Ok, up until this point I have only posted background information explaining the research that I have been conducting for the past 7 weeks. Now, I will post two tables detailing some of the work that I have done and the resulting data. Following the charts will be an example NMR spectrum of one of the resulting compounds.Mol % Comparisons of Tandem Reactions2-Component ISMS
Example Spectrum
So,I thought that I would give an example of the reactions that I have been conducting. Below is the generic reaction equation for a Bismuth mediated, epoxide rearrangement and intramolecular silyl-modified Sakurai Reaction which afford disubstituted dihydropyrans. This is a very useful reaction sequence that we are developing into a one-pot reaction. Furthermore, this synthesis can be used to study the behavior of Bi(III) compounds as catalysts. The following shows the reaction involving the starting reagents (epoxide and vinyl silane) reacting in the presence of a catalytic amount of Bi(III) or TfOH to afford the desired dihydropyran product:The next image is of the mechanistic pathway of the 2-component ISMS reaction:
Q: Why don’t Catholics pray for forgiveness when sitting down?
A: Because there’s no syn elimination in the chair conformation!
Here is a historical note: In the 1980′s, in an effort to increase public awareness about the importance of chemistry, the American Chemical Society posted billboards with a picture of C6H10 and the title, “It takes alkynes to make a world.”
Continuing the pattern of lab superheroes, today’s episode focuses on the antics of The Flask. While some might view The Flask as a bit overweight and underwhelming, his position simply cannot be filled by anyone else. Here’s the story of how The Flask became so indispensable. Flask was born into a family populated by superpowers. The most famous relative being Flask’s cousin, The Flash. Growing up, Flask was always jealous of Flash. He got all the attention, both from the family and from the media. Because of this, he decided he was going to make himself famous.
Flask left home to go to college. He figured that an education was the most sure-fire way of improving his lot in life. While in school, Flask really enjoyed himself. He found a special love for Chemistry; something about the chemicals, reactions, colors, smells, and dangerous fumes drew him in. He was the one everyone went to during lab to explain the procedures and results. One professor in particular noticed Flask’s ability. Dr. Erlenmeyer was the head researcher in the Chem department, and generally had several undergrad students working for him. He approached Flask individually and asked him if he wanted a summer job in the lab. Flask happily agreed, and hasn’t left yet. Most of the time he uses the speed that runs in his family to catch drips before they splash onto the hood. Where at home, he was mocked for his rather pear-shaped form, in the lab it allowed him to contain more of these drops while still pouring smoothly. Eventually Flask fell in love an married a pretty little piece of glassware and had many little Flasks. You can still find them all, populating the lab, using their particular gifts to aid the chemists they work for.
-Emily Shmemily
So, this week has begun with frustration. I guess I should first explain the basic game-plan or strategy that guides my research. I am trying to determine whether or not Bismuth triflate acts as a Lewis acid or as a Bronsted acid. At first, we attempted to study the kinetics of various epoxide rearrangements in order to determine the behavior of the reaction components. However, this proved impossible. Each of the bismuth catalyzed ring opening reactions occurred at such a rapid rate, that the strategy of chemical kinetics was thrown out. Now, after searching through the literature, we have discovered a different approach.
Many examples have been cited throughout the literature that show various Lewis acids and the products they give with respect to differing starting epoxides. I was able to find a paper that gives epoxide reactions in which the epoxides all rearrange in two distinct ways. The study gives ratios of the two products for each epoxide and each Lewis acid used (ie: SbF5 or BF3-OET2). So, we have somewhat extended their study to include our bismuth compounds in addition to the Lewis acids cited in the paper. The ratios of products given by the bismuth compounds will be compared to the ratios given in the paper and also to the products of the same reactions run with Bronsted acids such as triflic acid. This should tell us whether the Bi(OTf)3 is acting as a Lewis acid or a Bronsted acid.
