Esters

L.O: To understand the structure of esters and how they are made

Friday, April 21, 2023

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Esters

Esters contain this group of atoms:

Esters are made from the reaction of a carboxylic acid with an alcohol:

...which is written as –COO–.

carboxylic acid + alcohol ester + water

+ +

+ +CH3CH2COOH CH3OH H2OCH3CH2COOCH3

propanoic acid methanol methyl propanoate water+ +

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Naming esters

Esters are named after the alcohol and the carboxylic acid from which they are made. The alcohol gives the first part of the name, and the carboxylic acid gives the second. Esters always end in “–anoate”.

ethanoic acid methanol

methyl ethanoate

For example:

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Matching carboxylic acids to their esters

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Practising naming esters

Esters

Esters have a –COO– functional group (pronounced –oate), formed from an alcohol and carboxylic acid

Alcohol + carboxylic acid ester + water

Ester Properties

Esters are volatile, smell nice but do not mix well with water

Esters smell nice so are used as perfumes / flavourings / aromas

Alcohol Organic acid Ester made Smell of ester

Pentanol Ethanoic acid Pentyl ethanoate Pears

Octanol Ethanoic acid Octyl ethanoate Bananas

Pentanol Butanoic acid Pentyl butanoate Strawberries

Methanol Butanoic acid Methyl butanoate Pineapples

Perfume Properties

Perfumes need to be non-toxic, not irritating to the skin, evaporate easily (very volatile), insoluble in water and do not react with water

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How are esters made?

Esters are made by reacting a carboxylic acid with an alcohol.

How could you speed it up?

The reactants could be heated in order to make the reaction faster.

A catalyst of concentrated sulfuric acid could be added.

However, the reaction is very slow at room temperature.

Preparation of butyl ethanoate

• Wear goggles.

• Using a plastic, disposable, 3 ml graduated pipette, add 10 drops of glacial ethanoic acid to a vial which contains one drop of concentrated sulfuric(VI) acid (this is the catalyst).

• Using another graduated pipette, add 10 drops of butan-1-ol to the vial.

• Add 10 ml of water to a 100 ml beaker

• Gently lower the vial of reagents into the beaker and place the beaker on a tripod and gauze. Heat the water to boiling so that the vial rattles in the beaker and then turn off the Bunsen burner. After 1 minute in the hot water, use tongs to remove the hot vial and place it on a heat-proof mat.

• When the contents of the vial have cooled down a little, pour them into a test tube half full of 0.5 M sodium carbonate solution. Pour the mixture into the vial and back again into the test tube. A layer of butyl

ethanoate floats on the water.

• Using the method shown to you by your teacher, smell the contents of the test tube.

Preparation of ethyl ethanoate

• Wear goggles.

• Using a plastic, disposable, 3 ml graduated pipette, add 10 drops of glacial ethanoic acid to a vial which contains one drop of concentrated sulfuric(VI) acid (this is the catalyst).

• Using another graduated pipette, add 10 drops of ethanol to the vial.

• Add 10 ml of water to a 100 ml beaker

• Gently lower the vial of reagents into the beaker and place the beaker on a tripod and gauze. Heat the water until the contents of the vial begin to bubble (boil). Turn off the Bunsen burner. After 1 minute, use

tongs to remove the hot vial and place it on a heat-proof mat.

• When the contents of the vial have cooled down a little, pour them into a test tube half full of 0.5 M sodium carbonate solution. Pour the mixture into the vial and back again into the test tube. A layer of ethyl

ethanoate floats on the water.

• Using the method shown to you by your teacher, smell the contents of the test tube.

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Making esters

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What are the stages in making an ester?