Dehydrobromination Double bromination experiment 04 02 2015 A dehydrobromination of the meso stilbene dibromide Optimal orientation is for the bromine and the hydrogen to be anti o They are on opposite sides of the carbon but on the same coplanar plane o But that can t happen with a tetrahedral carbon But we can have is anti pariplanar Will be E2 elimination So the hydrogen leaves a the bromine leaves o The first product will be Locked in this orientation We have a high activation energy o But we need the two bromines to leave So we will heat it we need 200 degrees Celsius Issues with high temperature reactions 1 Solvent How do you keep things in solution with such a high temperature o Can t be water or toluene boils at 100 boils at 110 o Two basic approaches 1st pressurize it dissolve everything heat it under pressure allows you to go past the normal bp of the solvent But its inherently dangerous 2nd you can use a high boiling point solvent We are using ethylene glycol bp 260 degrees 2 Heating we gotta help them along o We ll do it microscale in conical vile o Put on aluminum heating plate with aluminum foil insulation Gives the hot plates some extra lil help 3 Safety boiling water is hot man o 200 degrees Serious burn We re turning the dial all the way So you have to be very careful o Not on fingers but on wrists from reaching over the hot plate for things Works fairly well Potassium hydroxide KOH o Only get it after you re totally ready o It absorbs water out of the atmosphere very well Product analysis o Melting point and yield o We need to recrystallize purifying is a problem Melting point of the product is lower than the solvent we use to recrystallized Oiling out the product precipitates out of solution at a temperature above its melting point so it melts into an oily layer As it cools down the crystals can form around impurities o WEIGH CRUDE PRODUCT SAVE A LIL CRUDE FOR MP We can t pick a different solvent so we re gonna do it in a test tube So we re going to cool it down while its still in the water bath water bath will have thermometers Once the temp of the water bath drops below the mp of the solid we will pull it out Focus on hot plate Safety Questions 04 02 2015 04 02 2015