Oxidation of benzenes

Benzene oxidation is the oldest method to produce maleic anhydride. The reaction occurs at approximately 380°C and atmospheric pressure. A mixture of V2O5/MO3 is the usual catalyst. Benzene conversion reaches 90%, hut selectivity to maleic anhydride is only 50-60% the other 40-50% is completely oxidized to C02 ° 

Currently, the major route to maleic anhydride, especially for the newly-erected processes, is the oxidation of hutane (Chapter 6). Maleic anhydride also comes from oxidation of n-hutenes. Properties and chemicals derived from maleic anhydride are noted in Chapter 9. 

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Biochemical Routes. Enzymatic oxidation of benzene or phenol leading to dilute solution of dihydroxybenzenes is known (62). Glucose can be converted into quinic acid [77-95-2] by fermentation. The quinic acid is subsequently oxidized to hydroquinone and -benzoquinone with manganese dioxide (63). 

Starting from Benzene. In the direct oxidation of benzene [71-43-2] to phenol, formation of hydroquinone and catechol is observed (64). Ways to favor the formation of dihydroxybenzenes have been explored, hence CuCl in aqueous sulfuric acid medium catalyzes the hydroxylation of benzene to phenol (24%) and hydroquinone (8%) (65). The same effect can also be observed with Cu(II)—Cu(0) as a catalytic system (66). Efforts are now directed toward the use of Pd° on a support and Cu in aqueous acid and in the presence of a reducing agent such as CO, H2, or ethylene (67). Aromatic... 

Other Methods. A variety of other methods have been studied, including phenol hydroxylation by N2O with HZSM-5 as catalyst (69), selective access to resorcinol from 5-methyloxohexanoate in the presence of Pd/C (70), cyclotrimerization of carbon monoxide and ethylene to form hydroquinone in the presence of rhodium catalysts (71), the electrochemical oxidation of benzene to hydroquinone and -benzoquinone (72), the air oxidation of phenol to catechol in the presence of a stoichiometric CuCl and Cu(0) catalyst (73), and the isomerization of dihydroxybenzenes on HZSM-5 catalysts (74). 

Process Technology Evolution. Maleic anhydride was first commercially produced in the early 1930s by the vapor-phase oxidation of benzene [71-43-2]. The use of benzene as a feedstock for the production of maleic anhydride was dominant in the world market well into the 1980s. Several processes have been used for the production of maleic anhydride from benzene with the most common one from Scientific Design. Small amounts of maleic acid are produced as a by-product in production of phthaHc anhydride [85-44-9]. This can be converted to either maleic anhydride or fumaric acid. Benzene, although easily oxidized to maleic anhydride with high selectivity, is an inherently inefficient feedstock since two excess carbon atoms are present in the raw material. Various compounds have been evaluated as raw material substitutes for benzene in production of maleic anhydride. Fixed- and fluid-bed processes for production of maleic anhydride from the butenes present in mixed streams have been practiced commercially. None of these... 

Maleic anhydride is made by oxidation of benzene with air above 350°C (662°F) with V-Mo catalyst in a mnltitiibiilar reactor with 2-cm tubes. The heat-transfer medium is a eutectic of molten salt at 375°C (707°F). Even with small tubes, the heat transfer is so hmited that a peak temperature 100°C (212°F) above the shell side is developed and moves along the tubes. 

Series reaetions also oeeur in oxidation proeesses where the required produet may oxidize further. An example is the produetion of maleie anhydride from the oxidation of benzene. In this ease, the maleie anhydride ean be oxidized further to earbon dioxide and water. Another example of a series reaetion oeeurs in the bioehemieal reaetion in whieh Pseudomonas ovalis is used to eonvert glueose to glueonie aeid via glueonolaetone in bateh eulture. This first order reaetion is represented by... 

Similar approaches are applicable in the chemical industry. For example, maleic anhydride is manufactured by partial oxidation of benzene in a fixed catalyst bed tubular reactor. There is a potential for extremely high temperatures due to thermal runaway if feed ratios are not maintained within safe limits. Catalyst geometry, heat capacity, and partial catalyst deactivation have been used to create a self-regulatory mechanism to prevent excessive temperature (Raghaven, 1992). 

Other routes to maleic anhydride are the oxidation of n-hutane, a major source for this compound (Chapter 6), and the oxidation of benzene (Chapter 10). 

Butadiene has the advantage of a relatively low heat of reaction (995 kJ/ mol compared with 1875 kJ/mol in the oxidation of benzene), but the disadvantage of a relatively high price compared with the other -C4 hydrocarbons. Good prospects has the n-butane route. Keeping the n-butane conversion at about 15%, the yield of maleic acid anhydride amounts to 50-60 mol %. 

In 1990 50% of the maleic acid anhydride was produced by oxidation of benzene and the other 50% by oxidation of the different n-C4 hydrocarbons. 

For many years the catalytic air oxidation of benzene was the main source of maleic anhydride. Obviously, two carbons from each ring are wasted as carbon dioxide in this process. Although some is still made that way, most modem maleic anhydride plants are based on butane oxidation. Because butane is forecast to be plentiful and low-cost, new routes to four-carbon chemicals from maleic anhydride are under active development. 

