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

How aldehydes and ketones are prepared from dry distillation of calcium salts? How aldehydes react with phenyl hydrazine? Describe one test to distinguish between aldehydes and ketones.

Accepted Answer

Dry distillation of calcium salts of carboxylic acids gives aldehydes or ketones. when calcium formate $({(HCOO)}_{2} Ca)$ is heated, formaldehyde $(HCHO)$ and calcium carbonate ( $({CaCO}_{3})$ ) are obtained.

The reaction is as follows:

${(HCOO)}_{2} Ca \overset{∆}{\to} HCHO + {CaCO}_{3} $

When calcium acetate ${({CH}_{3} COO)}_{2} Ca$ is heated, acetone and calcium carbonate are obtained.

The reaction is as follows:

${({CH}_{3} COO)}_{2} Ca \overset{∆}{\to} {CH}_{3} - CO - {CH}_{3} + {CaCO}_{3} $

Carbonyl compound (acetone) forms condensation product with hydrazine, phenyl hydrazine, aniline etc. Reaction of acetone with Phenyl hydrazine gives Phenyl hydrazone.

Acetaldehyde and acetone can be distinguished by the Tollen's test: Tollens’ reagent being a mild oxidizing reagent oxidizes aldehyde groups to its respective acid and it gets reduced, the reduction from $+ 1$ oxidation state of Silver $({Ag}^{+})$ to elemental form of Silver $(Ag)$ . Ketones do not reduce Tollens’ reagent (except alpha diketones (i.e. two ketone functionalities on the adjacent atoms) and alpha hydroxy ketones (keto and alcohol functional groups on adjacent atoms) which can tautomerize into aldehydes via keto-enol tautomerism in an alkaline medium).

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

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

How aldehydes and ketones are prepared from dry distillation of calcium salts? How aldehydes react with phenyl hydrazine? Describe one test to distinguish between aldehydes and ketones.

Important Questions on Aldehydes and Ketones

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