Contributed by Abigail Giarrosso, Research Assistant at the Toxics Use Reduction Institute
As a sophomore chemistry major at the University of Massachusetts, Lowell (UMass Lowell), it was my time to take the chemistry major-specific organic laboratory course, a difficult and rigorous class. At the same time, I was working as a lab assistant at the Toxics Use Reduction Institute (TURI) where I was learning about green chemistry and working on replacing the solvent methylene chloride in commercial paint strippers. As I learned more about green chemistry through my time at TURI, I became very interested in being involved in the green chemistry community. As a result, I went to the Green Chemistry and Commerce Council (GC3) conference and I joined the nonprofit Beyond Benign. I learned about green chemistry from every source except my own university. I wanted to learn formally in class about green chemistry techniques and sustainable chemistry, but no courses were offered. As I thought back to my organic laboratory experience, I realized it would be a perfect opportunity to learn about waste reduction and using safer chemicals in hands-on lessons. I knew from my experience with the green chemistry community that places such as Gordon College had completely integrated green chemistry into their organic curriculum and so I was confident that finding safer experiments was feasible. I realized that this was an opportunity for awareness of sustainability and green chemistry to be formally taught at my school, making it easier for the next student to be informed and increasing awareness for future chemists.
I approached Dr. Jessica Garcia, the director of the undergraduate organic labs at UMass Lowell, and asked how she would feel if I tried to substitute some of the experiments for Organic Lab II with peer-reviewed, safer experiments. She was very enthusiastic about the idea because she was trying to do the same thing. So that is how came to take on helping “green” the organic labs as my senior thesis.
The project started in Spring 2016 with an initially straight-forward search to find safer replacements for the more complicated reactions. I found peer-reviewed articles on the Greener Education Materials for Chemists (GEMS) website on Diels-Alder, Wittig, and Michael and Aldol addition reactions. I also proposed that the experiments be conducted in microscale instead of miniscale to reduce the amount of waste generated. The highlight of the project was when I formally introducing green chemistry in class to the sophomore chemistry majors; covering what is green chemistry, why it should be important to them, and comparing and contrasting the previous and the new experiment in terms of safety.
#1: Replacing a Diels-Alder Reaction
The first experiment that we replaced was the Diels-Alder reaction from the textbook Gilbert and Martin, which creates the byproduct sulfur dioxide and utilizes the solvents xylenes and petroleum ether.1 The safer experiment that I found in a different textbook was atom economic, created no byproducts, and eliminated the use of harmful solvents by using water.2 Both experiments involved heating under reflux, but the green experiment refluxed for three times as long as the original experiment. The students seemed to understand the safety improvements of the experiment but complained about the experiment being boring due to the long reflux. The substitution was successful and demonstrated the green principles clearly.
#2: Replacing a Wittig Experiment
Two different Wittig reactions were chosen to replace the original Wittig experiment. The original experiment, again from the Gilbert and Martin textbook, involved a very hazardous Wittig reagent benzyltriphenylphosphonium chloride, used dichloromethane (methylene chloride!), and concentrated sodium hydroxide.3 Two greener experiments were chosen to demonstrate the concepts of stereospecificity and isomerization. Both are considered solvent-less reactions and use safer Wittig reagents, and only took about 15 minutes to complete each one.4 The only issue I had with this experiment was that it needed hexanes to triturate the product. I tried substituting hexanes with undecane (heptane was not available) and successfully removed the product, but the boiling point of undecane was too high to isolate the product with adequate purity. The students struggled to perform two experiments simultaneously and struggled with the small amount of product produced at microscale. Since the minor isomer of the reaction with benzaldehyde was not detectable with a 60 MHz NMR the experiment will be discontinued. The stereospecificity reaction with 9-anthraldehyde will be kept on the curriculum for the next year.
