芳香族ニトリルの接触合成反応に関する研究 (第5報)

酸化剤としてBr₂を用いる芳香族アンモ酸化反応

抄録

In order to confirm the reaction mechanism for the previously reported ammoxidation reaction using SO₂, ammoxidation reaction of toluene and ethylbenzene using Br₂ as an oxidizing agent was investigated.
C₆H₅CH₃+NH₃+3Br₂→C₆H₅CN+6HBr+25.0kcal/mol
(1) Activated alumina (γ-Al₂O₃), diatomaceous earth and fused alumina (Alundum; α-Al₂O₃) catalyzed the reaction at lower temperatures by 130-140°C than that in the case of SO₂, and particularly γ-Al₂O₃ and diatomaceous earth were very active, but the activity of these catalysts rapidly decreased in the course of reaction, and benzylbromide instead of benzonitrile was formed over the decayed catalyst or at lower temperatures. The rapid decay of catalyst activity resulted from the deposit of NH₄Br crystal and carbonaceous matter over the catalyst surface. In the case of ethylbenzene benzylcyanide was produced together with styrene and benzonitrile. It was inferred that the formation of benzylcyanide in this case was due to far lower reaction temperatures than those in the case of SO₂.
(2) From the above experimental results and the theory of radical reaction by Semenov, the reaction mechanism was inferred as follows;
C₆H₅CH₃→Br•→HBrC₆H₅CH₂→Br₂→Br•C₆H₅CH₂Br→NH₃γ-Al₂O₃C₆H₅CH₂NH₂→Br•γ-Al₂O₃→HBrC₆H₅CN
NH₃→γ-Al₂O₃NH₃(ads.)→Br•→NH₂(ads.)→HBr→γ-Al₂O₃
where the route (1) is probably a main process. This mechanism is similar to that of the reaction using SO₂.