Besides the structure of the alcohol, what other variables may be explored?

1)      One variable for this reaction that could be investigated is the nature of the catalytic acid. Aqueous acids, such as the 85% H₃PO₄ typically used for this experiment, contain some water which is also product of the reaction. I may also add that, the amount of acid is not always in catalytic proportion to the substrate. In my current protocol 0.075 moles of acid is used to dehydrate 0.2 moles of alcohol. Non-aqueous acids may give different results. Acidic resins are an interesting substitute for aqueous acids. For example, John Ludeman and Kurt Field of Bradley University presented a poster at the 2006 ACS Great Lakes Regional Meeting on the use of Dowex 50WX2-100, Amberlite IRC-50S, and Amberlyst 15, for the dehydration of alcohols.

2)      Another variable would be the reaction conditions. In the current paradigm, the alkene is distilled away from the reaction mixture. Presumably, it is being distilled away as it is formed. An ad-hoc observation is that students seem to get somewhat different product ratios if they distill is carefully or if they “crank up the heat” and distill it quicker. What if the reaction mixture was refluxed to equilibrium before distillation? Would we see more thermodynamic products?

3)      Reaction conditions could be changed in other ways too. Microwave irradiation is currently being explored as an alternative to heating reactions. Possibly, sonication could also be performed on the alcohol.

4)      Another avenue to explore may be different strategies to push the reaction towards the products other than distilling off the alkene. For example, removing water with molecular sieves may be tried.

The dehydration of methylcyclohexanols provides a fecund problem to explore. The key is to develop methods to determine the distribution of alkene products in terms of % total alkenes. There are four possible positional isomers: I. methylenecyclohexene (Aldrich, Acros 1192-37-6); II. racemic 3-methyl-1-cyclohexene (Acros, 591-48-0); III. 1-methyl-1-cyclohexene (Aldrich, Acros 591-49-1) IV. racemic 4-methyl-1-cyclohexene (Aldrich, Acros 591-47-9). Two of the alkene positional isomers contain an asymmetric carbon.

The obvious place to start is by studying how the alcohol structure affects the product distribution of alkenes. There are 5 positional isomers of methylcyclohexanol: I. cyclohexanemethanol (Aldrich 100-49-2); II. 1-methylcyclohexanol (Aldrich 590-67-0); III. racemic cis&trans 2-methylcyclohexanol (Aldrich 583-59-5) IV. racemic cis&trans 3-methylcyclohexanol (Aldrich 591-23-1) V. cis&trans 4-methylcyclohexanol (Aldrich 589-91-3). Three of the alcohols are present in cis and trans diastereomer pairs: cis 2-methylcyclohexanol (Aldrich 7445-70-1) trans 2-methylcyclohexanol (Aldrich 7445-52-9) cis 3-methylcyclohexanol (5454-79-5) trans 3-methylcyclohexanol (7443-55-2) cis 4-methylcyclohexanol (Aldrich 7731-28-4) trans 4-methylcyclohexanol (Aldrich 7731-28-4). In addition there are 4 entaniomer pairs among the alcohol starting materials. Most of them are commercially available, for a price.

The “Center for Authentic Science Practice in Education” (CASPiE), as a part of the NSF’s Undergraduate Research Centers efforts received a 4-year, 2.5 million dollar grant starting August 15^th, 2004 to introduce research rich experiences to first and second year college students. As part of their dissemination requirements they are holding a series of workshops to promote the CASPiE method to college instructors. I attended their first promotional workshop this past week at the University of Illinois, Chicago. The workshops participants enjoyed a hands-on experience working in the lab on the experiments that students in the CASPiE modules perform. It was fun to part of a workshop where we were in involved in doing science. They have developed at least 3 “modules” that would be appropriate for sophomore organic chemistry lab. A module is a series of 4 to 6 lessons that include skill-building labs and Peer Led Team Learning that culminate in the students participating in a research experiment that is part of a larger research project proposed by a principal investigator. It is a great way to introduce students to a research-rich undergraduate experience in organic laboratory. CASPiE participants have admittance into remote-access instrumentational analysis (GC-FID, GC-MS, FTIR, HPLC, and Raman) through Purdue University which is explained quite well in their website. The program is well thought-out, attentively organized, amply funded, and thoroughly assessed.

Even though it takes advantage of some open access friendly techniques such as remote-access instrumentation and mutlilab collaborative experiments, it is, unfortunately, not open science. Participation in the program requires a considerable commitment to following the scripted methodologies of the program. Content is only shared with an inner-circle of participants and not publically accessible. This can be easily ascertained from their website. Ostensibly, the reason for this secrecy is to allow the module’s principle investigator the proper control of her/his research project’s data. It’s a wonderful idea but the research aspect, in my opinion, is saddled with other requirements (such as the skill-building labs, 3-student teams, and peer-led team leaders) that do not necessarily enhance the quality of the research or the research experience. In addition, I do not see where the student-generated data is being fed back to the students themselves to help them see where they fit into the ongoing research program they are participating in.

