How the Principles of Green Chemistry Changed the Way Organic Chemistry Labs Are Taught at the University of Detroit Mercy

1 Introduction

Over 10 years ago, a reexamination of the organic chemistry curriculum at the University of Detroit Mercy was embarked upon. The need for such a review was multifaceted. First, rising enrollments encouraged instructors to scrutinize material and equipment usage over time from the perspective of both student safety and course objectives. Increasing ranks of students prepared to study organic chemistry for their preprofessional or scientific training raises questions about the proper number of students to enroll in a lab. This judgment, in turn, engenders discussion about student safety with regard to volatile reagents/solvents, as well as appropriate course learning objectives. The University of Detroit Mercy has utilized the ideologies espoused by the Lab Safety Institute [1], whose work and recommendations are tied to current research in the field of safe lab instruction. In addition, a move toward institutional program review by way of internal self-study forced many labs at the University of Detroit Mercy to reevaluate the goals each course purported to help students achieve.

Second, financial resources at the university were limited, and therefore, economical solutions would be required. While this is no doubt a planning aspect shared by many institutions of higher learning, the University of Detroit Mercy organic chemical lab courses would be bound by the teaching space assigned to them. The space in question, a garden-level laboratory of approximately 2,000 square feet, had several unique characteristics that would need to be kept in mind throughout the course reform. For example, there were only seven fume hoods in the lab, all abutting the outer wall. None of the four long workbenches would have dedicated hood space. Each workstation could accommodate two students working as a pair, but no more than two pairs per bench side would be possible without severely impeding movement in the lab, and therefore, affecting safety. Incidentally, this would set the upper limit of student enrollment for any 3 h lab period to 32 total, even though the recommended number of enrollees would be set lower by square footage standards. There was no house vacuum, house air, or house gases delivered to the benchtop in this lab, and one of the hoods would be used for satellite storage of liquid organic waste.

Third, and most importantly, a call to incorporate the 12 principles of green chemistry into the learning outcomes of requisite courses was set to be heeded. Indeed, the primary impetus for curricular change in the University of Detroit Mercy’s organic chemistry lab courses was a need to integrate value into students’ instruction. After much dialogue on how to cast the degree outcomes for the Department of Chemistry and Biochemistry, the following four “pillars” were set: scientific method, technical presentation, instrumentation, and social and professional responsibility. The last of these learning outcome groups was to encompass awareness of ethical issues in the chemical sciences, critical reading of the chemical literature, and green chemistry concepts and methods. These objectives align well with both the educational purpose of the American Chemical Society’s (ACS) Green Chemistry Institute [2] and the current ACS strategic plan [3]. In fact, it is a main goal of the ACS to improve education by fostering “the development of the most innovative, relevant, and effective chemistry education in the world” [3]. Key to achieving this goal is the incorporation of the theory and application of the 12 principles of green chemistry [4] into higher education instruction. This directive feeds into another of the main goals of the ACS strategic plan, and that of communication of chemistry’s value. This goal is summarized by helping chemists communicating chemistry’s vital role in addressing the world’s challenges to the public and policymakers.

All in all, these chief factors converged with a complete reimagining of three organic chemistry laboratory courses at the University of Detroit Mercy: CHM 2250, a one-credit introductory lab for all science majors; CHM 2260, a one-credit second-semester lab for biology majors; and CHM 2300, a two-credit advanced synthesis lab for chemistry and biochemistry majors.

2 Green Chemistry Principles Affect Course Learning Outcomes

Looking back, the most profound change that resulted from the incorporation of the theory and application of green chemistry principles into the University of Detroit Mercy’s organic chemistry lab courses was the inclusion of green chemistry metrics. Popular generalizations of the 12 principles divide the spirit of their responsibility into four major groups: energy usage, toxicity, waste, and atom economy. Throughout the semester, students were asked to monitor the 12 principles from the standpoint of each of these criteria. For instance, with regard to energy usage, students were asked to compare a transformation involving a heating mantle used for 60 min with a conventional microwave oven used in the 1990s. In the way of toxicity, students were asked to research the Material Safety Data Sheet (MSDS) for some compounds prior to using them in the lab. For wastes, students were instructed to scrutinize the number of trips they take to the liquid (hazardous) organic waste container versus what is allowed “down the sink drain.” While each of these is emphasized throughout the lab units at the University of Detroit Mercy, it is atom economy that receives the most attention.

Using the CHM 2300 lab [5] as a prototype, the green chemistry principle of atom economy [6] is specifically highlighted in our lab courses. This is done for two reasons. First, most students will arrive at their second year with a basic understanding of the concept of percent yield. This simple calculation allows students to quickly ascertain the effectiveness of a transformation by measuring the measured versus the theoretical yield. Second, students were straightforwardly able to extend their understanding of percent yield into atom economy calculations [7]. While other metrics for mass balance of synthetic reactions exist [8–10], simple experimental atom economy calculations allow students to immediately evaluate matters of wasted reagent mass, scale, and effects of catalysts using relatively uncomplicated algebra. With atom economy ratings, students in CHM 2300 can be asked to compare the “greenness” of one transformation versus another or suggest areas to improve the overall adherence of a transformation to the 12 principles. These calculations are simple enough that they can be templated (Figure 1) so that students spend less time manipulating numbers and more time relating the meaning of the ratings with regard to green chemistry.

