Explanation:
Chloroform is oxidised to a poisonous gas, by aerial oxidation.
\[\begin{array}{*{20}{l}}
{{\rm{CHC}}{{\rm{l}}_{\rm{3}}} + [{\rm{O}}] \to \mathop {{\rm{COC}}{{\rm{l}}_{\rm{2}}}}\limits_{{\rm{Phosgene}}} + {\rm{HCl}}}\\
{{\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {\mkern 1mu} }
\end{array}\]
Ethyl alcohol is used as a negative catalyst for the aerial oxidation of chloroform in presence of light. It converts \(\mathrm{COCl}_{2}\) to non-poisonous ethyl carbonate.
\[\begin{array}{l}
{\rm{COC}}{{\rm{l}}_{\rm{2}}}\,{\rm{ + }}\,\,{\rm{2}}{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}} \to {\rm{O}}\,\,{\rm{ = }}\,\,{\rm{C(O}}{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{{\rm{)}}_{\rm{2}}}\\
\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,{\rm{ + }}{\mkern 1mu} {\rm{2HCl}}
\end{array}\]
