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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: MətHylFrÆtH on May 30, 2013, 04:54:01 PM

Title: Will this work? buta-1-en-3-yne + H-Br -----> 2-Bromo-1,3-butadiene
Post by: MətHylFrÆtH on May 30, 2013, 04:54:01 PM
I need help in a synthesis and this ends up being one of the steps, so I was wondering if this would work if the equivalent amount of H-Br is added



buta-1-en-3-yne + H-Br   :rarrow: 2-Bromo-1,3-butadiene





..or would it work with PBr3 



I was wondering if the desired product would be created at all, though I have a feeling it would but would not be the major product.

So if there is an ene-yne then if there any priority to what bond is protonated first, and if so would the resonance structure affect this reaction in any way?


Note: I'm not looking for a "real" answer but one that works on paper, and would be in a typical undergrad textbook, so I would prefer an answer (if possible) to not include some obscure chemical I haven't heard of. thanks

Title: Re: Will this work? buta-1-en-3-yne + H-Br -----> 2-Bromo-1,3-butadiene
Post by: sjb on May 30, 2013, 05:03:22 PM
Quote from: MətHylFrÆtH on May 30, 2013, 04:54:01 PM
I need help in a synthesis and this ends up being one of the steps, so I was wondering if this would work if the equivalent amount of H-Br is added



buta-1-en-3-yne + H-Br   :rarrow: 2-Bromo-1,3-butadiene





..or would it work with PBr3 



I was wondering if the desired product would be created at all, though I have a feeling it would but would not be the major product.

So if there is an ene-yne then if there any priority to what bond is protonated first, and if so would the resonance structure affect this reaction in any way?


Note: I'm not looking for a "real" answer but one that works on paper, and would be in a typical undergrad textbook, so I would prefer an answer (if possible) to not include some obscure chemical I haven't heard of. thanks

Perhaps see http://dx.doi.org/10.1080/00397919108020841
Title: Re: Will this work? buta-1-en-3-yne + H-Br -----> 2-Bromo-1,3-butadiene
Post by: khemophore on May 31, 2013, 06:01:47 AM
According to David Kline's Organic Chemistry, hydrohalogenation of alkynes proceeds through a termolecular transition state but is only slightly slower than the hydrohalogenation of alkenes. Hence, in all likelihood, you'll get a mixture of products, with your desired product being the minor one. That said, if you want a one-step synthesis, I'm not aware of any superior alternatives.