#3: Replacing a Michael and Aldol Addition
The replacement of the Michael and Aldol addition was not as successful as the previous two experiments. The original experiment was a good candidate for replacement because of its hazardous starting materials and it uses toluene as a solvent.5 The safer experiment was a solvent-less experiment that used safer reactants and eliminated the use of toluene. The experiment involved mixing the reactants together, which made a liquid, and grinding them with a mortar and pestle until a solid formed and then refluxing the solid to get the product. Sadly, as hard as I tried, I couldn’t get my reactants into a solid. It became a very sticky paste, but not as the solid should have looked as described in the journal article. When I refluxed the paste, it did not result in the expected product. The students had a very similar experience to mine and the lab period consisted of 20 people furiously grinding paste. It was a good demonstration of how real research sometimes fails, but it was not a successful example of green chemistry.
Creating a New Organic Lab Experiment for Non-Majors
The second semester of my senior project Dr. Garcia and I wanted to create a new reaction that could introduce green chemistry in Organic I lab to other majors such as biology and chemical engineering that do not take the Organic II lab for chemistry majors. One experiment that could be replaced was the E1 dehydration of 4-methylcyclohexanol. The issues with this experiment was that the reactant and products had minor health issues and the reaction used concentrated sulfuric and phosphoric acids. The driving force behind replacing this experiment was that the product has a strong, unpleasant odor. Our goal became to create a new E1 reaction that had a more pleasant odor and utilized reusable acid catalysts to replace the use of concentrated acids. Dr. Garcia came across the journal article “Unsaturated Hydrocarbons with Fruity and Floral Odors” whose structures could theoretically be made through an E1 dehydration and were known to have a pleasing smell.7 The simplest molecule in the paper was butylidenecyclohexane which was a possible dehydration product of 1-cyclohexyl-1-butanol or 1-n-butylcyclohexanol. We decided to see if the alcohols could be dehydrated using the standard concentrated acids, reusable K10 montmorillonite clay, and reusable amberlyst catalyst. The products were analyzed by gas chromatography, NMR spectroscopy, and IR spectroscopy.
It was found that all three proton sources did dehydrate both alcohols resulting in varying ratios of products since the E1 dehydration results in multiple products due to carbocation rearrangement. The concentrated acids produced two products, including butylidenecyclohexane. While the reusable catalysts had about four different products, including the desired product. Sadly, through the synthesis of standards and dehydration of the alcohols, it was found that the new reaction did not have a strong fruity and floral odor and had more of a gasoline smell. Although one of the product standards created by Wittig reaction had a wonderful fruity smell, it was never the dominant product of the dehydration. Due to the cost of the starting alcohols and the lack of improvement of the smell of the experiment, the new reaction will not be implemented in the Organic I Lab curriculum. It was found that the original dehydration of 4-methylcyclohexanol works with the reusable K10 montmorillonite clay, creating an opportunity to introduce green chemistry earlier in the undergraduate academic career. Other E1 dehydration reactions are still being investigated for a new experiment.
Overall, I am very proud to have brought an aspect of green chemistry to my school and I hope it will inspire other faculty members to look at their own teaching lab experiments to reduce waste and hazardous materials. Although I am graduating, Dr. Garcia is looking for other students who are interested in creating new, safer experiments for the UML teaching lab.
- Gilbert and Martin. Experimental Organic Chemistry: a miniscale and microscale approach, 5th edition, 261-268.
- Pavia, D.L.; et al. A Small Scale Approach to Organic Laboratory Techniques, 3rd edition, 400-411.
- Gilbert and Martin. Experimental Organic Chemistry: a miniscale and microscale approach, 5th edition, 421-426.
- Nguyen, K. C.; Weizman, H. Greening Wittig Reactions: Solvent-Free Synthesis of Ethyl trans-Cinnamate and trans-3-(9-Anthryl)-2-Propenoic Acid Ethyl Ester. J. Chem. Educ., 2007, 84 (1), 119-121.
- Gilbert and Martin. Experimental Organic Chemistry: a miniscale and microscale approach, 5th edition, 625-630.
- Pavia, D.L.; et al. A Small Scale Approach to Organic Laboratory Techniques, 3rd edition, 324-326.
- Anselmi, C.; et al. Unsaturated Hydrocarbons with Fruity and Floral Odors. J. Agric. Food. Chem., 2000, 48, 1285-1289.
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