Esters Flashcards
when are esters formed?
when a carboxylic acid reacts with an alcohol
carboxylic acid + alcohol –> (reversible reaction)
ester + water
condensation reaction
when two molecules join together with the elimination of water
naming esters
1st part from alcohol add ‘yl’
2nd part from carboxylic acid add ‘oate’
functional group of ester
ester linkage “coo” group
hydrolysis
to split a molecule apart using water
hydrolysis of esters
esters can be hydrolysed to their parent alcohol and carboxylic acid
ester linkage C-O bond is broken
acid catalysed hydrolysis
H+ used as a catalyst
still reversible
will always get a mixture of ester, water, carboxylic aicd and alcohol
alkali catalysed hydrolysis (“Alkaline Hydrolysis”)
if an alkali is used we get a complete hydrolysis of the ester (all ester hydrolysed)
forms carboxylic acid and alcohol but NaOH present so the carboxylic acid will react to form the salt
final products of alkaline hydrolysis
salt of the carboxylic acid + alcohol
method of making an ester
- equal quantities of the reactants (alcohol and carboxylic acid) are added to a test tube
- concentrated sulphuric acid is added as a catalyst
- a wet paper towel is put around the top of the test tube to act as a condenser.
- the tube is placed in a beaker of hot water/water bath.
- reaction mixture is poured onto sodium hydrogen carbonate solution to neutralise the conc. sulphuric acid and any unreacted carboxylic acid
why is the tube not heated with a bunsen?
Not heated with a bunsen since alcohols are flammable.
evidence the ester has formed
- distinct smell
2. two layers are formed (oily layer on top)
main use of esters
flavouring and fragrances i.e. perfumes and deodorants
examples of esters and their smells
methyl butanoate - pineapple
ethyl pentanoate - apple
benzyl ethanoate - peach, flowers
why can esters be used as fragrances?
because they are volatile
what is volatility?
the ease at which a substance evaporates i.e. l–>g
what is volatility controlled by?
intermolecular bonds
stronger - less volatile
weaker - more volatile
other uses of esters
industrial solvents (able to dissolve variety of compounds which are insoluble in water) used as solvents for dyes, inks, paints and varnishes used to extract caffeine from coffee/tea
properties of esters
volatile
distinctive smells
flammable
what catalyst is used when making esters?
concentrated sulfuric acid
what does the wet paper towel act as when making an ester?
a condensor
what is the opposite of a condensation reaction?
a hydrolysis reaction
what is heating under reflux?
heating the mixture with a condenser attached
