[Nescafe]

Are they equally good leaving groups or are tosylates better than lets say Br?

Cheers,

Nescafe.

[Schrödinger]

I think tosylates are better. The leaving group is stabilized by resonance, as against the halide ions which have no resonance whatsoever.

[408]

Workup of one containing halides is far easier though.  Tosylate sucks to purify your compound from.

[discodermolide]

Workup of one containing halides is far easier though.  Tosylate sucks to purify your compound from.

Surley it's just a matter of mild base (NaHCO₃) extraction?

[408]

Depends on the polarity of your compound.  Say you are aminating a  heterocycle using tosylhydroxylamine.  The resultant amino compound has a high aqueous solubility, and anything taking it out of water also ends up taking excessive tosylate salts.  It took columns with really weird solvent mixtures to purify it.

But if your compound is mostly C and H, yeah that should work. 

[Babcock_Hall]

On pp. 340-341 of the second edition of Mechanism and Theory in Organic Chemistry (Lowry and Richardson) there are tables of leaving group abilities in SN1 reactions.  Tosylate appears to be 5000 times faster than bromide under the particular reaction conditions tested, despite the pKa values that indicate H-Br is a stronger acid than tosylic acid (if that is the proper term).  On the other hand in SN2 conditions they are about equal, but it depends on the nucleophile.

[james_a]

Yes, this is a notable exception to the rule of thumb that leaving group ability is inversely proportional to base strength.