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Author: Subject: Diethylamine Hydrochloride Synthesis
Boffis
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[*] posted on 29-9-2019 at 08:07


OK, I am now 4 hours into the KOH hydrolysis experiement and a volatile amine is slowly passing over and collecting in 4.5ml of 30% HCl diluted with 20ml of water. For 9.5g of DEET the theory dictates that just over 5.2ml of 30% HCl should be requred to neutralise all of the diethylamine liberated. So when the receiver becomes alkaline I will know that the reaction is about 85% complete. Via a little jiggery pockery I estimate that hydrolysis was about 60% complete at 3.5 hours so I estimate that 8 hours should be sufficient time.

The reaction is being carried as follows: I placed 30ml of ethylene glycol and 20ml of 50% KOH solution in a 100ml conical flask, added a stir bar and then 10ml of 95% DEET (the contents claim 0.1% pyrimethrines and an unspecified amounts of lime oil). The mixture was heated until it just started to boil and then maintained at this temperature and condition. A still head and a reduction adapter act like a crude reflux condenser. The still head feeds into a liebig condenser inclined away from the flask and on the end of it a long receiving spout guides condensate and vapours into a small beaker containing 20ml of water and the HCl. The length and diameter of the spout being sufficient to prevent suck-back. After 4 hours of heating very little has distilled over though what has is cloudy and smalls of limes! The contents of the flask have turned a brown colour and now contain only a little undissolved oil.

Update:

Reflux stoped at 9.25 hours, the flask content has become a clear light brown, tea-like liquid that smells strongly of the amine and more acid had to be added to the collection beaker to hold the amine that distilled over. Hydrolysis would appear to be complete. Tomorrow I'll work up the fractions to see what can be recovered.

[Edited on 29-9-2019 by Boffis]
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Tsjerk
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[*] posted on 30-9-2019 at 03:25


Quote: Originally posted by Boffis  
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.


Appearantly 70% sulfuric makes crap out of DEET, I didn't say the acid concentration was too low, more the opposite.

My proposed work up doesn't require distillation.
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Boffis
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[*] posted on 30-9-2019 at 04:55


Tsjerk. Have you actually tried your proposed method?

My experience already is that there is too much crap even in 95% DEET to simply use any form of hydrolysis and expect to get clean products. I assure you that you will need to purify the amine hydrochloride and distillation is the easiest method as recrystallising the diethylamine hydrochloride is actually difficult due to its high solubility and low thermal solubility gradient.
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Tsjerk
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[*] posted on 30-9-2019 at 05:44


No I didn't try, I thought that was clear from my post. I have to admit catching diethylamine directly from a KOH hydrolysis is a nice approach.
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Boffis
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[*] posted on 30-9-2019 at 13:02


I evaporated down the acid collection liquor to recover the diethylamine hydrochloride which worked but the almost white crystalline mass in very deliquescent making it very difficult to manipulate and then get an accurate weight but I'm working on it and the yield looks pretty good. The flask residue was dilute with an equal volume of water, distilled to remove any remaining amine and then treated with charcoal and filtered. The filtrate was still cloudy with tiny droplets of oil but was acidified anyway; fairly coarse straw coloured crystals formed. The crystals were filtered off, washed with a little cold water then petroleum ether (Bp 40-60 C) to remove an oily contaminent and are currently drying.
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S.C. Wack
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[*] posted on 30-9-2019 at 14:36


Could you not have boiled off your lime oil first? I assume that the amide is less volatile in steam, and that ether lowers solublity of the salt in alcohols. BTW the somewhat pure acid can be an oil.



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Boffis
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[*] posted on 1-10-2019 at 03:15


The lime oil seems to distil off with the amine so I had to extract the hydrochloric collection liquor with DCM which seemed to work. I then evaporated it to dryness to obtain a very deliquescent white solid.

I am not sure how much of the oil is lime oil and how much is residual toluamide but I suspact there lime oil is added to perfume the product and I doubt that it is 5% more likely <0.5%, hours of boiling with KOH can't do it any good either.

The yield of crude m-toluic acid was 5.060g which is about 75% while the diethylamine hydrochloride weighs about 4g (rapidly deliquescese) so about 70%.

I am going to try and convert the amine to the oxalate salt which is less soluble and not deliquescent.



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Pumukli
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[*] posted on 2-10-2019 at 10:40


Thanks Boffis for your efforts!

At last it seems proven that one can forget the acid hydrolysis method with this particular amide. The alkaline hydrolysis is the way to go.

You got about 70% amine and 75% acid. They are in good correlation, but it seems that you stopped too soon. Maybe a few more hours boiling would have improved the yield. How many hours did you reflux (refluxed?) the mixture?