I want to pursue point #5 further by first grappling with the current literature concerning the “Evelyn Effect.” The JCE article by David Todd, “The Dehydration of 2-Methylcyclohexanol Revisited: The Evelyn Effect” observes a kinetic effect that can be explained by proposing that in a mixture of cis/trans 2-Methylcyclohexanol the cis isomer reacts much faster than the trans isomer to give predominately 1-methylcyclohexene. The formation of 1-methylcyclohexene from cis-2-methylcyclohexanol would involve an “E2-like” anti-elimination of proton and the protonated alcohol. The dehydration of the trans isomer would go through a E1 mechanism that requires the formation of a carbocation before elimination of a proton. A follow-up study by Cawley and Linder: “The Acid Catalyzed Dehydration of an Isomeric 2-Methylcyclohexanol Mixture” involves a detailed kinetic study. Students began with a 36.6/63.4 cis/trans mixture of 2-methylcyclohexanol with a cyclohexanol impurity (% impurity was not reported). They performed thy typical reaction+distillation and collected fractions at 4, 8, 16, 24, and 28 minutes. They also collected a 0.1 mL volume of the sample of the reaction mixture at each of these time intervals. These fractions were analyzed by 1H NMR and GC for composition. The cis/trans rate constants for the dehydration of reaction were determined to be 8.4/1.0 – much less than 30/1 ratio reported in 1931 by Vavon and Barbier. An intriguing study! It would be very interesting to have the raw (student) data on this one. Very little is said about the product ratios in the distillate fractions, they just report that they obtained 2.1% methylene cyclohexene and not the 4% previously reported.

There are several advantages of studying the dehydration of methylcyclohexanols in the first semester of Organic Chemistry.

1) The experiment involves reactions that are typically studied during first semester: E1, E2, and the 1,2-hydride shift. It is a time-tested protocol that has been run in hundreds of labs by thousands of students.

2) Analysis of the experiment involves the understanding of all three mechanisms mentioned previously and how they may compete with each other. In other words, it is a simple experiment that demands a rather involved interpretation of results.

3) It shows that textbooks “rules” such as the Zaitzev’s rule in this case, are not necessarily rules as such, but rather astute observations of general trends that can vary experimentally depending on the reactant and the reaction conditions.

4) Analytically, we are observing/measuring the presence of 3 known methylcyclohexene and methylene cyclohexane products that can be separated and detected by Gas Chromatography. I believe that the product mixtures can also be analyzed by NMR.

5) The reaction lends itself to an inquiry format that involves the study different reactants and reaction conditions on the ratio of products. In fact, this experiment, in my opinion, is an ideal candidate for a multi-institution collaborative study that combines and interprets student data.

As predicted from the Journal of Chemical Education articles, three methylcyclohexene products were observed. Their relative abundance measured by peak height was 80, 16, and 4%. The alkene products represented by these peaks apparently correspond to 1-methycyclehexene, 3-methycyclehexene, and methylene cyclohexane respectively.

The dehydration of 4-methylcyclohexanol produce two products, that can be distinguished by our current GC column, at 90 and 10% with retention times that match 3-methycyclehexene and 1-methycyclehexene respectively. My current theory is that the retention times 3 and 4-methycyclehexene could not be distinguished with GC column and temperature program. However, there is still the issue of how 1-methycyclehexene is produced from 4-methylcyclohexanol.

The dehydration of 3-methylcyclohexanol yields two products, that can be distinguished by our current GC column, at 80 and 20% with retention times that match 3-methylcyclohexene and 1-methycyclehexene respectively.

Samples of 1-methyl and 3-methyl cyclohexenes purchased from Aldrich chemical confirmed two of compound assignments for the dehydration of 2-methylcyclohexanol. Obviously, it remains to separate the 3 and 4-methylcyclohexene by GC.

A common Sophomore Organic Chemistry laboratory experiment that has great potential for further research is the acid catalyzed dehydration of simple alcohols. The classic dehydration of 2-methylcyclohexanol experiment that was introduced in Journal of Chemical Education in 1967 Taber(1967)JCE:44,p620. The rather simple procedure of distilling an alcohol with an aqueous acid has spawned several investigations that have resulted in formal journal articles. At the same time, the experiment has retained its popularity in the Sophomore Organic Chemistry laboratory curriculum. In one line of inquiry it has been observed that a mixture of 2-methylcyclohexanol diastereomers gives rise to a mixture of three isomeric alkenes Todd(1994)JCE:71,p440; Feigenbaum(1987)JCE:64,p273; Cawley(1997)JCE:74l,p102. Explaining the presence of the three alkene products requires an intense synthesis of information communicated in a typical SOC textbook. The continued popularity of this experiment is corroborated by the observation that Googling the phrase “Dehydration of 2-Methylcyclohexanol” on January 13^th, 2008 returned no less than 20 hits for online student handouts and/or guides for this SOC laboratory experiment. Moreover, this experiment provides fertile ground for experimentation and innovation that has not yet been fully explored. At Dominican University, the SOC students performed this experiment during the Fall 2007 semester with not only the dehydration of 2-methylcyclohexanol (Aldrich 153087) but also the 4-methyl (Aldrich 153095) and 3-methyl (Aldrich 139734) positional isomers. The reaction products were submitted to GC-FID analysis. The exciting results will follow next week…

