Your set up will look like this: The method will be: 1. While these chemicals present their own cautions, they are more innocuous than the previously used chemicals. The product is useful as its reaction with derivatives results in the formation of. Rinse the flask with cold distilled water. The , which are structurally but not synthetically related to E -stilbene, exhibit activity. Impurities would also have a confounding effect on the percent yield making it artificially high. Collect crystals and use cold water to rinse flask.
In the case of this experiment E-stilbene is halogenated to form 1,2-dibromo-1,2- dibenzylethane or dibromostilbene. The reaction first started off as a bumblebee yellow, then faded to an egg yellow color. The Mizoroki approach produced the higher yield. As more H 2O 2 was added the color darkened to a carrot-orange. Bromination of an alkene is an example of an electrophilic addition reaction.
Examples include and its cousin,. This suggests there was excess bromine in the mixture because of the persistent yellow color. Even after adding the distilled water and placing it in the ice bath, there were still some specks of light yellow. Stilbene exists as two possible. This indicates that the product was not pure dimbromostilbene though the melting point was close. Ullmann's Encyclopedia of Industrial Chemistry. It would probably look like this: Just as you had started with a molecule with two phenyl substituents on the same side, the product has the configuration on each stereocenter the same as the other R, R; S, S.
For the bromination of e -stilbene the results were favourable. The isomerization of stilbene under the influence of radiation. Add concentrated solution of sodium bicarbonate to the flask until pH of the reaction mixture is between 5 and 7. Heat to 185-195 ºC with sand bath thermometer!! Concentrated aqueous hyrobromic acid 1. Use a thermometer to Sand bath measure temperature on top of in the sand bath.
The percent yield may also be high if the final product is not completely dry when weighed because of additional water weight. The are naturally occurring stilbene derivatives. This suggests there was excess bromine in the mixture because of the persistent yellow color. Suction dry as much as possible. After five minutes, the reaction still remained the light egg yellow.
Not all the crystals precipitated resulting in loss of product. Once the remaining solid had been collected and weighed, the product was analyzed for purity using melting point determination. Add 12 mL of distilled water instead of 6 mL. Cool the reaction mixture in an ice bath. Measure both mp and mass.
Reflux for at least 15 min instead of 5-10 min. Allow the product to dry, determine its mass and melting point. For example, using , oxidation of cis-stilbene produces 0. Measure both mp and mass. It can be converted to cis-stilbene , and further reacted to produce. Wash crystals twice with 1 mL each of cold methanol. Stilbene is one of the used in.
Another reason could be that during the vacuum filtration, a small amount of crystals remained in the mother liquor. The entire apparatus was heated in a hot water bath until all stilbene had dissolved. Although an ice bath if somewhat effective, not all of the sample may have crystallized. Trans-stilbene occurs as a white crystalline solid at room temperature and is highly soluble in organic solvents. Of these atoms the only waste products are the 2 water molecules produced in reaction 1.