Lab Report Chemistry 341L: Preparation of Cyclohexene

Introduction: The purpose of this lab was to prepare an alkene, cyclohexene, by the dehydration of an alcohol, cyclohexanol. In this experiment cyclohexanol is dehydrated to prepare cyclohexene, using phosphoric acid as a catalyst. Unsaturation tests are then done to ensure cyclohexene was prepared.
Experimental Scheme: The procedure for the Preparation of Cyclohexene lab started with first having to add 10mL of cylcohexanol (clear liquid with strong odor), and 2.5mL of phosphoric acid (clear liquid) to a 50-mL round bottom flask. These liquids were mixed together well; a boiling stone was added to the flask in order to allow for a smoother and gentle boil. Below is the equation for the reaction that took place in this lab.
Equation 1: Formation of the product cyclohexene, from the reactant cyclohexanol with the aid of a catalyst phosphoric acid4

Next a distillation apparatus had to be assembled, using a 25-mL round bottom flask as a receiving flask, this flask was then placed into a beaker of ice water refer to figure 1.
Figure 1: Distillation apparatus5 Distillation is used in order to dehydrate the cyclohexanol. After the apparatus was assembled we circulated the cooling water in the condenser, while heating the mixture in the flask. The flask was heated until the product started to distill, and collect into the receiving flask in the ice water bath. We continued to heat the mixture, making sure the temperature did not exceed 100°C; distillation occurred until no more liquid remained in the flask. After distillation was done the receiving flask contained cyclohexene, water, and phosphoric acid. Now that distillation was done it was now time to saturate the distillate with the help of sodium chloride. We added salt little by little until the salt no longer dissolved; once the salt no longer dissolved we added enough saturated aqueous sodium carbonate solution to make our distilled solution basic to litmus. This was done in order for us to be able to test the pH of our solution, which came out to be around the neutral range.
The mixture now had to be separated into two separate layers, using a separatory funnel. We poured the solution into the funnel and allowed the layers to separate out; the aqueous layer (bottom layer) was then drained out through the stopcock. The cyclohexene (top layer) was poured out through the top of the funnel into a pre-weighed 50-mL Erlenmeyer flask, or in my group’s case a 10-mL Erlenmeyer flask. We also took what we could get out of the condenser tube, to get as much cyclohexene as possible. Once the cyclohexene was poured into the Erlenmeyer flask it was then dried with anhydrous sodium sulfate, until the liquid took on a snow globe type of appearance. Unsaturation tests were done next to confirm that what we had was actually an alkene. In two test tubes we placed 4-5 drops of cyclohexanol, and onto two separate watch glasses we placed the little amount of cyclohexene we prepared. Next we added 2-3 drops of a solution of bromine in carbon tetrachloride to one of the test tubes, and one of the watch glasses. The other test tube, and the other watch glass were tested with a solution of potassium permanganate and again 2-3 drops were added. Potassium permanganate, however, is not miscible with organic compounds so we had to add 0.3mL of 1,2-dimethocyethane to the test tube and watch glass before we added the potassium permanganate. Next was to do another distillation but my group was not able to do it, because of the little amount of cyclohexene we recovered. What we did before our unsaturation tests was, weigh the liquid that was in the 10-mL Erlenmeyer flask that we transferred our cyclohexene into. Weighing this is what allowed us to determine how much cyclohexene we had prepared, and then we calculated our percent yield.2
Equation 2: % yield equation6
% yield = (actual yield / theoretical yield) x 100
Data: Table 1: Chemical Table3 Name | Formula | MW (g/mol) | Amount | State | Density (g/mL) | MP (°C) | BP (°C) | Moles | Hazards | Cyclohexanol | C6H12O | 100.16 | 10.0mL | L | 0.948 | 26 | 161 | .0946 | Skin, eye, nose irritant | Phosphoric acid | H3PO4 | 98 | 2.5mL | L | 1.685 | 42.35 | 158 | .043 | Burns skin and eyes, irritant to nose | Water | H2O | 18.02 | - | L | 1.00 | 0 | 100 | - | None | Sodium Chloride | NaCl | 58.44 | - | S | - | 801 | 1,413 | - | Ingestion may cause nausea | Sodium Carbonate (aq) | Na2CO3 | 105.99 | - | S | - | 851 | 1,633 | - | Eye, skin, nose irritant | Anhydrous sodium sulfate | Na2SO4 | 142.04 | - | S | - | 884 | 1,429 | - | Skin, eye, nose irritant | Potassium Permanganate | KMnO4 | 158.03 | - | L | 1.00 | 240 | - | - | Severly burns skin & eyes | 1,2-dimethoxyethane | C4H10O2 | 90.12 | 0.3mL | L | 0.867 | -58 | 85 | .003 | Skin and eye irritant | Carbon tetra-chloride | CCl4 | 153.82 | - | L | 1.594 | -23 | 76.77 | - | May cause irritation and headache | Bromine | Br2 | 159.81 | - | L | 3.119 | -7.2 | 58.8 | - | Corrosive to tissue, very toxic! | Cyclohexene | C6H10 | 82.143 | - | L | 0.811 | -104 | 83 | - | Skin, eye, nose irritant |

