Name: Acetaldehyde and Acetone
Uploaded: 2019-07-19
Duration: 3 min 15 s
Description: Do you know carbonyl compounds are used in medicines? In this video, you will be able to understand the important uses of the two most common compounds, acet...

Question

Give simple chemical tests to distinguish between benzaldehyde and acetophenone pair of compounds.

Accepted Answer

Benzaldehyde and acetophenone can be distinguished by the following tests.
Benzaldehyde is $C_{6} H_{5} CHO$ having aldehyde group and acetophenone is $C_{6} H_{5} {COCH}_{3}$ having a ketonic group.

a) Tollen’s Test:
Aldehydes respond to Tollen’s test, benzaldehyde being an aldehyde reduces Tollen’s reagent to give a red-brown precipitate of $C u_{2} O,$ but acetophenone being a ketone does not.
$\underset{Benzaldehyde}{C_{6} H_{5} CHO +} \underset{{Tollen}^{'} s reagent}{2 {[Ag {(N H_{3})}_{2}]}^{+}} + 3 O H^{-} ⟶ \underset{Benzoate ion}{C_{6} H_{5} CO O^{-}} \underset{}{+ \underset{Silver mirror}{2 Ag ↓} + 4 N H_{3}} + 2 H_{2} O$

b) Iodoform test
Acetophenone being a methyl ketone undergoes oxidation by sodium hypoiodite $(N a O I)$ to give a yellow precipitate of iodoform. But benzaldehyde does not have methyl ketone group. So, does not respond to this test.
$\underset{}{\underset{Acetophenone}{C_{6} H_{5} {COCH}_{3}} + \underset{Sodium hypoiodite}{3 NaOI}} \to \underset{Sodium benzoate}{C_{6} H_{5} COONa +} \underset{}{\underset{\begin{matrix} Iodoform \\ (yellow ppt) \end{matrix}}{{CHI}_{3}} + \underset{Sodium hydroxide}{2 NaOH}}$

Give simple chemical tests to distinguish between benzaldehyde and acetophenone pair of compounds.

Important Questions on Aldehydes, Ketones and Carboxylic Acids

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