Question

Which one of the following occurs by an addition-elimination mechanism?

• A. Toluene, $B{r}_2$, $FeB{r}_3⟶$ p-bromotoluene
• B. Benzene, $HN{O}_3$, $H_{2}S{O}_4⟶$ nitrobenzene
• C. Benzene, $CO$, $HCl$, $AlC{l}_3$, $CuCl⟶$ benzaldehyde
• D. 2,4-dinitrochlorobenzene, $NaOH$, heat, then $H^{+}⟶$ 2,4-dinitrophenol

Answer 1

Answer: (A), (D)

Toluene, $B{r}_2$, $FeB{r}_3⟶$ p-bromotoluene
2,4-dinitrochlorobenzene, $NaOH$, heat, then $H^{+}⟶$ 2,4-dinitrophenol

When 2,4-dinitrochlorobenzene is heated with sodium hydroxide, the hydroxide ion is first added to the carbon atom bearing chlorine atom. This is followed by the elimination of chloro group in the form of chloride ion.
Thus, the reaction proceeds through addition elimination mechanism.