Dehydration of 2-Methylcyclohexanol PDF

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Lab report regarding alkene by elimination...

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Dehydration of 2-Methylcyclohexanol Synthesis, Distillation and Gas Chromatography.

Name: Cristian Acuna Vasquez Date : November 3rd, 2020 Class: CHM 2210 L Professor: Dr. Rajendra Shakya

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Purpose The purpose of this the experiment is to dehydrate 2-methylcyclohexanol. Introduction There are two main ways to produce alkenes by elimination reactions. A dehydration of an alcohol and dehydrohalogenation of an alkyl halide will lead to unsaturated products. Dehydration of an alcohol will proceed in a highly acidic environment, while strongly alkaline conditions are necessary for the dehydrohalogenation of an alkyl halide. Zaitsev’s rule will dictate the way the elimination will be governed; This rule states that the most highly substituted alkene will be formed preferentially. They proceed by completely different mechanisms. In this experiment, we will performing a dehydration of an alcohol; The first step is the protonation of the OH substituent, resulting in the conversion of a poor leaving group, OH-, into a very good leaving group, H2O. The protonated alcohol can undergo elimination by E1 which is first order. The E1 mechanism, a unimolecular elimination of water will result in an alkyl cation, which then eliminates a proton. In this lab, 2-methylcyclohexanol will react with phosphoric acid to yield 1methylcyclohexene , 3-methylcyclohexene and water. We will pay attention to technique since there is no such thing as 100% yield. Materials : Fractional distillation apparatus, column, round bottom flask, graduated cylinder, water, heating mantle, boiling chips, aluminum foil, thermometer, rubber hose, packing material, 10 mL 2Methylcyclohexanol, 3 mL 85% phosphoric acid, calcium chloride pellets, sodium hydroxide, pH paper, cyclohexene, bromide, potassium permanganate, separatory funnel, Erlenmeyer flask.

3 Procedure: A fractional distillation apparatus was assembled and then 10 mL of 2-methylcyclohexanol into a 50 mL round-bottom flask. Then 3 mL of 85% of phosphoric acid were added as well as several boiling stones. The flask was attached to the distillation apparatus and heated slowly with the heating mantle. It continued to distill until around 9-10 mL of liquid was collected. The flask with the distillate was placed to the side. The round-bottom flask was diluted with soap and water to prevent it from solidifying when it cools. The distillate was transferred to a separatory funnel with some water to complete the transfer. The water layer was drawn down and then the acidity was tested with pH paper. Since acid was present, the product layer was washed with 3 mL of 10% sodium hydroxide solution and followed by 5 mL of water. It was then transferred to an Erlenmeyer flask and then the remaining water was removed by adding anhydrous calcium chloride pellets and swirling the flask. Then it was decanted and weighed to determine the grams of product obtained. Then the IR of it was taken. In addition, unsaturation tests were performed on the products and starting materials. 4- 5 drops of methyl cyclohexene product and 2methylcyclohexanol were each placed in two clean test tubes. Then it was added bromine and potassium permanganate to the test tubes. Table of reagents 1. Calcium chloride Formula: CaCl2 MW: 110.98 g/mol MP: 772 to 775◦C BP: 1935◦C Density: 2.15 g/cm3 Physical Description: white powder 2. 2-Methylcyclohexanol Formula: C7H14O MW: 114.18 g/mol MP: -9.5◦C BP: 166◦C

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Density: 0.93 g/cm3 Physical Description: colorless liquid Phosphoric Acid Formula: H3O4P MW: 97.99 g/mol MP: 42.35◦C BP: 158◦C Density: 1.685 g/mL Physical Description: white solid Sodium hydroxide Formula: NaOH MW: 39.99 g/mol MP: 318◦C BP: 1388◦C Density: 2.13 g/cm3 Physical Description: white waxy crystals Potassium permanganate Formula: KMnO4 MW: 158.034 g/mol MP: 240◦C BP: N/A Density: 2.703 g/cm3 Physical Description: pink liquid Bromine Formula: Br MW: 79.90 g/mol MP: -7.9◦C BP: 58.8◦C Density: 3.1028 g/cm3 Physical Description: reddish brown liquid

Data and Observations: In the first part of the experiment, the fractional distillation began around 79◦C. Weight of the product obtained: 6.93 g Unsaturation Test: The first test tube with the cyclohexene turned yellow after bromine was added but then It decolorized as soon as the test tube was shaken. The second test tube was supposed to be with potassium permanganate but the video did not show it.

