when stilbene is used is reacted with bromine it forms 1,2-dibromo-1,2-diphenyle
ID: 838836 • Letter: W
Question
when stilbene is used is reacted with bromine it forms 1,2-dibromo-1,2-diphenylethane, then when reacted with KOH it forms diphenylacetylene. My question is when this synthetic sequence is performed starting with 2-butene rather than stilbene why is is 2-butyne not formed? and what is the product that is formed preferentially to 2-butyne? Thanks
Also, i understand in this lab that cyclohexene is used to discharge the bromine color to make the liquid clear again but why does the cyclohexene not contaminate the 1,2-dibromo-1,2-diphenylethane?
Explanation / Answer
Because when this reaction is conducted in water, halohydrins are formed instead of dihalo-compounds. So, the product with but-2-ene would be 2-hydroxy-3-bromobutane.
In the case of stilbene the dihalo product is formed due to the favourable electronic effects of the two phenyl groups.
Again, due to the lack of favourable electronic effects of the two phenyl groups, the dibrmocyclohexene is not able to interfere in the next step of the reaction. Also as the product of cyclohexene in the first step is a halohydrin, it does not give an alkyne in the next step. The desired product in the end is extracted as a solid under vacuum filtration.
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