Name: Uses of Alkyne
Uploaded: 2019-07-19
Duration: 6 min 18 s
Description: We all read about the unsaturated hydrocarbon, alkyne. Have you ever wondered where they are used? Let us learn more about alkynes through its uses in our da...

Question

How is acetylene prepared from following compounds a) maleic acid b) calcium carbide? Explain the acidic character of acetylenic hydrogen. How does acetylene react with (i) Alkaline

{KMnO}_{4}

solution (ii)

HOCl

Accepted Answer

Acetylene can be prepared by maleic acid and calcium carbide in the following manner-

Acetylene can be prepared by the electrolysis of the concentrated solution of potassium or sodium salt of maleic acid.

For producing acetylene $(C_{2} H_{2})$ , the reaction of calcium carbide $({CaC}_{2})$ with water $(H_{2} O)$ is used, wherein acetylene and milk of lime $(Ca {(OH)}_{2})$ is generated.
${CaC}_{2} + 2 H_{2} O \to C_{2} H_{2} + Ca {(OH)}_{2}$

Acetylene is mildly acidic due to presence of terminal acidic hydrogen atoms. It reacts with sodium metal(one equivalent) to form sodium acetylide with liberation of hydrogen gas which is detected by pop sound test. This proves the acidic nature of acetylene.

$H - C \equiv C - H + Na \to H - C \equiv CNa + \frac{1}{2} H_{2}$

(i) Acetylene undergoes oxidative hydrolysis in presence of alkaline ${KMnO}_{4}$ solution to form oxalic acid as:

$CH \equiv CH \overset{{KMnO}_{4} / {OH}^{-}}{\to} {(COOH)}_{2} Acetylene Oxalic acid$

(ii) Dichloro acetaldehyde is formed as the main product when acetylene reacts with $HOCl$ (hypochlorous acid).
$HC \equiv CH + 2 HOCl \to [{CHCl}_{2} = CH {(OH)}_{2}] \overset{- H_{2} O}{\to} {CHCl}_{2} - CHO Acetylene Intermediate gem diol Dichloro acetaldehyde$

Odisha Board Solutions for Chapter: Unsaturated Hydrocarbons-Alkynes, Exercise 1: QUESTIONS

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