants. These examples are in contrast to common inorganic reagents, even when used in stoichiometric quantities (e.g. potassium carbonate…), which have been ignored. Inorganic reagents and/or other material are not included in the calculations as long as at least two other reacting substances are identified.”

Constable, Curzons, and Cunningham, Green Chemistry, 2002, 521-527

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Question:

What is the balanced chemical equation for this reaction?

OH1) BH3 THF

2) H2O2/NaOH

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Question:

Is this one reaction or two?

OH1) BH3 THF

2) H2O2/NaOH

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Question:

What is the atom economy?

OH1) BH3 THF

2) H2O2/NaOH

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OH

3 + BH3THF + THFB

3

3B

3

STEP 1STEP 1

STEP 2 + 3 H2O2

+ NaOH+ NaB(OH)4

Overall Atom Economy = 60%

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OH

3 + BH3B

3

3B

3

STEP 1STEP 1

STEP 2 + 3 H2O2

+ NaOH+ NaB(OH)4

Overall Atom Economy = 72%

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OH

3 + BH3THF + THFB

3

3B

3

STEP 1STEP 1

STEP 2 + 3 H2O2

+ NaOH+ NaB(OH)4

STEP 3 BH3THF + 3 H2O + NaOH THF + NaB(OH)4 + 3 H2 (g)

In practice, Step 3 is important!

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Lessons learned:• Getting students thinking about the overall

process is good.• Expecting them to do it on their own because it’s

“simple” is asking too much.• The Green Chemistry Assistant enables us to

explore the nature of green chemistry processes and green chemistry measures.

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FacultyGary Spessard, Marc Klingshirn, Paul Jackson

StudentsPaul Campbell, Allison Christensen, Elizabeth R.

Johnson, Tim Barker, Tyler Drake, David Harris Technology Support

Dan Beach Financial support

WM Keck FoundationHoward Hughes Medical Institute


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Upcoming double-header symposia of possible interest in 2006:

“Web-Based Applications for Chemical Education”

ACS CCCE online CONFCHEM, May 5 – June 30 www.stolaf.edu/depts/chemistry/bh/confchem

“Web-Based Applications for Chemical Education”

19th BCCE, July 31 – Aug 2


Documents

Green Chemistry The Green Chemistry Assistant: Expanding the horizons of green chemistry in chemical education Robert M. Hanson, Paul R. Campbell, Elizabeth