Issue Date: May 28, 2007
Grassroots Green Chemistry
THE PURPOSE of green chemistry and green engineering is to help clean up the chemical enterprise—that is, to serve as a form of molecular-level pollution prevention. In practice, that means developing ever-better chemical processes and products that require fewer reagents, less solvent, and less energy while generating less waste. In addition to being cost-effective, these processes and products should be designed to have low toxicity and be safer to use than their predecessors.
It's simple to state the purpose of a principles-based ethical construct like green chemistry. But it takes know-how and a focused effort to put words into action. That's why a cadre of chemists from a variety of institutions???including the American Chemical Society, ACS's Green Chemistry Institute (GCI), the Environmental Protection Agency, and colleges and universities???has spent the past decade devising and refining fundamental strategies for teaching green chemistry and engineering to students and educators at all levels. The outcome has been a growing collection of introductory texts, lab experiments, case studies, and other materials, as well as online networks through which these materials can be shared.
These educational tools now are finding their way into high school and entry-level undergraduate courses, as well as into research and upper-level courses focused on green chemistry and engineering. C&EN profiles two institutions that have been part of these developments.
About 10 years ago, James E. Hutchison, Kenneth M. Doxsee, and colleagues at the University of Oregon had run into a dilemma: The university's organic chemistry lab space had too few fume hoods, and the department didn't have enough manpower to run additional small lab sessions for the undergraduate organic lab course. "We were holding organic labs in the evenings and on weekends," Hutchison recalls.
Hutchison had read a little about the fledgling green chemistry movement, and he thought it might be worth a shot to develop a lab course that could get around or reduce the need for fume hoods, which would allow the organic students to use the general chemistry lab space. After the department chair gave the project the green light, Hutchison, Doxsee, and a team of graduate students began developing a range of greener organic experiments. "Before long, we realized the tremendous benefits of the approach, and the project took on a life of its own," Hutchison says.
One of the first greened-up experiments involved the synthesis of adipic acid, which is used to make nylon. The revised experiment transforms cyclohexene into adipic acid using hydrogen peroxide and a catalyst instead of the nitric acid oxidant traditionally employed in the industrial process. The procedure is safer and avoids formation of the by-product nitrous oxide, which is a greenhouse gas.
Another revised experiment improved the safety of olefin bromination by replacing the carcinogenic methylene chloride or carbon tetrachloride solvent with ethanol. Yet another example involves the extraction of limonene from orange peel by using melting dry ice (CO2) as a benign solvent rather than an organic solvent.
THE EXPERIMENTS teach students to consider the environmental cost of the chemistry they are doing, Hutchison points out. They are required to quantify the chemical hazards associated with a method and learn to take appropriate precautions, he explains. Overall, the experiments emphasize core organic lab skills, illustrate the benefits and strategies of green chemistry, and reduce the impact on human health and the environment, he notes.
The success of the green organic lab program "has been incredible," Hutchison says. The Oregon chemistry department has received a total of about $2 million from the National Science Foundation, ACS, GCI, EPA, and private sources to promote its green chemistry efforts. All undergraduate organic students now use the green experiments, which have been published in a lab textbook. A building renovation project has resulted in a new green organic lab space that can accommodate plenty of students, so they no longer have to put up with odd lab schedules, he adds.
The green emphasis has spilled over into the general chemistry lab course, providing a safer environment for introductory students, Hutchison says. And it's slowly working its way into analytical and physical chemistry, although "it's a harder fit" for those disciplines, he says.
Hutchison, Doxsee, and colleagues also share their expertise by holding an annual summer green chemistry workshop, now in its seventh year, for 20-25 college and university teachers.
In addition, the Oregon chemists are involved in a couple of unique outreach programs. Greener Education Materials for Chemists (GEMs) is a "living database" of freely available teaching resources shepherded by Oregon's Julie A. Haack. GEMs started in 2002 to complement ACS, GCI, and EPA green chemistry education materials and help boost accessibility of lab exercises, lecture materials, demonstrations, course syllabi, and multimedia content, Haack tells C&EN.
So far, the database contains 51 searchable entries, some published and some unpublished, that cover topics ranging from biodiesel synthesis to case studies on developing greener pharmaceuticals. A feature that was just unveiled is a Google map showing the location and contact information for green chemistry educators and researchers worldwide. Another feature available to GEMs users is the ability to participate in online discussions about the database content. In such a dialogue, an original message that suggests a modification or recounts a success story can be displayed, along with subsequent replies.
