Esters are produced from a reaction between an organic acid and an alcohol, with water as a byproduct. Natural esters include fats, oils, and aromas in fruits. Man-made esters are now commonly produced industrially for uses such as perfumes and flavors. Esters have properties including volatility, solubility in organic solvents but not water, and high melting points for large esters like fats. They are used in applications such as solvents, cosmetics, flavors, and fragrances due to these properties. Esters can be prepared through the reaction of a carboxylic acid and alcohol with an acid catalyst and heat.

1. EstersC3 Extension ChemistryTopic 4

2. Exam Specificationdescribe the useful chemical and physical properties of esters, such as miscibility, odour and use as a solventdescribe the uses of alcohols in the preparation of estersdescribe the uses of esters in cosmetics and fruit flavourings

3. What is an esterEsters are produced when an organic acid reacts with an alcohol (you can think of this as neutralisation)Water is made as a by-product of the reaction, just like neutralisationEsters are either natural or man-madeNatural esters:Fats and oils: an ester of a fatty acid and glycerolAromas from fruits like apples, pears, and strawberries are estersPheromones are natural estersEssential Oils like patchouli and lavender are estersMan-made:Many esters are now manufactured industrially as it is easier than extracting them from plants and animals, e.g. for perfumes and sweets

4. EstersThis one is used in nail varnish remover as it is a good solvent – it dissolves the nail varnish but not your nails

5. Common estersPineapple - AllylhexanoatePear, strawberry and jasmine - Benzyl acetateBanana - Ethyl butyrateCinnamon - Ethyl cinnamate

6. Properties of estersQuite volatile – small esters have lower boiling points than the carboxylic acids This is useful for plants or animals to attract others by scentThey aren’t able to take part in hydrogen bonding as well as carboxylic acidsThis also makes the larger esters very insoluble in water, but more soluble in organic solventsThis why they are very useful as solvents for other organic compounds – like the large alcohols were.Very large esters (like oils and fats) have higher boiling points and melting points – remember: a fat is simply a solid oilThe larger the ester molecule, the higher the boiling and melting point.

7. Link to C2 AdditionalSaturated vs Unsaturated fatsRemember – saturated means only single C-C bonds and unsaturated means double C=C bonds.Saturated fats don’t have any kinks, so the chains can line up closely and the have higher melting points (solid at room temperature – fats)Unsaturated fats have kinks in their chains, and so they can’t get very close together and they have lower melting points (liquid at room temperature – oils)

8. Uses of Esters

9. Preparation of EstersCarboxylic Acid + Alcohol  Ester + WaterEthanoic acid + ethanol  Ethylethanoate + waterMethanoic acid + ethanol  Ethyl Methanoate + waterOften carried out in the presence of an acid catalyst (e.g. conc sulfuric acid) and with gental heating

10. Making an esterA Pour some boiling water into a 250 cm3 beaker. Leave it to stand.B Put about 2 cm3 of ethanol into a test tube.C Go to the fume cupboard and ask your teacher to add 1 cm3of concentrated ethanoic acid and three drops of concentrated sulphuric acid to your tube.D Stand your tube in the beaker of hot water for about 5 minutes.E While you are waiting, collect a 100 cm3 beaker and fill it about half full with sodium hydrogen carbonate solution.F After 5 minutes, carefully tip the liquid from the test tube into the beaker and stir well.G Carefully smell the product in the beaker.

11. Questions to practice 1. On the Moodle course KS4 Triple Science (Chemistry), at the top under C3 Extension Topic 4 is a worksheet calledFruity FlavoursDownload it and rearrange the cards.2. Next, download and complete the worksheet calledThe reactions of Ethanoic Acid QsThis will help you review the last two topics (Acids and Esters)