1. Diels-Alder Reactions of Anthracene and N-(substituted-phenyl)maleimides
Using a Household Microwave Oven
Rory T. Moffat* and Bruce A. Hathaway,
Department of Chemistry & Physics, LeTourneau University, Longview, TX, 75607-7001
mmoles of
Maleimide
mmoles of
Anthracene
Microwave
Power Level
(1000W)
Period
(minutes)
Product
(% Yield)
2.3 2.3 50% 2 38%
2.3 1.6 70%, then
100%
1, then 1 45%
2.3 1.6 100% 2 67%
2.3 1.6* 100% 2 ~75%
*Two flasks of molar ratio 1:0.7 were placed in the microwave at the same time.
Goals
Scheme 1
React para-phenetidine with maleic anhydride to make N-(4-ethoxy)maleanilic
acid (92%).
Scheme 2
React the N-(4-ethoxy)maleanilic acid with acetic anhydride to form the
N-(4-ethoxyphenyl)maleimide (35%).
Scheme 3
• Prepare different N-substituted maleimides: [N-(4-ethoxyphenyl), and N-
(3-Nitrophenyl)].
• Successfully synthesize the Diels-Alder product within a microwave.
• Develop a lab procedure that would let OChem students synthesize a
maleimide, and then use their maleimide in the Diels-Alder reaction.
What we wanted in a student Diels-Alder (DA) reaction: Good yields, soluble in
NMR solvents, and easily purified.
Synthesis
Synthesis Continued
The conditions were worked out for DA reaction of Anthracene with
N-(4-ethoxyphenyl)maleimide. We are satisfied with this research and ready to
move this procedure on as a lab. However, conditions were not perfected with
our DA reaction of anthracene with N-(3-nitrophenyl)maleimide. More research
could be done one this particular N-substituted maleimide. The 1:0.7 mole ratio
of maleimide to anthracene was due to anthracene still being in solution with
the product upon analysis.
The other reactions weren’t useful because they did not met the introductory
goals. N-(3-butoxyphenyl)maleimide was not a solid and would be difficult to
purify on a small scale. The N-phenylmaleimide DA product was not a good
choice because it was not easily soluble in NMR solvents and was hard to
purify.
Results
Other Reactions (which weren’t useful to us)
Scheme 1
React meta-nitroaniline with maleic anhydride to make 3-nitromaleanilic acid
(55%).
Scheme 2
React the 3-nitromaleanillic acid with acetic anhydride to form the
N-(3-nitrophenyl)maleimide (55%).
Scheme 3
1:0.7 ratio of maleimide to anthracene (0.917 mmoles of maleimide and 0.642
mmoles of anthracene). Ran for two minutes at 100% power (30%).
Procedure
References and Acknowledgements
1. Bari, S. S.; Bose, A. K.; Chaudhary, A. G; Manhas. M. S.; Raju, V. A.;
Robb, E. W. “Reactions Accelerated by Microwave Radiation in the
Undergraduate Organic Laboratory”. J. Chem Educ. 1992, 69 (11), 938
2. Mori, K.; Izawa, T.; Mizuno, Y.; Matsui, S.; United States Patent,
“Composition for Inhibiting Adhesion of Shellfish and Algae”. Ihara
Chemical Industry Co. Ltd. Toyko, Japan. Appl. No. 736,339. 1976.
Special thanks to:
The Welch Foundation, for funding
LeTourneau University
Joshua Pickle, for his previous work
The first scheme was with para-phenetidine and maleic anhydride. We started
by weighing out 2.00g of maleic anhydride and dissolving it in 50ml of ether.
Once dissolved we added 20mmols of para-phenetidine. We stirred for 5
minutes then let it sit for 15 minutes. We put the flask then in an ice bath and
suction filtered off the maleanilic acid.
The basic procedure to make the maleimide (scheme 2) was to take 0.50g of
sodium acetate and added it to a RBF with 7ml of acetic anhydride. We then
added our maleanilic acid and refluxed for 35 minutes. We took the flask and
let it cool to RT then poured it into a beaker with 20ml of cooled water that was
cooled in an ice bath. We suction filtered off the solid maleimide.
To make the maleanilic acid of the meta-nitroaniline compound, we used 2.85g
of m-nitroaniline instead of p-phenetidine but did the above procedure. We
kept the filtrate which evaporated overnight and left a fluffy yellow powder. We
added the solid from the filtrate and the suction filtered solid to a 500ml flask
and added 250ml of methanol to boil for recrystallization. We did a hot gravity
filtration of some insoluble particles and transferred the methanol solution to a
400ml beaker. We cooled the beaker to RT then in an ice bath and suction
filtered off the solid.