Chem253 Report 13 Form Cyclohexene PDF

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Experiment 13: Formation of Cyclohexene from Cyclohexanol Lab 13: Formation of Cyclohexene from Cyclohexanol 5 November 2020 Purpose To form cyclohexene by performing an acid-catalyzed dehydration of cyclohexanol using phosphoric acid. Theory Cyclohexene is commonly used as an intermediate in the synthesis of industrial compounds like adipic acid, maleic acid, and caprolactam, which forms nylon. Cyclohexene can be synthesized from cyclohexanol via an E1 reaction with phosphoric acid as a catalyst. In this acid-catalyzed dehydration reaction, the OH group of cyclohexanol is protonated by the acid so that water, a good leaving group, can be removed. Then, the compound is deprotonated to form the final alkene, cyclohexene. This reaction is exothermic, as ΔG is negative. Cyclohexene is the only alkene formed in this reaction, and there is no regiochemistry or stereochemistry. Reaction Reaction: Cyclohexanol (C6H12O) (H3PO4) Cyclohexene (C6H10) + H2O Acid catalyst = phosphoric acid Amounts: Cyclohexanol: 10 mL 85% Phosphoric Acid: 2.5 mL Final mass: 3.26 g Boiling point: 66°C Methods/Procedures The experiment was followed verbatim from the lab manual as found on pages 107-108. There are multiple safety precautions to be followed in this lab. Phosphoric acid is a strong acid and will severely burn the skin and eyes in the event of contact. In case of contact, remove contaminated clothes and rinse the affected areas. If acid gets into the eyes, rinse immediately at the eyewash station for 5-10 minutes. Cyclohexene and cyclohexanol are flammable, so keep away from flames and hot labware. These chemicals are also harmful if splashed in the eyes and must be removed by eye washing. Observations/Results During the separation, the organic (top) layer was removed. This layer was clearer than the inorganic layer. Small water bubbles could be seen in the round bottom flask of organic layer, but these were eliminated using sodium sulfate to dry the substance. The chemicals used in this lab had a very unpleasant smell. In the final distillation of the organic layer, the product started to burn, so only 9.5 mL of distillate was obtained. The final mass of the purified product was 3.26 1

grams. The boiling point of the product was determined to be 66°C. The product was then analyzed using GC-MS and nuclear magnetic resonance (NMR). The GC-MS output displays two peaks at retention times of 1.265 and 2.067 minutes. The peak at 1.265 is much taller than the peak at 2.067. The NMR output displays a peak at 5.598 and 10 peaks between 1.193 and 2.096, 2 of which are much taller than the rest.

Figure 1: GC-MS data showing peaks at 1.265 minutes and 2.067 minutes.

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Figure 2: GC-MS data showing relative intensities of the two peaks identified, with maximum peaks at 67.06 m/z and 57.05 m/z.

Figure 3: NMR data displaying a peak at 5.598 and 10 peaks between 1.193 and 2.096, 2 of which are much taller than the rest. Discussion/Conclusion The experiment went as planned. Cyclohexene was successfully formed in an E1 reaction using phosphoric acid and cyclohexane. The final product was 3.26 grams with a boiling point of 66°C. This boiling point is less than the boiling points of cyclohexene (83) and cyclohexanol (100.16), indicating the product is impure. GC-MS data indicates the presence of cyclohexene and cyclohexanol in the product with retention times of 1.265 minutes and 2.067 minutes, respectively. Peak #2 (Fig. 2) has peaks farther on the x axis toward the mass of 100, as compared to Peak #1, so Peak #2 is cyclohexanol and Peak #1 is cyclohexene, since cyclohexanol has a greater molar mass (100.16 g/mol) than cyclohexene (82.14 g/mol). The peaks from GC-MS indicate that the product is 71.16% cyclohexene and 28.28% cyclohexanol. The product is not pure cyclohexanol, which may be due to not achieving a full distillation before the distillate started burning, or that the amount of phosphoric acid and water wasn’t adequate to fully react the cyclohexanol. The NMR displays a peak at 5.598, indicating a C=CH, and peaks between 1.193 and 2.096 indicating -CH2- and CH groups, which makes sense considering the structure of cyclohexene includes a C=C double bond with C-H’s on either side and C-H2 making up the rest of the ring. Exercises

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1) 4) This is a reversible, acid-catalyzed reaction. This means that in equilibrium, both products and reactants are present. Shifting equilibrium will shift the amount of products vs reactants. In the hydration reaction forming cyclohexanol, water is in excess since the acid is dilute, so hydration is favored. With a more concentrated acid, dehydration is favored and therefore the formation of cyclohexene is favored. Raw Data See below --

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