Submitted by J. S. Reichert and J. A. Nieuwland.
1. Procedure
A
2-l. three-necked flask, containing
606 g. (700 cc., 6.6 moles) of toluene,
70 cc. of concentrated sulfuric acid, and
7 g. of mercuric sulfate, is fitted with a
stirrer, a
thermometer reaching into the liquid, and an
inlet tube connected with a
gasometer containing
acetylene, as shown in Fig. 11 (Note
1). The flask and its contents are tared and cooled to 10° before the absorption of
acetylene is begun. The gas from the
tank, A, is washed free from
acetone by being passed first through water in the gasometer, B, and then through the
concentrated sulfuric acid wash bottle, C.
Fig. 11.
The
acetylene is absorbed rapidly, with the evolution of considerable heat. The temperature of the reaction mixture is maintained at 10–15° by immersing the flask in a freezing mixture. When at intervals the reaction slows down, it becomes necessary to sweep the system free from air which accumulates in the flask. The absorption is continued until about
60 g. (2.3 moles) of acetylene has been absorbed, which requires a period of about two hours (Note
2). During the absorption, the mixture turns first a reddish brown, then a dark brown, and finally almost black.
The reaction mixture is freed from the acid by washing once with pure water and then with
sodium carbonate solution, to which some
sodium chloride is added to aid the separation of the hydrocarbon layer. If emulsification takes place, the addition of
ether will remedy the difficulty.
The
toluene layer is transferred to a
1-l. flask, without drying, and the unchanged
toluene distilled off; the
ditolylethane is then collected over a range of
295–310°. There is practically no intermediate fraction, but a tarry residue of about 75 g. remains in the flask. Upon redistillation, the
ditolylethane is collected at
295–300°. The yield is
290–310 g. (
60–64 per cent of the theoretical amount) (Note
3) and (Note
4).
2. Notes
1. The
acetylene is absorbed with unexpected rapidity so that it is unnecessary to deliver the gas beneath the surface of the liquid. In an ordinary reaction involving a gas it would be advisable to use a special stirrer, and to deliver the gas beneath the distributing tube of the stirrer.
2. It is scarcely necessary to remove the flask for weighing until near the end of the experiment, since the volume of
acetylene is known and practically complete absorption takes place. If a tank of compressed gas is not available, the
acetylene may be prepared from
calcium carbide by the usual laboratory methods.
1
3. Subsequent redistillation yields a product boiling practically over a 2° range. The best product was obtained by a final fractionation under diminished pressure, when the boiling point was found to be
144–145° /8 mm.
3. Discussion
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved