6.1.3 - Carboxylic Acids and Esters Flashcards
Why are carboxylic acids soluble in water?
Due to the highly polarised d+ hydrogen and d- oxygen which form hydrogen bonds with water molecules.
What do carboxylic acids form with water?
Dimers (both hydrogen and oxygen react with water)
Why are longer hydrocarbon chain carboxylic acids less soluble in water?
The long chain is non-polar.
Why aren’t hydrogen bonds in alcohols as strong as in carboxylic acids?
Carboxylic acids form dimers.
What are carboxylic acids?
Weak acids.
Acid + metal
metal salt + H2
Acid + carbonate
metal salt + CO2 + H2O
Acid + base
metal salt + H2O
Test for hydrogen?
Lighted spill goes out with a squeaky pop.
Test for water?
Cobalt chloride paper turns blue.
Test for CO2?
Turns limewater cloudy.
Functional group of esters?
-COO-
How are esters formed in esterification?
By reacting carboxylic acids with an alcohol in the presence of a concentrated H2SO4 catalyst.
What is the drawback of esterification?
Low yield as reaction is reversible so product must be separated using distillation as soon as it forms.
How are esters named?
First part comes from the alcohol, second the acid.
Methanoic acid + ethanol?
Ethyl methanoate
How are acid anhydrides formed?
Two carboxylic acids react eliminating a water molecule.
How are acid anhydrides used to form esters?
They are heated without a catalyst with an alcohol.
What is produced when acid anhydrides form esters?
The ester and a carboxylic acid which must be separated by fractional distillation.
Why does the formation of esters by acid anhydrides give a better yield?
The reaction is not reversible.
What is the hydrolysis of esters?
A chemical reaction where water causes the breaking of bonds in a decomposition reaction.
General equation for hydrolysis of esters?
ester + water -> carboxylic acid + alcohol
What happens in acid hydrolysis?
Reflux the ester with the dilute sulphuric acid catalyst. This is a reversible reaction.
What happens in alkali hydrolysis?
Reflux the ester with aqueous NaOH solution to form the alcohol and carboxylate salt of the acid.
Why is alkali hydrolysis not reversible?
No acid is formed, only the salt.
How are acyl chlorides formed?
Carboxylic acid + SOCl2 -> acyl chloride + SO2 + HCl
How do you separate the byproducts from the acyl chloride in the formation of acyl chloride?
Distillation as although the byproducts are both gases there may be excess acid.
How are carboxylic acids formed by acyl chlorides?
A nucleophilic substitution reaction with water.
acyl chloride + water -> carboxylic acid + hydrogen chloride
How are esters from acyl chlorides, and why is it a good way of forming esters?
A nucleophilic addition reaction with an alcohol.
acyl chloride + alcohol -> ester + hydrogen chloride. Not a reversible reaction so should give a better yield.
How are primary amides formed from acyl chlorides?
Reaction with ammonia.
acyl chloride + ammonia -> amide + hydrogen chloride (ammonium chloride if excess ammonia used)
How are secondary amides formed from acyl chlorides?
Reaction with amines.
Acyl chloride + amine -> amide + hydrogen chloride
