Carbonyl compounds - reactions

Question 1

Describe the oxidation of primary alcohols

Answer 1

Primary alcohols –> distil -> aldehyde

primary alcohol -> reflux -> carboxylic acid

Question 2

what colour change occurs with the oxidation of alcohols?

Answer 2

the acidified potassium dichromate changes from orange to green

Question 3

How can you control the oxidation product that occurs when oxidising a primary alcohol?

Answer 3

Distilling the aldehyde from the reaction mixture as it is formed prevents the aldehyde from being oxidised into a carboxylic acid.
When making the carboxylic acid, the reaction mixture is often heated under REFLUX

Question 4

What happens to secondary alcohols when you oxidise them?

Answer 4

They turn into ketones. They cannot be oxidised further.

Question 5

What reducing agent is used to reduce carbonyl compounds (eg ketones and aldehydes) to alcohols?

Answer 5

NaBH4

Question 6

What are aldehydes reduced to?

Answer 6

primary alcohols

Question 7

what are ketones reduced to?

Answer 7

secondary alcohols

Question 8

describe the nucleophillic addition mechanism for aldehydes and ketones

Answer 8

• BH4 acts as a source of hydride ions
• :H- hydride ion is the nucleophile
• electron deficient C atom is attacked by the hydride ion
• lone pair from :H- forms bond with C atom
• the pi bond in the C=O breaks -> negatively charged intermediate
• intermediate donates electron pair to H atom of H20, forming a dative covalent bond and a OH- ion
• final product is an alcohol