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Ruthimitu Mixed Secondary School 2017

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1 Ruthimitu Mixed Secondary School 2017
Esters Notes by Onyango Ngoye For My Dear Form 4T Class Ruthimitu Mixed Secondary School 2017

2 What are Esters? How are Esters formed?
Esters are sweet smelling organic compounds formed when an alkanol reacts with a carboxylic acid in a condensation reaction. It is a slow reaction, so acid catalyst is used (usually sulphuric acid) The condensation reaction between the hydroxyl group and the carboxylic acid known as esterification. Reverse reaction is called 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)

3 Names of esters end in –oate.
Naming Names of esters end in –oate. Named after alcohol & carboxylic acid from which they are derived. O 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

4 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.

5 Fragrance raspberries pears apples jasmine Some Common Esters
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. They are used as: 1. Food flavourings. 2. Perfumes. 3. Organic compounds solvents.

6 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

7 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 A condensation reaction is when two molecules react to form a larger molecule with the elimination of a small molecule such as water

8 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

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

10 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


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