rp5a - preparing cyclohexene by the dehydration of cyclohexanol and to distil the cyclohexene from the reaction mixture

describe the method for the dehydration of cyclohexanol to form cyclohexene:

in a fume cupboard:

1. pour approx 20 cm³ of cyclohexanol into a weighed 50 cm³ pear shaped flask

2. reweigh the flask and record the mass of cyclohexanol

3. using a plastic graduated dropping pipette add approx 8 cm³ conc phosphoric acid to the flask, with frequent shaking

4. add a few anti bumping granules to the flask and assemble the semi micro distillation apparatus so that the contents can be distilled

5. gently heat the flask, distilling over any liquid which boils below 100^oC

6. pour the distillate into a separating funnel and add 50 cm³ of saturated sodium chloride solution, before shaking the mixture, allowing the two layers to separate

7. carefully run off the lower layer into a beaker (for later disposal) and then transfer the upper layer, containing the crude cyclohexene, into a small conical flask

8. add a few lumps of anhydrous calcium chloride to the crude cyclohexene to remove water - stopper the flask, shake the contents and allow this to stand until the liquid becomes clear

9. decant the liquid into a clean, dry, weighed sample container

10. reweigh the container, calculate the mass of dry cyclohexene produced and determine the % yield of your product

11. test the distillate as described below to confirm it contains an alkene

how can we test the product to confirm that it contains an alkene?

• bromine water test: orange → colourless

• acidified potassium manganate test: purple → brown precipitate

name 7 hazardous materials involved in rp5a and explain why they are hazardous:

• cyclohexanol - skin/eye/respiratory irritant

• anhydrous calcium chloride solution - eye irritant

• potassium manganate (VII) solution - eye/skin irritant and stain to skin/clothing

• dilute sulfuric acid - potential eye/skin irritant

• concentrated phosphoric acid - corrosive to eyes/skin

• cyclohexene - eye/skin irritant, highly flammable

• glassware/apparatus - if broken, sharp edges could cut skin, chemicals could be released if apparatus insecure

how can we use control measures to decrease the risks presented by cyclohexanol?

wear gloves, lab coat and goggles to prevent irritation

how can we use control measures to decrease the risks presented by anhydrous calcium chloride solution?

wear goggles to prevent irritation

how can we use control measures to decrease the risks presented by potassium manganate (VII) solution?

wear gloves, lab coat and goggles to prevent irritation/staining

how can we use control measures to decrease the risks presented by dilute sulfuric acid?

wear gloves, lab coat and goggles to prevent irritation

how can we use control measures to decrease the risks presented by concentrated phosphoric acid?

wear gloves, lab coat and goggles to prevent irritation

how can we use control measures to decrease the risks presented by cyclohexene?

wear gloves, lab coat and goggles to prevent irritation

how can we use control measures to decrease the risks presented by glassware/apparatus?

• ensure any joints in apparatus are secure so that volatile chemicals are not released when the reaction occurs

• add reactants to reaction flask slowly with cooling to prevent dangerous splashing

• use of anti bumping granules to prevent formation of large bubbles and so bumping/breaking of glassware