Chemistry Reference
In-Depth Information
AROMATIC ORGANIC CHEMISTRY
C
ARBOXYLIC
A
CIDS
COOH
COOH
COOH
benzene carboxylic acid,
1,2-benzenedicarboxylic acid,
benzoic acid
ortho
-benzenedicarboxylic acid,
phthalic acid
COOH
COOH
COOH
COOH
isophthalic acid
terephthalic acid
Benzoic acid is made by the oxidation of toluene with air (oxygen) at
moderate temperatures under conditions whereby the toluene remains as a
liquid during the reaction. However, the three benzene diacids are made from
the corresponding dimethylbenzenes (xylenes) by oxidation with air (oxy-
gen) over a catalyst at high enough temperature so that the reacting xylenes
are in the gaseous state. In the case of the 1,2-derivative (phthalic acid), it
is not isolated as free phthalic acid (the structure shown), but rather in the
form of a cyclic compound called an
anhydride
, which can occur with the
loss of a molecule of water. This anhydride (phthalic anhydride) is used
mainly to make high-boiling organic liquids, which, in turn, are used to
soften certain types of plastic. These are called
plasticizers
. The odor asso-
ciated with new cars is caused by these compounds. Isophthalic acid is used
