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 will you show that acetylene is an unsaturated compound? How will you use it to prepare a) Benzene b) Acetaldehyde c) Ethane d) Copper acetylide e) ethene f) propyne

Accepted Answer

Acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The bromine water test is a qualitative test for the presence of unsaturation. Bromine water is brown in colour, when it is treated with acetylene then brown colour of solution decolorise due to the consumption of bromine.

Acetylene is a compound of great synthetic importance as it is used to synthesise many organic compounds.

a) Benzene : Acetylene on cyclic trimerisation in presence of red hot iron at $873 K$ yields benzene.

b) Acetaldehyde : Acetylene on hydration in presence of $40 % H_{2} {SO}_{4}$ and $1 % {HgSO}_{4}$ gives vinyl alcohol,which subsequently tautomerises to form acetaldehyde (keto form).

$CH \equiv CH \to_{H_{2} {SO}_{4}}^{{HgSO}_{4}} [{CH}_{2} = CH - OH] \overset{tautomerisation}{\to} {CH}_{3} CHO Acetylene Vinyl alcohol Acetaldehyde$

c) Ethane : Ethane can be obtained by acetylene by catalytic hydrogenation using excess of hydrogen with suitable catalyst. During the catalytic hydrogenation of ethyne, ethene is formed first which in the next step is further reduced to ethane.

$H - C \equiv C - H + H_{2} (excess) \overset{Pd}{\to} [H_{2} C = {CH}_{2}] \to {CH}_{3} - {CH}_{3} Acetylene ethene ethane$

d) Copper acetylide : Acetylene react with ammoniacal cuprous chloride to form copper acetylide.

$HC \equiv CH + amm . {Cu}_{2} {Cl}_{2} \to CuC \equiv CCu Acetylene Copper acetylide$

e) Ethene : Ethene can be obtained by acetylene by controlled catalytic hydrogenation using hydrogen with suitable catalyst.

$H - C \equiv C - H + H_{2} (limited) \overset{Pd}{\to} H_{2} C = {CH}_{2} Acetylene ethene$

f) Propyne : Acetylene on reaction with one equivalent metallic sodium forms sodium acetylide which on reaction with methyl iodide produces propyne.

$CH \equiv CH \overset{Na}{\to} CH \equiv CNa \overset{{CH}_{3} I}{\to} CH \equiv C - {CH}_{3} + NaI Acetylene Propyne$

How will you show that acetylene is an unsaturated compound? How will you use it to prepare a) Benzene b) Acetaldehyde c) Ethane d) Copper acetylide e) ethene f) propyne

Important Questions on Unsaturated Hydrocarbons-Alkynes

Learn and Prepare for any exam you want !