Because any water present will interfere with the

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Because any water present will interfere with the distillation (water will co-distill and will not separate), prior to a final distillation, to obtain pure product, all water must be removed. This is done in two steps. First, the sample is mixed well with an aqueous saturated sodium chloride solution (sat’d salt) and the lower aqueous layer is removed and discarded. This is a pre-drying step that removes most of the water. Next, anhydrous calcium chloride pellets are added. Anhydrous CaCl 2 is an inorganic drying agent that binds strongly with water and thus removes any traces of water from the solution. After about five minutes, the solution is separated from the pellets and transferred to the clean and dry fractional distillation apparatus. The dried solution is then fractionally distilled to produce purified cyclohexene. To achieve optimal separation, the distillation must be done at a slow steady rate. To ensure that the fraction collected as product is relatively pure cyclohexene, this fraction is collected over a narrow range at the boiling point of cyclohexene. The purity of the cyclohexene is determined by gas chromatographic (GC) analysis and a % yield calculated.
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4 Chemical Tests . The presence of the alkene functional group can be indicated by carrying out simple reactions in which a color change can be observed. One such reaction is with bromine in dichloromethane. The bromine reagent is a reddish-orange color. When it is dripped slowly into a sample of alkene, the bromine reacts with the alkene to form a nearly colorless dibromide. Because the bromine is consumed, the mixture loses the reddish-orange color. If a sample decolorizes bromine under these conditions it can be inferred that an alkene functional group is likely present. Br Br Br 2 A second color test is the reaction with potassium permanganate. An alkene reacts with potassium permanganate to form a colorless diol. Under acid conditions the diol reacts further to form a mixture of colorless carboxylic acids or in the case of a cyclic alkene, a dicarboxylic acid. As the permanganate is consumed, the mixture loses its deep purple color. At the same time manganese dioxide, a brown precipitate, forms. If a sample decolorizes permanganate and forms a brown precipitate it can be inferred that an alkene functional group is present. OH OH KMnO 4 COOH COOH Procedure . (rev 6/10) During Weeks 2 and 3 of lab, you will do two experiments - Cyclohexene and Melting Points (MPs). Because of a limited number of melting point devices and gas chromatographs, one half of the class will do Cyclohexene during the 2nd week and the other half will do MPs. During Week 3, you will switch and do the experiment that you did not do during Week 2. The experiment that you will do during Week 2 will be posted on the web. Be sure to prepare for the correct experiment . Melting Points are described in a separate handout.
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