IN a 12-l. round-bottom flask, arranged so that the contents
can be mechanically stirred, are placed 4600 g. (5750 cc.)
of technical acetone. The flask is then well cooled with an
ice-and-salt mixture, until the temperature of the acetone
is between 0'0 and 5'0. Stirring is started, and 4160 cc.
of commercial concentrated sulfuric acid is run in at such a rate
that the temperature of the mixture never rises above about 10'0.
This addition is accomplished in about five to ten hours.
The stirring is continued for three to four hours longer,
while the flask still remains immersed in the original
freezing mixture to which no further amount of ice is added.
The mixture is then allowed to stand at room temperature for eighteen
to twenty-four hours.
A 5-l. round-bottom flask is fitted with a rubber stopper or a cork
stopper coated with pitch, carrying two glass tubes, one of which
(for the entrance of steam) reaches to the bottom of the flask,
while the other extends into the open end of a condenser set for
downward distillation. The stopper should be wired into the flask.
The glass delivery tube into the condenser should not be less than a
12-mm. bore, and the condenser should consist of two 120-cm. water-cooled
condensers attached end to end. To the end of the condensing system,
an adapter is attached, the small end of which is at least 8 mm.
in bore and is fitted tightly into a stopper in a 2-l. suction flask.
To the side-arm of the suction flask is attached a tube leading to an
exhaust fan, in order to carry away the gases which are evolved during
the subsequent distillation. In the 5-l. flask are placed about 2 l.
of the sulfuric acid-acetone reaction mixture, and the flask
is then heated with a free flame and shaken occasionally.
A reaction starts at the end of about fifteen or twenty minutes,
as shown by the evolution of gas (chiefly sulfur dioxide), and is
allowed to run for about three minutes. At the end of this time,
a current of steam is passed in and continued for about three minutes.
During this period a large proportion of the mesitylene distils
and should be kept separate from the subsequent distillate.
The steam distillation is continued at such a rate that about 800 cc.
distils in twenty-five to thirty minutes and is collected as a
second distillate. At the end of this time, the distillation
is stopped, the water poured off from the distilling flask
and the tarry material emptied out while hot into waste jars.
The total amount of original reaction mixture requires
five distillations similar to the one just described.
The first distillates from each of the five distillations are mixed,
and the layer of mesitylene is separated from the water.
This is shaken with sodium hydroxide solution until no more odor of sulfur
dioxide is noticeable, then washed twice with water and distilled.
The first portion of the distillate consists of a small amount of water
and mesitylene and is added to the combined second distillates.
The fraction which distils up to 210'0 is saved. The second distillates
are combined, washed in the same way as the first and then distilled;
the fraction which distils up to 210'0 is combined with the corresponding
fraction from the first distillates.
These combined fractions (which boil up to 210'0) and 15 g.
of sodium are placed in a 2-l. distilling flask, the side-arm of
which is closed with a rubber tube and pinchcock and which is fitted
with a reflux condenser. The mixture is heated just below the boiling
point for about three hours, during which time the impurities are
attacked by the molten sodium, and a gelatinous, reddish mass forms.
The reflux condenser is now removed and one set for downward
distillation is attached to the side-arm. The mixture is distilled
and about two-thirds of the liquid removed in this way.
The residue is cooled, the liquid poured off from solid material
and distilled up to 210'0.
The distillates from the sodium treatment are now fractionated with
a good column (at least 30 cm. long), and the portion which boils
at 163-167'0 is collected. The yield of this fraction varies in
different runs from 430 to 470 g. (13-15 per cent of the theoretical
amount), but very often will be as high as 500 g., and has reached,
in certain experiments, 600 g.
An alternative method for the purification of the crude material
has been employed by Clarke and Hartman, and yields a slightly
higher-grade product than the sodium method. It is as follows:
The combined distillates are treated with an equal volume of concentrated
sulfuric acid and the solution warmed on a water bath for an hour,
under a reflux condenser, with occasional shaking or, better, with
mechanical stirring. Upon cooling, mesitylene sulfonic acid crystallizes
and the unsulfonated material remains as an oil on the surface.
The mixture is filtered through flannel or a "filtrose" plate,
and the crystals are washed with 60-70 per cent sulfuric acid.
The oily layer is again warmed with sulfuric acid, as before.
The acid and oily filtrates from the two sulfuric acid treatments are steam
distilled, and the distillate combined with the next batch of material.
The crystals are mixed with 2 l. of 15 per cent hydrochloric
acid and heated under a reflux condenser for two to three hours.
The reaction mixture is now steam distilled, the mesitylene separated,
dried over calcium chloride and fractionated; the portion which boils
at 163-167'0 is collected.