Sciencemadness Discussion Board

Preparation of dimethylamine

almaz - 27-10-2020 at 10:20

I found a bottle in the inventory without a label, opened it and smelled this disgusting smell - it was dimethylaniline. It has been lying since the time of tetril). I need dimethylamine, so I decided to use it as a source. Nitrosation of dimethylaniline and further hydrolysis with concentrated alkali will give dimethylaniline gas, which can be cooled below 0 degrees into a liquid. But the likely Carcinogenicity of nitrosodimethylaniline is frightening, because the mixture needs to be heated. How do I protect myself? Will nitrosodimethylaniline go with the gas in the form of steam?

karlos³ - 27-10-2020 at 12:06

Don't you have DMF around,because thats so much simpler and apparently, more harmless than what you intend to do?

Boffis - 30-10-2020 at 04:07

@Almaz, there is a technique of preparing very pure dimethylamine from dimethylaniline via the p-nitroso compound that can probably be done without isolation of the nitroso compound. I'll have to dig out the details but I intend to try it because I am interested in the other product: 4-aminophenol-2,6-disulphonic acid. Basically it involves the reduction of nitroso compound with sodium sulphite and in a foot note it mentions that the byproduct is very pure dimethylamine. The sulphonic acid is an azo dye intermediate hence my interest in the reaction, I have little use for dimethylamine.

ChemichaelRXN - 30-10-2020 at 04:19

What if you use methyl iodide in the right amount to ammonia and keep the product under 7C to have it in liquid and methylamine will boil off since it has a boiling point of -6C? Just wondering if anyone has tried this. You might have triethylamine etc. produced too unfortunately, but maybe the right amount of methyl iodide will reduce this and you can always distill the dimethylamine in a very cold condenser. I never needed this gas before, so I dont know other ways at the moment.

Boffis - 30-10-2020 at 05:32

Quote: Originally posted by ChemichaelRXN  
What if you use methyl iodide in the right amount to ammonia and keep the product under 7C to have it in liquid and methylamine will boil off since it has a boiling point of -6C? Just wondering if anyone has tried this. You might have triethylamine etc. produced too unfortunately, but maybe the right amount of methyl iodide will reduce this and you can always distill the dimethylamine in a very cold condenser. I never needed this gas before, so I dont know other ways at the moment.


I think the OP was looking at using dimethylaniline specifically because he has some and wants to use it. The preparation of mono- di- and tri- methylamines from ammonia and a methylating agent has been discussed to death already elsewhere on this form, the problem in nearly all of these methods is the separation of the mixed products. Preparing dimethylamine by degradation of a dimethylamine/amide avoids this problem.

almaz - 11-11-2020 at 04:28

Quote: Originally posted by Boffis  
@Almaz, there is a technique of preparing very pure dimethylamine from dimethylaniline via the p-nitroso compound that can probably be done without isolation of the nitroso compound.

It would be nice to make it through sodium sulfite...

zed - 12-11-2020 at 05:53

Dimethylamine is easy to make, without resorting to this reaction sequence. Seems like there must be a better use for Dimethylaniline.

If you aren't familiar with safe handling of noxious materials, I suspect routes involving Dimethylaniline are a bad place to start your studies.

Do you have access to solid campstove fuel? It is easily converted to Methylamine or Dimethylamine. Likewise Dimethylformamide, yields Dimethylamine Hydrochloride, simply by treating with HCl.

Since Dimethylamine Hydrochloride can be crystalized, producing a relatively pure product, should not be difficult.

Your kind of new here. Have you seen our library?

Vogel, page 416. http://library.sciencemadness.org/library/books/vogel_practi...

[Edited on 12-11-2020 by zed]

[Edited on 12-11-2020 by zed]

Boffis - 13-11-2020 at 14:04

I could not find the original description of the preparation of dimethylamine and 4-aminophenol-3,5-disulphonic acid. It is referred to in Fierz-David & Bangley's book "Fundimental processes of Dye Chemistry, 4th ed, English translation, p202 but the note isn't referenced.

