Write reactions of the final alkylation product of aniline with excess of methyl iodide in the presence of sodium carbonate solution.

When aniline is treated with excess methyl iodide in the presence of sodium carbonate, the reaction leads to the formation of N,N-dimethyl aniline as the final alkylation product. This process involves a series of steps that illustrate the reactivity of the amino group in aniline and how it can be transformed through alkylation.

The Reaction Mechanism

Aniline, which has the formula C₆H₅NH₂, contains an amino group that is a strong nucleophile. When we introduce methyl iodide (CH₃I) into the reaction, the methyl iodide acts as an electrophile. The sodium carbonate (Na₂CO₃) serves as a mild base to help deprotonate the aniline, making the amino group more nucleophilic.

Step-by-Step Process

• Deprotonation: The amino group of aniline can be deprotonated by sodium carbonate, forming the anilinium ion (C₆H₅N^-H) and releasing a proton (H⁺).
• Nucleophilic Attack: The nucleophilic aniline attacks the electrophilic carbon in methyl iodide, resulting in the formation of N-methyl aniline (C₆H₅NHCH₃).
• Further Alkylation: In the presence of excess methyl iodide, N-methyl aniline can undergo further alkylation, where it acts as a nucleophile and attacks another molecule of methyl iodide to form N,N-dimethyl aniline (C₆H₅N(CH₃)₂).

Final Product and Properties

The final alkylation product, N,N-dimethyl aniline, is a stable compound characterized by having two methyl groups attached to the nitrogen atom. This structure enhances the basicity of the amine compared to aniline itself due to the electron-donating nature of the methyl groups. However, this compound can also be more sterically hindered, which can affect its reactivity in further reactions.

Potential Side Reactions

While the primary reaction leads to N,N-dimethyl aniline, it's important to note that under certain conditions, over-alkylation can occur, leading to N,N,N-trimethyl anilinium iodide (C₆H₅N(CH₃)₃⁺I^-). This compound can form when there is an excess of methyl iodide present, and it can exist as a quaternary ammonium salt.

Conclusion

In summary, alkylation of aniline with excess methyl iodide in the presence of sodium carbonate results primarily in N,N-dimethyl aniline through a two-step nucleophilic substitution process. Understanding this reaction highlights the significance of the amino group's nucleophilicity and the potential for further alkylation under appropriate conditions.