Lab Report

Professor George Barany, Chemistry 4311W, Fall 2019
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Green Chemistry: Diels-Alder Reaction in Water
Introduction: The Diels-Alder Reaction is an atom-economical reaction that is very
useful in synthetic organic chemistry. Two new carbon-carbon bonds are formed
simultaneously in a cycloaddition process, leading to a new unsaturated six-membered
ring structure similar to what is found in many natural products. Most examples of this
reaction rely on benzene, toluene, or xylenes as reaction solvents, often at reflux. Since
the reaction is slow, many laboratory courses run Diels-Alder reactions with highly
reactive reagents (e.g., cyclopentadiene or 1,3-butadiene) that must be generated in situ
by special preparative procedures. However, it has been observed relatively recently that
when such reactions are carried out in water, the rate is substantially accelerated due to
what is called the hydrophobic effect [as you research this reaction, you may come across
additional explanations]. The purpose of this experiment is to demonstrate that water, a
benign solvent, can serve as a replacement for the more toxic solvents used previously,
and that less reactive reagents can be used for quicker reactions in the environment of a
teaching laboratory. Avoidance of organic solvents, safer starting materials, rateacceleration without catalysts or extensive heating, and an easily isolated product all
make this a good example for a green chemical reaction. Furthermore, the relatively
simple procedure is a point of departure to get you acclimated to various experimental
characterization techniques, as well as software and web-based tools, as you will be using
them throughout this semester.
Experimental Procedure: Weigh out 65 mg of anthracene-9-methanol [calculate how
many mmol this is] into a 100-mL 14/20 round-bottom flask, and add a stir bar. Next,
add 3 equivalents of N-methylmaleimide [corrosive; handle with gloves; you need to
calculate the amount], followed by 50 mL of deionized water. The reaction is carried out
at reflux, with continuous stirring, for 1.5 h. Make careful observations about the
physical appearance of the reaction. When complete, allow the mixture to cool to 25 ºC
(room temperature), and then cool it down further in an ice-water bath. Collect the
product by suction filtration on a Hirsch funnel (with hose attached to house vacuum),
and rinsing with cold water to harvest and then wash all of the crystals, as well as to
remove unreacted excess starting material. In a subsequent lab period, recrystallize a
portion of the product from ethanol and water [dissolve in hot ethanol, add hot water to
incipient turbidity, then allow to cool – please keep track of masses pre- and postcrystallization, and all solvent volumes, and describe these in your report].
Characterization: [Do these in whatever order makes sense and consult with your TA if
you are not sure]. Obtain IR and 1
H NMR spectra for your dry product, and compare
them to corresponding data for your two starting materials [this latter is covered on
subsequent pages of this handout]. When your product is completely dry, record the
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final weight (for yield calculation) and melting range of your product [do both fast and
slow temperature gradient – which is more accurate? – and see if the mp is the same
when retaken after the melted product has been allowed to resolidify. After you have
recrystallized the product, compare the mp range of crude vs. purified material]. Develop
a TLC system [your TA may give some hints] that separates both starting materials and
the product, and report (a) Rf values in your solvent system; (b) how each one of these
three compounds appears when observed under near and far UV light. It may be
necessary to investigate other means of visualization for one of more of the compounds
under study.
Reading: As a general point, as you prepare to carry out any experimental work, look in
your textbook for descriptions of the theory and practice any technique that you need to
apply, and consult with your TA about any aspects that are idiosyncratic to the glassware,
equipment, materials, and/or other resources available to students in this course. Also,
identify any salient safety aspects.
Specifically for this experiment, you should read: Chapter 2, Keeping a Notebook, pp.
11-24; Chapter 12, The Melting Point Experiment, pp. 74-91; Chapter 13,
Recrystallization, pp. 92-107; Chapter 17, Sources of Heat, pp. 131-139; Chapter 22,
Reflux and Addition, only pp. 183-189; and Chapter 27, TLC, pp. 202-212. We also
expect you to have read and mastered Chapter 1, Safety First, Last, and Always, pp. 1-10
[as a bonus, there is a brief discussion about green chemistry towards the end of that
chapter], and at least browsed through the early Chapters 3 through 6 with the author’s
take on common laboratory glassware, equipment, and other apparatus, plus some hints
on finding chemical information. For that portion of your work that involves acquisition
and interpretation of spectral data, refer to Chapters 32 and 33, and review your personal
notes and previous textbooks from earlier lecture and laboratory organic chemistry
courses. Additional information is provided in other handouts from Professor Barany.
Please note that this experiment was inherited from earlier instructors of this course, who
in turn based their material on a handout prepared by L. M. Huffman, L. C. McKenzie,
and J. F. Hutchison at the Department of Chemistry, University of Oregon-Eugene, based
on published work of Breslow and others: (a) Breslow, R.; Zhu, Z. J. Am. Chem. Soc.
