Oranges, lemons, grapefruit and limes - discover more than just the fruits from which we find limonenes
Peel away the mysteries of this pant oil in a comprehensive class practical. Students can distil plant oils from oranges and discover the role of limonene in these fruits.
Equipment
Apparatus
- Eye protection
- Grater
- Bunsen burner
- Heat-resistant mat
- Tripod and gauze
- Orange x 2
- Thermometer up to 110°C
- Measuring cylinder, 100 cm3
- Measuring cylinder, 50 cm3
- Round bottomed flask, 250 cm3
- Still head
- Thermometer pocket
- Condenser
- Receiver adapter
- Test tubes and bungs x 3
- Dropping pipette
- Anti-bumping granules
Chemicals
- Bromine water, no more than 0.2% v/v
- Potassium manganate(VII), 0.001 M
- Cyclohexene
- Distilled water, 100 cm3
Health, safety and technical notes
- Read our standard health and safety guidance.
- Always wear eye protection.
- Always wear gloves when handling cyclohexene.
- Always use a gauze on the tripod or the orange will burn.
- Cyclohexene is Highly flammable, Harmful if swallowed and Toxic in contact with skin and cyclohexane is Highly flammable and a skin and respiratory irritant.(see CLEAPSS Hazcard HC045c).
- Bromine water is toxic and irritant. The concentration should not exceed 0.2% v/v.(see CLEAPSS Hazcard HC015b).
- 3 0.001M potassium manganate(VII) solution is of low hazard. This is a substitute for bromine water for student use (see CLEAPSS Hazcard HC081).
See below for the appropriate construction of a limonene distillation apparatus.
Procedure
Stage 1
- Grate the outer orange coloured rind of two oranges and add to 100 cm3 of distilled water in the 250 cm3 round bottomed flask. Add anti-bumping granules to the round bottomed flask.
- Set up the distillation apparatus as shown above.
- Heat the flask so that distillation proceeds at a steady rate, approximately one drop per second of distillate. (Note: Take care not to let the liquid in the round bottomed flask boil too strongly).
- Collect approximately 50 cm3 of distillate in the measuring cylinder. The oil layer will be on the surface.
- Using a dropping pipette, carefully remove the oil layer into a test tube for the next stage.
Stage 2
Odour
- Cautiously smell the extracted oil by wafting the fumes towards the nose. Do not breathe in directly from the test tube.
Action of bromine water
- Measure out approximately 1 cm3 of bromine water into each of three test tubes.
- Add a few drops of the limonene oil to one test tube, a few drops of cyclohexane to another, and a few drops of cyclohexene to the third. Place in the bungs and agitate. If the bromine water is decolourised the molecule contains double bonds.
- 0.001 M potassium manganate(VII) can be substituted for the bromine water for class use. However, students need to know the action of bromine water.
Notes
- Limonene (1-methyl-4-prop-1-en-2-yl-cyclohexene) is an unsaturated hydrocarbon, classed as a terpene.
- At room temperature, it is a colourless oily liquid with the smell of oranges. Its molecular formula is C10H16 and its boiling point is 176 °C.
- Limonene is a chiral molecule with two optical isomers (enantiomers).
- The major biological form dlimonene, the (R)-enantiomer, is used in food manufacture and medicines.
- It is also used as a fragrance in cleaning products, a botanical insecticide, and due to its flammability, a potential biofuel.
- The (S)-enantiomer, l-limonene, is also used as a fragrance but has a piney, turpentine odour.
- It is possible to allow students to observe the optical activity of chiral molecules by comparing saturated glucose solution with distilled water in a polarimeter.
- The amount of oil extracted varies considerably with the variety, season and storage of the oranges, however, it is always possible to extract sufficient oil.
- Do not distil more than 50% of the initial volume of water, or solid “jam” will form in the flask which is difficult to remove.
- Limonene (1-methyl-4-prop-1-en-2-yl-cyclohexene) is an unsaturated hydrocarbon, classed as a terpene.
- At room temperature, it is a colourless oily liquid with the smell of oranges.
- Its molecular formula is C10H16 and its boiling point is 176 °C.
Downloads
Extracting limonene from oranges - teacher notes
PDF, Size 0.21 mb
Additional information
This practical is part of our Chemistry for non-specialists collection. This experiment was written by Andrew Thompson on behalf of the RSC.
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