Dehydration of Methylcyclohexanols - Lab Report

Dehydration of Methylcyclohexanols Introduction: During the dehydration of 2-methylcyclohexane and 4-methylcyclohexane, an alkene and a water molecule are formed. The purpose of this experiment was to verify the presence of the Evelyn Effect in the dehydration of either 2-methylcyclohexanol or 4-methylcyclohexanol by heating alcohols with phosphoric acid. The Evelyn Effect is a change in the product distribution throughout the duration of the reaction. In this experiment, the problem is that experimenters were unsure whether the E1 or E2, or a mixture of the two mechanisms are utilized in the dehydration of cis and trans isomers of 2methylcyclohexanol and 4-methylcyclohexanol. The experiment was performed by running a dehydration reaction of both 2- and 4-methylcyclohexanol with H 3PO4 in order to distill the byproducts and serve as a driving force for the reaction, according to Le Chatelier’s Principle. Two fractions were collected and washed, then gas chromatography was utilized to identify the alkene products in each fraction. Results: Theoretical yield 2 2-methylcyclohexanol (18ml* 4-methylcyclohexanol (18ml* 0.930g ∗1 molmethylcyclohexanol 1mL ∗1 molmethylcyclohexene 114.2g 14. ∗96.2g 1molmethylcyclohexanol ¿= ¿ 1 molmethylcyclohexene 0.914g ∗1molmethylcyclohexanol 1mL ∗1 molmethylcyclohexene 114.2g 13. ∗96.2g 1 molmethylcyclohexanol ¿=¿ 1molmethylcyclohexene 1. Theoretical Yield of 2-methylcyclohexanol and 4-methylcyclohexanol: 2. Percent yield of 2-methylcyclohexanol and 4-methylcyclohexanol: Percent yield 2-methylcyclohexanol 4-methylcyclohexanol (6.39g +3.29g) ∗100=68.65% 14.1g (7.62g+ 2.93g) ∗100=75.89% 13.9 3. Boiling Point ranges: 2-methylcyclohexanol 4-methylcyclohexanol Fraction One 100-104 ° C 104-106 ° C 4. Product composition - Fraction One: 2-methylcyclohexanol Fraction Two 103-103 ° C 105-109 ° C 3 o Total area: 2076623 + 68716830 + 15559152 + 2667544 = 89020149 Compound 3-methylcyclohexene 1-methylcyclohexene 2-methylcyclohexanol - 2076623 ∗100=2.33% 89020149 68716830 ∗100=77.19% 89020149 (15559152+2667544) =20.47% 89020149 Fraction Two: 2-methylcyclohexanol: o Total Area: 44829660 + 8199848 + 79785326 + 12818738 = 145633572 Compound 3-methylcyclohexene methylenecyclohexane 1-methylcyclohexene 2-methylcyclohexanol - % Compositions Fraction One: 4-methylcyclohexanol % Composition 44829660 ∗100= 30.78% 14563372 8199848 ∗100=5.63% 14563372 79785326 ∗100=54.78% 14563372 12818738 ∗100=8.8% 14563372 4 o Total Area: 62084266 + 8861396 + 2967949 + 9594243 = 83507854 Compound 4-methylcyclohexene 1-methylcyclohexene 4-methylcyclohexanol - % Composition 62084266 ∗100 =74.35% 83507854 8871396 ∗100 =10.61% 83507854 (2967949+9594243) ∗100=15.04 % 83507854 Fraction Two: 4-methylcyclohexanol o Total area: 65277852 + 28379838 + 2508303 = 96165993 Compound 4-methylcyclohexene 1-methylcyclohexene 4-methylcyclohexanol % Composition 65277852 ∗100=67.88% 96165993 28379838 ∗100=29.52% 96165993 2508303 ∗100=2.61% 96165993 In this experiment, all of the methylcyclohexene fractions were contaminated with the starting alcohol. For fraction one of 2-methylcyclohexanol products, alcohol contaminated 20.47%, and for 5 fraction two of 2-methylcyclohexanol products alcohol contaminated 8.8%. In fraction one of 4methylcyclohexanol products, alcohol contaminated 15.04% and for fraction two, alcohol contaminated 2.61%. Discussion: The purpose of this experiment was to confirm the Evelyn Effect and the use of Zatizev’s rule. In this experiment, both 2-methylcyclohexanol and 4-methylcyclohexanol went through a dehydration reaction to yield an alkene. In order to run this reaction, phosphoric acid was first mixed with 2methylcyclohexanol and 4-methylcyclohexanol. Then the two flasks were individually placed in a simple distillation set up. Once distillation began, the first 8 mL and the next 6 mL of alkene were collected in separate test tubes for both alcohols. Sodium bicarbonate was then added to each of the test tubes in order to separate and remove the aqueous layer. The organic layer was then run