[anilin]

Would someone tell me which one of the attached mechanisms are correct?
Many thanks

[azmanam]

They're the same.  I know one has the bromide formally plucking the proton off the product, but they're mechanistically the same.  I prefer the 2nd, because I like to see arrows from nucleophiles... not just leaving groups leaving on their own, but different people could have a good faith disagreement.

see also:
http://www.chemicalforums.com/index.php?topic=29772.msg113095#msg113095

[macman104]

I also prefer the second mechanism as well.

[azmanam]

...although if you want to play the pKa game, Br- is about the worst nucleophile you could pick to pluck off that proton.  HBr has a pKa ~-9.  Protonated alcohols (and probably protonated ethers) are around -2.5 or so.  Weaker Acid Wins.  Proton will stay on the ether until workup.  If water's present (doubtful), water will take the proton (pKa ~-1.7).

[anilin]

...although if you want to play the pKa game, Br- is about the worst nucleophile you could pick to pluck off that proton.  HBr has a pKa ~-9.  Protonated alcohols (and probably protonated ethers) are around -2.5 or so.  Weaker Acid Wins.  Proton will stay on the ether until workup.  If water's present (doubtful), water will take the proton (pKa ~-1.7).

Thanks but I don’t understand what you mean by pka. Is it Br- that picks up the H? or the compound with O+ becomes deprotanated ?

[nj_bartel]

Why would an alcohol be a weaker base than water?

[azmanam]

Thanks but I don’t understand what you mean by pka. Is it Br- that picks up the H? or the compound with O+ becomes deprotanated ?

see the post I linked to - in the end it doesn't matter.  Conventional wisdom would say Br-, and I wouldn't mark off on an exam for it (check with your instructor for your instructor's grading rubrik).

What  I was saying about pka is this:  The removal of the proton from the final intermediate is an acid base reaction.  Acid base reactions are equilibria.  The favored side of the equilibrium is determined by pka.  Mix HCl and NaOH and you get H2O.  HCl has a pka ~ -7.  H2O has a pka of around 15.  Water with a pka of 15 is a weaker acid than HCl with a pka of around -7.  

This Weaker Acid Wins mnemonic works for all acid base equilibria - including the one in this reaction.  In the final intermediate, the ether is protonated.  it is an acid.  As a protonated ether, it has a pka of around -2.5.  For the reaction ether-H⁺ + Br^- --><-- ether + HBr, the protonated ether has a pka of -2.5, and HBr has a pka of -9.  Weaker acid wins.  The protonated ether is a weaker acid.  The equilibrium lies on the side of the protonated ether.

Why would an alcohol be a weaker base than water?

Good question. I'm drawing a blank, but quantitatively it is true.  See Evan's pKa table.  Protonated water is in the first column on the first page, and protonated alcohols and ethers are in the last column on the first page.

http://www2.lsdiv.harvard.edu/labs/evans/pdf/evans_pKa_table.pdf