Gallate Diesters

The products from the acid catalyzed Fischer esterification of gallic acid with isopropanol (see “Fantastic Fischer” April 25, 2009) was chromatographed to purify isopropyl gallate. In addition to isopropyl gallate, another chromatographic peak was observed. This peak was collected and the NMR performed. Interestingly, this spectrum displayed three aromatic hydrogen signals at 7.207 (d), 7.153 (d) and 7.092 (s). Isopropyl gallate gives a singlet at 7.05 ppm. It also had four distinct septets at 5.130, 5.115 (overlapped), 4.692, and 4.562. Isopropyl gallate gives a septet at 5.129 ppm. The total integration for the aromatic hydrogens and the septets is about equal. I think what I am looking at is a mixture of two compounds created by the esterification of isopropyl gallate at the C3 and C4 hydroxy groups.

Sludge Test

I have continued to investigate the dehydration of methylcyclohexanols this summer. Just for fun, I have neutralized the “still pot” solution with sodium bicarbonate after the distillation has taken place. In theory, the still pot solution contains phosphoric acid, unreacted alcohol, and undistilled alkenes. After the acid catalyzed dehydration of a methylcyclohexanoel, the methy t-butylether extract of the neutralized still pot was analyzed by GC-MS. The major components seemed to be a group of closely related high-boiling point compounds. The obvious identity of these compounds is that they are dimers created by carbocation reaction with alkenes. The Single Ion Monitoring MS for the still pot compounds from the phosphoric acid catalyzed dehydration of 1-methyl-1-cyclohexanol shows two prominent peaks at m/z 192, that have m/z 96 fragments. This supports the formation of carbocation intermediates for the overall dehydration reaction.

Summer Undergraduate Research Experience

Last week Dominican University hosted a Summer Undergraduate Research Experience for community college sophomores who wanted a week-long assortment laboratory experiences. For my part, we did an analysis of energy drinks. This experiment was adapted from the “caffeine extraction” sophomore organic chemistry laboratory sequence. First, we did a colorimetric array for each of 6 different energy drinks in a battery of 24 different indicators. The second session was comparing the list of ingredients for the six different brands. We did some internet research on the identity and probably usefulness of the ingredients. In afternoon session we did the extraction of caffeine from energy drinks with liquid-liquid extraction. We analyzed our products by TLC and UV. We also prepared samples for HPLC. In addition to liquid-liquid extraction we performed a solid phase extraction (SPE) of energy drinks. We passed 20 mL of energy drink through an equilibrated 3 mL C18 column, washed the column with water, and eluted the caffeine with methanol. I was very informative to compare the HPLC of 1) the original energy drink, 2) the caffeine extracted by liquid-liquid extraction, 3) the aqueous fraction from the liquid-liquid extraction, and 4) the SPE methanol fraction. In brief there were two or three compounds detectable with HPLC (260nm) in the SPE fraction that were not present in the liquid-liquid extract.

New Results for the Dehydration of Methylcyclohexanols

This Spring, a research project was performed by one of my Sophomore Organic Chemistry students. The research project was designed to continue investigations into the dehydration of methylcyclohexanols that we explored Fall 2008. I have written several entries for this project, and will likely write several more. In short, the simple dehydration of an alcohol with a phosphoric acid becomes a very intriguing experiment when the alcohol is a methylcyclohexanol. Multiple alkene products are formed in varying amounts depending on the starting position of the methyl in 1-, 3-, and 4-methyl-1-cyclohexanol. The student wanted to investigate the likelihood that an alcohol ↔ alkene ↔ alcohol equilibrium was being established in the reaction mixture. In once series of inquiries, the dehydration experiment was performed by just refluxing the alcohol without distillation. The reaction mixture showed no signs of other positional isomer alcohols being formed other than the original 4-methyl-1-cyclohexanol. When the reaction was done with only cis or only trans 2-methyl-1-cyclohexanol, no detectable isomerization was observed. Refluxing the alkene with concentrated phosphoric acid did not produce any alcohols. This was rather suprising, since there is nor reason why the reverse reaction (acid catalyzed hydration of a alkene) should not happen. The reason we did not observe the hydration reaction may the solubility of the alkene. The series of experiments performed this spring was helpful in a negative short of way – there is no convincing evidence that an alcohol ↔ alkene ↔ alcohol equilibrium is being established.

Answer/Question the Questions/Answers

This is a continuation of last week’s entry on how grading (evalution) can be rendered more efficient. How an assignment is to be graded determines what kinds of questions can be asked. For an instructor graded scenario, anything goes from multiple choice to lab-report format to critical thinking design. If a teaching assistant is going to grade the assignment, the questions need to be tightened up and/or the grading rubric has to be very detailed about what kinds of responses are acceptable. The more mechanical/digital the grading instrument, the tighter the responses have to be – my guess is that this works better with classroom material (OWL, Ace, ect…) than with lab reports. The flip side states that the types of questions posed in the assignment determine the possible modes of evaluation. Questions can be divided into different grading categories: 1) answers that have numerical or precise written answers, 2) critical thinking questions where a particular thought process is desired, 3) critical thinking questions that are meant to provoke reflection but not necessarily a precise answer, 4) questions that require creativity to answer well. The first and second types are relatively easy to grade, once the parameters have been established such as the acceptable format of a numerical answer. The third and fourth categories tend to be questions where I give full credit for any and every thoughtful answer. The third and fourth categories tend to be questions where I am poised to learn from my students, since I am not looking for a particular, pre-determined answer. It seems unfortunate that we almost have to choose between what is most beneficial to students and what is manageable by the instructors.

