SplendidAcylation
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Mysterious DEET insect-repellent formulation
Hi,
I recently obtained some DEET based insect repellent, with the intention of subjecting it to hydrolysis, in order to obtain diethylamine (not for
making LSD!), as was documented in Boffis's excellent write-up
This is the product I bought, I chose this one because it came in a non-pressurized container, and I purchased it relatively cheaply.
Unlike many other brands, this product doesn’t have a complete ingredient list, it only states that it contains 48.7% DEET.
I thought nothing of this, assuming that the solvent would be ethanol, as is commonly the case.
Once I got my hands on the product, a 100mL bottle, I decanted the contents of the bottle into a measuring cylinder to determine the density, the
liquid occupied 99mL and weighed 100.50g, corresponding to a density of ~1.015.
It is a slightly yellow liquid, with a very faint plasticky odour, however it is surprisingly viscous, given that the density is equal to that of
water.
It seems comparable in viscosity to propylene glycol.
There was no perceptible odour of ethanol, or any alcohol, for that matter.
In order to purify the DEET, I thought of two (obvious) methods:
1) Distill off the alcohol that I assumed was present, leaving the DEET behind in the distilling flask.
2) Add water, causing the alcohol to move into the aqueous phase, the DEET remaining as an oily phase.
The boiling point of DEET is listed as 288 to 292C, however there seems to be little data regarding its solubility in water.
The Merck Index states that it is “soluble” in water, whereas other sources online indicate that it is almost insoluble; One value I found was
10g/L.
Anyway, I decided to attempt to distill off the alcohol, considering that there was a 200C difference in boiling-point between DEET and ethanol, I
figured there would be no problems with azeotropes.
This, however, did not go as planned.
With the hot-plate set to 150C, nothing began to distill.
I continued to increase the temperature of the hot-plate, eventually reaching 250C.
At this temperature, the DEET solution was not boiling, however a clear liquid began to distill slowly over (1 drop every 10 seconds).
The thermometer in the still-head initially read 73C, however this rose to ~77C and remained there, so it seemed reasonable to assume that this was
ethanol.
Furthermore, the distillate smelled of ethanol, and evaporated readily leaving no oily substance behind.
However, the distillation was extremely slow, which didn’t seem right, if it were to be believed that the product was 50% alcohol!
After around 15 minutes, with the hot-plate still set to 250C, the distillation rate began to drop, with only around 5mL of distillate collected.
At this point, I began to have serious doubts as to whether or not there was a significant quantity of alcohol in the product, or whether a different
solvent had been used.
I looked online for more information regarding the composition, but I found nothing, except the MSDS, which states only two ingredients; “48.7% DEET” and “1-5% 2-propanol”.
So what is the main inactive ingredient, and why list 2-propanol, if they aren’t going to list ethanol?
So now I’m thinking perhaps they have used a less volatile solvent, such as propylene glycol, for instance, however I have no easy way to verify
this.
I added a small quantity of the insect-repellent to water, and it separated into two phases, however the phase-separation is not clean, resembling a
lava-lamp, due to the closeness of the densities of DEET and water.
Now I am really not sure what to do, so I thought I had better ask the experts! 
There seems to be a few possibilities as to what I am dealing with:
1) The insect-repellent does indeed contain 50% ethanol, yet, for some reason, it refuses to distil over; I am not aware of any phenomenon that would
cause this; Furthermore, the liquid seems excessively viscous to contain 50% ethanol, and ethanol is not listed in the MSDS.
2) A different solvent has been used. This could be anything that dissolves DEET, which is probably any sufficiently non-polar solvent, in addition to
alcohols, glycols, etc.
If the solvent is soluble in water, such as an alcohol or a glycol, then it should be possible to separate it (indeed, if I knew it were a glycol, I
wouldn’t need to remove it, as this is the solvent in which the hydrolysis is carried out!), however if the solvent were something like mineral oil,
for example, then I have a serious problem, as it is not easy to separate this from DEET, and mineral oils are not very good solvents for sodium
hydroxide, to carry out the hydrolysis.
