芳香族ニトリルの接触合成反応に関する研究 (第6報)

In order to improve the ammoxidation reaction using Br₂ as reported in the previous paper, aromatic ammoxidation reactions substituted O₂ for part of Br₂ were investigated as follows:C₆H₅CH₃+NH₃+(3-n)Br₂+n/2O₂→C₆H₅CN+(6-2n)HBr+nH₂O<br>It was found that the activity of catalyst (γ-Al₂O₃) was stable during by far the longer period of time and the optimum reaction temperature was higher by 50-60°C than in the case of Br₂. The reaction rate equation was obtained as follows in consequence of the kinetic analysis over γ-Al₂O₃:<br>r=6.6×10⁴exp(-8000/RT)P^0.3_toluene P^0.3_NH₃ P^0.5_Br₂ P^1.5_O₂ (at 330-375°C)<br>This reaction was promoted over γ-Al₂O₃ and silica-alumina, but silica and diatomaceous earth were less active. The reaction wes improved remarkably over γ-Al₂O₃ -Cu and γ-Al₂O₃ -Fe, so-called Deacon's type catalyst; the ratio of Br₂ to toluene could be less than 0.05, where bromine functioned as a catalyst for hydrogen abstraction.<br>The activity of the Deacon's type catalyst depended on calcining of γ-Al₂O₃ and a ratio of CuBr₂ to γ-Al₂O₃, and the maximum activities were obtained Ca. 800°C of the calcination temperature and in Ca. 4 wt% of CuBr₂/γ-Al₂O₃ ratio respectively. In the case of this reaction, the temperature and the contact time were very critical for the conversion and the selectivity. The maximum one-pass conversion of 40% to benzonitrile was obtained in Ca. 4sec of the contact time at 350°C and the maximum selectivity of 90% to benzonitrile was done in Ca. 3sec of that at Ca. 300°C. Also I₂ and Cl₂ as well as Br₂ catalyzed formation of benzonitrile at by far the higher temperature than the case of Br₂ and bromine containing compounds i.e. bromoform and benzylbromide catalyzed that too.<br>The reaction of ethylbenzene formed styrene, benzonitrile and small quantity of benzylcyanide but cumene converted to α-methylstyrene, benzonitrile and no α-phenylpropionitrile.