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mbrown3391
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Yesterday, I mixed the stoichiometrically correct amounts of DEET and water (saturated with NaOH) and propylene glycol as a cosolvent. The mixture was
placed in a stoppered flask and left at room temperature over night. When i checked it this afternoon, it had turned from white to yellow/orange
colored. Clearly, some type of reaction is occurring. Are you sure this will not work at room temperature for extended time periods?
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Klute
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It's the base that needs to be in stoechiometric amount, not the water. This isn't a catalyzed reaction like acidic hydrolysis, but stoichiometric: if
there isn' enough base around, you amide will not hydrolyze further....
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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mbrown3391
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oh i forgot about the base reacting with the methylbenzoic acid. I will add more tonight
But thats not the point. Is this reaction producing diethylamine at room temperature? or is there another possible reaction that would cause the
coloration?
[Edited on 8-9-2008 by mbrown3391]
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pantone159
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When I tried this reaction (DEET + NaOH + H2O + MeOH/EtOH), I got a pale yellow color as soon as I mixed all these up. Upon heating with a water
bath, a pink/purple color formed, particularly on the surface of the liquid, and near the stopper on the test tube. I assume that there was some kind
of reaction with air?
The pink/purple color seemed to be a reversible pH indicator, changing to yellow upon acidification, it also seemed to be a neutral organic compound
(it stayed in a DCM layer vs. aq layer, both in acid and base conditions.)
However, I got these observations even when there seemed to be no sign of any free amine. (Meaning no ammonia-like smell. If you are making any
significant amount of Et2NH in basic conditions, it should be obvious.)
[Edited on 8-9-2008 by pantone159]
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Klute
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There could be lots of polymerisation, condensation and other reactions going on at RT. Your DEET mixture is surely far from pur.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
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mbrown3391
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A transparent, red-brown third-layer has now formed in my solution and the mixture is in fact developing an ammonia-like smell. Apparently
Diethylamine can have a brownish tint if it is impure. Even if i am producing Diethylamine, however, i'm sure at some point this reaction will reach
an equilibrium. I could, however, distill out the diethylamine developed up to this point and let it keep going.
[Edited on 15-9-2008 by mbrown3391]
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panziandi
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are you using the glycol-hydroxide method? I suspect if you are you are getting condensation reactions perhaps. Collect you crude amine and redistil.
You can dry the DEA with solid KOH and then distil it again if desired.
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mbrown3391
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I am using a solution of 50% propylene glycol/distilled water saturated with NaOH. This is combined with 1 oz of 99% DEET. It has been sitting in a
stoppered flask for 7 days now.
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mbrown3391
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Actually, will an equilibrium be reached? If the DEA is in a separate layer then it is essentially removed from the reaction.
It Appears that the propylene glycol solution is on the bottom, followed by the DEET, followed by DEA on top. I guess the reaction is occurring very
slowly where the bottom two layers meet, then the product rises to the top.
[Edited on 15-9-2008 by mbrown3391]
[Edited on 15-9-2008 by mbrown3391]
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panziandi
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I don't see why it would be in a separate layer, it is incredibly soluble in water. Can you not reflux the reaction mixture? It will almost certainly
reduce the time required and should limit side reactions such as condensations which would develop over time in a stoppered flask.
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mbrown3391
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I don't currently have a hotplate/stirrer and im not sure if it is a good idea to attempt to reflux it without one.
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panziandi
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If you clamp it well and have a descent reflux condenser you should be able to reflux it fine with a small burner. If your water isn't cold from the
tap chill water with ice in a bucket and pump it through you condenser with a pond pump should do wonders. Boiling will also keep the layers moving so
the DEET and hydroxide will be constantly mixed together. And little DEA should escape, even so do it outside if possible. Then swap the setup around
and distil off the amine, dry it with KOH and redistil. You could probably set up something where the DEA distils off as it is formed. Chill the
reciever with iced-water though!
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S.C. Wack
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I'd recommend a Friedrich condenser for the reflux, I should have put on a 24/40 adapter and used one instead of the 19/22 Liebig. The receiver
contained fuming HBr. The hydrobromide is no less hygroscopic than the HCl salt.
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mbrown3391
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All i have is an Allihn condenser and its quite oversized to say the least (around 30 inches a believe!)
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panziandi
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You could try it I suppose, Lead a vapour tube from the top through a wash bottle of HCl or water that way any escaping DEA fumes will be caught and
you can maximise your yields by reducing losses.
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S.C. Wack
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Back in the day, some people were happy with preparation of ethylamines from ethyl bromide, with separation of the mixed amines utilizing ethyl
oxalate. Authors preparing their own amine reagent tend not to detail this separation method in their journal references decades after this was
introduced, and there seemed to be some conflicting vague details, so I searched for the best way of doing this in the original lit and here it is; I
suppose Houben-Weyl has details as well. There are other methods in the older lab manuals.
The methylamines are also made here, in a way that I don't recall hearing of before, using methyl nitrate instead of a halide.
68 pages in French. An abstract in English starts on page 6 here.
Oh BTW after my experiment above, I ended up isolating a considerable amount of additional hydrobromide salt after workup, so my yields given above
were quite low. Do not use HBr for neutralization of the amine.