Have you tried the oxalic acid method yet? Opinion?
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Boffis
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[*] posted on 2-10-2019 at 13:11


I am having some problems purifying the toluic acid. I first attempted to recrystallise it from isopropanol with or without the addition of some water but I invariably got an oily precipitate that refused to crystallise. So next I tried dissolving it in sodium hydroxide solution and then evaporating it down until it crystallised: unfortunately it won't. It has evaporated to <10ml of pale straw coloured liquid that does not appear to evaporate further on a steam bath but refuses to crystallise. I have tried scratching the basin etc but to no avail. Anyone has any data on solubilities of m-toluates?

I also carried out today a larger scale experiment (45ml of crude DEET) using essentially the same conditions except that the KOH was added as a solid and then only 20ml of water were added to help create a homogeneous solution. The hydrolysis was run for 10 hour but the initial collection solution containing 20ml of 30% hydrochloric acid was neutralised in 3.5 hour indicating about 80% completion at this point. The final solution in the flask is quite transparent and tea-coloured.
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clearly_not_atara
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[*] posted on 2-10-2019 at 20:00


http://www.orgsyn.org/demo.aspx?prep=CV3P0820

"Pure white needles of o-toluic acid may be obtained by recrystallization from water (2 l. of water for 20 g. of acid), Darco being used for decolorization. The recovery is about 85% of white needles melting at 101–103°."

Water! Amazing choice, no? Soaps like Na toluate are extremely hydrophilic and might not dry without decomp. However I'm not sure if this technique makes sense when your contaminant is the amide and not the alkane.

Anyway calcium benzoate has very low water solubility so I'm guessing the metatoluate is similar.




[Edited on 04-20-1969 by clearly_not_atara]
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Pumukli
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[*] posted on 3-10-2019 at 11:02


As a kid I recrystallized nitro-salicylic acid from water. It was quite voluminous but worked. :)
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Boffis
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[*] posted on 3-10-2019 at 13:27


I actually did a test with 1g in 5ml of water and then added more water in 5ml batches, bringing it to a boil each time before adding the next batch. I got to 50ml, the working capacity of the flask, without getting near complete solution so I gave up and tried IPA instead. I have now found that boiling the diluted sodium salt solution with charcoal and then slowly acidifying while hot with HCl precipitates the acid as pale straw coloured crystals which settle rapidly on cooling and are easily filtered and washed. But I'll give the water method a go. With the new larger batch a longer reaction time and more concentrated KOH has produced a much better, cleaner, cream coloured primary ppt of toluic acid. I haven't worked up the collection liquor yet.

I'm writing up the results of the larger batch with photos for the pre-pub section.
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Boffis
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[*] posted on 4-10-2019 at 08:40


I am just working up the products from yesterday's larger scale batch and the recovery is nearly quantitative! The recovery of the crude cream coloured m-toluic acid is about 97% and the diethylamine hydrochloride >100% but this is due to problems obtaining it dry and keeping it dry long enough to weigh it. However, it is quite clear that with careful manipulation this reaction can be used to secure both diethylamine and m-toluc acid in very high yields.
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Boffis
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[*] posted on 5-10-2019 at 12:01


I dried the diethylamine hydrochloride today in a pre-weighed bowl on a steam bath for 2 hours until no more HCl fume could be detected and the material had the appearance of a cream coloured powder and weighed it hot. It gave 23.747g of amine salt which is again about 97% recovery.

I then attempted to recrystallise the crude m-toluic acid from water. I boiled 1 gm of acid with 100ml of water for 20 minutes but it did not dissolve and the water remained colourless. I left the failed experiment to cool. When I returned several hours later the undissolved acid had solidified and stuck to the bottom of the beaker but the aqueous portion was now full of delicate white needles. So not a complete failure but it is going to take more than 150ml of water per gram of acid.
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Pumukli
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[*] posted on 6-10-2019 at 11:28


Congrats!

Maybe sublimation would be a better option. Benzoic acid sublimes easily and makes great, long needles if heated in a closed jar around 100 C. At least it is my experience.

I'm glad that the recovery is almost quantitative too. Waiting for the prepub article! ;)
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S.C. Wack
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[*] posted on 6-10-2019 at 12:42


Such a recrystallization (the directions I gave in the other thread) is proven to work; the Merck agrees, giving a solubility of 1:60 in boiling water. If something doesn't dissolve in boiling water it either isn't m-toluic acid or something on the surface isn't. An alternative would be dissolving in alcohol and adding water.



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Boffis
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[*] posted on 7-10-2019 at 03:13


The recovery of crystalline white m-toluic acid by recrystallisation from boiling water was 67% of good material. Boiling the globules of brownish residue with fresh water failed to recovery any further acid so I presume that the residue is either undecomposed amide or lime oil from the perfume (this toluic acid was from the first experiment in which hydrolysis was not nearly complete).

