SC CHEM 333 - Dehydration of Cyclohexanol to Cyclohexene Pre-Lab (6 pages)

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Dehydration of Cyclohexanol to Cyclohexene Pre-Lab



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Organic Chemistry 333L 03M Laboratory Pre Lab Dehydration of Cyclohexanol to Cyclohexene By Cameron Kahn 5 November 2013 TA James Collie 1 Page Objective In this experiment one will learn how to do an acid catalyzed dehydration of cyclohexanol into cyclohexene Then use fractional distillation to purify the product After purification identify the product using qualitative organic tests Intro Theory In an acid catalyzed dehydration an alcohol can proceed to change to an alkene This process is cause by a molecule of water is eliminated from a carbon compound This process is known to be called dehydration Dehydration is most commonly done through the means of heat and either the presence of phosphoric acid or sulfuric acid to catalyze the reaction Sciences In this lab one will use a secondary alcohol because they undergo dehydration easier than primary alcohols Handy A secondary alcohol requires much lower temperature to perform the acid catalyzed dehydration This will allow one to obtain the final product alkene much easier than the use of a primary alcohol In this experiment the reaction will undergo an E1 reaction This is due to the water molecule being eliminated from the two adjacent carbons The leaving group will leave first in order to create a carbocation in the molecule Therefore the first step is the slow rate determining step followed by a more rapid step Alkenes that form from this process are known to undergo alkene addition reactions In some instances these reactions can be used to determine the presence of an alkene in the final product In order to understand this theory look at Bromine for example Bromine is a brown liquid that turns clear with the presence of an alkene KMnO4 will form a brown precipitate 2 Page Mechanism Mechanism is a photocopy from the Chemistry lab manual written by George Handy Procedures Start by placing 0 9mL of water 1 2mL of 85 phosphoric acid 6 2mL of cyclohexanol and a boiling stone into a 25mL round bottom flask Next heat the mixture using a heating mantle located under a fractional distillation apparatus Make sure the bulb of the thermometer is positioned correctly inside the distillation head Heat the mixture with the variac setting at an initial 60 Then gradually increase the variac setting until only 1mL of mixture is left in the flask and most of the material is done distilling Water and product will be the two phases of the distillate Record the boiling point of the solution Transport the distillate into a separatory funnel and then wash with 4mL of saturated aqueous NaCl solution Using the separatory funnel discard the bottom layer and retain the top layer in a test tube Add a micro scoop of anhydrous 3 Page magnesium sulfate to the test tube swirl and then let the solution settle Cap off the test tube holding the product and leave sit until next lab period In the next lab period use the shorter fractional column and set up the fractional distillation apparatus Lightly grease all connections Next add a boiling stone and the product from the last lab period to a 25mL round bottom flask Heat the mixture using a variac setting of 60 initially Then after a few minutes increase the heat by turning the variac setting up gently Collect the product and determine the volume Then calculate the mass of purified product using the volume and its density Using a pipette remove the product Determine the volume and using the density calculate the mass of purified product Handy Then one must clean and set up 4 small test tubes to perform qualitative tests on the product In two test tubes add 1mL of cyclohexanol and in the other two add 1mL of the product cyclohexene Using a test tube from each pair add 10 drops of 1 KMnO4 solution and record the results for both test tubes Take the other two test tubes and add 10 drops of Bromine water solution and record the results for both test tubes Apparatus Figure 2 Figure 1 Figure 1 Fractional distillation Figure 2 Separatory funnel Both figures are courtesy of UMass Amherst Department of Chemistry and Biochemistry Reagent Table Name Structure MW g mol Melting oC 20 22 Cyclohexanol 100 16 4 Page Boiling oC 161 Density g mL 0 962 Properties Colorless viscous liquid with a faint camphor odor HYGROSCOPIC Safety Toxic Irritant Flammable 21 158 1 685 Viscous colorless odorless liwuid solidifies at 70oC Ph osphoric Acid 97 99 Sodium Chloride 801 1413 2 165 White crystals HYGROSCOPIC NaCl 58 44 1124 2 66 Mag HYGROSCOPIC drying agent white powder Corrosive to tissue and irritating to the skin mucous membranes upper respiratory tract and eyes Fatal if swallowed This compound may cause eye irritation When heated to decomposition it emits toxic fumes Desiccant nesium Sulfate 120 36 Colorless liquid 104 83 0 811 Irritant to skin mucous membranes upper respiratory tract and eyes Cyclo hexene 82 15 Bromine Br Br 7 2 137 8 3 102 79 904 Potassium Permanganate KMnO4 158 09 Disposal 5 Page 270 2 7 Brown clear liquid with strong bromine smell TOXIC Purple crystals with a static charge Keep reagent under at or below 4oC at all times Heating can cause decomposition and bromine gas being generated Strong irritant to eyes nose and lungs Violent oxidizer of alcohols If ingested damage is done to kidney and lungs resulting in edema and burns Inhalation can cause serious irritation Thoroughly wash any and all glass wear using acetone and if approved by the TA then rinse with water Dry all glass wear and properly put back any and all materials in the designated areas or drawers Soiled gloves should be disposed of in the proper glove container Any paper towels should be disposed of in the general waste basket Organic solvents need to be properly disposed of in the organic liquid waste container located under the fume hood Consult with the TA for further instructions or any questions one may have before disposing of any content inappropriately References 1 Ali George Handy and Salman Essentials of Organic Chemistry Montgomery Al QDE Press 2012 Sciences Department of Chemistry in the College of Natural Department of Chemistry in the College of Natural Sciences 01 01 2012 UMass Amherst 02 23 2013 http www chem umass edu samal 269 aak pdf 2 6 Page


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