Ok, so the strategy sounds good, but before any epoxide ring opening reactions can be run, I must first make the starting material. The paper gives what seems to be easy procedures for the various epoxides that are used. However, after three attempts, my epoxidations have succeeded only once. It is possible that there are separable byproducts and my epoxide can still be isolated in decent yield, but what baffles me is that the reaction was clean and efficient the first it it was run. The possibility of decomposition upon work-up remains because when the epoxide breaks open it can give a tertiary carbocation stabilized by a neighboring benzene ring. So, perhaps the stability of this carbocation is causing loss of product during the work up of the reaction. Regardless, it has caused much frustration.
-What did the mass spec say to the gas chromatograph?
Breaking up is hard to do!
- The Physicist, upon seeing all the waves, gets very excited and runs into the water, disappearing.
The Marine Biologist, aware of tremendous variety of marine life in the ocean, also gets very excited, and runs into the water, disappearing.
The Chemist pulls out her notebook, and writes, “The Physicist and the Marine Biologist are soluble in water.”
So as many know, Williamsburg during the summer can have some unbearably high humidity levels. It seems every day in lab, we look out the windows to see beautiful sunny days and blue skies. By the time we get out at 5:30, however, so much water has evaporated that we have a mini-thunderstorm. By the time the clouds exhaust their excess moisture, it’s dark outside and too late to get any Vitamin D. So due to extreme discomfort, the citizens of the ‘burg sent out a plea for help. Their relief: The Dessicator.
He came on a day that would have been beautiful, had it not been for the 99% humidity. He surveyed the sweltering scene in front of him; the steam rising from Barksdale Field cast a haze on everything in the distance. He took special note of a couple of miserable friends, Doug and Jenny. These two had wanted to go to the beach every day for the past week, but because of the continuous thunderstorms, wouldn’t have been able to swim. While the beach can be fun in the rain, lightening might have put a damper on the festivities. As the Dessicator watched their obvious disappointment in the weather, he devised a plan. He explored the surrounding skies, and noticed a front that would sweep through Virginia, narrowly missing the Coastal Plain. That’s when the figurative lightbulb went on. He called in a few favors from his gang of friends, the Hood Vents, and described his plan.
All week, the rain came like clockwork. That is to say, when the clock hit 5, the clouds opened. Doug and Jenny watched in despair as Thursday night, a veritable hurricane drenched the campus. Then things started to change. After the downpour, the clouds suddenly disappeared. All Friday, they watched in anticipation as the sky remained clear. By the time lab let out, the sky was vivdly blue, the weather gorgeous, and the beach sandy. The Dessicator watched, satisfied as Doug and Jenny lounged on the beach, a well-deserved rest after a long week in the lab. Hood Vent 1 nodded his approval as he dusted his palms. The storm he had blown through town had cleared up all the moisture, ensuring the perfect beach day.
(Note to readers: a dessicator and the hood vents are devices used in lab to remove moisture from glassware.)
-Emily Shmemily
This summer I have been generously supported by the Chappell Fellowship to conduct synthetic chemistry research under the guidance of Prof. Hinkle. My research will focus on reactions involving catalytic bismuth compounds, namely bismuth triflate (Bi(OTf)3). The basis of the investigation is to determine the mechanism by which the bismuth catalyzes the reactions. Its possible that the bismuth is acting as a Lewis acid. If this is in fact the case, then it would be lucrative to create chiral auxilaries or ligands that could be used in catalytic synthetic reactions giving enantiomerically pure compounds. If, however, the bismuth compounds react in situ to give a Bronsted acid such as triflic acid (trifluoromethane sulfonic acid or TfOH) then the development of such expensive and complex ligands would be in vain. Even though there are known, reliable Lewis acids that can be used to catalyze similar reactions, cost and toxicity have and continue to cause organic chemists to search for alternatives. Bismuth has become increasingly popular in such uses. Furthermore, bismuth compounds are relatively inexpensive, exhibit low toxicity and are environmentally friendly. Most Bismuth compounds that we use (including BiCl3, and BiBr3) are comparable to table salt with respect to toxicity. In addition, not only are compounds such as bismuth triflate stable and easy to work with, they are also commercially available or can be made in a relatively simple reaction. So, why does all of this matter? Basically we are finding ways that will eventually provide simpler and cleaner synthetic pathways for the creation of many compounds including medicinal compounds and antifungal agents.