Lab report 4 experiment 4 PDF

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lab report 4 from 2021 CH237 (organic chemistry LAB I)...

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September 22, 2021 CH-237-014 Lab Report 4 Experiment 4: Dehydration of Methylcyclohexanols Introduction Throughout the dehydration of 2-methylcyclohexane and 4-methylcyclohexane, an alkene and a water molecule are formed. The purpose of the experiment was to verify the presence of the Evelyn Effect in the dehydration of either 2-methylcyclohexanol or 4-methylcyclohexanol by heating alcohol with phosphoric acid. The Evelyn Effect entails a change in the distribution of product throughout the duration of the reaction. In this experiment, the problem at hand is whether the E1 or E2 or a combination of the two mechanisms are utilized in the dehydration of the cis and trans isomers of 2-methylcyclohexanol and 4-methylcyclohexanol. The experiment was conducted by running a dehydration reaction of both 2methylcyclohexanol and 4-methylcyclohexanol with H 3PO4 in order to distill the byproducts and act as a driving force for the reaction, according to Le Chaterlier’s Principle. Two fractions were collected, washed and then gas chromatography was used to determine the identity of the alkene products within each fraction. Results 1.

Theoretical yield of methylcyclohexenes based on the amount of methyl cyclohexanol used. - 2-methylcyclohexanol

(150 mmol cyclohexanol)(1 mol/1000 mmol)(

1 mol cyclohexene 96.2 g methylcyclohexene )=¿ )( 1 mol 1 mol cyclohexanol

14.43 g methylcyclohexene -

4-methylcyclohexanol

(150 mmol cyclohexanol)(1 mol/1000 mmol)( 14.43 g methylcyclohexene

1 mol cyclohexene 96.2 g methylcyclohexene )=¿ )( 1 mol 1 mol cyclohexanol

2.

The percent yield of methylcyclohexene product recovered (total of both fractions). -

(Actual yield)/(Theoretical yield) ✕ 100% = Percent yield

-

Amount used = 14.43 g(18mL)

-

2-methylcyclohexanol Mass of flask 1

Mass of flask 1 + methylcyclohexene (when alkene volume is 8 mL)

Mass of mixture

21.21 g

27.82 g

27.82 g − 21.21 g = 6.61 g

Mass of flask 2

Mass of flask 2 + methylcyclohexene (when alkene volume is 6 mL)

Mass of mixture

22.13 g

25.85 g

25.85 g − 22.13 g = 3.72 g

-

Percent yield = [(6.61g + 3.72 g)/14.43 g] ✕ 100% = 71.58%

-

4-methylcyclohexanol (measurements obtained from classmate)

-

Mass of flasks and mass of flasks +methylcyclohexene pre calculated by the students data I recieved Mass of mixture in flask 1 4.81 g Mass of mixture in flask 2 3.10 g -

Percent yield = [(4.81g + 3.10 g) /14.43 g] ✕ 100% = 54.81 %

3. Boiling range over which the alkenes are distilled. -

2-methylcyclohexanol = 84°C - 100°C

-

4-methylcyclohexanol = 94°C - 106°C

4. Product composition (for both 2-methylcyclohexanol and 4-methylcyclohexanol) -

2-methylcyclohexanol: Fraction 1

➢ Total area = (2076623 + 68716830 + 15559152 + 2667544) = 89020149

-

Compound

% compositions

3-methylcyclohexene

(2076623 / 89020149) ✕ 100% = 2.33 %

1-methylcyclohexene

(68716830/ 89020149) ✕ 100% = 77.19%

2-methylcyclohexanol

(15559152 + 2667544) /89020149 ✕ 100% = 20.47%

2-methylcyclohexanol: Fraction 2

➢ Total area = (44829660 + 8199848 + 79785326 +12818738) = 145633572

-

Compound

% compositions

3-methylcyclohexene

(44829660 /145633572) ✕ 100% = 30.78 %

1-methylcyclohexene

(79785326/145633572) ✕ 100% = 54.78 %

2-methylcyclohexanol

(12818738 /145633572) ✕ 100% = 8.8%

methylenecyclohexane

(8199848/ 145633572) ✕ 100% = 5.63 %

4-methylcyclohexanol: Fraction 1

➢ Total area = ( 62084266 + 2967949 + 8861396 + 9594243) = 83507854

Compound

% compositions

4-methylcyclohexene

(62084266 / 83507854) ✕ 100% = 74.35%

1-methylcyclohexene

(8861396/ 83507854) ✕ 100% =10.61%

4-methylcyclohexanol

-

(2967949 +9594243) /83507854 ✕ 100% =15.04 %

4-methylcyclohexanol: Fraction 2

➢ Total area = ( 65277852 + 28379838 + 2508303) = 96165993

Compound

% compositions

4-methylcyclohexene

(65277852 / 96165993) ✕ 100% = 67.88%

1-methylcyclohexene

(28379838 / 96165993) ✕ 100% = 29.52%

4-methylcyclohexanol

( 2508303 /96165993) ✕ 100% =2.61 %

In this experiment, all of the methylcyclohexene fractions were contaminated with the beginning (starting) alcohol. For the first fraction of 2-methylcyclohexanol products, alcohol contaminated 20.47% , and for fraction two of 2-methylcyclohexanol products, alcohol was shown to contaminate 8.8%. In

