Dehydrating Cyclohexanol Essay
The purpose of the lab experiment is to prepare cyclohexene from cyclohexanol through an acid-catalyzed dehydration. In order to produce the cyclohexene from cyclohexanol, an elimination reaction was performed. First by protonating the oxygen of the alcohol and creating an oxonium ion we replaced the poor leaving group (OH) into a better leaving group (OH2+). Second, dehydrating the cyclohexanol using phosphoric acid and sulfuric acid as acid catalysts and heat to create a charged carbocation which then creates the carbon-carbon pi bond of cyclohexene from the release of a proton that is adjacent to the positively charged carbon.
As a result we were able to distill a total of 2. 5098 grams of cyclohexene •Reaction Scheme and/or structure of compounds used Compounds used: Cyclohexanol Molecular formula: C6H12O Molar Mass: 100. 158 g/mol Density: . 962 g/ml, liquid Melting point: 25. 93 C Boiling point: 160. 84 C Phosphoric Acid Molecular Formula: H3PO4 Molar Mass: 97. 995 g/mol Density: 1. 885 g/mL , liquid Melting point: 42. 35 C (anhydrous) Boiling point: 158 C (decomp) Sulfuric Acid Molecular Formula: H2SO4 Molar Mass: 98. 079 g/mol Density: 1. 84 g/cm3 Melting point: 10 C Boiling point: 337 C •Results and Discussion:
To begin the procedure of dehydrating cyclohexanol into cyclohexene, we assembled a simple distillation apparatus, using a heating element that did not include a flame. The reason behind this is because the cyclohexene is highly flammable, so as to remove any unnecessary risk we used a heating pad. We then created our cyclohexanol mixture of cylcohexanol (6mL), sulfuric acid (10 drops), phosphoric acid (8 mL), and a boiling cheap which we then used on our apparatus. We heated the mixture to no more than 88 C so as to be sure we distilled all the cyclohexene, and not the phosphoric, sulfuric, and cyclohexanol.
Having distilled our mixture to a temperature of 88 Degrees Celsius we then took our receiving round bottom flask (which has been cooled with ice on the distillation apparatus) and pipetted as much water out as possible. This was possible due to the fact that cyclohexene is a non-polar, hydrophobic hydrocarbon, so that we see a distinct separation of it and the water. Having pipetted as much water out possible, the next step was to add the calcium anhydrous to the cyclohexene mixture to get out the rest of the water.
Lastly, we weighed our solution with the flask (having previously weighed the flask when it was empty) to find out how much of the cyclohexene was distilled from our cyclohexanol solution. Our results were as followed: Erlenmeyer flask empty : 23. 6022g Erlenmeyer flask with cyclohexene: 26. 112g Because the above reaction yields one product from one reactant. The balanced reaction is a 1:1 ratio of cyclohexanol to cyclohexene and since there is only one reactant, the limiting reagent is the cyclohexanol.
Moles cyclohexanol = (6mL x . 962g/mL)/100. 58g/mol = . 057629 mol Theoretical yield of cyclohexene: . 057629mol x 82. 143g/mol =4. 7338g Actual Yield: 2. 5098g Percent yield: 2. 5098g/4. 7338g x100 = 53% yield. Reasoning for such a small yield could include the idea that the cyclohexanol was not 100% pure. Another explanation could be that we did not distill the mixture long enough, or that when we pipetted the water from the receiving flask, we accidentally also pipetted some of the product. •Conclusion:
This lab was a helpful real life application of an elimination learned in Organic Chemistry I. The protonation of an OH group, into a better leaving group and then removing the water to produce 2-methyl-2-butene and 2-methyl-1-butene with a majority of it being 2-methyl-2-butene due to Saytzeff’s rule which states that the orientation of the double bond favors the more thermodynamically stable alkene, in other words, the alkene with the most alkyl groups bonded to the carbons of the double bond.
The results of the experiment did not completely uphold the theory of the balanced equation that one mole of cyclohexanol would create one mole of cyclohexene. Our experimental data yielded only 53% of the initially theorized 4. 733grams. Questions: 1. Calculate the percent yield that you obtained in this experiment. Please see above 6. 1-methylcyclohexene according to Saytzev’s rule.