Data analysis will play a larger role in the new collaborative Organic Chemistry curriculum. I performed three experiments Fall 2007 where students entered their data before leaving the lab. The students were then directed to analyze the “class data” as part of their lab report. This is typically not done in traditional experiments for unknown reasons. One “class data” lab was our first lab using TLC to look at known compounds and compare them to a mixture of unknowns. On one hand, TLC R_f values are easily accessible. However, TLC is rather imprecise method, depending on the volume of sample spotted, the concentration of the sample, operator skill, time of development, etc… Asked to compare their data with class data, most students gave very qualitative responses: “My data was pretty good,” or “My data was about the same as everybody else’s.” This was not what I expected. Obviously, more deliberate treatment of data analysis is necessary. The second “class data” lab was a solubility lab where students were asked to determine whether a substance was insoluble, somewhat soluble, soluble, or very soluble in a given solvent. Each of these categories can be given a value and the numbers crunched from there. The third “class data” lab was a kinetics lab where they explored an S_N1 substitution reaction. Students did better with the analysis part on this lab. However, the repeatability of the experiment itself is difficult due to the fact that it is very sensitive to the exact molarity of the reagents and the volume measurement techniques of the students. The comparative data gets pretty crazy sometimes due to systematic errors. My idea was to use this data as a starting point for Fall 2008 experiments. What can be learned from last year’s data? Are there ways to correct poor technique or poor reporting from last year? What is the next step in exploring this phenomenon? I’m thinking that more class time will be needed to prepare and plan the experiment this Fall, especially if students are going to participate in analyzing last year’s data and propose changes/modifications. The goal here is to make OChem laboratory more dynamic by moving forward instead of simply repeating last year’s experiment. Even if we repeat last year’s experiment, to a certain extent, there is a bigger goal that is being envisioned and students are participants in the process.

There is currently a great deal of interest in using the information sharing capabilities of blogs, wikis, and discussion forums to promote undergraduate learning as well as to facilitate collaboration among scientists. In a recent article in Chemical & Engineering News entitled “Wired for Learning: Teachers are tapping into youths’ digital savvy to take science education into the future,” a science teacher at the Red Lion Area High School, Ben Smith, remarks “Wouldn’t it be great if you could start a lab in Pennsylvania and it finishes in California or in China?” This got me thinking about the collaborative potential of social networking. What could we accomplish if each sophomore organic chemistry section did one or two labs in collaboration with other schools? A low-level collaboration would simply be to compare results of one procedure done the same way at different institutions. The classic example would be the synthesis of some compound with an identity characterization (melting point for solids and refractive index for liquids) and purity analysis (chromatography) We would certainly have a bigger data sets (percent yield for example) with which to do statistical analysis. I have a hunch that we will see some discrepancies between schools. If one school has a consistently higher (or lower) % yield, what is the explanation? In my experience different chromatography analyses of purity tend to give different results. What are the likely impurities? How did they get there? My assertion is that, even at this rather simple level, we could learn from each other and at the same time open our students up to the reality of a wider scientific community.

We an assessment instrument similar to the one described was in the supplement for Lorena Tribe & Kim Kostka article is, “Peer-Developed and Peer-Led Labs in General Chemistry” J. Chem. Ed. 2007, 84(6), 1031-1034. I set it up online on the Student Assessment of Learning Gains (SALG) website There were six questions that asked about students appreciation of the project. It was scored on the SALG five-point scale from no help (1) to very much help (5). The average scores for all six questions were between moderate help (3) to much help (4). Twenty out of 22 students recommended this experience for next year. The students were given a chance to write comments on their overall appreciation of the sequence. A number of students had an increased appreciation of these labs over last semesters more traditional labs. “It was better this semester than last. I enjoyed the labs more and found it more interesting to pick the lab and design it.” The most common shortcoming of the labs was a lack of clarity about how what they were doing in lab related to the lecture material. “The labs did not really help me in understanding or translating information to classroom discussions and worksheets.” A related shortcoming was the common difficulty in developing a deep understanding of what the lab was demonstrating beyond simply being able to perform the techniques. “At some points (especially towards the end) people seemed not to really understand what was going on, and were simply following the directions on the handout.”