What is the purpose of ammonium chloride in anti hydrogenation of alkynes?

In my organic chemistry textbook, lithium is used to create a free radical of the alkynes, to then allow the anti addition of hydrogen to get an alkene.


"The Dissolving Metal Reduction of Alkynes" is a reaction that then uses $\ce{NH4Cl}$. Why put $\ce{NH4Cl}$?


[![](https://i.stack.imgur.com/dN0x9.png "source: imgur.com")](https://i.stack.imgur.com/42Q5T.jpg)
[![](https://i.stack.imgur.com/Y4fVT.png "source: imgur.com")](https://i.stack.imgur.com/CFcKF.jpg)




Products from reaction step (1) are the *trans*-alkene and 2 equivalents of the amide $\ce{LiNHEt}$, a strong base. Step (2) is the workup of the reaction mixture with aqueous $\ce{NH4Cl}$ solution, which serves several purposes. First, it quenches the lithium amide and unreacted lithium metal.


$$\ce{LiNHEt + NH4Cl ->~ EtNH2 + NH3 + LiCl}$$
$$\ce{Li + H2O ->~ LiOH (aq) + \frac{1}{2} H2\uparrow}$$


Secondly, the *trans*-alkene is usually less water-soluble than ethyl amine and the lithium and ammonium salts, and can be separated from the workup mixture by precipitation or extraction with an organic solvent.


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