Esters

What are they? How are they made? Formed when an alcohol reacts with a carboxylic acid. Very slow reaction, unless! an acid catalyst used (usually sulphuric acid) A condensation reaction The condensation reaction between the hydroxyl group and the carboxylic acid known as esterification. Reverse reaction = ester hydrolysis information action button links to slide number 9 – condensation reaction in more detail. Return to this slide via another action button (check notes on slide 9)

Names of esters end in –oate. Naming Names of esters end in –oate. Named after alcohol & carboxylic acid from which they are derived. O let’s name some esters! C CH3 CH3 CH2 O ‘let’s name some esters’ action button links to slide 10 – check notes on slide 10 ethyl ethanoate this part comes from the alcohol & is named after it this part from the acid and is named after it

In this version the acid part has been written first Structural formulae Although the previous structural formula are the clearest way of showing esters, they can draw out in a shortened form. In this version the acid part has been written first ethyl ethanoate Or… O Either… O CH3 C O CH2 CH3 CH3 CH2 O C CH3 Identify the group attached to the C=O – this is from the acid The group attached to the –O- is from the alcohol.

Wait! What’s that smell? ester fragrance ethyl methanoate raspberries 3-methylbutyl ethanoate pears ethyl 2-methylbutanoate apples phenylmethyl ethanoate jasmine Esters have strong, sweet smells. Their bouquet is often floral or fruity. This means they are used in food flavourings & perfumes. Also, very good at dissolving organic compounds so often used as solvents.

Ester hydrolysis Breakdown of an ester by water. Process sped up by catalysis Can use an acid to catalyse (H2SO4) Alkali catalysts (e.g. sodium hydroxide) can also be used but instead of producing carboxylic acid a carboxylate salt is formed. Alkaline hydrolysis goes to completion & hence is usually preferred. ‘can use acid to catalyse’ hyperlink takes to slide 11 ‘carboxylate salt’ hyperlink takes to slide 12

R O H O ⇋ C R’ + O R O C R’ + H O This is why it is a condensation reaction because water is produced! H2O return to previous slide by clicking on big red box Definition of a condensation reaction = two molecules reacting to form a larger molecule with the elimination of a small molecule such as water

O CH ethyl methanoate CH3 CH2 O O C CH2 CH3 methyl propanoate CH3 O O methyl propanoate is an isomer of ethyl ethanoate – hence the big red box round it. clicking on this box will take you ‘structural formulae’ slide (number 4) O methyl methanoate CH CH3 O

FORWARD REACTION = condensation reaction, the esterification of an alcohol using acid catalyst under reflux. R O H O ⇌ C R’ + O R O C R’ + H O click on bottom red box to return to ester hydrolysis (slide8) H2O REVERSE REACTION = ester hydrolysis, same catalyst works for both forward & reverse reactions.

not a reaction that exists in equilibrium (unlike using acid catalyst) ethanol ethyl ethanoate O CH3 CH2 OH C CH3 CH3 CH2 O → + + O OH- C CH3 click on text box in red box to return to ester hydrolysis slide -O not a reaction that exists in equilibrium (unlike using acid catalyst) ethanoate ion