Question

Which of the following is the industrial method of preparation of acetaldehyde?

A) \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{CN}}\xrightarrow[{{\text{HCl}}}]{{{\text{SnC}}{{\text{l}}_{\text{2}}}}}{\text{ C}}{{\text{H}}_{\text{2}}}{\text{CH = NH}}\xrightarrow{{{{\text{H}}_3}{O^ + }}}{\text{C}}{{\text{H}}_{\text{3}}}{\text{CHO}}\]
B) \[{\text{C}}{{\text{H}}_{\text{3}}}{\text{COCl + }}{{\text{H}}_{\text{2}}}\xrightarrow[{{\text{BaS}}{{\text{O}}_{\text{4}}}}]{{{\text{Pd}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{CHO + HCl}}\]
C) \[{\text{C}}{{\text{H}}_{\text{2}}}{\text{ = C}}{{\text{H}}_{\text{2}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O }}\xrightarrow{{{\text{P}}{{\text{d}}^{{\text{2 + }}}}}}{\text{C}}{{\text{H}}_{\text{3}}}{\text{CHO}}\]
D) All of the above

Answer 1

Hint: Wacker process is used for the industrial preparation of acetaldehyde. In the Wacker process, acetaldehyde is prepared by oxidation of ethylene using an acidified solution of \[{\text{PdC}}{{\text{l}}_{{\text{2 }}}}\]and\[{\text{CuC}}{{\text{l}}_{\text{2}}}\].

Complete step by step answer:
A Wacker process is the most popular industrial method of preparation of acetaldehyde. In this method, an alkene is directly oxidised by using a homogenous \[{\text{PdC}}{{\text{l}}_{{\text{2 }}}}\] and\[{\text{CuC}}{{\text{l}}_{\text{2}}}\] system. To prepare acetaldehyde oxidation of ethylene is performed using an acidified solution of \[{\text{PdC}}{{\text{l}}_{{\text{2 }}}}\]and\[{\text{CuC}}{{\text{l}}_{\text{2}}}\].
The reaction given to us in option A is:
\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{CN}}\xrightarrow[{{\text{HCl}}}]{{{\text{SnC}}{{\text{l}}_{\text{2}}}}}{\text{ C}}{{\text{H}}_{\text{2}}}{\text{CH = NH}}\xrightarrow{{{{\text{H}}_3}{O^ + }}}{\text{C}}{{\text{H}}_{\text{3}}}{\text{CHO}}\]
This is Stephen reduction where acetaldehyde is prepared by the reduction of methyl cyanide (\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{CN}}\]) using tin (II) chloride (\[{\text{SnC}}{{\text{l}}_{\text{2}}}\]) and hydrochloric acid (HCl) followed by quenching of aldimine (\[{\text{C}}{{\text{H}}_{\text{2}}}{\text{CH = NH}}\]) with water. This is not an industrial method of preparation of acetaldehyde.
Thus, option (A) is incorrect.
The reaction given to us in option B is:
\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{COCl + }}{{\text{H}}_{\text{2}}}\xrightarrow[{{\text{BaS}}{{\text{O}}_{\text{4}}}}]{{{\text{Pd}}}}{\text{ C}}{{\text{H}}_{\text{3}}}{\text{CHO + HCl}}\]
This is Rosenmund reduction where acetaldehyde is prepared by the reduction of acyl chloride
(\[{\text{C}}{{\text{H}}_{\text{3}}}{\text{COCl}}\]) using molecular hydrogen (\[{{\text{H}}_{\text{2}}}\]) in presence of a catalyst \[{\text{Pd/BaS}}{{\text{O}}_{\text{4}}}\]. This is not an industrial method of preparation of acetaldehyde.
Thus, option (B) is incorrect.
The reaction given to us in option C is:
\[{\text{C}}{{\text{H}}_{\text{2}}}{\text{ = C}}{{\text{H}}_{\text{2}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O }}\xrightarrow{{{\text{P}}{{\text{d}}^{{\text{2 + }}}}}}{\text{C}}{{\text{H}}_{\text{3}}}{\text{CHO}}\]
This is a Wacker reduction of ethylene using homogenous \[{\text{PdC}}{{\text{l}}_{{\text{2 }}}}\] and \[{\text{CuC}}{{\text{l}}_{\text{2}}}\] system.
Thus, the correct option is (C) \[{\text{C}}{{\text{H}}_{\text{2}}}{\text{ = C}}{{\text{H}}_{\text{2}}}{\text{ + }}{{\text{H}}_{\text{2}}}{\text{O }}\xrightarrow{{{\text{P}}{{\text{d}}^{{\text{2 + }}}}}}{\text{C}}{{\text{H}}_{\text{3}}}{\text{CHO}}\].

So the correct option is (C).

Note: There are various methods of preparation of acetaldehyde. Like the reduction of methyl cyanide by the Stephen process, reduction of acyl chloride by Rosenmund and reduction of ethylene by the Wacker process. However, the most popular industrial method is the Wacker process.