In order to confirm the reaction mechanism for the previously reported ammoxidation reaction using SO
2, ammoxidation reaction of toluene and ethylbenzene using Br
2 as an oxidizing agent was investigated.
C
6H
5CH
3+NH
3+3Br
2→C
6H
5CN+6HBr+25.0kcal/mol
(1) Activated alumina (γ-Al
2O
3), diatomaceous earth and fused alumina (Alundum; α-Al
2O
3) catalyzed the reaction at lower temperatures by 130-140°C than that in the case of SO
2, and particularly γ-Al
2O
3 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 NH
4Br 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 SO
2.
(2) From the above experimental results and the theory of radical reaction by Semenov, the reaction mechanism was inferred as follows;
C
6H
5CH
3→Br•→HBrC
6H
5CH
2→Br
2→Br•C
6H
5CH
2Br→NH
3γ-Al
2O
3C
6H
5CH
2NH
2→Br•γ-Al
2O
3→HBrC
6H
5CN
NH
3→γ-Al
2O
3NH
3(ads.)→Br•→NH
2(ads.)→HBr→γ-Al
2O
3where the route (1) is probably a main process. This mechanism is similar to that of the reaction using SO
2.
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