Cyclohexene (boiling point = 83∘C83^\circ\text{C}83∘C) can be prepared by the dehydration of cyclohexanol (boiling point = 161∘C161^\circ\text{C}161∘C) using concentrated sulfuric acid as a catalyst:
C6H12O→H2SO4C6H10+H2O \text{C}_6\text{H}_{12}\text{O} \xrightarrow{\text{H}_2\text{SO}_4} \text{C}_6\text{H}_{10} + \text{H}_2\text{O} C6H12OH2SO4C6H10+H2OA student prepared cyclohexene by placing 12.5 cm3 of cyclohexanol (density = 0.96 g cm-3) into a round-bottomed flask. Next, 4 cm3 of concentrated sulfuric acid and a few anti-bumping granules were added. The mixture was heated, and the fraction distilling below 95∘C95^\circ\text{C}95∘C was collected.
The distillate was washed in a separating funnel with sodium hydrogencarbonate solution, periodically venting the funnel, and the aqueous layer was discarded. The organic product was dried using anhydrous sodium sulfate and then filtered under reduced pressure.
Answer the following questions about this preparation:
The student collected 6.50 g of purified cyclohexene. Calculate the percentage yield of cyclohexene to three significant figures.
Describe a test-tube reaction on the cyclohexene product to show that the cyclohexanol had been successfully dehydrated, and state the observation.
Suggest why sodium hydrogencarbonate solution was used to wash the distillate.
Explain why it is important to open the tap of the separating funnel periodically during the washing process.
Give one property of anhydrous sodium sulfate, other than its ability to absorb water, that makes it suitable as a drying agent in this preparation.
The cyclohexene was analytical-grade pure except for a trace contamination of cyclohexanol. They can be separated by column chromatography using silica gel as the stationary phase and cyclohexane as the mobile phase. Explain why cyclohexene has a shorter retention time than cyclohexanol.
Explain how an infrared (IR) spectrum would confirm that the cyclohexene obtained did not contain any cyclohexanol.
