Conversion of benzene

Benzene-Based Catalyst Technology. The catalyst used for the conversion of ben2ene to maleic anhydride consists of supported vanadium oxide [11099-11-9]. The support is an inert oxide such as kieselguhr, alumina [1344-28-17, or sUica, and is of low surface area (142). Supports with higher surface area adversely affect conversion of benzene to maleic anhydride. The conversion of benzene to maleic anhydride is a less complex oxidation than the conversion of butane, so higher catalyst selectivities are obtained. The vanadium oxide on the surface of the support is often modified with molybdenum oxides. There is approximately 70% vanadium oxide and 30% molybdenum oxide [11098-99-0] in the active phase for these fixed-bed catalysts (143). The molybdenum oxide is thought to form either a soUd solution or compound oxide with the vanadium oxide and result in a more active catalyst (142). 

Recendy, the myelotoxicity has been proposed to occur through initial conversion of benzene to phenol and hydroquinone in the fiver, selective accumulation of hydroquinone in the bone marrow, followed by conversion of hydroquinone to benzoquinone via bone marrow myeloperoxidase. Benzoquinone is then proposed to react with macromolecules dismpting cellular processes (108). 

A route to phenol has been developed starting from cyclohexane, which is first oxidised to a mixture of cyclohexanol and cyclohexanone. In one process the oxidation is carried out in the liquid phase using cobalt naphthenate as catalyst. The cyclohexanone present may be converted to cyclohexanol, in this case the desired intermediate, by catalytic hydrogenation. The cyclohexanol is converted to phenol by a catalytic process using selenium or with palladium on charcoal. The hydrogen produced in this process may be used in the conversion of cyclohexanone to cyclohexanol. It also may be used in the conversion of benzene to cyclohexane in processes where benzene is used as the precursor of the cyclohexane. 

Benzene dioxygenase is a complex enzyme consisting of three protein components, that catalyse the conversion of benzene to benzene cis-dihydrodiol. Give two reasons why this biotransformation should be carried out using whole cells as opposed to using enzyme preparations. 

The price of cyclohexane tracks that of benzene and is only marginally higher because the conversion of benzene to cyclohexane is readily accomplished in very high yield. 

Much research has been carried out into direct amination of aromatic substrates, typified by the direct conversion of benzene to aniline using ammonia and a catalyst. Although there have been many patented routes conversions, are normally low, making them uneconomic. Modem catalysts based on rhodium and iridium, together with nickel oxide (which becomes reduced), have proved more active,and such is the research activity in this area that it is only a matter of time before such processes become widely used. 

Iron impregnated on activated carbon was used as catalyst for the direct synthesis of phenol from benzene. The effect of Sn addition to the catalyst was studied. The prepared catalysts were characterized by BET, SEM and XRD analysis. The catalyst 5.0Fe/AC showed good activity in the conversion of benzene and addition of Sn seemed to improve the selectivity of phenol in the reaction. 

Catalysts were prepared with 0.5, 1.0, 2.0 and 5.0 wt% of iron loaded on activated carbon. Benzene hydroxylation with hydrogen peroxide as oxidant was carried out. The conversion of benzene, selectivity and yield of phenol for these catalysts are shown in Fig. 4. As the weight of loaded metal increased the benzene conversion increased by about 33% but the selectivity to phenol decreased. The yield of phenol that was obtained with S.OFe/AC was about 16%. 

Benzene hydrogenation was used to probe metal site activity. A 12/1 H2/benzene feed was passed over the catalysts at 700 kPa with a weight hourly space velocity of 25. The temperature was set to 100°C and the conversion of benzene to cyclohexane was measured after 2 hours at temperature. The temperature was then increased at 10°C increments and after two hours, the conversion remeasured. 

The total hydrogenation of benzene derivatives represents an important industrial catalytic transformation, in particular with the conversion of benzene into cyclohexane, a key intermediate in adipic acid synthesis, which is used in the production of Nylon-6,6 (Scheme 1). This reaction is still the most important industrial hydrogenation reaction of monocyclic arenes [1]. 

