carboxylic acids and esters Flashcards
How does the strength of carboxylic acids vary with carbon chain length and why?
● Increasing length means weaker acid.
● Increasing the length pushes e- density onto the COO- making
it more negative thus less stable thus less likely to form.
What are salts of carboxylic acids called?
Carboxylates. E.g, (CH3COO-)Na+ is called sodium ethanoate.
What is different about methanoic acid to other carboxylic acids?
It can be oxidised as its structure as it has an aldehyde group
How are esters named?
The alcohol ends in -yl and is the prefix. The carboxylic acid ends in - anoate and is the suffix
Describe the 2 types of
esterification
- Esterification using acid catalyst:
Carboxylic acid + alcohol ⇌ ester + water
○
Sulfuric acid catalyst required for H+ ions
○heat under reflux - Esterification using acid anhydrides:
○ Acid anhydride + alcohol → ester
○ Room temperature
○ Higher yield achieved
What is an acid anhydride?
Two different carboxylic acids joined together.
Give 2 ways esters can be hydrolysed (with conditions)
- Heating with HOT AQUEOUS ACID:
○ Use sulfuric acid catalyst under reflux.
○ Forms the original reactants. ○ CH3CH2CO2CH2CH3 + H2O ⇌ CH3CH2COOH + CH3CH2OH (reversible so doesn’t give a good yield) - Heating with HOT AQUEOUS ALKALI (saponification):
○ Use sodium hydroxide under reflux.
○ Forms a carboxylate and alcohol.
○ CH3CH2CO2CH3 + NaOH → (CH3CH2CO2- )Na+ + CH3OH
The anion in the salt is resistant to attack by weak nucleophiles such as the alcohol so this reaction isn’t reversible.
How and why are acyl chlorides better than carboxylic acids?
They are more reactive than carboxylic acids as Cl is a good leaving group.
How are acyl chlorides formed?
● By reacting carboxylic acid using SOCl2 (thionyl chloride). ● CH3COOH + SOCl2 → CH3COCl + SO2 + HCl
How do acyl chlorides react with water?
To produce a carboxylic acid.
How do acyl chlorides react with alcohols and why is it good?
● To produce an ester.
● It’s faster (∵ more reactive) and not reversible.
How do acyl chlorides react with ammonia?
To produce a primary amide.
How do acyl chlorides react with primary and secondary amines? (with example equation)
● To produce secondary and tertiary amides respectively.
How do acyl chlorides react with phenol and why is this used?
● Form an ester.
● Phenol doesn’t react readily with carboxylic acids.
What 2 things are common for most reactions of acyl chlorides?
- Carried out at room temperature.
- Any HCl (g) is given off at steamy white fumes
