Question

Choose the incorrect reaction.
A. \[{\text{2}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{I + 2 Na }}\xrightarrow{{{{\left( {{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}} \right)}_{\text{2}}}{\text{O}}}}{\text{ }}{{\text{C}}_{\text{4}}}{{\text{H}}_{{\text{10}}}}{\text{ + 2NaI}}\]
B. \[{\text{2}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{Br + Zn }}\xrightarrow{{{\text{EtOH}}}}{\text{ }}{\left( {{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}} \right)_{\text{2}}}{\text{Zn + B}}{{\text{r}}_2}\]
C. \[{\text{2}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{I + N}}{{\text{a}}_2}{\text{S }} \to {\text{ }}{\left( {{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}} \right)_{\text{2}}}{\text{S + 2 NaI}}\]
D. \[{\text{2}}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{Br + NaI }}\xrightarrow{{{{\left( {{\text{C}}{{\text{H}}_3}} \right)}_2}{\text{C}} = {\text{O}}}}{\text{ }}{{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{I + NaBr}}\]
E. All are correct reactions

Answer 1

Hint: For each given reaction predict the products expected and compare them with the given products. The reactions are name reactions. Each reaction has its characteristic product.

Complete answer:
A. The reaction given in option A represents Wurtz reaction. It is used to synthesize higher alkanes by the reaction between lower alkyl halides and sodium metal. For example, if you react with two molecules of ethyl iodide with sodium metal in the presence of solvent such as diethyl ether, you will obtain n-butane. Thus, the option A represents the correct reaction.
B. The option B represents an incorrect reaction. If you use zinc instead of sodium metal in Wurtz reaction, then you can name the reaction as Frankland reaction. In this reaction, like in the Wurtz reaction, the product should be a higher alkane and not a dialkyl zinc.You should get n-butane as the product of the reaction between zinc and ethyl bromide.
C. The reaction in option C is named as Williamson synthesis of alkyl sulfides. For this reaction, you should react with alkyl halides and sodium sulfide. Thus, the option C represents a correct reaction.
D. You can name the reaction of option D as the Finkelstein reaction. In this reaction, you treat an alkyl bromide with sodium iodide and acetone. You will get a halogen exchange reaction and the product formed will be an alkyl iodide. Hence the option D also represents a correct reaction.

Thus, the reaction of option B is an incorrect reaction. Hence, the correct answer is option B.

Note:
All the given reactions transform alkyl halides into either alkanes, another alkyl halides or alkyl sulphides. Thus, these reactions represent functional group transformation reactions.