Saturday, November 24, 2012


I am contemplating some hypothetical difficulties in the synthesis of 2,5-dibromohexane from 1,5-hexadiene. I am aware that this is a simple reaction that can be achieved in many ways but I would like to accomplish it in such a way that a messy separation is minimally necessary, be it via selective chemical extraction, column chromatography, or fractional distillation. The main unwanted side-products in this synthesis would be the mixed-Markovnikov product and the full anti-Markovnikov product. My first option is simple bromination with (aq) HBr and an appropriate phase transfer catalyst or a similar reaction involving hydrogen bromide gas. My second option is oxymercuration-demurcuration yielding hexane-2,5-diol which can then be subjected to a high yielding and selective bromination with PBr3. The third option is acid catalyzed hydration to the diol with H2SO4 and water followed by bromination with PBr3.

I would prefer not to use hydrogen bromide gas or mercuric acetate (which will require recycling of the metallic mercury liberated during demercuration) and so I lean toward acid catalyzed hydration. Would anyone with practical experience using the above methods enlighten me regarding their relative regioselectivity for the Markovnikov product? I believe it would be something like this: oxymercuration-demurcuration>acid catalyzed hydration>HBr addition.

Sunday, November 11, 2012