So I decided to give it a try; the idea was a one-pot synthesis based on 3.25g of crude, very old dimethylaniline dissolve in 7.5ml of 36% HCl and 10ml of water. To this were added 1.89g of sodium nitrite in 6ml of water. The solution became orangebrown, warm and gas was evolved so I decided to try chilling it but this cause copious brown ppt (p-nitrosodimethylaniline?). 5.6g of sodium metabisulphite dissolved in 15ml of water were then added dropwise. The mixture did not decolourise as was expected so once all of the bisulphite solution had been added the mixture was warmed to about 50-60 C and then filtered. The filtrate was pale orange and soon began to deposit sparingly soluble colourless crystals (the aminosulphonic acid?); when made strongly alkaline the liquid gave a stongly ammoniacal smell. The filter cake was dissolved in 20ml of water and made alkaline with 50% NaOH. The mixture gave a bright green ppt of nitrosodimethylaniline. The ppt was filtered off, washed and dried to give 1.275g of free p-nitrosodimethylaniline.

I think that the mistake I made here was that the solution was not heated long enough and at a suffiecently high temperature after the addition of the bisulphite solution to complete the reduction-rearrangement. The use of impure dimethylaniline may have caused other problems too. As I am interested in the disulphonic acid I think that the reaction is worth persuing but as a source of dimethylamine.... hmmm tricky... I think there may be easier methods!

Boffis - 16-11-2020 at 12:47

I decided to have another go with this reaction. So I dispersed the 1.257g of lovely green nitrosodimethylaniline into 10ml of water and added 1.6g of sodium metabisulphite. The solution was boiled until all had dissolved to a dark brown solution but no smell of amine could be detected and when acidified with a little dilute HCl no amino phenol precipitated. Clear this is not an easy reaction. :(

Bedlasky - 21-11-2020 at 16:06

Almaz: You can also use dimethylaniline for production of several azodyes, like methyl orange, methyl red, methyl yellow, crystal violet, malachite green etc.

Opylation - 4-6-2021 at 08:53

I would just like to mention, “2,4-D” is an herbicide readily sold in hardware stores in the US composed a little less than 50% dimethylammonium salt of 2,4-dichlorophenoxyacetic acid. 32oz of the stuff can be purchased for $10. That’s plenty of NH(CH3)2 for, pretty much anything

[Edited on 4-6-2021 by Opylation]

clearly_not_atara - 6-5-2023 at 06:10

Dimethylamine may be obtained by the controlled reaction of methylamine with formaldehyde, which may be made into a single process from ammonia:

https://ia800708.us.archive.org/view_archive.php?archive=/28...
Quote:

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 C, and maintained as nearly as possible at this h i- prature 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 reac- tion (3). It was noticed that whilst a volatile liquid commenced to distil at about 52 C in the first stage, 92 C 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 C 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 C, until a portion when cooled became a semi-solid, crystalline mass, after which it was allowed t o 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 (Found, C1= 43.14. Calc., C1= 43.5 percent.) 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 per cent. with the use of 700 grams of formaldehyde solution. Knudsen obtained a yield of 70 per cent. from 100 grams of ammonium chloride and 1000 grams of formalin.

A discussion in a recent thread prompted me to wonder how DMF was produced historically, before the advent of gas-phase chromatography and methylation with methanol. I think it was something like this. The large quantities employed suggest that this may also allow the "OTC" production of DMF, mostly of interest for the challenge.

SplendidAcylation - 6-5-2023 at 13:15

@opylation, I wish that these amine salt weedkillers were available here where I live, it would have made my life a lot easier! :P


@clearly_not_atara, I have done this formaldehyde + ammonium chloride reaction a few times.

I think it does work, but it isn't the most fun reaction imaginable, the extraction with hot chloroform is particularly unsatisfactory.

I did a write-up on it, maybe I should upload it, might be useful to someone mad enough to attempt it :p

ErgoloidMesylate - 6-5-2023 at 13:37

Quote: Originally posted by SplendidAcylation  


@clearly_not_atara, I have done this formaldehyde + ammonium chloride reaction a few times.


I did a write-up on it, maybe I should upload it, might be useful to someone mad enough to attempt it :p


Sure, I wouldn't mind seeing it.

One of the reasons I was looking for a slightly different synth on a different thread / topic, was a specific use case.

I was aiming to find a high volume method easily OTC, for this exact reason.

The fact it mimics the industrial method seems fine to me.

If you have a gas and you want to store certain chemicals under it, for instance, amines in general, etc, and your inertness levels were analysed and detected at 20ppm of co2, you would want to reduce it to 2 ppm or below.

If you bubbled that through ethylamine, it would scrub the co2 levels down, reducing them to acceptable levels. It would also permit working around potentially unstable alkaloids.