In addition to nonheme iron complexes also heme systems are able to catalyze the oxidation of benzene. For example, porphyrin-like phthalocyanine structures were employed to benzene oxidation (see also alkane hydroxylation) [129], Mechanistic investigations of this t3 pe of reactions were carried out amongst others by Nam and coworkers resulting in similar conclusions like in the nonheme case [130], More recently, Sorokin reported a remarkable biological aromatic oxidation, which occurred via formation of benzene oxide and involves an NIH shift. Here, phenol is obtained with a TON of 11 at r.t. with 0.24 mol% of the catalyst. 

Oxidation of benzene (and also chlorobenzene and toluene) by Mn(III) acetate in glacial acetic acid gives a mixture of products including benzyl acetate (from benzene) indicating an initial attack on the aromatic by CH2C02H . The kinetics and actual rate of disappearance of Mn(III) are the same for CgHs and... 

The oxidation of benzene to phenol and 1,4-dihydroxybenzene (Figure 2.11a) (Hyman et al. 1985), both side chain and ring oxidation of ethyl benzene, and ring-hydroxylation of halogenated benzenes and nitrobenzene (Keener and Arp 1994). 

Tao Y, A Fishman, WE Bentley, TK Wood (2004) Oxidation of benzene to phenol, catechol, and 1,2,3-trihydroxybenzene by toluene 4-monooxygenase of Pseudomonas mendocina KR 1 and toluene... 

In a classical study, it was shown that during bacterial oxidation of benzene to catechol both atoms of oxygen came from 62 (Gibson et al. 1970). This initiated the appreciation of the role of dioxygenases in the degradation of aromatic xenobiotics, and many examples are given in Chapter 8, Parts 1 and 2. 

Nitrous oxide as an efficient oxygen donor was noticed when used in such a delicate reaction as the direct oxidation of benzene to phenol ... 

Adamska-Rutkowska, D., 1992, An Identification of the Model of the Process for Oxidation of Benzene to Maleic Anhydride , Ph.D. Thesis, Warsaw University of Technology, Warsaw. 

Hensen EJM, Zhu Q, van Santen RA. 2005. Selective oxidation of benzene to phenol with nitrous oxide over MFI zeolites. 2. On the effect of the iron and aluminum content and the preparation route. J Catal 233 136-146. 

Pd(II) Wacker-type catalysts were also studied.146 Selective oxidation of benzene to phenol by molecular oxygen in the presence of Pd and heteropolyacids have been published.147... 

Vaidyanathan and Doraiswamy [Chem. Eng. Sci., 23 (537), 1966] have studied the catalytic partial oxidation of benzene in a composition range where the reactions of interest all follow pseudo first-order kinetics. The pertinent stoichiometric equations are... 

Oxidation of benzene to phenol. This was attempted in the former U.S.S.R. and Japan on a pilot-plant scale. High yields were reported, but full-scale operation apparently was discontinued because of destruction of product by irradiation and the possibility of explosion in the reaction vessel. The latter danger can be controlled in the oxidation of halo-genated hydrocarbons such as trichloro- or tetrachloroethylenes, where a chain reaction leads to the formation of dichloro- or trichloro-acetic acid chlorides through the respective oxides. 

Scheme 10.12 Oxidation of benzene with hydrogen peroxide.

Titanium-containing zeolite was an efficient catalyst for oxidation of benzene with hydrogen peroxide in a microwave field, affording phenol with high selectivity. It was reported that microwaves had a strong effect on the selectivity of the reaction. 

Co/A1203 [35] Reaction tested was complete oxidation of benzene to C02... 

Vaidyanathan and Doraiswamy (1968) studied the kinetics of the gas-phase partial oxidation of benzene (CgHg, B) to maleic anhydride (C4H2O3, M) with m in an integral PFR containing... 

An increased selectivity for phenol in the oxidation of benzene by H202 with TS-1 catalyst in sulfolane solvent was attributed to the formation of a bulky sulfolane-phenol adduct which cannot enter the pores of TS-1. Further oxidation of phenol to give quinones, tar, etc. is thus avoided. Removal of Ti ions from the surface regions of TS-1 crystals by treatment with NH4HF2 and H202 was also found to improve the activity and selectivity (227). The beneficial effects of removal of surface Al ions on the catalytic performance of zeolite catalysts for acid-catalyzed reactions have been known for a long time. 

Direct production of benzoquinone (BQ) from benzene is one of the targets in industrial chemistry. Considerable efforts have been made to develop the electrochemical oxidation of benzene to p-benzoquinone to the industrial scale thus forming a basis for a new hydroquinone process [40]. Benzene in aqueous emulsions containing sulfuric acid (1 1 mixture of benzene and 10% aqueous H2S04) forms, at the anode, p-benzoquinone which can be reduced cathodically to yield hydroquinone in a paired synthesis. A divided cell with Pb02 anodes is used. 

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