Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

CHAPTBK IV
8ULPH0NIC ACIDS
1. BENZENE MONOSULPHONIC ACID FROM BENZENE AND
SULPHURIC ACID
BENZENE (45 c.c. =O5 mole) is gradually added in small portions to
150 g. of liquid fuming sulphuric acid containing 5-8 per cent of
anhydride ; no fresh portion is run in until the previous one, which
first floats on the surface of the acid, has been dissolved by shaking.
The acid is contained in a 200-c.c. flask which is kept cool with water
and is shaken well throughout. The time required for the sulphonation
is about ten to fifteen minutes. The reaction mixture is run
slowly from a dropping funnel into a beaker containing three to four
times its volume of cold saturated brine kept cool with ice and stirred
while the mixture is added. After some time the sodium benzene
sulphonate separates in the form of lustrous nacrous plates and on
prolonged standing forms a thick crystalline sludge. (Crystallisation
may be started by scratching the beaker with a glass rod.) The
sludge is filtered at the pump and the crystals are pressed with a
cork or glass stopper and then washed twice with a little saturated
sodium chloride solution. Finally, the salt is dried in air on filter
paper or on porous plate, powdered, and heated to 110° in a drying
oven until it forms a dry dust. The yield is about 100 g., but the
material contains sodium chloride.
Of the crude product 5 g. may be purified by recrystallisation
from absolute alcohol. (The admixed sodium chloride is insoluble
in alcohol.)
To isolate the diphenylsulphone, which is produced as a byproduct,
30 g. of the powdered salt are warmed with 50 c.c. of ether,
the mixture is filtered with suction while hot and the undissolved
material is washed with ether. The ether leaves on evaporation a
small quantity of a crystalline residue which is recrystallised from
ligroin in a test tube. Melting point 129°.
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