Question

Acetylene reacts with ammonium chloride in presence of cuprous chloride to form:
A) $\text{ CuC}\equiv \text{CCu }$
B) $\text{ C}{{\text{H}}_{2}}\equiv \text{CHC}\equiv \text{CH }$
C) $\text{ CH}\equiv \text{CCu }$
D) $\text{ CuC}\equiv \text{CN}{{\text{H}}_{4}}\text{ }$

Answer 1

Hint: The Glaser coupling reaction is a coupling reaction. The reaction involves the coupling reaction between the acetylenic group with itself in presence of the cuprous chloride $\text{ CuCl }$ or the $\text{ CuBr }$ and additional oxidant like oxygen.
The general reaction scheme is as follows:
$\text{ R}-\text{C}\equiv \text{H }\xrightarrow[\text{N}{{\text{H}}_{\text{4}}}\text{OH , EtoH}]{\text{CuCl}}\text{ 2 R}-\text{C}\equiv \text{Cu}\to \text{R}-\text{C}\equiv \text{C}-\text{C}\equiv \text{C}-\text{R}$

Complete Solution :
> The Glaser coupling is a coupling reaction. It is a synthesis reaction for symmetric or cyclic bis acetylene through the coupling reaction. This coupling reaction takes place at the terminal alkyne. The mechanism uses the catalytic copper (I) which is then oxidized by the oxygen present in the medium.
The method is applicable to the coupling reaction alkynes.
> Now, as mentioned it is an example of Glaser coupling. Let us know about the Glaser coupling.
> In this case, we can see that the acetylene is a terminal alkyne. So, the chemical reaction can be written as:
$\text{ 2CH}\equiv \text{CH}\xrightarrow[\text{CuCl}]{\text{N}{{\text{H}}_{4}}\text{Cl}}\text{C}{{\text{H}}_{2}}\text{=CHC}\equiv \text{CH }$
> Now, in this reaction, 2 molecules of acetylene are used.
> Thus, there will be an addition of a triple bond to the one molecule of acetylene to that of other molecules of acetylene.
> In the last, we can conclude that the acetylene reacts with ammonium chloride in presence of cuprous chloride to form but-1, 3-yne, or vinyl acetylene, i.e. $\text{ C}{{\text{H}}_{2}}\text{=CHC}\equiv \text{CH }$

So, the correct answer is “Option B”.

Note: Note that, the Glaser coupling reaction strictly produces the symmetrically coupled compounds. The Glaser coupling reaction is modified in what is known as the Eglinton reaction. In these reactions the terminal alkynes are coupled in presence of copper (II) salt (cupric acetate $\text{ Cu(OAc}{{\text{)}}_{\text{2}}}\text{ }$). The reaction has a wide application to synthesis the fungal antibiotics.