Toluene disproportionation oxidation

In the case of toluene disproportionation, reduction to benzene occurs when a methyl group pops off (hydrodealkylation takes place) and oxidation to xylene occurs as that methyl group that popped off attaches itself to another toluene molecule (a transalkylation reaction.)... 

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

Figure 7. (a) Catalytic activity for toluene disproportionation, and (b) possible Fe-species distribution estimated from TPR and TPS results (A) ion-exchanged type species, (B) Fe-oxide clusters inside die supercages with strong interaction to the framework oxygen atoms, and (C) Fe oxide without interaction to the zeolite. 

Hidaka and co-workers have proposed that the adsorption of H2S on such oxidic Fe-species accounts for the generation of the unique acidity required to catalyze the hydrocracking reaction as well as the toluene disproportionation [1]. From the standpoint of the production control, it is desirable that the Fe-treated Y-zeolite should be taken out at a time when the amount of the small Fe-oxide clusters inside the supercages reaches its maximum, and when the amount of the aggregated ferric oxide is still at a minimum. 

Toluene is oxidized in die liquid phase in the presence of a soluble cohalt-based catalyst The neutralization of benzoic add by potash yields insoluble potassium benzoate, which is separated by centrifuging. The disproportionation of potassium benzoate takes place between 400 and 430 C, under C02 pressure ranging from 13 to 3.106 Pa absolute, in the presence of a catalyst consisting of cadmium or zinc oxides. The reaction takes place in the solid phase. Tercphthalic add is released from its salt by the action of sulfuric add. 

Dewaxing, Methanol to gasoline, Methanol to olefins and products, FCC additive, Hydrocracking, Olefin cracking and oligomerisation, Benzene alkylation, Xylene isomerization, Toluene disproportionation, Aromatisation, NOx reduction, Oxidations, Hydration, Animation, Beckmann rearrangement, Cyclodimerisation,... 

The Henkel Il-process was also preferably operated in Japan. In this process, toluene is oxidized with air over cobalt catalysts to yield benzoic acid which is then transformed into potassium benzoate by subsequent neutralization. In the presence of cadmium oxide or zinc oxide, at temperatures of 450 °C and under CO2 pressure, disproportionation to dipotassium terephthalate occurs this is then converted into terephthalic acid. Benzene is a by-product of the disproportionation. 

Fig. 4.7 Aira-selectivity in toluene disproportionation over ZSM-5 modified with magnesium oxide (Mg=ll wt %).

Toluene, an aLkylben2ene, has the chemistry typical of each example of this type of compound. However, the typical aromatic ring or alkene reactions are affected by the presence of the other group as a substituent. Except for hydrogenation and oxidation, the most important reactions involve either electrophilic substitution in the aromatic ring or free-radical substitution on the methyl group. Addition reactions to the double bonds of the ring and disproportionation of two toluene molecules to yield one molecule of benzene and one molecule of xylene also occur. 

Another approach is the oxidative coupling of toluene to stilhene followed hy disproportionation to styrene and benzene ... 

Toluene (methylbenzene) is similar to benzene as a mononuclear aromatic, but it is more active due to presence of tbe electron-donating metbyl group. However, toluene is much less useful than benzene because it produces more polysubstituted products. Most of tbe toluene extracted for cbemical use is converted to benzene via dealkylation or disproportionation. Tbe rest is used to produce a limited number of petro-cbemicals. Tbe main reactions related to tbe cbemical use of toluene (other than conversion to benzene) are the oxidation of the methyl substituent and the hydrogenation of the phenyl group. Electrophilic substitution is limited to the nitration of toluene for producing mono-nitrotoluene and dinitrotoluenes. These compounds are important synthetic intermediates. 

Aqueous HCI solutions hydrolyze the P-N bond to give the amine hydrochloride and R2P-OH, which then disproportionates and is oxidized to diphenylphosphinic acid. A free phosphinous amide anion, with the countercation complexed by a crown ether, has been shown to be hydrolyzed and oxidized to the corresponding phosphinite with unusual ease [119]. Formic acid in toluene can be utilized for converting P,P-disubstituted phosphinous amides into their respective phosphane oxides [30]. 

For the non-oxidative activation of light alkanes, the direct alkylation of toluene with ethane was chosen as an industrially relevant model reaction. The catalytic performance of ZSM-5 zeolites, which are good catalysts for this model reaction, was compared to the one of zeolite MCM-22, which is used in industry for the alkylation of aromatics with alkenes in the liquid phase. The catalytic experiments were carried out in a fixed-bed reactor and in a batch reactor. The results show that the shape-selective properties of zeolite ZSM-5 are more appropriate to favor the dehydroalkylation reaction, whereas on zeolite MCM-22 with its large cavities in the pore system and half-cavities on the external surface the thermodynamically favored side reaction with its large transition state, the disproportionation of toluene, prevails. 

Disproportionation. A chemical reaction in which a single compound serves as both an oxidizing and reducing agent such as the dealkylation of toluene to give benzene (the more reduced product) and xylene (the more oxidized product). 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

The lifetime of the carbenium ion formed will be limited by transferring a proton back to the zeolite, thus completing the dehydrogenation ofthe hydrocarbon. Hydride abstraction from xylene is assumed to be the initial step in its disproportionation into toluene and trimethylbenzene [9]. The parent compound (7, Fig. 22.9) ofthe carbenium ion formed (6) has such a high proton affinity (1031 kj mohh Table 22.1) that proton transfer back to the zeolite does not occur at all. However, the lifetime of carbenium ions in zeolites is not only limited by proton transfer, but also formation of a C-O bond between the carbenium ion and a framework oxygen atom, yielding an alk-oxide, needs to be considered. In ferrierite (FER) the alkoxide of 6 is found to be 50 to 60 kJ mofi more stable than the carbenium ion [9]. 

The best approach to improving separations is to work toward reactions that achieve 100% yields at 100% conversions. Frequently, this will require more selective catalysts. The previous chapter contained an example moving in this direction. Toluene was disproportionated to benzene and xylenes using a silica-modified zeolite catalyst.23 After removal of benzene and unchanged toluene by distillation, the xylene remaining was a 99% para-isomer. It was clean enough to put directly into the process of oxidation to terephthalic acid. This avoided the usual separation of xylenes by crystallization or by a molecular sieve. There are times when an equilibrium can be shifted by removal of a product or by-product continuously to give 100% conversion. The familiar esterification with azeotropic removal of water or removal of water with a molecular sieve is an example. 

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