However, unless you need analytically pure m-toluic acid it is much easier to simply treat the diluted reaction mixture with a good amount of decolourizing charcoal and then acidify it, this gives the product as a soft cream powder. If this is dissolved in the minimum of dilute NaOH solution, charcoal treated again and acidified the product is abtained as a pure white powder in high yield.
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[*] posted on 7-10-2019 at 04:19


But what uses does m-toluic acid have, other than making deet?



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Boffis
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[*] posted on 7-10-2019 at 08:48


Hi Fusso, I don't know yet but its OTC so worth an investigation :D. Actually I did these experiments simply because I had a bottle of jungle strength insect repellant that I am unlikely to use and because so many people have discussed extracting diethylamne from this source but no one has every published anything like a workable method that they have ACTUALLY tried. I will do this shortly, I am just tidying up a few loose ends.

I was recrystallising some of the crude toluic acid from the first batch today on a larger scale than yesterday and I have discovered an interesting feature that suggests that the acid is a mixture of two substances in about 70:30. The more abundant material crystallises in delicate white needles while the second compound crystallises in scales that are so hydrophobic they float on the water. I suspect the insoluble brown residue is the same material. I am wondering if the DEET contains some of the o or p-isomer?

Just investigated the brown globules which had now solidified so I simply picked them out, they weighed 1.060g from 3.28g of crude acid. They are a crystalline solid, Mp about 80 C and insoluble in water but soluble in hot dilute NaOH.

[Edited on 7-10-2019 by Boffis]

[Edited on 7-10-2019 by Boffis]
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S.C. Wack
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[*] posted on 7-10-2019 at 16:12


The USA product does not require any decolorizing, as noted in the relevant thread. There was nothing unreacted or unexpected under mild conditions. I suspect that the problems above have roots in not steam distilling contaminants before the reaction, because it's one of the easier syntheses there is.



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Boffis
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[*] posted on 19-10-2019 at 14:18


I have now tried to recrystallise the better m-touic acid from the larger scale hydrolysis experiment from water as suggested by S.C. Wack and I have found that it can be recrystallised from about 100ml per g giving about 86% recovery of soft, pure white needles (less water can be used but it make filtration impossible).

I have also experimented with the barium salts, this method also looks promising as the volumes of water required are much less and the salt has a steep solubility gradient; it crystallises in dense glassy crystals. Experiments with bought laboratory grade p-toluic acid confirm that the Ba salt is much less soluble. This is analgous to the phthalic acids; the Ba salt of m- or isophthalic acid are much more soluble than the p- or terephthalic acid isomer. I don't have any o-toluic acid but I suspect that it solubility is similar to that of the p- isomer as in the case of the phthalic acids.

I have also found a paper in French that descries the properties of derivatives, particularly the nitro derivatives, of all three toluic acids and there are some interesting properties described for the nitro m-toluic acid derivatives. I have translated part of it and will post it shortly:

Rec. Trav. Chim. de Pays Bas 1901 v20 p149 to 182 toluic acid van Scherpenzeel
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draculic acid69
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[*] posted on 19-10-2019 at 15:50


You could turn the toluic acid into toluene the same way benzoic acid to benzene.
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Boffis
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[*] posted on 20-10-2019 at 08:23


Quote: Originally posted by draculic acid69  
You could turn the toluic acid into toluene the same way benzoic acid to benzene.


Yes but its a bt of a waste.
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Boffis
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[*] posted on 17-11-2019 at 05:11


I finally got round to distilling the free diethylamine from my hydrochloride. The distillation was easy and the process simple. I dissolved the roughly 46g of crude brown diethylamine hydrochloride in to 30ml of water and added 50ml of 50% sodium hydroxide solution slowly. Both solutions were cold circa 10 C and there was no perceptible exotherm and virtually no amine was lost as vapour. The solution turned cloudy as both salt and the amine separated out. On warming the salt dissolved and two phases formed. The upper brown layer is clearly the amine and rapidly boils off between 55 and 58 C when distillation suddenly stalls. At this point distillation was stopped and the receiver removed, just over 40ml were recovered or about 30g of colourless liquid which is over 80% yield based on 100g of 95% DEET.

Purification of the m-toluic acid is also working well. Fractional crystallisation of the barium salt is the best method I have found. Interestingly I prepared some barium p-toluate from Sigma-Aldrich p-toluic acid and it is clear that the main impurity is NOT this compound so it is probably o-toluic acid to the extent of 5-10%.
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[*] posted on 17-11-2019 at 06:24


Does it mean that the DEET you used did contain some (5-10%) diethyl-o-toluamide too? Could this be detected on say TLC?
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