All in all I’m quite surprised, I expected this to be simply a solution of DEET in ethanol.
I will probably end up adding water, and weighing the oily phase; If it is ~50% of the initial weight, then it will be apparent that the solvent is
soluble/miscible in water, however if, after addition of water, the oily phase is the same weight, then it appears that the solvent might be some sort
of oil…
Any advice would be much appreciated.
Once I manage to solve this problem, I shall do a photo-essay of the hydrolysis process, as Boffis did.
Thanks.
[Edited on 22-2-2023 by SplendidAcylation]
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Boffis
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Hi SplendidAcylation; Were you using a flat bottom flask (conical or otherwise) on a flat hotplate? If so the difference in temperature between the
plate setting and the boiling liquid is normal. With a fat bottom flask the base is never completely flat and the contact is always poor unless you
use a liquid heat transfer medium. For example, just a couple of days ago I recovered some methanol from a reaction filtrate. In spite of the fact
that methanol boils at about 65 C I had to turn up the hotplate to about 200 C to get even a moderate rather of distillation. my infra red thermometer
showed the hotplate temperature to be about 190 C, so close to the setting. There are two phenomena at work here. The first is the efficiency of heat
transfer and the second is the heat of vaporization. The former is probably the more important but the second should be borne in mind too; polar
solvents light alcohols tend to have higher vaporisation energies that non polar solvents. Hence even once you have reached the boiling point of the
liquid alcohols still require more energy to turn them into a vapour that do solvents like petroleum ether or chloroform of similar Bp. I think
though, that the main issue is the rate of heat transfer. The larger the difference in temperature between the hotplate and the liquid Bp the higher
the rate of heat transfer! So your source material may not be as weird as you think.
A simple test you can carry out on your source material is to mix it with about 3 times its volume of water and see how much of it dissolves. Pure
DEET is practically insoluble in cold water. You can use this method to upgrade you starting material but since the adulterants are likely to be
volatile or inert glycols +/- a trace of perfume. I used what was claimed to be 95% DEET directly without any purification, the conditions of
hydrolysis are so brutal most will either boil off or decompose! With 50% DEET I think I would wash it with water first or evaporate it in a shallow
bowl on a steam bath first to get rid of some of the volatiles, particularly if it is the diethylamine you are after.
Incidentally I need posted a revised write-up but someday I should since I continued my work-up on the toluic acid as various salts and succeeded in
separating out about 5-7% of the o and p isomers; identified by comparison with the same acid prepared from the appropriate xylenes and nitric acid or
alkaline permanganate or from p-methylacetophenone and sodium hypochlorite.
Good luck with your endeavours!
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Texium
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Thread Moved
22-2-2023 at 21:28 |
SplendidAcylation
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Hi Boffis, thanks for the helpful reply!
I will reply to all of your comments shortly, but I'm just making a quick post now so that I can briefly explain that I have solved the problem!
Given your suggestion that maybe the thermal conduction wasn't too great, I reattempted the distillation, this time maintaining the hot-plate at 250c
for longer.
After about one hour, a clear, viscous liquid began to distil over at 188-192C!
The liquid distillate was then tested separately for boiling-point by heating it in a test-tube with a few boiling stones, and a thermocouple held
above the liquid.
I obtained a steady value of 185C
Furthermore, the liquid has a sweet taste and is miscible in water, so it seems very likely that it is propylene glycol!
This means I won't have to distil it off, as this is a suitable solvent for the hydrolysis! 
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phlogiston
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It is not advisable to taste-test any chemical, especially not unknown ones, and es-especially not anything that you obtained by distillation from a
mixture containing a high concentration of something as neurotoxic as DEET.
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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SplendidAcylation
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Quote: Originally posted by phlogiston  | | It is not advisable to taste-test any chemical, especially not unknown ones, and es-especially not anything that you obtained by distillation from a
mixture containing a high concentration of something as neurotoxic as DEET. |
You're absolutely right, it is a bad habit of mine!
I wasn't aware that DEET is neurotoxic, at least not to any significant degree, so maybe I shouldn't apply it liberally to keep the bugs at bay?
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