Thank you for your translation Nemo_Tenetur.
In the introduction of the article[1] they say that the total yield is 40-50% and the purity is 95%.
This is another text from the same persons:
Bequeme Darstellung von reinen N-Methylalkylaminen durch Zink/Salzsäure-Reduktion von 1,3,5-Tris(alkyl)-hexahydro-1,3,5-triazinen Mohammed Al Shaik und Herbert Oelschläger Arch. Pharm. (Weinheim) 317, 214-219 (1984)
(Convenient Synthesis of Pure N-Methylalkanamines by Reduction with Zn/Hydrochloric Acid of 1,3,5-Trialkyl(hexahydro)1,3,5-triazines.)
N-Methylalkanamines are avaiable by reduction of 1,3,5-trialkyl(hexahydro)-1,3,5-Triazines with Zn/Hydrochloric acid at -5°C using a drop-in procedure. The purity (GLC) is in the range of 95%.
They say the same synthesis can be utilised to synthetize some other N-alkyl-N-methyl-derivative from the appropriate 1,3,5-Tris(alkyl)-hexahydro-1,3,5-triazinen. Another text with this method is [3].
Table 1:
Boiling point of the N-alkyl-methylamines avaiable from the respective triazines (no cristalline picrates are obtained from these one):
alkyl= allyl: bp 62
propyl: bp 62
n-butyl: bp 89-91
isobutyl: bp 78-79
tert butyl: bp 66-69
cyclohexyl: bp 145
Otherwise they say the N-alkyl-methylamine are also avaiable from reduction of the schiff base in anh. EtOH with PtO2 and 3 atm of H2. This way N-methyl-ethylamine is prepared in 32% yield and N-methyl-isobutylamine in 67%.
Experimenteller Teil
Synthese der 1,3,5-Tris(alkyl)-hexahydro-1,3,5-triazine
Sie erfolgt gemäss [1]. Die hierbei anfallenden öligen Hexahydrotriazine werden ohne weitere Reinigung mit Zn/Salzsäure reduziert. Zur Überprüfung der physikalischen Konstanten haben wir kleine Mengen destilliert bzw. umkristallisiert.
see table 1; Cyclohexylderivat Schmp 72-73°.
Reduktion der 1,3,5-Tris(alkyl)-hexahydro-1,3,5-triazine
Sie wird gemäss [1] durchgeführt. see table 1.
Reduktion der Schiff'schen Basen
N-Methyl-n-propylamin
58g (1mol) n-Propanal werden innerhalb 2h zu einer mit Eis/Kochsalz gekühlten Methylaminlösung (77.5 g einer 40proz. wässrigen Lösung) unter starkem Rühren zugetropft. Nach Zugabe des aldehyds wird der Ansatz noch 1h in der Kälte gerührt, in einem Scheidetrichter mit festem Kaliumkarbonat und Kaliumhydroxid (1:1) versetzt, kräftig geschüttelt und 15 min stehengelassen. Man trennt die wässrige Phase ab, tocknet die obere Aldiminschicht 2h über K2CO3 und KOH und fraktioniert anschliessend. Das Aldimin geht bei 53° über, Ausb 35% d. Th.
D8ie Hydrierung von 0.3 mol Aldimin wird bei 20° in einer Skita-Apparatur unter 3,5 atü in absol. EtOH mit vorreduziertem PtO2 durchgeführt. Die Aufnahme der berechneten Menge H2 (0.3 mol) dauert ca. 3h. Die übliche Aufarbeitung ergibt 25% d. Th. N-Methyl-n-propylamin vom Sdp. 62°.
N-Methyl-ethylamin
Analog N-Methyl-n-propylamin Aldimin: Ausb. 55% d. Th., Sdp. 28-29°. Amin: Ausb. 80% d. Th., Sdp. 32-34°. Check also ref [15]
N-Methyl-isobutylamin
Analog N-Methyl-n-propylamin Aldimin: Ausb. 65% d. Th., Sdp. 67-69°. Amin: Ausb. 67% d. Th., Sdp. 78-79°, lit.: Sdp 76-78°.
Reduktion eines Ketimins (2-Methyliminopropan)
58g (1mol) Aceton werden langsam zu einer mit Eis/Kochsalz gekühlten 40proz. Methylaminlösung (77,5g = 1 mol) zugetropft und anschliessend 30 min gerührt. Nach 24 h Stehen und Zugabe von 4 ml Methylaminlösung wird das gebildete Ketimin in einer Skita-Apparatur unter 3,5 atü bei 20° mit 0.5 g PtO2 hydriert. Nach 5 h ist die berechnete Menge H2 verbraucht und die Hydrierung kommt zum Stillstand. Die übliche Aufarbeitung ergibt 60% d. Th. N-Methyl-isopropylamin vom Sdp. 50-51°.
Literatur:
[1]: Look two post higher.
[3]: J. Graymore, J Chem Soc 1931, 1490 and 1932, 1353.
[15]: http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p0758 (http://www.orgsyn.org/orgsyn/prep.asp?prep=cv5p0758)
It would be nice to have a translation of the experimental part.... ;)
Methylation by Means of Formaldehyde. Part I., A. Werner, J. Chem. Soc., pp844-853 (1917)
(same ref than in https://www.thevespiary.org/rhodium/Rhodium/chemistry/methylamine.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/methylamine.html)
)
Experimental:
Preparation of Dimethylammonium Chloride.
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.
Expt II: Dimethylamine
Two hundred grams of ammonium chloride and 400 grams of formalin were heated to 104°, 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.
Preparation of Methylammonium Chloride.
The proportions of ammonium chloride and formaldehyde (40% formalin)* 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.
Expt I: Methylamine
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°, 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° to about one-half of the original volume. After removal of 19 grams of ammonium chloride**, 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° 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%.
* Analyses of seven different samples of commercial formalin gave as a mean result 35% of formaldehyde, and in no case was a sample found to contain 40%. The highest value was 37.4%, the lowest 33.2%.
** Ammonium chloride is very sparingly soluble in a concentrated solution of methylammonium chloride, and consequently its separation from the later salt is very sharp.
Really, I dont get it why people hydrolise expensive DMF when cheap and easily accessible formaline give a great yield of dimethylamine. ;D
Maybee paraformaldehyde could bee used, but its not 100% sure...
In https://www.thevespiary.org/rhodium/Rhodium/chemistry/methylamine.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/methylamine.html)
there is some reaction with it, but this part:
With an excess (4 moles) of formaldehyde, enough water and a reflux temperature of 115°C, dimethylamine is the main product, as the temperature rises, more dimethylamine is formed. Dry heating of paraformaldehyde and ammonium chloride produces trimethylamine through reaction of dimethylamine with formaldehyde, giving rise to tetramethylmethylenediamine and formic acid, and the base further reacts with HCl, giving trimethylamine hydrochloride and methyleneimine hydrochloride.
Say you need water to make dimethylamine otherwise trimethylamine is formed.
Otherwise, they stop at 104° to put some more formaldehyde, as one more eq is needed, and to filter off the remaining NH4Cl, while the methylammonium chloride stay in solution, for they dont want the formaline they just put react with NH4Cl to yield methylamine, they want it to react with CH3NH3Cl to make dimethylamine.
see the illustrative figures at Rhodium's methylamine document.
You could try it, with some water and at 115°, but the reaction woulds surely needs some tweaking... better stay with the above procedure, which is optimized for dimethylamine, as you realise minor change can make great difference in products and yields.
BTW formaline is really cheap and OTC, ask your local pharmacist (not our's ;) ), say you found some kind of dead reptile and wanna put it in a nice vase in your room, and you need formaline to put it in. :)