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Author: Subject: Diethylamine Hydrochloride Synthesis
Dr.Bob
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[*] posted on 2-1-2016 at 19:47


If you have Et2NH HCl in ethanol, just let the ethanol evaporate, and you will get a solid which is safe to store and dispose of.

And to make it, using 6N HCl and DEET for about 6-12 hours at 100 C should cleave the amide to the amine HCl salt.
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careysub
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[*] posted on 2-1-2016 at 21:38


Quote: Originally posted by Dr.Bob  

And to make it, using 6N HCl and DEET for about 6-12 hours at 100 C should cleave the amide to the amine HCl salt.


Are you speaking from actual experience?

One thing I noted on the very lengthy DEET thread(s) was an apparent lack of SM members confirming a successful procedure.
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clearly_not_atara
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[*] posted on 3-1-2016 at 00:58


I've seen a couple reports claiming success with DEET but not on SM. What successful reports have in common is that they're done in small batches using alkaline hydrolysis with excess NaOH or KOH and the NHEt2 is distilled right out of the rxn mixture.

No idea about acidic hydrolysis. It sounds difficult. I would try using a PTC with the acidic hydrolysis, and maybe a water/acetone solvent mixture or water/DMSO if you have it.

I've heard some salts, notably copper nitrate, can catalyze amide hydrolysis. I don't know how well it will work with this substrate.

[Edited on 3-1-2016 by clearly_not_atara]
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byko3y
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[*] posted on 3-1-2016 at 09:27


Tell me more about acidic PTC catalyst. AFAIK for most cases tosylic or trifluoroacetic acid plays the role of catalyst.
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nlegaux
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[*] posted on 3-1-2016 at 15:46


I was able to successfully prepare freebase diethylamine with the following procedure. I refluxed 50ml DEET with 32ml 8M HCl(aq) for 1.5h. Following this, I added 15g NaOH (which was first dissolved in 20ml water) and distilled off the resulting diethylamine with a 75% yield. It may be easier to purify the freebase in this way and form the salt afterwards than attempt to purify the salt from the m-toluic acid produced.

nlegaux


[Edited on 1-3-2016 by nlegaux]
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JJay
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[*] posted on 13-8-2017 at 20:17


I'm giving this a try with 5 mL DEET and 4.4 mL azeotropic HCl.




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JJay
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[*] posted on 13-8-2017 at 23:53


After refluxing gently for about three hours and seeing little change aside from a light pink color forming, I turned up the heat to establish a rolling boil. This quickly resulted in the formation of a light precipitate, likely m-toluic acid. Fortunately, the increased reflux didn't threaten to flood the air condenser that had been placed over the flask. I'm going to let it run for a while longer and then add some base and distill the DEA!






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JJay
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[*] posted on 14-8-2017 at 09:21


I ended up adding 2 mL more azeotropic HCl and running for about five hours, with two hours at a rolling boil. I definitely got some product (smells like ammonia), but there's a lot of DEET still left, and however much product there is, it's not enough to distill through a microscale column in a boiling water bath. I'm doing a simple distillation right now, but I don't expect much (maybe a mL if I'm really lucky, probably more like 0.1 mL), and it will probably have some water in it. I'm actually headed out of town, but when I get back I want to try with sulfuric acid.

Edit: Oh and I should mention that I added 2.2 grams of NaOH in 5 mL water before trying to distill it, and I basically only got enough diethylamine to wet the inside of the still head, although it does have a strong ammonia odor.

[Edited on 14-8-2017 by JJay]




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sykronizer
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[*] posted on 17-12-2017 at 04:09


If you are desperate or out of reagents there is a simple source of dimethyl, diethyl and isopropyl amine....it's in your hardware store, or garden store etc. The weed killers (bare with me!) the ones that contain only Glyphosate, and there are plenty of them, are made water soluble by creating an amine salt...that's right...so, all you need to do is get the stuff that's around 36 percent Glyphosate and chill it, add some non polar solvent, then some concentrated sodium hydroxide, mix thoroughly and the amine will become freebase and dissolve into your organic solvent which will separate out in minutes. Different brands use different amines, but I have seen at least these three.
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DJF90
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[*] posted on 17-12-2017 at 15:23


Quote: Originally posted by JJay  
I'm doing a simple distillation right now, but I don't expect much (maybe a mL if I'm really lucky, probably more like 0.1 mL)
...I basically only got enough diethylamine to wet the inside of the still head, although it does have a strong ammonia odor.

[Edited on 14-8-2017 by JJay]


You know the boiling point of dimethylamine is 7 *C, right?
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JJay
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[*] posted on 17-12-2017 at 15:52


I wasn't really expecting any dimethylamine... I'd expect most diethylamine to be condensed by an air condenser, though. I think a better workup is likely to heat more strongly, neutralize the distillate with clean hydrochloric acid, and boil off the water. The diethylamine hydrochloride could be heated with sodium hydroxide and the vapors condensed and dried to obtain pure anhydrous diethylamine (I think).

I've been meaning to try it again with 60% sulfuric acid on a larger scale.




