Chemistry Reference
In-Depth Information
it forms. This is also considered a condensation reaction because methanol is
removed by condensation of the methyl benzoate with ethanol.
O
O
CH
3
O
O
+
OH
+ CH
3
OH
These reactions are the basis for the commercial preparation of polyesters.
Polyesters are formed from a dicarboxylic acid and a dialcohol. The largest
volume polyester is polyethylene terephthalate (PET). Rynite
®
(Dupont) is a
common brand. This is a condensation polymer and made by the removal of
water in the condensation reaction of ethylene glycol with terephthalic acid.
Note that all of the atoms of the monomers are not present in the final polymer.
This is different from addition polymers.
O
O
H H
C
H
O
C
O
+ 2x H
2
O
+
OH
H
H
O
O
H
OH
O
x
O
Both terephthalic acid and ethylene glycol are prepared by oxidation of
chemicals isolated from petroleum and are therefore economically attractive.
O
H
CH
3
O
O
C8 distillate
Petroleum
BTX stream
O
H
H
3
C
O
H
2
O
OH
O
O
Petroleum
OH
The polymerization is catalyzed by acid and the equilibrium is driven to the
right by the removal of water. However, there is another competing reaction,
etherification, which is also acid catalyzed and driven by the removal of water.
ROR + H
2
O
2 ROH
Ether formation
OH
O
2
+ H
2
O
HO
OH
OH
Diethylene glycol
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