ASCII by Chimimanie
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The formation of the above salt in this reaction has been recently pointed out by Knudsen, but the method adopted for its preparation distinctly shows the absence of a reasonable appreciation of the probable mechanism of the changes. Thus, in an experiment designed with the object of obtaining the best yield of the secondary amine, a useless, not to say a wasteful, excess of formaldehyde was employed without any particular advantage. The following experiment, carried out on the lines of the present theory, gave a very good result.
Two hundred grams of ammonium chloride and 400 grams of formalin were heated to 104°C, as in Expt. I, and 65 grams of ammonium chloride were recovered. To the filtrate 300 grams of formalin were now added, and the solution was again heated at this stage to 115°, and maintened as nearly as possible at this temperature until no more liquid distilled. This required about three and a half hours. Since methylammonium chloride, produced during the first stage, is less easily dissociated than ammonium chloride, a higher temperature was required to bring about reaction. It was noticed that whilst a volatile liquid commenced to distil at about 52° in the first stage, 92° was reached in the second stage before any liquid distilled, which is quite in agreement with theory.
The product was concentrated by evaporation at 100° until a scum appeared on the surface of the hot liquid ; 7 grams of ammonium chloride, and 27 grams of pure methylammonium chloride were recovered from the material which had separated after cooling. The product was now heated to 120°, until a portion when cooled became a semi-solid, crystalline mass, after which it was allowed to remain for two days in a partial vacuum over sodium hydroxide. It was then treated with chloroform as described under Expt. I, and 122 grams of nearly pure dimethylammonium chloride were ultimately obtained. The final residue contained some trimethylammonium chloride, but was not further dealt with.
The yield of dimethylammonium chloride calculated on the weight of ammonium chloride which had entered into reaction (that is, 200-72=128 grams) was therefore 95.3% with the use of 700 grams of formaldehyde solution. Knudsen obtained a yield of 70% from 100 grams of ammonium chloride and 1000 grams of formalin.
The proportions of ammonium chloride and formaldehyde (40% formalin)a recommended by Brochet and Cambier, namely one part by weight of the former, and two parts by weight of the latter, were found after several trials to give the best results. Since about 35% of ammonium chloride has always been recovered unchanged, the molecular ratios NH4Cl:2CH2O required by theory are very closely represented by the above proportions.
Two hundred and fifty grams of ammonium chloride and 500 grams of formaldehyde solution were gradually heated in a distillation flask, which carried a thermometer with the bulb well below the surface of the liquid. The temperature was slowly raised to 104°C, and not allowed to rise above this point, at which it was maintened until no more volatile liquid distilled; this required about four and a-half hours. The distillate weighed 110 grams. The product was allowed to cool, and after filtration from 62 grams of ammonium chloride which had separated, was concentrated by evaporation at 100°C to about one-half of the original volume. After removal of 19 grams of ammonium chlorideb, the liquid was again concentrated by evaporation until a crystalline scum had formed on the surface of the hot solution.
After cooling, 96 grams of methylammonium chloride were separated ; after further concentration a second crop (18 grams) was obtained. The filtrate was now concentrated as far as possible at 100°C and was left for twenty-four hours in a vacuum over sodium hydroxide, after which the semi-solid residue was digested with chloroform, when 20 grams of methylammonium chloride which had been washed with chloroform to remove dimethylammonium chloride, were obtained. The total yield was 128 grams.
From the chloroform solution, after removal of much of the solvent by distillation, 27.5 grams of dimethylammonium chloride were obtained.
A viscous residue (76 grams) which did not crystallise after remaining for a week in a vacuum over sulphuric acid, was finally obtained ; it contained Cl=40.37%. It was distilled after the addition of an excess of a 40% solution of sodium hydroxide, and the alkaline vapours evolved were absorbed in an alcoholic solution of hydrochloric acid, when a small quantity of methylammonium chloride and a relatively large quantity of dimethylammonium chloride were obtained, but no trimethylammonium chloride could be detected. Formaldehyde was also regenerated by the action of sodium hydroxide on the viscous material, which no doubt contained much tetramethylmethylenediamine hydrochloride, CH2(NMe2)2·2HCl, which require Cl=40.57%.