1995, 117, 9923-9924. (b) Myers, K.E.; Kumar, K. J. Am. Chem. Soc. 2000, 122,
12025-12026. (c) Breslow, R.; Groves, K.; Mayer, M.U. Pure Appl. Chem., 1998, 70,
1933-1938. The Huffman et al. handout has also been expanded into a procedure in at
least one lab textbook that we know about; you are on your honor to turn in work that
represents your own observations and thinking, rather than repackaging material readily
found on the internet.
Assignment: Prepare a report (first draft, then final), following the general guidelines of
Professor Barany’s handout, but also covering a few additional points as indicated below:
• One-paragraph introduction, with a reference or two, stating in your own words
those principles of green chemistry that are applicable here.
• Name the final product if you can, but otherwise refer to it as the anthracene-Nmethylmaleimide Diels-Alder adduct.
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• Draw the reaction with ChemDraw using the standard ACS journal preferences –
push electrons to show the reaction transition state.
• In addition to interpreting and annotating the spectral data on your product, do the
same for both starting materials – the data for which are covered later in this
handout. When analyzing your product, comment on the presence or absence of
unreacted starting materials; if one or both are present, try to quantify, and if they
are both absent, set a threshold level of how much could be there, e.g., < 2%
(depending on what your data show).
• In your “Results and Discussion” section, provide a detailed explanation of how
your spectral data supports the structures that you have assigned, and go over your
evidence for purity.
• Study the references provided in the third paragraph of “Reading” and try to find
several additional articles based on any of a variety of literature searching
strategies that will be taught to you in a number of ways. [At the discretion of the
instructor and TAs, we may provide you with some, if it turns out that the
majority of students are pressed for time.]
• Based on your reading of the literature, provide a brief rationalization, with
references, for why there is substantial rate acceleration when the Diels-Alder
reaction is carried out in the presence of water, as you have actually shown with
your own experimentation. Suggest a further experiment that could possibly
provide more insight as to whether or not your rationalization is correct.
• Although you are expected to look at several articles as part of preparing your
report (see above), choose a single one that you have downloaded from the
University of Minnesota library site, and attach it to your report.
• Locate and printout an SDS sheet for N-methylmaleimide, and mark the one or
two properties that are relevant to its safe handling for this experiment. Attach
the annotated SDS sheet to your report.
Timeline: This handout is distributed during recitation on Tuesday, September 3, at
which time the experiment is described and discussed. Start experimental work either
Monday or Tuesday (September 9 or 10), working around the timing of the other
activities. The entire procedure can be done in a single lab session, but at least some of
the characterization generally must wait until the next lab session due to the need to allow
product to dry (it comes out of water). We also require all students to recrystallize a
portion of their initial product, and to compare the crude and the pure.
A draft report is due, submitted to your TA at the beginning of the lab session on Monday
or Tuesday (September 30 or October 1), approximately three weeks after the
assignment was distributed. Your TA will strive to return the draft, complete with
extensive corrections and critiques, to you in a timely manner [selected drafts will also be
spot-checked by Professor Barany]. You then have a full week to return a revised final
version that takes into account all comments and suggestions (attach the draft at the same
time for comparison). Barring unforeseen circumstances, then, the final deadlines are
October 14 for Monday/Wednesday students, and October 15 for Tuesday/Thursday
students. Your grade will reflect almost exclusively the final version, with bonus points
for especially good drafts.
Professor George Barany, Chemistry 4311W, Fall 2019
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Appendix: As part of this assignment, you are asked to compare spectral data on your
reaction product with corresponding data for your two starting materials. First of all,
work up 1
H NMR spectra from the following file names:
N-methylmaleimide: 150202v3_5702.fid
Anthracene-9-methanol: 150202v3_5802.fid
Note that in order to access those, you need to: (a) log on to echo.chem.umn.edu as
“zzzadv” ; (b) open folder “old_vnmr” ; and (c) open folder “y7”
Second, see pages 5 and 6 for the corresponding IR spectra, already taken for you to work
with.
Third, see pages 7 and 8 for relevant GC/MS data. Note that under our laboratory
conditions it is difficult to obtain useful GC/MS data for the final product.
Fourth, review notes from class discussion and PowerPoint presentations, especially the
slide called “Issues with Experiment #1” that includes some things to be thinking about in
terms of optimizing experimental results. For example, is there an advantage to grinding
the anthracene-9-methanol with a mortar and pestle before starting the reaction? Does
use of a three-neck flask improve matters, by comparison to the 14/20 round-bottom flask
that we recommended?
Finally, we remind you that it is OK to repeat the experiment, and the repeat can be done
with one or two partners from your section. However, please be sure to report your solo
results separate from your group results (in the latter case, identify your partners by
name). The data analyses need to be completely your own.
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N-methylmaleimide IR:
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Anthracene-9-methanol IR:
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N-methylmaleimide GC/MS:
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Anthracene-9-methanol GC/MS:

 
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