fraction one of 4-methylcyclohexanol products, alcohol contaminated 15.04% and for the second fraction of 4-methylcyclohexanol, 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 that yielded an alkene. To perform this reaction, phosphoric acid was mixed with 2methylcyclohexanol and 4-methylcyclohexanol, then the two flasks were placed individually in a simple distillation set up. Once the distillation process began, the first 8 mL and 6 mL of alkene were collected in separate tubes for both alcohols. Next, sodium bicarbonate was added to each of the test tubes in order to separate and remove the aqueous layer. The organic layer was then run through the process of gas chromatography in order to determine the composition of each mixture of products ( this step was provided to the class with previously recorded data from the professor). The product distribution proved to show changes over time for both 2-methylcyclohexanol and 4methylcyclohexanol. As examined in the paragraph above, the distillation process collected two different fractions. Based on the chromatography, fraction one of 2-methylcyclohexanol was 2.33% 3methylcyclohexene and 77.18% 1-methylcyclohexene. In contrast with the second fraction of 2methylcyclohexanol where the composition changed to 30.78% and 3-methylcyclohexene and 54.78% 1methylcyclohexene. The percent composition of 3-methylcyclohexene showed an increase and the percent composition of 1-methylcyclohexene showed a decrease between the two fractions of 4methylcyclohexanol. The percent composition of 4-methylcyclohexene decreased from 74.35% to 67.88% between the fractions of one and two. Furthermore, the percent composition of 1methylcyclohexene increased from 10.61% to 29.52% between the fractions of one and two.

Questions

1. a. Formation of 1-methylcyclohexene starting from 2-methylcyclohexanol

b. Formation of 3-methylcyclohexene starting from 2-methylcyclohexanol

c. Formation of methylenecyclohexane starting from 2-methylcyclohexanol

2.

a. Cis-2-methylcyclohexanol (E2)

b. Trans-2-methylcyclohexanol (E2)

c. cis-4-methylcyclohexanol (E2)

d.

Trans-4-methylcyclohexanol (E2)

Below are the less stable conformations for the E2 mechanism e. Trans-2-methylcyclohexanol - less stable chair conformation (E2)

f.

Trans-4-methylcyclohexanol - less stable chair conformation (E2)

4-methylcyclohexanol The cis-4-methylcyclohexanol would react faster sa the most stable chair conformation, due to the fact that it allows an E2 product to be produced. The trans isomer has to react in the less stable chair conformation, which allows an unfavorable chair flip to progress through the E2 mechanism. 2-methylcyclohexanol The cis-2-methylcyclohexanol product would react faster; when it is the cis isomer it is the most stable conformation. The trans isomer would react slowly because it only goes through the E2 mechanism in the less stable chair conformation. There is in fact a strain for this chair conformation because it has to reveal an unfavorable chair flip to go through the E2 mechanism. Conclusion

Within the reaction there is a reliance on time, which is necessary in order to acquire a higher amount of the 1-methylcyclohexene product. As the time is increased the ratio of the 1methylcyclohexene to the other alkenes in this reaction is decreased.According to the results obtained by the class in the gas chromatography for 2-methylcyclohexanol and 4-methylcyclohexanol, it is clear that the product distribution did change between the two portions. The 2-methylcyclohexanol, the percent composition of 3-methylcyclohexene increased from 2.33% to 30.78%, and the percent composition of 3methylcyclohexene decreased from 77.19% to 54.78% between the two portions. Likewise, in two portions of 4-methylcyclohexanol the percent decomposition 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. The results obtained suggest that the Evelyn Effect was present in both reactions, because there was a fluctuation within the distribution of products between two portions. Based on the results of this experiment, both E1 and E2 mechanisms are proven to exist in the dehydration of 2-methylcyclohexanol and 4-methylcyclohexanol. The E2 mechanism of the dehydration of 2-methylcyclohexanol was able to yield 1-methylcyclohexene, 3-methylcyclohexene and 4methylcyclohexene. In comparison, the E1 mechanism of the dehydration of 2-methylcyclohexanol yields 1-methylcyclohexene, 3-methylcyclohexene, and methylenecyclohexene. The cis isomer in the chair conformation of 2-methylcyclohexanol seems to favor the E2 mechanism in order to form the more Zaitsev or substituted product, seeing that it is already in the most stable conformation state. For the trans isomer chair conformation, it has to go through a chair flip to be able to go through an E2 reaction, hence making it the less favorable isomer in contrast to the cis isomer. The trans isomer that is favored is enabled to undergo the E1 mechanism. Observing the gas chromatograph for 2-methylcyclohexanol, methylenecyclohexene is present. This observation verifies the use of both E1 and E2 mechanisms, due to the yield of methylenecyclohexane being only possible if the alcohol goes through an E1 mechanism. Therefore, the E2 mechanism is put to use when the cis isomer is used, as the chair conformation is not required to undergo a chair flip. This vindicates for the decreasing ratio of the two products over a period

of time and the variation or changes of product distribution between the first fraction and second fractions of both alcohol starting materials....