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Author: Subject: Preparation of dimethylamine
almaz
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[*] posted on 27-10-2020 at 10:20
Preparation of dimethylamine


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?



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karlos┬│
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[*] posted on 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?
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Boffis
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[*] posted on 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.
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ChemichaelRXN
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[*] posted on 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.



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Boffis
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[*] posted on 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.
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almaz
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[*] posted on 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...




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[*] posted on 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.

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[Edited on 12-11-2020 by zed]

[Edited on 12-11-2020 by zed]
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Boffis
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[*] posted on 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!
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[*] posted on 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. :(
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[*] posted on 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.



If you are interested in aqueous inorganic chemistry look at https://colourchem.wordpress.com/main-page/

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