${C_2}{H_5}I\xrightarrow{{Alco.\,\,KOH}}X\xrightarrow{{B{r_2}}}Y\xrightarrow{{KCN}}Z$
$ 3 \mathrm{ROH}+\mathrm{PCl}_3 \rightarrow 3 \mathrm{RCl}+\mathrm{A} $
$ \mathrm{ROH}+\mathrm{PCl}_5 \rightarrow \mathrm{RCl}+\mathrm{HCl}+\mathrm{B}$