[mreff555]

I'm told that if I were trying to do a nucleophilic substitution on an 1st degree alkyl alcohol eg. "C2H6O" using an acid to protonate a hydroxyl group on an alkyl alcohol would result in protonation of the nucleophile.
I understand the principal behind this. What I don't understand is why a Tosylate ester conversion is possible yet, something like HBr would be unsuccessful at turning an alkyl alcohol in to a alkyl halide. Can anyone explain?

[Mitsunobo]

Since bromide is a better leaving group than hydroxide, it is difficult to do a halogenation of alcohols via direct SN2. If you have converted your molecule to a tosylate ester, I think it would be possible to do a substitution with a bromide since tosylate is a better leaving group than bromide.

But I think the best way to halogenate your alcohol is to undergo elimination first then addition of HBr.

Hope that helps.

[aldoxime_amine]

Concentrated HBr can do the job, its not like its unsuccessful...but as the previous post said, the tosylate is, any day a better leaving group than the bromide.