Haack also has been instrumental in creating the Green Chemistry Education Network (GCEdNet), which is evolving as a virtual reservoir of information for curriculum development for U.S. high schools, community colleges, and four-year colleges and universities. The network has been in place for several years, but it was formalized in July 2006. It's composed of regional "ambassador sites" in New England, the Pacific Northwest, Arkansas, and Minnesota that currently include a total of 16 institutions. These hubs are helping to facilitate regional cooperation and development among network members, Haack explains.
This approach not only enhances the capabilities of the members through the exchange of knowledge and experience, but it also provides unique opportunities for innovation and rapid change, Haack says. As an example, Haack and her Oregon colleagues helped produce a green edition of the Prentice Hall textbook "Chemistry for Changing Times," which the department uses for an introductory course for nonscience majors.
The Oregon chemists had been using their own material to supplement the book. Then Haack made contact with Prentice Hall at an ACS national meeting and asked about revising the book to include green chemistry concepts. The publisher agreed, and Haack reached out to members of GCEdNet. On short notice, network members prepared a green section for each chapter in the book. Prentice Hall published the 11th edition of the book, the "green edition," less than a year ago, and it is now being used at Oregon and other institutions.
"Students tend to resist being taught material that is not in a book," Haack says. "But once the material is in a book, as in this case, the resistance is gone. Now we can focus on teaching the details of green chemistry, rather than spending time convincing students of its value."
TAKEN TOGETHER, the teacher workshops, GEMs, and GCEdNet demonstrate the diversity of educators and institutions that are actively drawn to green chemistry, Haack says. These chemists "are creating a new type of community-based approach to curriculum development that's not limited by traditional chemistry discipline boundaries or by institutional settings," she observes. "Our faculty is getting excited about it, momentum is building, and the dynamics of our teaching and the culture of our department are changing."
A similar green chemistry success story has emerged at Hendrix College, a small liberal arts institution in Conway, Ark. The chemistry department there has developed its entire curriculum with green chemistry in mind, note analytical chemist Liz U. Gron and organic chemist Thomas E. Goodwin, two Hendrix faculty members who are leading the green charge.
Some 2.5 million students enter U.S. universities each year, according to U.S. Census Bureau statistics, Gron points out. Of those students, about 15,000 will end up with undergraduate degrees in chemistry and chemical engineering. "That's a possible 15,000 new green scientists per year," she says.
At Hendrix, more than half of the incoming freshman class takes introductory chemistry, either a course for science majors (35%) or one for nonmajors (19%). "That presents a great opportunity to introduce green chemistry into education," Gron notes. "While not all these students will become chemists—about 4% of Hendrix freshmen become chemistry majors—they will enter society with green on their minds." It's a small local effect at Hendrix, but it's magnified globally through the students as they venture out on their own, she adds.
Developing a green chemistry curriculum doesn't require diving right in, Gron says. A good approach is to start small by modifying existing experiments to replace obvious toxic substances, reduce the volume of solvent, and add green pre-lab exercises. The next step can involve adopting new procedures taken from established resources, like those offered by GEMs, ACS, and GCI. Finally, the big step is to create a new course or an entirely new curriculum—a department-wide approach.
But that's not all. One can tell students that green chemistry "is the right thing to do for the chemistry profession and our society," Gron says. But students need more concrete images and lively experiences to help that message sink in.
With that idea in mind, Goodwin in jest created the Toad Suck Institute for Green Organic Chemistry. Toad Suck is the name for a ford on the Arkansas River, near where Hendrix is located. In the olden days, steamboats and barges on the river sometimes had to stop there to wait if the river was running low, Goodwin explains. The crews would tie up their boats, and while waiting, they visited the tavern. The local citizenry, displeased by the sometimes unsavory crowd, were fond of saying "they suck on the bottle 'til they swell up like toads." Thus, the name Toad Suck stuck.
The Toad Suck Institute serves as a platform for Goodwin's research on elephant and other mammalian pheromones and for him and his students to create greener versions of standard organic lab course experiments.
IN THE SAME VEIN, Gron is applying her specialty in analytical chemistry to develop Green Soil and Water Analysis at Toad Suck (Green-SWAT) as a program to teach first-year students spectroscopic and chromatographic techniques that can be applied to environmental chemistry. "It's a means for chemists to serve the environment by doing environmental chemistry in an environmentally friendly way," she says.
