Question

Which of the following reagents is used in Hofmann's elimination reaction of amines?

Options

• CHCl₃ + KOH

• CH₃COCI

• Ag₂O/H₂O, Δ

• NaNO₂ + HCl

Answer 1

Ag₂O/H₂O, Δ

Explanation:

When tetraalkylammonium halide is heated with damp silver oxide, it produces quaternary ammonium hydroxide, which undergoes β-elimination to produce alkenes when heated to a high temperature; this reaction is known as Hofmann elimination. The least substituted alkene is the primary result in this reaction, for example

\[\begin{array}{cc}
\phantom{}\ce{CH3}\phantom{.........................................}\ce{CH3}\phantom{...................}\\
\phantom{}|\phantom{............................................}|\phantom{.....................}\\
\ce{[CH3 - N^+ - \overset{α}{C}H2\overset{β}{C}H3]I^- + AgOH ->[Ag2O/H2O][\Delta] [CH3 - N^+ - \overset{α}{C}H2 - \overset{β}{C}H3] OH^- + AgI}\\
\phantom{}|\phantom{............................................}|\phantom{.....................}\\
\phantom{}\ce{\underset{Ethyl trimethyl ammonium iodide}{CH3}}\phantom{...................}\ce{\underset{Ethyl trimethyl ammonium hydroxide}{CH3}}\phantom{.................}
\end{array}\]

\[\begin{array}{cc}
\ce{CH3}\phantom{................................................}\\
|\phantom{...................................................}\\
\ce{[CH3 - N^+ -\overset{α}{C}H2 - \overset{β}{C}H2] OH^- ->[\Delta] \underset{Ethylene}{CH2 = CH2} + \underset{trimethyl amine}{(CH3)3N} + H2O}\\
\phantom{.....}|\phantom{............}|\phantom{...........................................}\\
\phantom{.}\ce{CH3}\phantom{........}\ce{H}\phantom{.......................................}
\end{array}\]