Organic - Carboxylic Acids and Derivatives

Question 1

Why are carboxylic acids reactive?

Answer 1

• the partially positive carbon is open to attack from nucleophiles
• the partially negative oxygen of the C=O may be attacked by positively charged species (e.g. H+, in which case you say it has been protonated)
• the partially positive hydrogen may be lost as H+, in which case the compound is behaving as an acid

Question 2

What happens when a proton is lost from a carboxylic acid?

Answer 2

If the hydrogen of the -OH group is lost, a negative ion (carboxylate ion) is left. The negative charge is shared over the whole of the carboxylate group. This delocalisation makes the resulting ion more stable. Carboxylic acids are weak acids, so the equilibrium is to the left.

Question 3

How can you distinguish carboxylic acids from other organic compounds that contain the -OH group?

Answer 3

Carboxylic acids are strong enough to react with sodium hydrogencarbonate, NaHCO3, to release carbon dioxide (which can be tested for using limewater). This distinguished them from other organic compounds that contain the -OH group, such as alcohols.

Question 4

Why can a proton be lost from a carboxylic acid?

Answer 4

The stability of the carboxylate ion is what allows the H+ ion to be released and makes the molecules acidic.

Question 5

How do carboxylic acids react?

Answer 5

Carboxylic acids are proton donors and show the typical reactions of acids.

They form ionic salts with the more reactive metals, alkalis, metal oxides, or metal carbonates in the usual way. The salts that are formed have the general name carboxylates, and are named from the particular acid.