But-1-ene is treated with $\mathrm{Br}{}_2$ in $\mathrm{CCl}{}_4$. The product is then heated with three equivalents of $\mathrm{NaNH}{}_2$ in liquid ammonia, followed by water. The final organic product is

Bromine adds to give 1,2-dibromobutane. Two equivalents of amide remove two HBr by successive E2 steps to give but-1-yne. The terminal alkyne is acidic and the third equivalent converts it to sodium but-1-ynide; aqueous work-up reprotonates it to but-1-yne.