Because LCEC had its initial impact in neurochemical analysis, it is not, surprising that many of the early enzyme-linked electrochemical methods are of neurologically important enzymes. Many of the enzymes involved in catecholamine metabolism have been determined by electrochemical means. Phenylalanine hydroxylase activity has been determined by el trochemicaUy monitoring the conversion of tetrahydro-biopterin to dihydrobiopterin Another monooxygenase, tyrosine hydroxylase, has been determined by detecting the DOPA produced by the enzymatic reaction Formation of DOPA has also been monitored electrochemically to determine the activity of L-aromatic amino acid decarboxylase Other enzymes involved in catecholamine metabolism which have been determined electrochemically include dopamine-p-hydroxylase phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase . Electrochemical detection of DOPA has also been used to determine the activity of y-glutamyltranspeptidase The cytochrome P-450 enzyme system has been studied by observing the conversion of benzene to phenol and subsequently to hydroquinone and catechol... 

Conversion of benzene to cyclohexene by partial catalytic hydrogenation is a very important industrial process, since it provides a new route to cyclohexanol, a precursor of nylon, when combined with hydration of cyclohexene. For example, Asahi Chemical Company of Japan developed a selective bilayer catalytic system including a Ru catalyst, Zr02 and ZnS04 under 50 atm of H2 pressure, a process affording the olefin with up to 60% selectivity after 90% conversion of benzene.72... 

The biotransformation that has caught the imagination of many synthetic organic chemists involves the conversion of benzene and simple derivatives (toluene, chlorobenzene, etc.) into cyclohexadienediols (20) using a recombinant microorganism E. coli JM109. The one step oxidation, via reduction of the... 

If the snlfate anion-radical is bonnd to the snrface of a catalyst (sulfated zirconia), it is capable of generating the cation-radicals of benzene and tolnene (Timoshok et al. 1996). Conversion of benzene on snlfated zirconia was narrowly stndied in a batch reactor under mild conditions (100°C, 30 min contact) (Farcasiu et al. 1996, Ghencin and Farcasin 1996a, 1996b). The proven mechanism consists of a one-electron transfer from benzene to the catalyst, with the formation of the benzene cation-radical and the sulfate radical on the catalytic snrface. This ion-radical pair combines to give a snrface combination of sulfite phenyl ester with rednced snlfated zirconia. The ester eventually gives rise to phenol (Scheme 1.45). Coking is not essential for the reaction shown in Scheme 1.45. Oxidation completely resumes the activity of the worked-out catalyst. 

Electrochemical oxidation affords a simple route for the conversion of benzene derivatives to the corresponding phenol via the phenyl acetate. In practice however high yields are difficult to achieve because the product readily undergoes further... 

Aptotic solvents can be used for the reduction of aromatic hydrocarbons, particularly the condensed ring systems. Solvents used for the conversion of benzene to cyclohexa-1,4-diene at a mercury cathode under constant current conditions include dimethoxyethanc [45] and N-medtylpyrrolidone [46]. Each solvent contained water as a proton source and tetraethylammonium bromide as supporting electro-... 

Since the thermal dehydrocondensation proceeds by a free-radical mechanism (37), various radical-forming promoters like acetone, ethanol, or methanol have been found useful in improving conversion of benzene to condensed polyphenyls. In the commercial dehydrocondensation process, benzene and some biphenyl are separated by distillation and recycled back to the dehydrocondensation step. Pure biphenyl is then collected leaving a polyphenyl residue consisting of approximately 4% o-terphenyl, 44% terphenyl, 25%terphenyl, 1.5% triphenylene, and 22—27% higher polyphenyl and tars. Distillation of this residue at reduced pressure affords the mixed terphenyl isomers accompanied by a portion of the quaterphenyls present. 

More recently the conversion of benzene into maleic add in the presence of vanadium oxides as catalysts has been studied with a view to throwing light on the mechanism of such oxidations. The data obtained seem to show that the action depends on an osdllation between the two oxides V205 and V204, the dissodation of the former supplying activated oxygen for the reaction but it is also shown that the nature of the products of the oxidation is a function of some other property of the catalyst not yet clearly understood.3... 

Reaction conditions were as follows Bz/02/He = 10 5 85 (mol.%) W/F = 37 gcat h (g molBz) 1. The conversion of benzene was taken at 20-30 min on stream. Using this catalyst [146], the phenol yield at 20-30 min on stream was approximately twice that reported previously [144, 145]. UV/Vis and Raman data indicated that the production of phenol was maximized in the presence of copper-polymeric (size-limited) species, though isolated copper species such as cations and dimers also catalyzed the benzene-to-phenol transformation. 

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