Question

KMnO₄ will oxidise acetylene to
(a) Ethylene glycol
(b) Ethyl alcohol
(c) Oxalic acid
(d) Acetic acid

Answer 1

Hint: Alkynes are electron-rich centres that primarily produce electrophilic addition reactions. They also operate as a powerful oxidising agent by donating nascent oxygen to oxidise other substrates, although at low temperatures or in alkaline conditions, they mimic oxidation.

Complete Step by Step Solution:
In qualitative analysis, potassium permanganate can be used to assess the permanganate value. Additionally, $KMn{O_4}$ can be used as a regeneration chemical in well water treatment to remove iron and hydrogen sulphide.

The test for unsaturation uses the decolourization of Baeyer's reagent, often known as cold-dilute KMnO₄. Alkynes oxidise due to the high oxidising effect of KMnO4. Alkyne's double bond will be transformed into two carboxylic groups as a result of the partial oxidation of alkyne into acid at low temperature.

Oxidising acetylene with a diluted KMnO₄ solution produces oxalic acid.
$$$CH \equiv CH\xrightarrow{{KMn{O_4}}}COOH - COOH$
Hence option C is correct.

A mild oxidising agent ($KMn{O_4}$) produces less oxidation and causes less oxidation overall. Initially a coloured chemical, Baeyer's reagent will eventually oxidise to become a colourless substance. This reaction results in the breakdown of solid potassium permanganate, which has an oxidation state of +7, into potassium manganate, which has an oxidation state of +6, manganese oxide, and oxygen. This released oxygen will cause the conversion of alkene to alcohol.

Note: Hot $KMn{O_4}$ is a very powerful oxidizer. If it reacts with acetylene in an alkaline media at a high temperature, it will fully oxidise the solvent into $C{O_2}$ and ${H_2}O$. With the addition of sodium carbonate, the solution of $KMn{O_4}$ becomes somewhat alkaline. It is crucial to create mild conditions for this reaction because under oxygenated products like acid or carbon dioxide will result from over-oxidation.