Osmiridium
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Registered: 13-3-2023
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DEET hydrolysis with HCl to diethylamine and toluic acid
I found that DEET hydrolysis actually works quite smoothly with hydrochloric acid and I prefer doing it that way to hydrolysis with alkali. There is
an nice write-up for alkali hydrolysis made by Boffis.
Take maybe 4-5 times excess 20% HCl (this is about the azeotropic concentration so it won't gas out any HCl) and reflux the DEET with it for at least
24h (better more as I found out later).
The toluic acid separated as an oil and solidified after cooling down and, obviously, the amine stayed in solution as hydrochloride. Distilling off
the hydrochloric acid (it can be recycled easily that way) and freeing the amine with NaOH or KOH (as described by Boffis) yields the amine then.
The toluic acid, and the amine hydrochloride residue may be contaminated with some unreacted DEET (or some other possibly unknown ingredients) but
this does not cause that much trouble.
Recrystallization of of the acid from isopropyl alcohol yielded good results. With the amine it caused no trouble due to it's high boiling point.
I used crudely refined DEET from repellent spray where I just distilled off the volatile components and obtained a diethyl amine yield of about 80%.
Generally regardless whether the hydrolysis is with hydrochloric acid or alkali the amine should be obtained in good yields since it's quite stable
and volatile.
With the toluic acid it might be more troublesome depending on how pure your DEET is. These repellent sprays often contain whatever ingredients or
perfumes and you find no exact info about the composition.
My crude solidified brownish toluic acid was quite unpure and contained oily stuff. But after recrystallization from isopropyl alcohol with a little
water added it yielded quite pure almost white nice crystals. About 61% yield.
This yield is not representative because the actual yield was actually better. Unfortunately I lost some of the crystals because I did not let it cool
down enough being somewhat impatient.
I suggest longer refluxing times since I had oily impurities in the acid and also some high boiling residue in the upper layer after dietyl amine
liberation. It should boost the yields too.
I assume it might be not reacted DEET but who knows, this might very well be something else that was in the spray.
Of course the DEET can be purified by vacuum distillation but I found it not being worth the trouble.
On last important thing to note: Some repellents contain mixtures of icaridin with DEET though it should be stated somewhere. It's will be hydrolyzed
as well. Shouldn't interfere that much with obtaining the diethyl amine but could interfere with the toluic acid because it introduces byproducts and
impurities.
[Edited on 10-4-2023 by Osmiridium]
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SplendidAcylation
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Registered: 28-10-2018
Location: Starving in some deep mystery
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Mood: No one I think is in my tree.
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Thanks for the info, this is really interesting; I recently did this reaction using sodium hydroxide, and although it worked, it did a lot of damage
to my flask; An acid hydrolysis would be much better!
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