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DJF90
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[*] posted on 17-12-2017 at 16:07


Apologies, I clearly misread the target wrong.

In any case, you might be better off running the hydrolysis (monitor for consumption of DEET by TLC), and then filter (?) or extract the acid with organic solvent. Concentate the aqueus to yield Et2NH*HCl, recrystallise for purity, and then proceed to the salt release.
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JJay
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[*] posted on 17-12-2017 at 17:02


That seems reasonable.



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clearly_not_atara
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[*] posted on 17-12-2017 at 17:58


Quote:
I ended up adding 2 mL more azeotropic HCl and running for about five hours, with two hours at a rolling boil. I definitely got some product (smells like ammonia), but there's a lot of DEET still left, and however much product there is, it's not enough to distill through a microscale column in a boiling water bath. I'm doing a simple distillation right now, but I don't expect much (maybe a mL if I'm really lucky, probably more like 0.1 mL), and it will probably have some water in it. I'm actually headed out of town, but when I get back I want to try with sulfuric acid.
I think you probably want to add more water. Azeotropic HCl should have a pretty strong affinity for water (hence its bp above that of pure water) but 1 M HCl is only 0.6 pH points less acidic than 6 M (azeotropic) HCl. I think about this in terms of the chemical potential of the H2O molecule:

http://en.wikipedia.org/wiki/Chemical_potential

The chemical potential of water roughly defined is the "energy released" when you add one molecule of H2O to the solution through cohesive forces. By conservation of energy, it's the energy cost of hydrolysis. In concentrated acids, the chemical potential of water is large -- the solution heats up when you add water -- so the reaction (R2NH + RCOOH <<=>> H2O + RCONR2) shifts to the right. In dilute acids, the chemical potential of water is less, so the reaction shifts left. You also see this effect in sulfonation reactions, where dilute acid promotes desulfonation and concentrated acid promotes sulfonation. So with 1 M HCl, the reaction should shift to the left and produce more diethylamine.

Fun fact: Azeotropic HCl is HCl*8H2O almost exactly.

[Edited on 18-12-2017 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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JJay
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[*] posted on 17-12-2017 at 18:08


Quote: Originally posted by clearly_not_atara  

I think you probably want to add more water.


Hmm... interesting idea... DEET is only slightly soluble in water....




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clearly_not_atara
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[*] posted on 17-12-2017 at 22:36


That will slow the reaction down, for sure, but most solubility numbers for deet in water that I see are at room temperature. At reflux it should be high enough to achieve a decent rxn rate I'd expect.



[Edited on 04-20-1969 by clearly_not_atara]
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gravityzero
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[*] posted on 26-1-2018 at 17:59


This seems like a fairly cheap and easy procedure to attempt. It is odd that no one has reported much success.

The procedure originally reported by Jon appears to be worth a try.
My only concern is it appears to be a sort of "pipe bomb" method.
Is the procedure describing heating a closed system in an autoclave bottle?
Seems dangerous to me. Am I misreading this method?

Another method describes refluxing ethylene glycol, NaOH, and DEET.
I assume a stoppered reflux column with a tube leading to cold water? or maybe ethanol? Where the diethylamine gas is collected.
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[*] posted on 30-1-2018 at 06:25


Quote: Originally posted by sykronizer  
If you are desperate or out of reagents there is a simple source of dimethyl, diethyl and isopropyl amine....it's in your hardware store, or garden store etc. The weed killers (bare with me!) the ones that contain only Glyphosate...


Diethylamine is not used afaik in herbicides. I have seen dimethylamine and isopropylamine and even potassium salts of glyphosate (and the former two amine salts of 2,4-D, and MCPA).
So you can't get diethylamine from these often handy sources.
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[*] posted on 31-1-2018 at 16:47


I lost most of my notes (among this synthesis), unfortunately. This is all I remember.

4,062 g repellent (assy 98% deet) was refluxed with NaOH/ EtOH (denaturated EtOH was distilled once) for about 4 hours. Not much change was noticed in the first hours. At 3-4 hour characteristic amine odor started escaping through the condenser. Reaction was stopped at the end of 4th hour . HCl was added to the mixture after it until PH 6.Thick white smoke (ph paper turned blue upon test) developed during hcl addition . The reaction mixture was filtered then evaporated to dryness. Snow white, soft crystals were scraped off and dissolved in minimum amount of EtOH. Insoluble residue was filtered off (NaCl). Thus obtained filtrate was evaporated to dryness, yield: 0,068 g HCl salt.

Qualitative test:
~0,010g of the above hcl salt was dissolved in ~1 ml ion changed water,a few drops of strong NaOH solution was added. Strong amine odor was detected. Ph paper turned blue holding it close to the mouth of the test tube. Test: +


Conclusion:
This reaction does work at atm pressure, however it has its limitations.


[Edited on 1-2-2018 by Mush]
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clearly_not_atara
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[*] posted on 1-2-2018 at 12:00


See the attached review on amide hydrolysis. Choice quotes:

"B. Occurence of a Rate Maximum -- Since the acid-catalyzed hydrolysis of amides is reasonably slow, reactions may be carried out in quite high acid concentrations, and as the acid concentration is increased the rate increases to a maximum and then decreases."