Figure 1:

Example atom economy calculation sheet from CHM 2300.

The CHM 2300 course involves a number of complex learning outcomes in the areas of writing/editing scientific manuscripts and advanced organic synthetic techniques. However, students who fully engage the outcomes with regard to green chemistry and atom economy are more likely to overlay this important way of thinking with their existing chemical knowledge. Such students can glean the impact of their benchwork with a reasonable amount of detail in a very short period of time.

3 Green Chemistry Principles Affect Materials and Equipment

In examining the 12 principles of green chemistry, reform in the curriculum of our organic chemistry lab courses at the University of Detroit Mercy also affected the equipment and materials that are stocked. As previously mentioned, the lab space used for instruction in these courses contained limitations with regard to storage space, fume hood usage, and benchtop work areas. In addition, after a partial building renovation in 2011 that included a decentralization of the department stockroom, more fine chemicals and solvents would need to be stored within the teaching lab proper. Perhaps the most marked change in the way the organic lab courses are taught that followed from these factors is the overall reduction in the type and amount of solvents kept on hand. With reduced storage room, space for large (ca. 20 L) solvent cans to be stored safely had to be meted out carefully. Only keeping the amount of solvent needed for the academic year can be problematic, but with proper planning, it can be realized. We also decided to reduce the total types of stored bulk solvents down to hexanes, ethyl acetate, methylene chloride, and some diethyl ether. Alcohols were pared down to methanol and ethanol only, and these solvents were purchased in different-sized containers so as to purposely exhaust the alcohol during the year.

A move was also made to using digital thermocouples with wire probes, which allowed us to eschew the use of mercury thermometers in the lab. Digital melting point apparatus, while expensive, can be another way to remove mercury thermometers from lab use. Experiments involving “grocery reagents” like caffeine [11], spinach [12], and terpenoids [13] helped reduce cost and deeply depress student safety concerns. Each semester, these items are incorporated into students’ instruction in the area of green chemistry as specific examples of reducing waste, toxicity, and hazards while increasing the safety of the learning environment. No changes with regard to equipment and materials were made without specifically choosing to enhance the learning and safety of the students.

4 Green Chemistry Principles Affect the Transformations Performed

The true power of organic chemistry lies in its ability to generate new structures through synthesis. Many of the green chemistry principles are tied directly to the methods of synthesis, predominantly from the perspective of energy efficiency, preventing waste, and increasing atom economy. With regard to the lab course learning outcomes already discussed, nearly all of the methods practiced and transformations performed in the University of Detroit Mercy organic lab sequence have been “greened” in several different ways. First, the 1980s and 1990s saw the arrival of microscale glassware and preparations. When these concepts first reached the academic teaching setting, they were mostly driven by cost and safety. The modern lab can take advantage of microscale work in efforts to adopt the 12 principles of green chemistry. Scale affects the waste generated, and our labs take this fact into consideration for each experiment performed. Also, over the length of the semester, total waste has been reduced significantly by teaching students about how atom economy is affected by transformation scale [7].

Second, there can be no doubt that microwave irradiation as a method of heating a reaction mixture has come into its own over the last 10–15 years, especially in the teaching laboratory. However, even a smaller microwave reactor apparatus can be expensive, and student throughput is of utmost significance at primarily undergraduate institutions, hence the advent of many reactions that reduce reaction times to hundreds of seconds (or less) by using nonfood-rated conventional microwave ovens [14, 15]. As long as these “reactors” are used in vented environments, students can compare energy usage and time of reaction between more green and less green transformations.

Third, transformations have been specifically chosen due to their solvent-free, water-based, or mechanochemical nature [16–18]. The pedagogical, educational literature has exploded with laboratory experiments that summon the most fundamental of green chemical applications: the exclusion of solvent from atom economy. A number of transformations forgo solvent altogether or use renewable resources like water to increase atom economy and overall “greenness” for a reaction. In addition, with this motif in mind, students can learn about more atypical reaction schemes, such as those that result from added mechanical pressure, like mechanochemistry.

Lastly, a cognizance of green chemistry in modern synthesis is taught in the organic labs at the University of Detroit Mercy using click, Suzuki, and Sonogashira couplings that rely on greened catalysts [19–21]. Again, using the metrics of atom economy, students can ascertain that small amounts of compounds that undergo transformations many times are beneficial to the overall greenness of a reaction. At the University of Detroit Mercy, we have even used these cycloadditions and cross-couplings, in conjunction with traditional, less green versions, to help students compare legacy conditions to new, greener ones. Each of the items -mentioned earlier benefits the student by way of learning outcome enhancement and safety, not to mention the general cost savings of running smaller, greener experiments for many students concurrently.

5 Conclusions

In summary, an initiative to incorporate the 12 principles of green chemistry in the organic chemistry laboratory courses at the University of Detroit Mercy has had multiple positive effects. From helping students learn how to merge green chemistry theory with their existing chemical knowledge, to altering the overall safety profile of the lab, to cementing application of the principles through microwave, solvent free, and green catalyst experimentation, students at Detroit Mercy are well poised to be the socially responsible scientists demanded by the modern scientific workplace.