Lab 7 - Debromination_10

Lab 7 - Debromination_10 -...

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The Debromination of  meso -Dibromostilbene Adapted   from   Williamson,   K.   L.   et   al.,   “Macroscale   Zinc   Dust   Debromination,”   Macroscale   and  Microscale Organic Experiements, 5th Ed. , 2007, pp363-364. Cholesterol isolated from natural sources contains small amounts (0.1 % - 3 %) of 3 β -cholesetanol, 7- cholesten-3 β -ol and 5,7-cholesten-3 β -ol.  These substances are so similar to cholesterol in solubility that  their removal by crystallization is not feasible.   However, complete purification can be accomplished  through the dibromonation, recystallization and subsequent debromination.   For this lab we will use  stilbene dibromide as our substrate, which can be readily debrominated by zinc in either acetic acid or  ethanol to produce the corresponding alkene.  Two possible mechanisms are suggested in the literature for  this   reaction:   a   concerted   two-electron   reduction   by   zinc   or   two   single-electron   transfers   in   rapid  succession.  Each of these mechanistic pathways could lead to the single  trans  stereoisomer, but only the  single electron transfer pathway could give rise to the 
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Lab 7 - Debromination_10 -...

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