Name: Isomerism in Aldehydes and Ketones
Uploaded: 2019-07-19
Duration: 4 min 23 s
Description: Aldehydes and ketones are functional isomers due to the difference in their functional groups. Ketones have R−CO−R, and aldehydes have R−CHO. Let' see the vi...

Question

Distinguish between acetaldehyde and acetone.

Accepted Answer

Acetaldehyde and acetone can be distinguished by the following tests.

(i)Tollen's test:

Acetaldehyde is an aldehyde. Thus, it reduces Tollen's reagent. But, acetoneone being a ketone does not reduce Tollen's reagent.

$\underset{Acetaldehyde}{{CH}_{3} CHO} + 2 {[Ag {({NH}_{3})}_{2}]}^{+} + 3 {OH}^{-} \overset{}{\to} {CH}_{3} {COO}^{-} + Ag + 4 {NH}_{3} + 2 H_{2} O$

$\underset{Acetone}{{CH}_{3} {COCH}_{3}} + 2 {[Ag {({NH}_{3})}_{2}]}^{+} + 3 {OH}^{-} \overset{}{\to} No reaction$

(ii) Aldehydes respond to Fehling's test, but ketones do not.

Acetaldehyde being an aldehyde reduces Fehling's solution to a red-brown precipitate of ${Cu}_{2} O$ , but acetone being a ketone does not.

$\underset{Acetaldehyde}{{CH}_{3} CHO} + 2 {Cu}^{2 +} + 5 {OH}^{-} \overset{}{\to} {CH}_{3} {COO}^{-} + {Cu}_{2} O + 3 H_{2} O$

$\underset{Acetone}{{CH}_{3} {COCH}_{3}} + 2 {Cu}^{2 +} + 5 {OH}^{-} \overset{}{\to} No reaction$

(iii) Iodoform test:

Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom respond to iodoform test. They are oxidised by sodium hypoiodite ( $NaOI$ ) to give iodoforms. acetone being a methyl ketone responds to this test, but acetaldehyde does not.

$\underset{Acetone}{{CH}_{3} {COCH}_{3}} + 3 NaOI \overset{}{\to} {CH}_{3} COONa + {CHI}_{3} + 2 NaOH$

$\underset{Acetaldehyde}{{CH}_{3} CHO} + 3 NaOI \overset{}{\to} No reaction$

Distinguish between acetaldehyde and acetone.

Important Questions on Aldehydes and Ketones

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