[Wingpin]

Specifically the initial reaction with catalytic PBr3 and a carboxylic acid. I tried drawing how the carboxylic acid would attack PBr3, but I'm always stumped by what species in the reaction that can remove the alcoholic hydrogen so a carbonyl group can be formed/stablized. I tried searching through Google for a while and the closest site I could find w/ a detailed mechanism was:
http://megan-organic.blogspot.com/2011/04/hell-volhard-zelinsky-halogenation.html 

In the first step, the alcoholic hydrogen is expelled after the original carbonyl attacks PBr3 (in order to reform a carbonyl group), but how? Does the hydron just float around or was it attacked by a base? If so, what base? I was thinking bromide, but then I would have HBr in the reaction and I wouldn't know how to get rid of it.

Also, a little off-topic, but how does catalytic p-toluenesulfonic acid (or any really strong acid really) reform itself if the conjugate base is exceptionally weak?

Thanks for the help / for reading.

[camptzak]

this reaction may keep going depending on the R group. its a poor drawing, but I hope it helps.

[camptzak]

and as or the ptsa question, lower the pH to below the acids pKa and you will reprotonate the acid

[discodermolide]

I think you will find that the H-V-Z reaction brominates the alpha carbon of carboxylic acids. Certainly via the acid bromide.

http://en.wikipedia.org/wiki/Hell–Volhard–Zelinsky_halogenation