Theoretical yield: Moles of cyclohexanol X molecular weight of cyclohexene 1 mol of cyclohexanol .0946 C6H12O X 82.143gC6H10 = 7.77g (theoretical yield of cyclohexene) 1molC6H12O

There were many observations and recordings that were made in this experiment. First off during the distillation when we were heating the flask, the ending temperature was around 68°C. When it was time for us to transfer our cyclohexene to the 10-mL Erlenmeyer flask, the weight before the transfer was 14.72g, and the weight after we transferred the cyclohexene into the flask was 14.82g. We then subtracted 14.72g from 14.82g to find what our actual yield was; our actual yield of cyclohexene that we recovered was .10g. Next we used equation 2 below to find out what our % yield was.
Equation 2:
% yield = (actual yield / theoretical yield) x 100
% yield =(.10g/7.77g) x 100 = 1.29% percent yield of cyclohexene

Discussion:
The overall aim of the experiment was to produce cyclohexene from cyclohexanol. Both compounds are six carbon structures, however, the presence of the hydroxyl group in cyclohexanol is the major difference between the two. Sodium chloride, which had a small, white grainy appearance, was used to saturate the distillate; and then sodium carbonate, a clear liquid, was used to make the solution basic to litmus, this allowed us to then test the pH of the solution, which ended up being neutral. The dehydration process removes the hydroxyl group and this then forms cyclohexene; Dehydration is a process by which water is lossed from a molecule, during the experiment, anhydrous sodium sulfate (white, fluffy powder) was used as the dehydrating agent. It worked by binding itself to the water molecules in order to ensure that pure cyclohexene could be obtained, phosphoric acid was used as a catalyst in this reaction. After the dehydration process was completed, unsaturation tests were done to confirm that we were able to obtain pure cyclohexene.
The unsaturation tests consisted of using bromine and potassium permanganate solutions. During the bromine test the color changed from reddish-orange to a faint yellow color; and the potassium permanganate, which was a purple color turned brown when added to the cyclohexene. We were able to confirm that was we had on the watch glasses was cyclohexene from the help of these tests. We were not able to get a very large percent yield; we ended up getting a yield of 1.29%. We also had to stop the reaction early due to time restraints; this definitely is a source of error that did not allow us to recover our entire product. Stopping this early also prevented us from being able to get a boiling point range for the reaction. Other sources of error could come from some spillages of the solutions we had to add to the reaction; solutions such as sodium carbonate and the sodium sulfate. Another source of error could have come from our condenser, which was not rinsed prior to doing this experiment. Ways to prevent these errors would be to make sure to handle materials carefully, and cleanse materials before starting the experiment. Overall we were able to confirm that we had in fact produced cyclohexene just not a large amount of it. This experiment was a success I believe in the aspect of producing cyclohexene, not in the aspect of the amount we recovered. If we would have produced a larger amount it would have been better, but still overall experiment was a success!

Questions: 2) What alkene would be produced on dehydration of each of the following alcohols? a. 1-Methylcyclohexanol methylene cyclohexene; 1-methyl-1-cyclohexene b. 2-Methylcyclohexanol methylcyclohexene c. 4-Methylcyclohexanol 3-hexanol; 2-pentanol d. 2,2-Dimethylcyclohexanol 1,2-methylcyclohexene e. 1,2-Cyclohexanediol cyclohexanone (hydride migration, tautomerization)

4) What is the purpose of adding the sodium carbonate solution? Give and equation. - The phosphoric acid that is used as a catalyst in this experiment co-distills with the products. What this means basically is that two substances will distill together; Cyclohexanol distilled with phosphoric acid will cause the cyclohexene (major product) and water (minor) to distill together. We don’t want this so we add sodium carbonate to wash the distillate mixture.

References:

1) Lab Manual:
Pavia, D. L; Lampman, G. M; Kriz, G. S
Preparation of Cyclohexene
Organic Chemistry Laboratory Manual, edition 3,
Radke, Karla; Stolzenber, Gary; Eds;
Cengage Learning: Mason, OH, 2008, 35-37.

2) Lab Procedure:
Pavia, Donald. L; Lampman, Gary. M; Kriz, George. S
Isolation of Caffeine from Coffee
Organic Chemistry Laboratory Manual, edition 3,
Radke, Karla; Stolzenber, Gary; Eds;
Cengage Learning: Mason, OH, 2008, 36-37.

3) Table 1:
Sigma-Aldrich. http://www.sigmaaldrich.com/united-states.html (accessed Nov 4, 2014).

4) Equation 1:
Pavia, D. L; Lampman, G. M; Kriz, G. S
Preparation of Cyclohexene
Organic Chemistry Laboratory Manual, edition 3,
Radke, Karla; Stolzenber, Gary; Eds;
Cengage Learning: Mason, OH, 2008, 35.

5) Figure 1:
Chromic. Distillation of Safrole. https://www.erowid.org/archive/rhodium/chemistry/safrole.distillation.html (accessed Nov 4, 2014)

6) Equation 2:
Yield. Chemistry Tutorial : Calculations, http://www.ausetute.com.au/yield.html (accessed Oct 1, 2014).