Aldehydes & Ketones

Question 1

With acidified potassium dichromate

Answer 1

<Aldehyde>
Type of reaction: oxidation
Condition: heat under reflux
Change in functional group: aldehyde --> carboxylic acid
Observation: orange --> green

<Ketone>
Observation: no colour change
</Ketone></Aldehyde>

Question 2

With Fehling’s or Benedict’s solution

Answer 2

<Aldehyde>
Type of reaction: oxidation
Condition: warm in water bath
Observation: blue solution --> brick red precipitate

<Ketone>
Observation: no precipitate
</Ketone></Aldehyde>

Question 2

With Tollens’ reagent

Answer 2

<Aldehyde>
Type of reaction: oxidation
Condition: warm in water bath
Observation: silver mirror precipitate

<Ketone>
Observation: no precipitate
</Ketone></Aldehyde>

Question 2

With HCN, in the presence of KCN

Answer 2

<Aldehyde & Ketone>
Type of reaction: nucleophilic addition
Condition: heat under reflux, pH ~8.0
Change in functional group: aldehyde/ketone –> hydroxynitrile

Question 2

With LiAlH4

Answer 2

<Aldehyde>
Type of reaction: reduction
Condition: in dry ether
Change in functional group: aldehyde --> primary alcohol

<Ketone>
Type of reaction: reduction
Condition: in dry ether
Change in functional group: ketone --> secondary alcohol
</Ketone></Aldehyde>

Question 2

With iodine and NaOH or KI and NaClO (only ethanal or methyl ketone)

Answer 2

<Aldehyde & Ketone>
Type of reaction: iodoform reaction
Condition: warm gently
Observation: pale yellow precipitate

Question 2

With 2,4 - DNPH (aka. Brady’s reagent)

Answer 2

<Aldehyde & Ketone>
Type of reaction: condensation
Condition: room temperature, in conc. sulphuric acid
Observation: yellow/orange precipitate