5 Boiling point range of the product: 82 C to 83 C Mass of empty round bottom flask: 135.35 g Mass of flask plus t-amyl chloride: 142.28 g Weight of product : 6.93 g Theoretical yield Density of 2-methylcyclohexanol = 0.93 g/mL M= ( 0.93 g/mL) ( 10 mL) = 9.3 g 2-methylcyclohexanol MM of 2-methylcyloxanol = 114.19 g/mol 9.3g C7H14O ×

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0.0814 mol C5H12

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= 0.0814mol C7H14O X

96.17g""C7H12"

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= 0.0814 mol C5H12

= 7.83 g C7H12

Found in product : 6.93 g 9.,:

Percent yield " '.;: X 100 88.5 %

Discussion: Dehydration of substituted alcohols produces a mixture of isomeric alkenes. In this experiment, refluxing 2-methylcyclohexanol in the presence of phosphoric acid gives 1-methylcyclohexene as a major product, 3-methylcyclohexene as a minor product. The product ratios in this elimination reaction are determined by several factors. In this lab, the higher yield is 1methyl cyclohexene over 3-methylcyclohexene and arises from the greater thermodynamic stability of the more highly substituted alkene. The rule that "the alkene formed in greatest amount is the one that corresponds to the more highly substituted double bonds are usually more stable alkene; this is known as the Zaitsev's rule. Thus, if Zaitsev’s rule is followed for the

6 dehydration of 2-methylcyclohexanol, then 1-methylcyclohexene would be the favored product. In the second part of the experiment with the unsaturation test, when bromine was added and it’ll go across the double bond and become a different compound. The yellow color not appearing anymore means there’s no more double bond. The IR spectrum of 2-metylcylocehexanol has a distinct OH bond show left hand side with wide band at 3368.67. On the other hand, this peak will be absent from IR spectrum from pure alkene The IR spectrum of the product contains a sp2 stretch around 3001.87cm-1. This peak is not always clear. A C=C stretch may also be observed around 1672.77cm-1. The experiment percentage yield was approximately 88.5 % which is due to manipulations where mechanical loss of product could have occurred while transferring products from glassware and during the filtration part. Also spillage, evaporation and probably drops lefts in pipettes. IR- image of the product – 1-methyl cyclohexene

IR- image of the reactant– 2-methyl cyclohexanol

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Conclusion: This experiment was useful to understand how alkenes are produced by an elimination reaction. Preparations include the dehydration of alcohols, the dehydrohalogenation of alkyl halides, and the dehalogenation of alkanes. In dehydration reactions, a molecule of water is eliminated from an alcohol molecule by heating the alcohol in the presence of a strong acid. A double bond forms between the adjacent carbon atoms that lost the hydrogen ion and hydroxide group. The Zaitsev rule can predicts that the major products resulting from the reaction are the alkene that are more substituted . Post Lab questions: 1. Why was it necessary to wash the crude methylcyclohexanes with aqueous sodium bicarbonate solution?

8 It is important to wash the product with sodium bicarbonate solution in order to neutralize any acid that may be left contaminating the product. 2. List the manipulations where mechanicals loss of product could have occurred? The manipulations where mechanical loss of product could have occurred while transferring products from glassware and during the filtration part. Also spillage, evaporation and probably drops lefts in pipettes.

3. Identities of the components in a mixture may be determined by a technique called spiking. Supposed you had run gas chromatography on your product and had then deliberately added a drop of knows sample of 3-methylcyclohexene to a drop of your products. what would you expect the new chromatography to show you?

The dehydration of 2-methylcyclohexanol gives a mixture of 1-methylcyclohexene and 3 methyl cyclohexene, with the expectation that 1-methylcyclohexene (the more substituted double bond) is the major product. In any case, a chromatogram will show you two products, but doesn't tell you anything about their identities, only relative amounts.

4. Do you consider this a good preparative procedure for making 3-methylcyclohexene ? why? It is not a good method to make 3-methylcyclohexene from dehydration of 2methyl cyclohexanol. If substrate undergoes dehydration two products are possible. One is highly substituted alkene and the other one is less substituted alkene. The highly substituted alkene is more favorable based on Zaitsev’s rule, which will be 1methyl cyclohexene, not 3-methylcyclohexene....