jimmyboy
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Phosphorus Tribromide
Anyone have some experience with it? I was wondering how toxic it really is and if it could be reliably reduced to phosphorus - maybe with some
powdered iron or another reducing agent to strip the bromine from it without alot of phosphine being formed
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Polverone
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As Sauron has mentioned before, see page 522 of the English edition of Brauer for a preparation of red phosphorus from PBr3 and mercury. It sounds
laborious, expensive, and potentially hazardous, but at least it is a complete procedure given by a trustworthy publication.
PGP Key and corresponding e-mail address
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garage chemist
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I have made about 20ml of PBr3 for use as a reagent to make an alkyl bromide from an alcohol that would only form the alkene if treated with aqueous
HBr (PBr3 is a very useful reagent for converting sensitive secondary and tertiary alcohols into the alkyl bromides).
It does not pose any special problems during synthesis or storage other than the fact that it hydrolyzes with moisture and oxidises to POBr3 with
atmospheric oxygen, just like PCl3.
It is much easier to make than PCl3 because red P and bromine in dichloromethane can be used as a preparation method (red P and chlorine in DCM only
gives PCl5).
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jimmyboy
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Sounds good - I am kind of shying away from PCl3 because of its low boiling point and toxicity - I just looked at the brauer prep for red phos from
PBr3 - mercury doesn't strike me as a strong reducer at all (and it is kind of in short supply around here) a few other metals would probably work as
well - with the calcium phosphide synth in brauer as well a roundabout way to phosphorus looks pretty straightforward - yields may stink though
calcium phosphate + Al -> calcium phosphide + Br2 -> PBr3 + Reduction metal -> P
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MagicJigPipe
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| Quote: | | I have made about 20ml of PBr3 for use as a reagent to make an alkyl bromide from an alcohol that would only form the alkene if treated with aqueous
HBr... |
I wonder if bromoethane (for Grignard reactions) could be obtained via HBr and ethanol with decent yields. I've read it works at least in small
yields. I know it would also produce Et2O and ethene but the Et2O shouldn't be a problem for a Grignard as it will be used with the EtBr anyway. A
few procedures I read a while back called for Et-MgBr but I forgot about it until I saw you mention alkyl bromides via HBr. Now I'm thinking of
trying this.
Is this not a viable alternative to PBr3 if phosphorus is almost completely unavailable (as it seems to be in the US)?
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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garage chemist
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Yes, of course bromoethane can be made via HBr, that's the normal method of preparation!
PBr3 is only needed for those alcohols that very readily eliminate water, and simple primary alcohols certainly don't fall into that category.
Haven't you read the isopropyl mercaptan preparation?
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