$\mathrm{PhCHOHCH}_{3}+4 \mathrm{I}_{2}+6 \mathrm{NaOH} \stackrel{\Delta}{\longrightarrow} $$\mathrm{CHI}_{3}+\mathrm{PhCOONa}+5 \mathrm{NaI}+5 \mathrm{H}_{2} \mathrm{O}$
$(I)$ $C{H_2} = CH - C{H_3} + {H_2}O\xrightarrow{{{H^ + }}}$
$(II)$ $C{H_3}CHO\xrightarrow[{(ii)\,{H_2}O}]{{(i)\,\,C{H_3}MgI}}$
$(III)$ $CH_2O\xrightarrow[{(ii)\,{H_2}O}]{{(i)\,\,C{_2}H_5MgI}}$
$(IV)$ $C{H_2} = CH - C{H_3}\xrightarrow{{nutral \,KMn{O_4}}}$