"B. Substituent Effects -- Reid investigated the effect of nuclear substituents on the rate of hydrolysis of benzamide and observed that meta- and para- substituents such as -NH2, -OMe, and -Me retarded the rate, whilst -I, -Br, and -NO2 increased it."

"C. Catalysts -- [...] Cationic acids of the amine type, e.g. monoethanolamine, which cannot both donate and accept a proton in a concerted mechanism and are therefore supposed to act only as general acids, can be very effective."

I think that based on Mush's report some of his diethylamine escaped because its bp is lower than ethanol and some of it was never formed because he stopped the reaction shortly after he first smelled it. It might have taken days at that rate, though.

Perhaps nitrating DEET deserves more attention. The product might undergo alkaline hydrolysis at a lower temperature, preferably below the boiling point of diethylamine. I also think that performing acid hydrolysis with a cosolvent would be a good idea.

Attachment: oconnor1970.pdf (805kB)
This file has been downloaded 136 times

[Edited on 1-2-2018 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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Boffis
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[*] posted on 28-9-2019 at 06:06


I have just tried the acid hydrolysis of DEET. I used 6.9g of crude m-toluyl-N,N-diethylamide extracted from bug repellant by dilution with water and allowing the liquid to separate into two phases. The organic phase was not dried. The crude DEET was mixed with 20ml of 70% sulphuric acid and heated to 180 C for 2 hours by which time the reaction mixture resembled crude oil! I cooled the mixture and diluted it with 50ml of water and neutralised it with 50% NaOH, reheated it with the addition of 2g of charcoal and 1g of cellite filter aid, filter it hot and cooled. The filtrate was now pale straw coloured to my amazement but did not smell fishy. Rendering a small sub-sample (c 5ml) strongly alkaline with 50% NaOH also fail to generate much evidence of diethylamine though the vapour did slowly blue moist litmus paper.

The remaining filtrate contained a few drops of brown oil so I tried to extract this with ether but the whole lot rapidly solidified into a mass of colourless crystals, these were filtered off and found to be sodium sulphate. The filtrate was allowed to stand in a small separating funnel, the aqueous phase run into a beaker and acidified with 36% HCl. The mixture became cloudy and a little oil separated but no m-toluoic acid crystallised out.

Conclusion. Sulphuric acid hydrolysis does not look like a practical method.

[Edited on 28-9-2019 by Boffis]
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[*] posted on 28-9-2019 at 07:05


I would use a lot less concentrated acid (HCl, so you have less hygroscopic stuff during drying). I think acid hydrolysis is the way to go as while protonated diethylamine won't be lost as a gas.

As a workup I would extract the m-toluic acid with for example toluene from the crude reaction mixture, neutralize to pH 7 with NaOH and boil down the aqueous layer to get the dry salts* and extract the amine.HCl salt with methanol. Evaporate the methanol.

*If you have toluene anyway you can use it to dry the salt mixture after getting rid of most of the water.

[Edited on 28-9-2019 by Tsjerk]
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Pumukli
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[*] posted on 28-9-2019 at 08:34


Thanks Boffis for the experiment! I'm amazed that 2 hours at 180 C in 70% H2SO4 was not enough! You saved me a failure and some wasted reagents because if I had tried this reaction I'd have done roughly the same.

The question is: how to proceed?
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Boffis
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[*] posted on 28-9-2019 at 10:27


Well I also did a test-tube scale test with KOH solution and enough alcohol to give a homogeneous solution and refluxed it for 2 hour with not even the faintest hint of fishy smell so for my next trick I will try more aggresive conditions. I am going try a modification of Dr.Bob's glycol method and catch the amine in dilute HCl.

@Tsjerk: If 70% H2SO4 produces vertually no hydrolysis after 2 hours why should 36% HCl do better? After all the first proton of sulphuric acid is about as ionised as HCl so there isn't really much difference in H+ ion concentration. The only difference is that carbonisation may be less with HCl so a much longer reflux can be used. I don't think you would need to extract the m-toluic acid, I think that it is sufficiently insoluble even in strong HCl to simply precipitate on cooling and can then be filtered off on a glass frit. Recovery of the amine would be best by neutralisation and distillation into fresh HCl and then evaporate this to dryness to remove the excess HCl.

I may try an HCl hydrolysis with a long reflux if the mixture doesn't blacken.
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Pumukli
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[*] posted on 28-9-2019 at 12:01


Refluxing with HCl may be trickier. The 20% azeotrope boils around 110 C... 36%? Wouldn't it loose too much HCl with time in an open system? 180 C vs. much lower temp that can be achieved with HCl with roughly the same H+ concentration. I doubt it would be much better.

Or maybe this one:
https://quod.lib.umich.edu/a/ark/5550190.p009.205/1

(Dioxane solvent, NaOH in MeOH, reflux at 80 C, several hours... but reportedly works on tertiary amides well.)
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