MADE TO BE MADE AGAINCHEMISTRY FOR A CIRCULAR ECONOMYExtracting limonene from orange peel

Lesson objectives:•Define the key terms chiral, stereoisomer and enantiomer.•Outline the process of steam distillation.•Describe the principles of a circular economy.•Explain using key definitions and diagrams why limonene is chiral and shows optical activity.

What does it take to make…?

Sort the cards to show every stage of processing.

The linear economy

The circular economy

The future is orange

How can we apply a circular economy approach to the production of orange juice?

A new ‘OPEC’ for a greener future

Read the article A new ‘OPEC’ for a greener future:

http://www.york.ac.uk/news-and-events/news/2011/research/waste-orange/

What alternatives to waste are the Orange Peel Exploitation Company able to produce?

What is limonene?

Whiteboards ready...

1.Draw the full structural formula of limonene.

2.Can you draw an isomer of the structure you have drawn?

3.What kind of isomer is it?

4.Put an asterisk against the chiral centre.

5.Draw a mirror image of the compound on the screen.

Key definitions

• Stereoisomers have the same structural formulae but differ by the arrangement of bonds in space.

• Optical isomers occur when a carbon atom is bonded to four different groups resulting in two isomers that are mirror images. This carbon is called the ‘chiral centre’ or ‘asymmetric carbon’.

• Optical isomers are described as ‘chiral’ meaning ‘handed’ because the mirror images can be thought of as left and right handed.

• A pair of chiral optical isomers are called ‘enantiomers’.

1. The extraction of limonene from oranges by steam distillation

1. Into a 250ml round bottomed flask, put the finely divided rind of two oranges and 100ml of water.

2. Heat the mixture while collecting about 50ml of distillate. The limonene separates out as an oily layer.

2. Testing for limonene

Method

Wear eye protection at all times. Bromine water is a hazard and irritant. Use in a fume cupboard and keep the lid on the bottle as much as possible.

Use a measuring cylinder to measure 1ml of bromine water into a test tube.

To the test tube add limonene dropwise using a pipette. Shake gently.