Goodwin got started in green chemistry in earnest in 2001 while reevaluating the merits of the organic course experiments at Hendrix. It occurred to him that the department should investigate greener ways to carry out the labs, guided by Material Safety Data Sheets and toxicology data. And when Goodwin found out about the first green chemistry teacher workshop at Oregon, he begged his way in at the last minute. With his new green knowledge, Goodwin adopted an "asymptotic approach" to developing a green organic lab course—that is, an approach that looks for continuous improvement to make reactions greener and greener over time (J. Chem. Educ. 2004, 81, 1187).
"When we choose to use any chemical in the lab, we are making a decision that the risk is acceptable, both for the students and the environment," Goodwin says. "Thus, it's incumbent on us to choose experiments wisely and to take all appropriate precautions. But there is no absolute in green chemistry. We can't make it perfect because there can always be a way to improve on an experiment."
One of Goodwin's experiments, developed with undergraduate student Courtney Rogers, is a solventless, room-temperature Diels-Alder reaction. The Diels-Alder reaction, in which a diene adds to an alkene to form a cyclic product, is one of the most important organic reactions taught in undergraduate organic labs, Goodwin says.
They started with a literature lab procedure that called for reacting 2,4-hexadien-1-ol (the diene) and maleic anhydride (the alkene) in refluxing toluene (110 °C). The diene has a low melting point (32 °C), so generally it is a viscous liquid at room temperature. At first, Goodwin and Rogers tried the reaction unsuccessfully with different solvents. Then they tried no solvent at all while heating at a lower temperature (90 °C). They also tried heating the reactants without solvent in a microwave oven. Both of the latter variants worked.
"Once you start thinking green, you tend to try things you might not normally do," Goodwin says. In the end, it occurred to the team that the reaction might go without solvent or heating by simply stirring the reactants together by hand. Students now add the solid maleic anhydride to the 2,4-hexadien-1-ol in a beaker and stir with a spatula for about 10 minutes in a fume hood, necessary because the reactants are irritants. The reaction takes place right before their eyes, as the reactants initially form a clear gel and then the crystalline product.
Beyond learning basic organic synthesis and analysis in the lab, Goodwin challenges students to answer three simple questions: What was green about the experiment? What was not green? How could the experiment be made greener? "This thought process is educational for the students," Goodwin says, "and we learn a lot from the answers that helps us improve the experiments."
For Gron's analytical experiments, it's important to choose simple and safe analytes and employ common instrumentation using proven methods, she says. One experiment involves ion chromatography to detect nitrate and phosphate anions in water samples. Students venture out to collect water from local creeks and lakes and then analyze and plot their results on a local map in the chemistry department.
The results are revealing: The highest concentrations of nitrates and phosphates are downstream of the local wastewater treatment plant. Although there aren't many farms in the area, the students discuss that the nutrient-rich runoff from animal farms and cropland in other parts of Arkansas can lead to eutrophication of lakes and contribute to the dead zone in the Gulf of Mexico at the mouth of the Mississippi River, Gron says.
ANOTHER POSITIVE learning experiment involves using iron as a stand-in for studying toxic metals. The quantitative analysis experiments on iron are similar to experiments the students would use to study toxic mercury, lead, chromium, and arsenic, Gron notes. For example, the students use UV-visible spectroscopy to analyze an iron-phenanthroline complex, and they use flame atomic absorption spectroscopy to analyze iron in water samples.
"Freshmen need to focus on learning techniques, not involving themselves in the risk of working with toxic substances," Gron says. But an important part of the lab is a discussion about the biological and environmental activity of the toxic metals, she adds. "While it really grabs the students' intellectual attention to study toxic materials, they appreciate working with a greener analyte."
The Green-SWAT program is creating students "who are a bit more savvy" about the choices they make while doing analytical chemistry, Gron observes. She and her Hendrix colleague M. Warfield Teague plan to expand the program through a $150,000 NSF grant they received for "Educating Green Citizens and Scientists for a Sustainable Future."
Green chemistry and engineering education has come a long way, but there's "still a long way to go," Oregon's Hutchison says. But most proponents of green chemistry and engineering believe that one day the term "green chemistry" will fade away as the concepts become a common part of everyday thinking.
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