Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

194 NAPHTHALENE-/3-SULPH0NIC ACID
water are obtained, partly from the sulphuric acid and partly produced
in the reaction (12-5 c.c).
The contents of the flask solidify when water
(12-5 c.c.) is added. To remove toluene and
toluene-o-sulphonic acid the solid is pressed well
on porous plate, the hydrated ^-sulphonic acid
which is thus obtained is dissolved in a little hot
water, and three volumes of concentrated hydrochloric
acid are added. The crystalline material
which separates is nltered with suction on an
acid-resisting filter, washed with ice-cold concentrated
hydrochloric acid, and then twice
recrystallised in the
same way. Finally,
the acid is dried in
a desiccator over
potassium hydroxide
until completely free
from hydrochloric acid.
(Test a sample.)
Owing to the presence
of some carbon particles
the crystals are
slightly grey in colour.
Melting point 104°-
FIG. 52
105°. Yield after
three recrystallisations about 50 g.
3. NAPHTHALENE-/3-SULPHONIC ACID
A mixture of 64 g. of naphthalene and 45 c.c. (80 g.) of pure
concentrated sulphuric acid is heated in an open flask in an oil bath
at 170°-180° for four hours. The solution is cooled somewhat and is
then cautiously poured with stirring into a litre of water and neutralised
while boiling in a large basin with a sludge of lime (from about
70 g. of slaked lime). The sludge should not be too thin. The
neutralised material is filtered as hot as possible through a large
Biichner funnel into a previously warmed filter flask. The solid on
the funnel is washed three times with hot water and the filtrate
(clarified, if necessary, through a folded filter paper) is evaporated
in a basin over a free flame until a sample solidifies to a crystalline