17.1 aldehydes and ketones

State the way by which aldehydes can be produced

• oxidation of primary alcohols with acidified KMnO4 and distillation to produce aldehydes

• Must be distilled and collected or else carboxylic acids can form

State the way by which ketones can be produced

Oxidation of secondary alcohols using acidified KMnO4 and distillation to produce ketones

Colour change when KMnO4 is oxidised

Purple to colourless

Describe the reduction of aldehydes and ketones.

NaBH4/ LiAlH4 2[H]

Aldehydes reduced to primary alcohols

Ketones reduced to secondary alcohols

Explain how aldehydes and ketones can react with HCN

Reacts via nucleophilic addition

HCN behaves as nucleophile and adds across C-O bond

Aldehydes and ketones react with HCN

KCN catalyst and heat to produce hydroxynitrilees

Draw out the mechanism for nucleophilic addition

2,4-DNPH

Tests for presence of carbonyl compounds

Forms orange precipitate

Fehling’s solution

• Oxidising agent that detects presence of an aldehyde group (-CHO)

• Clear blue to opaque red precipitate

Tollen’s reagent

Detects presence of aldehyde by oxidising it

Forms silver mirror

Iodoform

Detects present of methyl ketones and ethanal (CH3CO)

Reagent heated with NaOH + Iodine

Forms yellow ppt of CHI3 and salt RCO2-

Ethanal is…

The only aldehyde to react with iodo form