Diels-Alder Reaction
Laboratory procedure used was written by Dr. John Barbaro of the
University of Florida.
http://www.chem.ufl.edu/~barbaro/2211L/diels-alder/da-proc.html
The Diels-Alder reaction is probably the most familiar example
of a reaction type known as a cycloaddition reaction, in which
the conjugated p-systems of two reactants join to generate a new
ring. The reactants in the Diels-Alder reaction are a 1,3-diene
and an alkene called the dienophile. The carbon-carbon double
bond in the dienophile is usually conjugated with an electronwithdrawing group such as a carbonyl, a nitrile or a nitro
group. Conjugate (or 1,4) addition of the double bond of the
dienophile to the diene produces a new six-membered ring. A more
detailed discussion of the Diels-Alder reaction can be found in
chapter 15 of your textbook, and you should read those sections
of your text for additional background material.
The Diels-Alder reaction appears to occur in a single step
without the intervention of radicals, carbocations, or other
intermediates. It is a powerful method for the construction of
cyclohexene rings, and has become such a mainstay of organic
synthesis that its discoverers, Otto Diels and Kurt Alder, were
awarded the Nobel Prize in Chemistry in 1950 for their discovery of this
reaction.
Diels-Alder Reaction (Diene Synthesis).
FIRST CITATION: O. Diels and K. Alder, Ann. 460, 98 (1928); 470, 62 (1929) Ber. 62, 2081,
2087 (1929)
Stereoselectivity:
 The Diels-Alder reaction is stereospecific with respect to
both the diene and the dienophile.
 Addition is syn on both components (bonds form from same
species at the same time)
 This is shown by the examples below:
cis-dienophile gives cissubstituents in the
product.
trans-dienophile gives
trans-substituents in the
product.
If both substituents on
the diene are Z, then
both end up on the same
face of the product
If substituents on the
diene are E and Z, then
they end up on opposite
faces of the product
Cyclic dienes can give stereoisomeric products depending on
whether the dienophile lies under or away from the diene in the
transition state. The endo product is usually the major product
(due to kinetic control)
Diene and dienophile staggered
Diene and dienophile aligned
with respect to each other
directly over each other gives
gives the exo product
the endo product
(dienophile exposed or out =
(dienophile under or in = endo)
exo)
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch10/ch10-52.html VERY COOL LINKS!!!!!
Reaction of Anthracene with Maleic Anhydride
The Diels-Alder reaction in this experiment uses an unusual
cyclic diene–the central ring of anthracene. Benzene and
naphthalene do not take part in typical Diels-Alder reactions
because the p-electrons of the diene are part of an aromatic
ring; if cycloaddition were to occur the aromaticity of that
ring would be lost. In anthracene however, as you will find if
you draw the structures of the possible resonance contributors,
all three rings cannot have benzenoid character simultaneously
so the resonance energy per ring is lower than that of benzene
and naphthalene (resonance energies: benzene, 36 kcal/mole;
naphthalene, 60 kcal/mole; anthracene, 84 kcal/mole). DielsAlder addition across the center ring of anthracene is possible
since it leaves two intact benzene rings in the adduct.
Techniques
In this lab you will learn how to perform two valuable
laboratory techniques that will be used throughout the semester:
heating a solution under reflux conditions and vacuum
filtration.
For refluxing a solution, you will use the ground-glass joint
glassware found in the kit in your drawer. The ground-glass
joints enable all of the various pieces of glassware in the kit
to connect together snugly, which allows you to build a wide
variety of set-ups from a few pieces of glassware. Make sure
that all of the ground-glass equipment in your kit has the same
size joints (i.e., the same taper) or else the pieces will not
fit together properly.
One problem with ground-glass joints is that they have a
tendency to freeze or stick together. This problem can be
avoided by applying a thin film of silicone grease to the inner
(male) member of the joint before connecting the two pieces.
After slipping the two pieces of glassware together, rotate the
joint to distribute the grease evenly. Do not use too much
grease on the joints since the excess might contaminate your
sample.
Safety and Waste Disposal
Xylene is flammable, so keep it away from flames and hot plates.
Experimental Procedure
Place 1.0 g of anthracene and 0.5 g of maleic anhydride in a
100-mL round-bottom flask. Add 15 mL of xylene and a boiling
chip. Attach a reflux condenser to the flask. It might be
necessary to run cooling water through the condenser; an aircooled condenser can be sufficient when using a high-boiling
solvent such as xylene on a small scale. Heat the mixture under
reflux for 30 minutes. At the end of the reflux period, cool the
flask to room temperature and then chill it in an ice bath for
about ten minutes to complete the crystallization of the
product.
Collect the crystals by suction filtration on a small Büchner
funnel and wash the solid with 15-20 mL of ice-cold xylene.
Allow it to dry on a piece of filter paper. Record the weight of
the product and calculate the percent yield for the reaction.
Don’t worry about getting a melting point (lit. mp 261-262 oC)
for your product.
POSTLAB QUESTIONS:
1. Explain why a 4M solution of maleic anhydride is made in
CH2Cl2 and not in water. Show the reaction between maleic
anhydride and water.
2. Give structures for the major Diels-Alder product of the
following reactions:
1,3-cyclohexadiene and tetrachloroethene
1,3-cylcohexadiene and fumaric acid, the trans isomer of maleic
acid