Standard Synthesis Lab Report Format
95
Diels-Alder Reaction
General Diels-Alder Reaction: A conjugated “diene” reacts with a “dienophile” to produce a
cyclohexene ring. The “dienophile” is activated by electron-withdrawing substituents (carbonyls).
The diene must be in a “cisoid” conformation in order to react. Attachments to the reactants remain
attached as spectator atoms.
Overview of Actual Reaction: Anthracene (1) will serve as a student-friendly low-smell Diels-Alder
diene, with the labeled carbons functioning as the reactive diene. Maleic anhydride (2) will function as
the dienophile. Xylene (dimethylbenzene) is used as a high-boiling solvent so that the reaction will
work fast enough to complete conveniently. In terms of activation, notice that maleic anhydride is a
highly reactive dienophile, due to the presence of two electron-withdrawing carbonyl substituents.
Anthracene, however, is an unusually unreactive diene. This is due to both steric effects, but more
importantly because the “diene” is really part of an aromatic ring system and is thus stabilized. This
stabilization in the reactant reduces the reactivity (stability/reactivity principle). The “cyclohexene”
ring produced in every Diels-Alder reaction is hard to visualize, but consists of the six labeled atoms in
the product.
Reaction Setup: Flame dry a 25-mL round-bottomed flask with a small stir bar. (The maleic
anhydride is slightly water sensitive). Weigh out 0.80g of anthracene and 0.40g of maleic anhydride
(both are solids). Add the two solids into the flask. (Be sure the flask has cooled for at least two
minutes before adding the solids, or they will melt.) Carry the round-bottomed flask to the hood
(carefully), and add 10mL of xylene via syringe. Carry the mixture back to your hood, and clamp the
flask very securely above a hot-plate/stir-plate near a sink. Attach a reflux condenser, and tubing so
that water can flow through the condenser. (The array needs to be set up near a sink so that the tubes
will reach.)
Reaction Conditions: Turn the magnetic stirrer on, then warm the solution to “reflux” (until it boils
steadily) by setting your hot plate to setting 8 (for the heater). Note: the boiling point for the xylene
solvent is 138º; the actual temperature is actually somewhat hotter than that, because the dissolved
solutes elevate the boiling point to some degree. Once the solution has begun to reflux, reduce the heat
1
2
345
61
2
3
4
5
6
+
O
O
O
+
xylene solvent (3)
heat
O
O
O
1
5
5
6
6
anthracene-1
mw = 178
mp = 216
maleic anhydride - 2
mw = 98
mp = 60
Diels-Alder Product (4)
mw = 276
mp =
1
2 2
33
44
230-300 range