[Edited on 1-1-2009 by S.C. Wack]
Attachment: ann_chim_phys5_23_289_1881.pdf (2.1MB)
This file has been downloaded 911 times
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poisoninthestain
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help hydrolyzing DEET
I've tried several times to hydrolyze DEET into its corresponding carboxylic acid and amine. I used 20%, 30%, and 98% DEET and still no success. I
added various solutions of NaOH and H20(distilled) and the first thing that comes over during distillation is something around ~80C WTF!
There was a definite color change after adding the NaOH to a red, and once heat was added it changed yet again to a "bromine" brown.
...still confused. maybe it needs more time to react. diethylamine is the goal here.
[Edited on 7-3-2009 by poisoninthestain]
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garage chemist
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Try using HCl instead, and reflux for a long time.
If it worked, you will immediately see it upon cooling the solution- the m-toluic acid will precipitate. Filter, basify, distill diethylamine.
If there is no reaction with refluxing HCl, try adding a solvent that dissolves both the organic and the aqueous phase.
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poisoninthestain
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| Quote: | Originally posted by garage chemist
Try using HCl instead, and reflux for a long time.
If it worked, you will immediately see it upon cooling the solution- the m-toluic acid will precipitate. Filter, basify, distill diethylamine.
If there is no reaction with refluxing HCl, try adding a solvent that dissolves both the organic and the aqueous phase. |
I'll try refluxing for 1 hour with concentrated HCl and report back. The diethylamine should form the hydrochloride salt too so I'll most likely have
to basify and distil again. Hopefully, acid catalyzed hydrolysis for amides is more effective than base. My organics text by "L.G. Wade" hints
otherwise.
[Edited on 7-3-2009 by poisoninthestain]
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garage chemist
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I just remembered my experience with hydrolysis of benzyl cyanide to phenylacetic acid- with 70% H2SO4, 10 minutes reflux were enough for complete
hydrolysis, while with 30% NaOH, there was still unconverted benzyl cyanide after 45 minutes reflux.
The H2SO4 has the big advantage of reaching higher temperatures.
If HCl doesn't do the job, try 70- 80% H2SO4 instead.
For workup, dilute with water and filter before basifying.
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Paddywhacker
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Original poster, with NaOH hydrolysis you do not need water.
Try a test-tube experiment.
Add 0.5 g NaOH to a clean dry test tube.
Add 5 ml of ethylene glycol, propylene glycol, or, maybe, glycerol.
Heat to dissolve the NaOH.
Cool.
Add 1 ml of DEET.
Add a boiling chip.
Carefully heat with agitation and report any observations.
Edit:
We all start out without much practical experience. Those of us that are canny enough to avoid killing or maiming ourselves, physically or mentally,
are the old hands you see today.
So take my advice when I strongly advise you not to scale up this hydrolysis as much as you have done. An accident with NaOH dissolved in hot glycol
will cut you to the bone. Keep it small.
Edit for pantone159 and DJF90
R.CO.N(Et)2 + NaOH -> R.CO.ONa + NH(Et)2
Note.... no free water involved, although you could argue that NaOH is Na2O bound to water.
[Edited on 8-3-2009 by Paddywhacker]
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pantone159
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| Quote: | Originally posted by Paddywhacker
Original poster, with NaOH hydrolysis you do not need water.
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But H2O is added to the products (H to the NHEt2, OH to the m-toluic acid), so I don't see how this could work without water.
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DJF90
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paddywacker: I think you will find that water is required for the reaction. The sodium hydroxide is employed as a catalyst (an acid could be
alternatively used). A concentration of about 2M NaOH is generally used for esters (IIRC) but amides will need a little more "wack" seeing as they are
less reactive carboxylic acid derivatives. A 5M NaOH solution ought to do it I would think? Using base has the advantage (over acid catalysis) that
the reaction is non reversible and so it is possible to hydrolyse all of the ester/amide, but acid hydrolysis can be good yielding so long as there is
a lot of water present (as this shifts the equilibrium).
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poisoninthestain
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after trial and error countless times i have arrived at a single conclusion...base catalyzed hydrolysis of DEET will work...the reaction just has to
be refluxed for a VERY VERY long time...unfortunately i do not have to the time or convience for that.
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Paddywhacker
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| Quote: | Originally posted by DJF90
paddywacker: I think you will find that water is required for the reaction. The sodium hydroxide is employed as a catalyst (an acid could be
alternatively used). A concentration of about 2M NaOH is generally used for esters (IIRC) but amides will need a little more "wack" seeing as they are
less reactive carboxylic acid derivatives. A 5M NaOH solution ought to do it I would think? Using base has the advantage (over acid catalysis) that
the reaction is non reversible and so it is possible to hydrolyse all of the ester/amide, but acid hydrolysis can be good yielding so long as there is
a lot of water present (as this shifts the equilibrium). |
Water is not required in the case of alkaline hydrolysis.
If you don't believe me then look up the hydrolysis of PET with NaOH in glycol in one of the other forums.
The only problem is that you will get a slurry of the sodium salt that might cake at the bottom and lead to overheating if you scale it up.
Do as I suggested and perform the experiment on a test tube scale, then tell me which of us is mistaken.
Edit:
I am quite prepared to eat my words.... I have been wrong before and will be so again.... that is how we all learn. But first do the experiment.
[Edited on 8-3-2009 by Paddywhacker]
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