The Diels-Alder reaction is a cycloaddition reaction, a reaction in which two
molecules undergo addition to yield a cyclic product. Various types of
cycloaddition reaction are known. Because a Diels-Alder reaction involves two
double bonds(four π electrons) of a conjugated diene and one double bond (two π
electrons) of the other reactant, this type of reaction is called [4+2]
cycloaddition. In a Diels-Alder reaction, the conjugated diene is referred to
as the diene; the other compound is called the dienopile.
[4+2]
cycloaddition
This
Diels-Alder reaction is carried out by boiling the reactants in xylene. Both
reactants are soluble in xylene, and the reaction is rapid because of the high
boilig point of the solvent, xylene. As the mixture cools, the product
crystallizes. The product is isolated by filtration; if the starting anthracene
was pure, it requires no further purification.
It is difficult to remove the high-boiling
xylene by “air-drying” the crystals. In addition, exposure to the air results
in the hydrolysis of anhydrides by atmospheric moisture.
For
this reason, the product is dried under an inverted beaker along with some
paraffin wax, which dissolves xylene vapors and thus acts as a “dessicant.”
Reaction Equation
Chemicals
1.
Anthracene: 1.0g
2.
Maleic anhydride: 0.5g
3.
Xylene: 17.5mL
Procedure
1.
Place 1.0g anthracene in a 25mL
round-bottomed bottle
2.
Pour 17.5mL xylene into the
bottle
3.
Add 0.5g maleic anhydride in
the solution
4.
Reflux the mixture for 30
minutes.
5.
After the round-bottomed bottle
cools to room temperature, put the bottle in an ice bath.
It is still very hot now
6.
Filter the solid by vacuum and
wash the product with ice-cold petroleum ether.
7.
Collect the solid in a sample
bottle and put some wax films with the solid.
Experimental Record
|
Weight of anthracene
|
1.000g
|
|
Weight of 9,10-dihydroanthracene-9,10-endo-α,β-succinic
anhydride
|
1.255g
|
|
Yield
|
89.5%
|
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