The_Davster
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Ether halogenation?
I am reading a procedure where diethyl ether is used as the solvent for a bromination reaction, however I have read here that ethers should not be
used for any halogenation reaction, due to the formation of the toxic/carcinogenic/war gas halogenated ethers.
Is this a sugnificant issue when done under ambient light? I have been looking online for definitive answers, but all I have came across is in
Sartori's book that it is done under difused sunlight.
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woelen
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Why not replace the ether solvent by pentane or hexane solvent? These have very similar properties (with respect to ease of halogenation), but if this
occurs, then the products are MUCH less toxic. Still toxic, but not nearly as toxic as the halogenated ethers.
The halogenated versions of ROR', RSR' and RNR'R'' all are very toxic. The N and S variations indeed were used as war gases, I do not know of such use
of the O-version.
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PHILOU Zrealone
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| Quote: | Originally posted by The_Davster
I am reading a procedure where diethyl ether is used as the solvent for a bromination reaction, however I have read here that ethers should not be
used for any halogenation reaction, due to the formation of the toxic/carcinogenic/war gas halogenated ethers.
Is this a sugnificant issue when done under ambient light? I have been looking online for definitive answers, but all I have came across is in
Sartori's book that it is done under difused sunlight. |
The mix of HCl, CH2=O and CH3-OH alows a synthetic pathway to CH3-O-CH2-Cl (chloromethyl-methylether), Bp= 59°C, density (20°C=1.0605).
The Cl must be activated, and the compound irritating...Read lacrymatory. It has the first active symptoms of a wargas...skin, eyes,nose,throat,
respiratory irritation (pulmonary edema)...active alkylating agent.
It suffers for rapid hydrolysis in moist air/in basic media with short half lifes (suposely surface catalysed decomposition).
(see: http://www.scorecard.org/chemical-profiles/html/chloromethyl...)
Simple NaOH wash will hydrolyse the toxic compound.
For the rest ether although unreactive do react with HBr, HI acids (HCl is unreactive!)...so if you have in your proces actually a part of your Br2 or
I-Br/I2 that is consumed and do form HBr/HI; there is a chance your ether to be split following:
R-O-R' + HX --> R-OH + R'-X
So If ever you have some R-O-R'-Br and HBr formation, it will be split into R-OH, R-Br, R'(Br)-OH (R'=O +HBr) and R'Br2.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Sauron
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The really nasty one is bis(2-chloroethyl) ether, which is the oxygen analog of sulfur mustard, the vesicant agent H or HD.
Study the preps of both of these and their variants, and see whether the conditions are similar enough to your prep to be considered about a possible
side reaction between the brominating agent and Et2O as solvent.
"O-mustard" is a lot less potent than the sulfur variety and formerly was used as an industrial solvent (maybe still.)
Sic gorgeamus a los subjectatus nunc.
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The_Davster
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Thanks, the procedure is essentially this (http://www.orgsyn.org/orgsyn/pdfs/CV3P0705.pdf) scaled down, I was wondering as it was a potential revision to a lab being preformed by
undergrads. It would seem under these conditions, that formation is unlikely, and even if small ammounts form, washing with water should destroy it.
[Edited on 4-2-2008 by The_Davster]
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Nicodem
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Ethers can get alpha-brominated with bromine. In case of diethyl ether, the product would thus be CH<sub>3</sub>-CHBr-O-Et (1-bromoethyl
ethyl ether). This is not a particularly healthy stuff to deal with!
However, different ethers react with different ease. While tetrahydrofuran reacts quite easily, diethyl ether is quite inert. 1,4-dioxane even forms a
quite stable adduct with Br2. So there will hardly form any brominated ether during that Org. Synth. procedure. Actually, even if it would, that steps
involves the use of bromine which is a hazard in itself, so all necessary precautions need to be taken anyway.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Methyl.Magic
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intersesting question.
Normally when you brominate a molecule the substrate is more reactive than the solvent, therefor there is no side product. But the problem is that
some solvent having a carbonyl group can form extremly toxic alpha-halogenated side product with the excess of bromine. I remember a bad experience
when I use ethyl acetate as exctraction solvent. It react with the excess of bromine and result the ultra toxic ethyl bromoacetate...
Sauron, you're talking about BCME (bis(2-chloroethyl)ether) : this is one of the most carcinogen product of the world ! And very very toxic as well.
The limit value of exposition is placed at 2 ppb !!!!
Diethylether is easily repalced with better solvent for bromination such as DCM or chloroform (avoid CCl4).
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