Question

The replacement of diazonium group by fluorine is known as:
A.) Gattermann reaction
B.) Sandmeyer reaction
C.) Balz-Schiemann reaction
D.) Etard reaction

Answer 1

Hint: When diazonium salt is reacted with the fluoroboric acid ($HB{F_4}$) then the benzene diazonium fluoroborate (${C_6}{H_5} - {N_2}B{F_4}$) is obtained which again on heating produce the required fluorobenzene (${C_6}{H_5} - F$).

Complete answer:
In this question, the Gattermann reaction is a chemical reaction in which when diazonium salt is treated with a halogen acid ($HBr{\text{ }}or{\text{ }}HCl$) in the presence of copper powder then the corresponding benzene halide is formed. This reaction is used to produce benzene chloride and benzene bromide. It can be given as:
${C_6}{H_5} - {N_2}^ + {X^ - }\xrightarrow[{(X = Cl,Br)}]{{Cu + HX}}{C_6}{H_5} - X + {N_2}$
The Sandmeyer reaction is used to obtain benzene chloride, and benzene bromide in the product when benzene diazonium salt is reacted with $C{u_2}{X_2}/HX(X = Br,Cl)$. This reaction can be represented as:
${C_6}{H_5} - {N_2}^ + {X^ - }\xrightarrow[{(X = Cl,Br)}]{{C{u_2}{X_2} + HX}}{C_6}{H_5} - X + {N_2}$
The Balz-Schiemann reaction is used for the preparation of benzene fluoride. When benzene diazonium salt is reacted with fluoroboric acid ($HB{F_4}$) and then heated to form benzene chloride. In it the diazonium group is replaced by the fluorine. This reaction can be represented as:
${C_6}{H_5} - {N_2}^ + C{l^ - }\xrightarrow{{HB{F_4}}}{C_6}{H_5} - {N_2}^ + B{F_4}^ - \xrightarrow{\Delta }{C_6}{H_5} - F + B{F_3}$
The Etard reaction is used for the preparation of benzaldehyde. In this reaction when toluene reacts with chromyl chloride ($Cr{O_2}C{l_2}$) then it gives corresponding benzaldehyde.
This reaction can be given as:
${C_6}{H_5} - C{H_3} + Cr{O_2}C{l_2} \to {C_6}{H_5} - CHO$

Hence, option C.) is the correct answer.

Note:
Always remember that if we want to prepare benzene chloride and benzene bromide from the diazonium salt then it can be obtained by the Gattermann reaction or by Sandmeyer reaction.