through gas chromatography in order to determine the composition of each mixture of products. The product distribution does change over time for both 2-methylcyclohexanol and 4methylcyclohexanol. As discussed above, throughout the distillation process two different fractions were collected. Based on the gas chromatography, the first fraction of 2-methylcyclohexanol was composed of 2.33% 3-methylcyclohexene and 77.18% 1-methylcyclohexene. In comparison with the second fraction where the composition changed to 30.78% 3-methylcyclohexene and 54.78% 1-methylcyclohexene. The percent composition of 3-methylcyclohexene increased and the percent composition of 1methylcyclohexene decreased between the two fractions, supporting the Evelyn Effect. Similar trends can also be see in the two fractions of 4-methylcyclohexanol. The percent composition of 4methylcyclohexene decreases from 74.35% to 67.88% between fractions one and two. In addition, the percent composition of 1-methylcyclohexene increases from 10.61% to 29.52% between fractions one and two. Questions: 3. The E1 electron pushing mechanism for dehydration of 2-methylcyclohexanol to 1-methylcyclohexene: 6 The E1 electron pushing mechanism for dehydration of 2-methylcyclohexanol to methylenecyclohexane: The E1 electron pushing mechanism for dehydration of 2-methylcyclohexanol to 3-methylcyclohexene: 4. Most stable chair confirmations of each of the four possible starting materials 7 a. Elimination product of chair structures above For the E2 elimination of trans-2-methylcyclohexanol and trans-4-methylcyclohexanol the major product would be 3-methylcyclohexene. For the 2-methylcyclohexanol, the cis isomer would react quicker than the trans isomer, as it does not require a chair flip, and produces 1-methylcyclohexene. Similarly, or the 4methylcyclohexanol, the cis isomer would react faster than the trans isomer as well. Conclusion: The gas chromatography for 2-methylcyclohexanol and 4-methylcyclohexanol, shows that the product distribution did change between the two portions. As, for 2-methylcyclohexanol, the percent composition of 3-methylcyclohexene increased from 2.33% to 30.78%, and the percent composition of 1- 8 methylcyclohexene decreased from 77.19% to 54.78% between the two portions. Similarly, in two portions of 4-methylcyclohexanol the percent composition of 4-methylcyclohexene decreased from 74.35% to 67.88%, and the percent composition of 1-methylcyclohexene increased from 10.61% to 29.52% between the two fractions. These results suggest that the Evelyn Effect was present in both reactions, as there was a fluctuation in the distribution of products between the two portions. Based on the results of this experiment, both E1 and E2 mechanisms are present in the dehydration of 2-methylcyclohexanol and 4-methylcyclohexanol. The E2 mechanism of the dehydration of 2-methylcyclohexanol could yield 1-methylcyclohexene, 3-methylcyclohexene, and 4methylcyclohexene. In contrast, the E1 mechanism of the dehydration of 2-methylcyclohexanol yields 1methylcyclohexene, 3-methylcyclohexene, and methylenecyclohexane. The cis isomer in the chair confirmation of 2-methylcyclohexanol appears to favor the E2 mechanism to form the more substituted or Zaitsev product, as it is already in the most stable confirmation state. The trans isomer chair confirmation must undergo a chair flip in order to go through an E2 reaction, thus making it the less favorable in comparison to the cis isomer. The favored trans isomer is able to undergo an E1 mechanism. Based on the gas chromatograph for 2-methylcyclohexanol’s, methylene cyclohexene is present. Therefore, verifying the use of both E1 and E2 mechanisms, as the yield of methylenecyclohexane is only possible if the alcohol undergoes an E1 mechanism. Thus, the E2 mechanism is utilized when the cis isomer is used, because the chair confirmation does not have to undergo a chair flip. This accounts for the decreasing ratio of the two products over time and the fluctuation of product distribution between the first and second fractions of both alcohol starting materials.