Elimination+reaction;+cyclohexene+from+cyclohexanol

Zach Chandler Megan Bernard


 * Lab #4:** Elimination Reaction: Cyclohexene from Cyclohexanol.


 * Objective:** To synthesize cyclohexene by an alcohol dehydration.

In this experiment, cyclohexene will be synthesized by an alcohol dehydration. This is an elimination reaction which will proceed primarily by an E1 mechanism. Dehydrations typically employ strong concentrated acids. Sulfuric acid is used commonly for this reaction, but phosphoric acid can be used as well, which is more mild. Phosphoric acid also does not cause problematic side reactions, which sometimes can interfere when sulfuric acid is used. However, phosphoric acid is still corrosive, which means it can still be hazardous to your eyes and skin. After the the cyclohexene is collected, the infrared spectrum of the compound will be obtained. Infrared spectroscopy produces spectra showing the characteristic absorption patterns for a given compound. The absorption of infrared spectra is related to molecular structure in a way that allows particular features to be recognized, such as certain bonds (ex. C-O) and functional groups, which can help identify a compound. The mechanism is seen below; along with H3O+ there is also heat that is not shown on the diagram.
 * Introduction:**




 * Procedure:**
 * Safety Precuations:** Phosphoric acid, while safer than surfuric acid, is corrosive. Avoid contact, and clean up any spills immediately. Cyclohexanol does not appear to present any unusual safety hazards. Cyclohexene is flammable and has a disagreeable odor.


 * Reaction:**
 * Step 1:** To a 50 mL round-bottom flask containing a magnetic stir bar (or boiling stone), add 0.074 moles (7.4 g) of cyclohexanol and 1.75 mL of 85% H3PO4. Use gentle swirling to mix the two layers.
 * Step 2:** Fit the flask with a fractionating column, a distillation adapter, a thermocouple (or thermometer), a condenser, and a vacuum adapter as for fractional distillation (see illustration). A rubber septum should be used to provide a seal between the thermocouple or thermometer and the glassware. Be sure that the seal is good -- if it is not, cyclohexane will escape from the glassware, causing the experiment to fail, and the other classmates might find the odor of cyclohexane objectable. A drying tube, as shown in the illustration, can help to control the disagreeable odor of cyclohexane.

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 * Step 3:** Heat the reaction mixture first at a gentle reflux for about 5 minutes, then heat the flask more strongly in order to distill the mixture into the collection flask. Keep distilling until the volume remaining in the distillation flask has been reduced to approximately 1 mL (or until the color changes).
 * Step 4:** Transfer the distillate to a separatory funnel and wash with approximately 5 mL of water. Carefully seperate the layers and transfer the organic layer into a small, dry Erlenmeyer flask. If any water droplets are visible, remove them before adding the drying agent (sodium sulfate). Add a small amount of anhydrous sodium sulfate to the flask. Let the mixture stand for 5 minutes, occasionally swirling it gently. If the drying agent completely clumps together, its capacity to remove water has been exceeded and a little more sodium sulfate should be added. If you have successfully removed the water, the liquid should be clear, and at least a little of the drying agent should remain free flowing.
 * Step 5:** Decant or pipette the organic liquid away from the drying agent and place it in a clean, dry round-bottom flask.
 * Step 6:** Transfer the distilled cyclohexene to a clean, dry, pre-weighted sample vial and determine the mass of product. Record an infrared spectrum of the distilled product.

As the distillation occurred, the lab quest recorded data values every 30 seconds. The first peak seen was when the distillation first started, but had dropped back down due to the tin foil (foil jacket) being removed right as the cyclohexene started to distillate (see Sources of Error). The next peak (middle peak) represents when the cyclohexane started to distillate again after the tin foil was replaced back onto the condenser packed with copper. When the first drop of distilled cyclohexene fell into the collection flask, the temperature was 62.8 C and when the last drop fell into the flask, the temperature was about 62.3 C. The temperature continued to rise as the distillation process continued proving that there were impurities within the final product. Below the distillation graph, the infrared spectrum of the cyclohexene obtained is shown. It is clear to see that there is a Csp3-H bond (alkane to an H) by the peak labeled 2916.58, as well as a Csp2-H bond (alkene to an H). Where? Get more specific when you analyze the spectrum. Explain your interpretation. Exactly how much cyclohexanol did you use? Describe your product.
 * Observations/Data:**

At the beginning of the experiment, the material still had water droplets inside, so it had to be dried out using compressed air, which could have added impurities to the glassware. Another source of error was that the cyclohexene started to distill while the foil around the condenser had been taken off to check on the progress. The distillation had stopped once it cooled from the removal of the tin foil, but had started back up after a couple minutes (as shown in the graph). A third source of error is when the 7.4g. of cyclohexonal was weighed, there was too much weight on the balance for it to be able to record a weight with the 50mL. round-bottom flask and another flask in order to stabilize it. So in the middle of obtaining 7.4g. of the cyclohexanol, it had to be transferred to a separate flask, then put back in the round bottom flask using a new balance that could calculate a weight of more than what both flasks weighed together.
 * Sources of Error:**

In the experiment, cyclohexene was obtained through an E1 elimination reaction by distilling cyclohexanol. in the presence of acid. After distilling 7.459g. (0.07459 mol.) of cyclohexanol, 2.696g. (0.0329 mol.) of cyclohexene was obtained be sure these numbers go in your data section! I've been looking for them. , which gave a 43% yield. show the calculation. (also, sig figs) While distilling the cyclohexanol, the beginning temperature was 62.8 C, while the literature value boiling point of cyclohexene is 82.98 C, which means that the product obtained through distillation is not pure cyclohexene. As shown above, the infrared spectrum displays that the final product obtained after distillation. There is a Csp3-H bond (alkane to an H) by the peak labeled 2916.58, as well as a Csp2-H bond (alkene to an H) shown on the spectrum, which indicates that there is a carbon-carbon double bond, such as in cyclohexene. In conclusion, the cyclohexanol was distilled successfully by producing cyclohexene after eliminating the hydroxyl group from the molecule, even though the cyclohexene is not pure.
 * Conclusion:**

Doxsee, K. M.; Hutchison, J. E. Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments, Print 2004; pp 129-134.
 * Reference:**