$\mathop {{\text{POC}}{{\text{l}}_3}}\limits_{(B)} + 3{{\text{H}}_2}{\text{O}} \to \mathop {{{\text{H}}_3}{\text{P}}{{\text{O}}_4}}\limits_{(C)} + 3{\text{HCl}}$
$C _{2} H _{5} OH + PCl _{3} \rightarrow C _{2} H _{5} Cl + A$
$A + PCl _{3} \rightarrow B$