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 acetaldehyde can be prepared from the following?

(a) Acetyl chloride (b) Acetylene

How does it react with Fehling's solution? Give equations. What is formalin? How is it used?

Accepted Answer

When hydrogen is bubbled through a heated suspension of the catalyst ( $Pd / {BaSO}_{4}$ ) in a xylene solution of acetyl chloride, it is reduced to give acetaldehyde. This catalytic hydrogenation of acid chloride is known as Rosenmund's reduction.

${CH}_{3} COCl + H_{2} \to_{Xylene}^{Pd / {BaSO}_{4}} {CH}_{3} CHO + HCl$

Acetylene in the presence of $42 %$ sulphuric acid followed by mercury sulphate produce acetaldehyde.

$CH \equiv CH \to_{{HgSO}_{4}}^{42 % H_{2} {SO}_{2}} {CH}_{3} CHO Acetylene Acetaldehyde$

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

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

A $37 %$ aqueous (water) solution of formaldehyde, a pungent gas, with the chemical formula $HCHO$ , used as an antiseptic, disinfectant, and especially today as a fixative for histology (the study of tissues under the microscope).

How acetaldehyde can be prepared from the following?

(a) Acetyl chloride (b) Acetylene

How does it react with Fehling's solution? Give equations. What is formalin? How is it used?

Important Questions on Aldehydes and Ketones

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