the green chemistry assistant: expanding the horizons of green chemistry in chemical education

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 CollegeNorthfield, MN [email protected]

231st ACS National Meeting, Atlanta, GeorgiaMarch 27, 2006

mailto:[email protected]

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.

Green Chemistry

Three Levels of Green Chemistry

Equations

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

Green Chemistry


Reactions

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

Green Chemistry


Processes

www.shelldeerpark.com/chemical.htm

Green Chemistry

Three Levels of Green ChemistryEquation

Atom Economy = 40%

Green Chemistry

Three Levels of Green ChemistryReaction

Atom Economy = 40%

Green Chemistry


Green Chemistry


Atom Economy = 40%

Green Chemistry


Atom Economy = 40%

before… …after

Green Chemistry

Three Levels of Green ChemistryReaction – Excess, Limiting Reactant

Experimental Atom Economy = 26%

before… …after

Green Chemistry


…provides context

Process...

Process MassEfficiency = 1%

unrecovered CH2Cl2

unrecyclablesilica gel

Green Chemistry



…can involve more than one step

Process…

Green Chemistry



…allows for comparison

Process…Process MassEfficiency = 1%

Green Chemistry

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?

Green Chemistry

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

Green Chemistry


Green Chemistry

My Goals Today


Green Chemistry


Green Chemistry


Lessons learned:• Students need help just writing the balanced

chemical equations.• Process is important, as most real experiments

involve more than one process step.

Green Chemistry


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.

Green Chemistry


Green Chemistry


Lessons learned:• Introducing green chemistry provides a

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

Green Chemistry


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.

Green Chemistry


Question:

What is the balanced chemical equation for this reaction?

OH TsCl / Et3N OTs

Green Chemistry


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

OH

OTs

+ TsCl

+ HCl

Green Chemistry


…or this? (atom economy = 66%)

OH

OTs

+ TsCl + Et3N

+ Et3NHCl

Green Chemistry


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

Green Chemistry


Question:

What is the balanced chemical equation for this reaction?

OH1) BH3 THF

2) H2O2/NaOH

Green Chemistry


Question:

Is this one reaction or two?

OH1) BH3 THF

2) H2O2/NaOH

Green Chemistry


Question:

What is the atom economy?

OH1) BH3 THF

2) H2O2/NaOH

Green Chemistry


OH

3 + BH3THF + THFB

3

3B

3

STEP 1STEP 1

STEP 2 + 3 H2O2

+ NaOH+ NaB(OH)4

Overall Atom Economy = 60%

Green Chemistry


OH

3 + BH3B

3

3B

3

STEP 1STEP 1

STEP 2 + 3 H2O2

+ NaOH+ NaB(OH)4

Overall Atom Economy = 72%

Green Chemistry


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!

Green Chemistry


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.

Green Chemistry

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


Green Chemistry

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


http://www.stolaf.edu/depts/chemistry/bh/confchem

the green chemistry assistant: expanding the horizons of green chemistry in chemical education

Documents

horizons of green chemistry

guiding students

chemical educationrobert

process step

balanced chemical equations

goals todaybriefly

edugcamy goals todayshare

important distinction