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Esters occur in nature and have been harnessed by the perfume industry. What are esters and how are they made and used?Key facts
- Esters give many fruits their scents, including bananas, lavender and pineapples.
- They are produced by a reaction between an alcohol and carboxylic acid.
- They are made of a sequence of carbon and oxygen atoms called an ester linkage.
Transcript
Bananas and lavender.
Pineapples and perfumes.
Like many other sweet-smelling substances, they owe much of their pleasant aroma to chemicals called esters.
Esters
Esters are organic compounds produced by a reaction between an alcohol and a carboxylic acid. They are made of a sequence of carbon and oxygen atoms, known as an ester linkage.
Ester Linkage
They're widespread in nature but they can also be created in laboratories by reacting two ingredients in the presence of a sulphuric acid catalyst.
Alcohol
One of these ingredients is an alcohol, like methanol or ethanol.
Carboxylic acid
The other is a carboxylic acid, like ethanoic acid or butanoic acid.
What is surprising about carboxylic acids is that they have sour and disagreeable odours, yet when combined with alcohol to make esters they create lovely smells.
For example butanoic acid gives rancid butter its putrid smell, but the ester it makes with ethanol has the scent of pineapple.
The ethanoic acid, which gives vinegar its pungent whiff, combines with different alcohols to create the aromas of pears, bananas, and citrus fruits.
Esters are widely used in manufacturing, particularly in the perfume industry.
But as well as having an appealing smell, perfumes need other qualities to be commercially successful.
To be used safely, they need to be non-toxic and must not irritate the skin.
And so they don't wash off easily or react with sweat, they need to be insoluble in and rather unreactive with water.
And for the scent to reach the nostrils quickly, the compounds in the perfume need to be volatile so that they evaporate easily.
The fragrant properties of esters are also exploited in the food industry, where they're used as flavouring agents.
Without esters, the scent of the world around us would be very different, and much less pleasant.
