Studies On Catalytic Reaction Systems Of Hydroxylation Of Benzene And Toluene

The direct functionalization of aromatic ring,which involves the activation of C-H bond,preserves a challenging topic in chemistry and attracts much attention recently.Phenol and cresol are important fine chemical intermediates and of high economical value.In present work, Phenol and catechol were obtained by using mature coupled technology or devising catalyst,which make traditional multi-step processes more easy and practical.(1)In order to reduce reserve and transportation for H₂O₂ and enhance selectivity for phenol,we devise to use H₂O₂ in situ by anthraquinone approach for the hydroxylation of benzene.It is found that anthraquinone and hydroanthraquinone can be most dissolved when the volume ratio for benzene and acetic acid is 4/10,contributing to appropriate polarity for the mixed solvents.Here,the only product phenol yield and the anthraquinone utilization efficiency are the highest, 0.255mmol and 26.6%,respectively.In addition,vanadium catalysts, especially NH₄VO₃ play a key role for oxidizing benzene among oxidation catalysts.It is discovered that the yield of phenol is the highest when the atom ratio for V/Pd is 4.What is more,the accumulated phenol yield could achieve 0.833 mmol after the system is recycled three times, which average yield is slightly higher than the phenol yield obtained in the first cycle(ca.0.255 mmol),indicating that such coupled reaction system could be recycled efficiently.At last,a synergistic mechanism is proposed to explain the favorable role of V compound on the Pd/γ-Al₂O₃ catalyst.(2)In the experiment of the catalyst Fe(DDS)₃ catalyzing the direct hydroxylation of benzene with H₂O₂,We study the reaction condition influence,including the type of catalysts,reaction solvent,reaction temperature,the amount of H₂O₂ and the mole ratio for reagents.At 50℃, the amount of catalyst is 0.05 mmol,benzene/H₂O₂(mole ratio)=1/1, benzene/CH₃CN(volume ratio)=1/4,the best results could be obtained with 14%conversion of benzene,99%selectivity of phenol and 14% efficient utilization of H₂O₂.Adding H₂O has little effect on the hydroxylation of benzene.(3)Explore an overall green process in which involves the preparation of FeCl₃ or CuCl₂ modifiedβzeolite(Fe-βor Cu-β)by use of the simple solid state reaction and check its catalytic properties in the direct hydroxylation of toluene with H₂O₂ as an green oxidant.It is found that Fe-βzeolite catalyst has good catalytic activity for the hydroxylation of toluene with more than 37%conversion of toluene and poor selectivity for cresol(63%)under the optimum reaction conditions while Cu-βcatalyst have good toluene conversion and better cresol selectivity,21% and 90%respectively.Therefore,with Cu-βcatalyst as a example,we study the reaction condition influence,such as the reaction solvents,the carrier,reaction temperature,the amount of catalyst and the amount of reactant.The best reaction activity is obtained with the mixed solvents including CH₃CN and H₂O.At the same time,the solid ion exchange for the active center and the carrier can enhance the toluene conversion and cresol selectivity efficiently.The carrier's acid density can affect the extent of active center exchange and the carrier's acid strength have an effect on the diffuse of active center,so the carrier's acid density and strength affect catalytic activity.At last but not least,the Cu-βzeolite catalyst is very stable and its active Cu sites are little washed away in the reaction process.As a result,it can be recovered and repeatedly used several times without any being loss of activity.