Submitted by Roger Adams and C. S. Marvel.
Checked by J. B. Conant and A. McB. Kinney.
1. Procedure
Five hundred grams (9.35 moles) of technical ammonium chloride and
1330 g. (14.8 moles) of paraformaldehyde are thoroughly mixed and placed in a
5-l. round-bottomed flask fitted with a
long reflux condenser (a jacket of about 100-cm. length and an inner tube of about 2-cm. diameter) (Note
1). By means of an
oil bath, the temperature of the reaction mixture is gradually raised. Between 85° and 105° liquefaction begins to take place at the bottom of the flask, and at the same time a very vigorous evolution of
carbon dioxide starts. The heat is at once withdrawn, and if the reaction is too violent, the oil bath should be removed. The reaction is allowed to continue without further heating until the gas evolution is less vigorous. This requires about one and one-half hours. Heat is again applied and the temperature of the bath raised to about 160°, where it is held until there is practically no more evolution of
carbon dioxide. This takes two and one-half to three and one-half hours, after which time the reaction is complete.
To obtain the
trimethylamine hydrochloride, it is now merely necessary to treat the mixture with
sodium hydroxide, and to distil the free amine into
hydrochloric acid. A
separatory funnel is therefore inserted through the stopper of the flask and the reflux condenser is changed to a downward position for distillation. The open end of the condenser is fitted tightly into the neck of a
distilling flask or suction flask, to the outside arm of which is attached, by means of
rubber tubing, a
glass tube which leads under
hydrochloric acid in a
receiver. Care must be taken to have all the joints in the apparatus tight as the
trimethylamine is very volatile and can easily be lost. The object of the intermediate boiling or suction flask is to catch any water which may distil with the
trimethylamine during the treatment with the
sodium hydroxide. This water is often colored yellow, and if allowed to go directly into the
hydrochloric acid in the receiver contaminates the
trimethylamine hydrochloride.
A solution of
1100 g. of sodium hydroxide (two and one-half to three times the amount theoretically necessary to liberate the free amine) in 2 l. of water is allowed to drop through the separatory funnel into the reaction mixture, which has cooled somewhat during the change of apparatus. The amine distils, passes through the condenser, through the
intermediate bottle, and into the receiver, in which is placed an amount of concentrated
hydrochloric acid (930 cc. of sp. gr. 1.19) slightly more than enough to neutralize the weight of amine which should theoretically be formed. To be certain that all the amine has been driven from the reaction flask, heat is finally applied for ten or fifteen minutes to the mixture. The whole procedure, from the beginning of the first reaction until a solution of
trimethylamine hydrochloride is obtained, requires not more than six to seven hours.
To obtain the
trimethylamine hydrochloride, the
hydrochloric acid solution is evaporated, first over a free flame, and later, when the crystals start to form, on a
steam bath. As the solution gets more and more concentrated, the
trimethylamine hydrochloride crystallizes out and is filtered from time to time, dried for a few minutes in an
air bath (temperature 100–110°), and then kept in a tightly closed bottle. If the
trimethylamine hydrochloride as it crystallizes is centrifuged, the product is obtained pure and dry at once. The average yield from four runs is
710 g. of pure
trimethylamine hydrochloride and
82 g. of product which is tinged slightly yellow (a total of
89 per cent of the theoretical amount based on the
ammonium chloride) (Note
2). The coloration results from the evaporation to dryness of the very last portion of solution.
2. Notes
3. Discussion
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