Question

The compound formed by passing ethylene gas into a cold alkaline solution of \[KMn{O_4}\] is.
(a) Ethyl alcohol
(b) Acetaldehyde
(c) Acetic acid
(d) Ethylene glycol

Answer 1

Hint: The double bond of an alkene can be easily oxidised by using a cold alkaline solution of Potassium permanganate (\[KMn{O_4}\]). The 1,2-diol or 1,2-glycols is formed as an oxidised product of an alkene. Whereas, during the oxidation process of alkene the \[KMn{O_4}\]reduced itself into \[Mn{O_2}\].

Complete Step by Step Answer:
The potassium permanganate (\[KMn{O_4}\]) is belongs to the category of an oxidizing agents. It can provide oxygen in neutral or in alkaline reaction conditions to an alkene and oxidize an alkene into syn-diol i.e., into ethane-1,2-diol or ethylene glycol.
Because in this reaction formation of a hydroxyl group is occurs, therefore this reaction also known as the hydroxylation reaction.
The oxidation of an alkene via cold and alkaline potassium permanganate (\[KMn{O_4}\]) can be described by the following reaction:

During the oxidation of alkene by potassium permanganate (\[KMn{O_4}\]) the formation of a cyclic diester of manganese intermediate is observed. Due to this cyclic diester formation of syn-diol or cis-diol is observed.

Image: Formation of a cyclic ester of manganese intermediate and syn-diol.
The reaction of potassium permanganate with an alkene is very useful to determine the unsaturation i.e., the presence of carbon-carbon double bond character. Therefore, the detection of carbon-carbon double bond in an alkene via using \[KMn{O_4}\]is known as Baeyer’s test.
Therefore, from the above discussion, it is quite clear that cold and alkaline potassium permanganate (\[KMn{O_4}\]) is the suitable reagent for the synthesis of Ethylene glycol (syn-diol) from ethylene gas . Hence option (d) will be the correct answer.

Note: Ethylene is obtained by heating the natural gases or by heating petroleum to 900 \[^\circ C\]. Ethylene helps in the ripening of the fruit faster. Ethylene is also used in the production of glass for the automobile industry.