17. Carbonyl

Question 1

reactions (reagents and conditions) by which aldehydes and ketones can be produced:

Answer 1

(a) the oxidation of primary alcohols using acidified K2Cr2O7 or acidified KMnO4 and DISTILLATION to
produce aldehydes

(b) the oxidation of secondary alcohols using acidified K2Cr2O7 or acidified KMnO4 and distillation to
produce ketones

Question 2

reduction of aldehydes and ketones using NaBH4 or LiAlH4 to produce alcohols

Answer 2

aldehydes get reduced to primary alcohol-

ketones get reduced to secondary alcohol

Question 3

reaction of aldehydes and ketones

Answer 3

HCN, KCN as catalyst, and heat to produce hydroxynitriles as exemplified by ethanal and propanone- mechanism

Question 4

2,4-dinitrophenylhydrazine (2,4-DNPH reagent)

Answer 4

detect the presence of carbonyl
compounds- both aldehyde and ketone

Question 5

determine nature of carbonyl (aldehyde or ketone)

Answer 5

Fehling’s reagent- brick red ppt
Tollens’ reagents- silver mirror
ease of oxidation- aldehydes get oxidised to carboxylic acids but ketones don’t so oxidising agent colour change.

Question 6

presence of a CH3CO– group in an aldehyde or ketone

Answer 6

presence of a CH3CO– group in an aldehyde or ketone- a methyl ketone or a secondary alcohol

CH3CO–R, from its reaction with
alkaline I2(aq) to form a yellow precipitate of tri-iodomethane and an ion, RCO2.