[RaInBowDaSh1488]

I've done a few brominations of alcohols with PBr3. I have always carried them out under nitrogen because the compounds I was brominating contained many double bonds. As a result, I was worried that any adventitious water would increase the likely hood of the double bonds reacting.

My question is, for compounds that are hydrocarbons containing only a single alcohol moiety; is it necessary to carry out this sort of reaction under an inert atmosphere? I believe that moisture in the atmosphere will would react with the PBr3, but I am not sure if it would be to an extent that would really effect the outcome of the reaction, especially if I used a small excess of PBr3.

I don't have a lot of experience with the ideal conditions for this reaction outside of reacting it with very unsaturated compounds. I was just wondering if there are certain situations in which it might be acceptable to brominate with PBr3 in the absence of an inert atmosphere.

Thanks!

[Hunter2]

Should be no problem to have no inert atmosphere. The PBr₃ will react with water to the Phosphorous acid H₃PO₃ and Bromine hydrogen HBr.

[antimatter101]

Hunter2 was sleeping when he typed that. Phosphorous acid has 4 oxygens, and hydrogen gas is also formed.

PBr₃ + 4H₂O     H₃PO₄ + 3HBr + H₂

[antimatter101]

Oh... Phosphorous, not phosphoric!

So:

PBr₃ + 3H₂O     H₃PO₃ + 3HBr

[Hunter2]

What do you mean I was sleeping. Use the right etiquette here. And better you had modified your first post, there was only 3 min. time difference between the two posts.