Esters Flashcards
Explain how esters can be made from reacting carboxylic acids with alcohols.
An ester can be made by reacting a carboxylic acid with an alcohol in the presence of an acid catalyst. - Concentrated sulfuric acid is often used as the acid catalyst. - This reaction is known as esterification.
Write out the reaction of propanoic acid with methanol.
Explain how esters can be formed from acid anhydrides.
Esters can also be prepared gently heating an acid anhydride with an alcohol. This method gives a much better yield of the ester than preparations from carboxylic acids.
Write out the reaction for ethanoic anhydride with methanol.
Explain how an acid anhydride is formed.
An acid anhydride is formed by removal of a molecule of water from two carboxylic acid molecules.
What is hydrolysis and ester hydrolysis?
Hydrolysis is the chemical breakdown of a compound by a reaction with water. Hydrolysis of esters is essentially the reverse of esterification. Hydrolysis of esters takes place with aqueous acid or aqueous alkali.
Explain the conditions and procedure of acid hydrolysis of esters.
Write the reaction for the acid hydrolysis of propyl ethanoate.
In acid hydrolysis, the ester is heated under reflux with dilute sulfuric acid or dilute hydrochloric acid. The ester is broken down by ater, with the acid acting as a catalyst.
Explain the conditions and procedure for the alkaline hydrolysis of esters.
Give the reaction for the alkaline hydrolysis of a general ester.
Esters can be hydrolysed in aqueous alkaline conditions. Aqueous sodium(or potassium) hydroxide is refluxed with the ester. This reaction is non-reversible ad leads to the formation of the sodium salt of the carboxylic acid. The reaction is sometimes called ‘sopanification’ and is the basis of soap-making.
What are the uses of esters?
- Esters as responsible for the flavour of many foods and the pleasent smell of flowers. So they are used as perfumes and flavourings.