I Corrected It Myself

I grade my own students’ lab reports. In truth, I do this because when I started teaching ten years ago, I had about a dozen students in Organic Chemistry. Lately, I have found that assignments and grading methods that I had developed for small class sizes were too labor intensive for larger classes. One common way to decrease the correcting load is to have teaching assistants that grade laboratory assignments. I’m not so sure that I want to go this route. The obvious reason that pops into my brain is that TAs can’t be trusted to grade well. This probably shows more bias than rationality, but it is true that a certain amount of TA training would be necessary for consistent and accurate grading. I wonder if the type of question I would ask would have to change. I assume that I would have to build the expectation of student grading into my questions. On the other hand, do I gain something from grading student papers? Assignments are a way for students to offer feedback to instructors. From grading assignments I discover: 1) what concepts the students are struggling with, 2) how they could be further challenged, 3) whether or not they understand the question the way I intended it, and 4) where they are getting their information from. I also learn thing about students and about the material that I didn’t know before. It is arrogant to assume that I cannot learn from my students. The thing is, I would miss the opportunity to understand my students better and to see if I could learn something new.

Chemical “Luminol”escence

The synthesis of Luminol is a great final experiment to cap off a year of organic chemistry laboratory work. It’s a relatively “old” experiment, I did it as in undergraduate. (Adapted from Experiment 48: Luminol, in Pavia, Lampman and Kriz, “Introduction to Organic Laboratory Techniques: A Contemporary Approach” (1976) Saunders.) The procedure involves a two-step reaction so its fairly involved. The chemiluminscent results are impressive, a very different outcome than the usual white solid or clear liquid products that need to be extensively characterized. Luminol is synthesized, reacted while still wet to give a dramatic display of luminescence and that is the end of it. If the glow does not appear immediately vigorous shaking of the crude luminol, KOH, DMSO, and oxygen will eventually start the luminescent reaction. The only problem we’ve had is breakage. Maybe it’s the combination of Bunsen burners, test tubes, and thermometers; or maybe students are just getting careless during the last lab. I haven’t come up with many ways to extend the experiment. One could add dyes to the luminol to change the color of the luminosity or try different methods of inducing the luminol + oxygen reaction.

Fantastic Fischer

We are again using a very old reaction, mineral acid catalyzed Fischer Esterification, to synthesize new compounds. Last year we synthesized propyl 2-methylbenzoate, propyl 4-methylbenzoate, and propyl 4-methoxycinnamate which have not been characterized by modern spectroscopic methods. This year I replaced 4-methoxycinnamic acid with gallic acid and added 2-propanol to the list of alcohols. Isopropanol worked will as the acid despite the fact that it is not a primary alcohol which are typically favored by undergraduate Fischer Esterification experiments. Gallic acid was also a challenge due to its three phenolic hydroxyl groups. The gallic acid products were a bit sticky and did not give very clean salt-plate IR spectra. Therefore, we also did UV scans of the gallate esters. Additionally, the gallic esters did not elute from the GC column so we did an HPLC chromatogram with detection at 254nm. The esters are easy to separate away from unreacted carboxylic acid by liquid-liquid extraction with an aqueous base. It was more difficult to separate the alcohol, soluble in both aqueous and organic phases from the ester. However, with prolonged evaporation the alcohol can be eliminated from the product mixture.

The Ancient Art (& Science) of Fermentation

Fermentation of alcoholic beverages is one of the oldest human technologies. Fermentation is also an interesting and educational laboratory exercise that can be done with all levels of students. I even do a fermentation lab with my Language Arts and Sciences summer course! The attraction of fermented beverages for college students does not need a lengthy explanation. However, fermentation technologies are at the forefront of the search for sustainable alternative fuels and chemical feedstocks. Ethanol from traditional sources has been used for fuel and chemical solvents for decades. A new generation of ethanol production from non-traditional sources is just beginning to be attempted on an industrial scale. Organisms may be induced or engineered to produce other small molecules besides ethanol. The large-scale production of small molecules from microorganisms is an exciting cutting edge in biotechnology. I have traditionally done this experiment with frozen corn as the carbohydrate source. In recent years I have expanded the carbohydrate source to (instant) rice and frozen (potatoes). One student even brought in the some quinoa this year. A careful distillation generates a high enough percentage alcohol to ignite. The mash can be tested for the presence of reducing sugars as well as alcohol content.

The Gallivanting Grignard

After last year’s “discovery” of the commercially available phenylmagnesiumbromide, I decided to branch out to more interesting reactant than benzophenone. (One redeeming feature of the Grignard synthesis of triphenylmethanol was the pink coloration of the reaction mixture.) This year we used the three positional isomers of methycyclohexanone as the ketone reagent. The resulting methylphenylcyclohexanols are not commercially available. The lack of commercial standards of the products is challenging but also adds a degree of novelty to the experiment. An interesting, somewhat unanticipated, outcome for this experiment was the unequal formation of two product diastereomers. The ratio of diastereomers varies for the three methylcyclohexanones. The ratios are 1:8, 1:3 and nearly 1:1 for the 2, 3, and 4-methyl-1-phenyl-1-cyclohexanols respectively. A 1971 article in the Canadian Journal of Chemistry by Rutherford, Wassenaar, Brien, and Fung “Preparation and Structural Elucidation of cis- and trans-1-phenyl-2-methylcyclohexanol” proposes that the “trans” isomer is the dominant one. In this case “trans” corresponds to the SR/RS enantiomer pair. Evidently, the position (and nearness) of the methyl group relative to the incoming phenyl group (as described by Cram) influences the stereochemical outcome of the reaction.