ABSTRACT: To extract an alkene from an alcohol, acid-catalysed dehydration process is conducted. effective dehydrating agent; phosphoric acid, and sulphuric acid, is required to remove the hydroxyl group from the cyclohexanol in order to produce cyclohexene. The product obtained from the distillation process is added with a salt solution due due to its volatility. It is then dried and distilled.
RESULTS AND DISCUSSION : MW (g)
Mass (g)
Volumes (mL)
Num. of moles
100 82
6.4425 2.6485
7.5 -
0.0722 0.0323
Cyclohexanol Cyclohexene
Process Cyclohexanol + KMn
Cyclohexanol +
Observation Purple colour of the potassium permanganate solution turns to brown precipitate. Take a long time. Brown colour of the bromine water turns to colourless. Take a long time.
Cyclohexene + KMn
Purple colour of the potassium permanganate solution turns to brown precipitate. Take a short time.
Cyclohexene +
Brown colour of the bromine water turns to colourless. Take a short time.
Density (g/mL) 0.962 0.811
Equation (CH2)5CHOH (CH2)5C=O KMnO4 C6H10
C6H10(OH)2 KMnO4
(CH2)5CHOH + Br 2 (CH2)5CBr 2 + H2O
C6H10 + Br 2
C6H10Br 2
From the experiment cyclohexanol undergoes acid-catalysed dehydration to give cyclohexene. Phosphoric acid, and sulphuric acid, act as the dehydrating agent to remove the hydroxyl group from the cyclohexanol and formed cyclohexene. The reaction occurs is as the following below:
OH
/ +
In the presence of strong acid, an alcohol can be dehydrated to form an alkene. The acid used in this experiment is 85% phosphoric acid and the alcohol is cyclohexanol. Based on the experimental result, the theoretical yield obtained for the cyclohexene produced is 5.9204 g. The percent yield calculated is 44.74 %. For the second part of this experiment was the unsaturation test. When 5 drops of potassium permanganate solution is added to cyclohexanol, the purple colour of the solution turn to brown precipitate after quite a long time. Meanwhile when the potassium permanganate solution is added to cyclohexene, the purple colour of the solution turn to brown precipitate and it take shorter time. Cyclohexanol solution turns colourless when bromine water is added into it after a long period of time. When the bromine water is added into the cyclohexene, the brown solution turns to colourless and it takes shorter time. This is because cyclohexanol and cyclohexene are unsaturated hydrocarbon. As most of organic substances are flammable and volatile, they should be handled in a well-ventilated area to prevent naked flame from reaching the chemicals or its vapour. In this case, heating is used to increase the reaction rate, so reflux setup should be employed. A stopper should be keep handy in case to stop the chemical from evaporating. Rubber gloves should be wore when handling the corrosive or highly acidic chemicals such as the concentrated sulphuric acid and phosphoric acid mixture, to avoid any unwanted injuries in case of spillage, a pipette or a dropper is recommended for the transfer of such chemicals in a specific amount. The handling of such corrosive chemical waste should alwa ys follow strict rules to avoid accidents or environmental pollution. Cleaning of synthesis involved apparatus is difficult even with the use of detergent, only organic substances are remained on the surface of glassware. From the experience gained, the apparatus should be washed with water and detergent, followed by an organic solvent which could completely evaporate. Acetone is the best choice as it is a common solvent for the most organic solvent and it is miscible with water.
EXPERIMENTAL : Step I - 7.5 mL of cyclohexanol into is measured into 100.0 mL round-bottom flask. Carefully, 2 mL of 85% phosphoric acid; H 3PO4, 30 drops of concentrated sulphuric acid and the glass bead is added and the flask is then mounted for simple distillation. Mixture is heated until it comes to a gentle boil. After 10 minutes of gentle boiling, the heat is increased sufficiently to cause distillation (the temperature of the distilling vapor should not exceed 100oC) and the distillate is collected in a clean 100 mL round bottom flask that was immersed in ice water bath.
Distillation set- up
To the distillate, 2 mL of sodium chloride is added to avoid the product from vapourized. The liquid is then transferred into a separatory funnel. The mixture is swirled gently and the lower aqueous layer is drained off. The upper organic layer is poured into a small, dry 50mL Erlenmeyer flask, and dry it over granular anhydrous sodium sulphate (add about on tea spoon) for 5 to 10 minutes with a cover. Step II - The dried cyclohexene is decant into a small round bottom flask and then attached it to a simple distillation assembly, and distill carefully. Step III – Use 4-5 drops of product in two small test tubes and test with drop-wise bromine (decoloration) and drop-wise potassium permanganate (dark brown precipitate) for purity and identification of alkene. This step is repeated by using the cyclohexanol.
REFERENCES : 1. Solomons and Fryhle. 10 th Edition. Organic Chemistry. Wiley 2011 2. https://www.lookchem.com 3. Synthesis of Cyclohexene The Dehydration of Cyclohexanol http://www.chem.umass.edu/-samal/269/cyclohexene.pdf 4. Synthesis of Cyclohexene from Cyclohexanol by (E1) Elimination http://academic.keystone.edu/JFalcone/SynthesisCyclohexene.htm
