Carboxylic acids
Carboxylic acids
- A carboxylic acid has the –COOH (carboxyl) group.
- It is a weak acid.
- It shows all the typical acid reactions.
Practice
The functional group of a carboxylic acid is:
Carboxylic acids contain the –COOH group and behave as weak acids.
Making carboxylic acids
- oxidation of a primary alcohol or an aldehyde (acidified $\text{K}_2\text{Cr}_2\text{O}_7$, with reflux for full oxidation).
- hydrolysis of a nitrile (then acidify).
- hydrolysis of an ester (then acidify).
Practice
A carboxylic acid is made by oxidising a primary alcohol or aldehyde, using:
Reflux ensures full oxidation all the way to the carboxylic acid (distillation would stop at the aldehyde).
Acid reactions
- with a reactive metal → salt + hydrogen.
- with an alkali (neutralisation) → salt + water.
- with a carbonate → salt + water + carbon dioxide (the fizz is a test for a carboxylic acid).
Two reactions change the group: esterification with an alcohol → an ester; reduction by $\text{LiAlH}_4$ → a primary alcohol.
Practice
A carboxylic acid added to a carbonate gives a salt, water and:
Like other acids, it releases CO₂ from a carbonate — the fizz is a useful test.
You've got it
Key idea
- carboxylic acid = –COOH, a weak acid
- made by oxidising a primary alcohol/aldehyde (reflux), or hydrolysing a nitrile/ester
- acid reactions: metal (+ H₂), alkali (+ water), carbonate (+ water + CO₂ — the fizz test)
- esterification → ester; reduction → primary alcohol
Practice
A carboxylic acid reacting with an alcohol (conc. H₂SO₄ catalyst) makes:
Esterification joins the acid and alcohol into an ester (losing water).