Oxidation of ethylbenzene

Ethylbenzene Hydroperoxide Process. Figure 4 shows the process flow sheet for production of propylene oxide and styrene via the use of ethylbenzene hydroperoxide (EBHP). Liquid-phase oxidation of ethylbenzene with air or oxygen occurs at 206—275 kPa (30—40 psia) and 140—150°C, and 2—2.5 h are required for a 10—15% conversion to the hydroperoxide. Recycle of an inert gas, such as nitrogen, is used to control reactor temperature. Impurities ia the ethylbenzene, such as water, are controlled to minimize decomposition of the hydroperoxide product and are sometimes added to enhance product formation. Selectivity to by-products include 8—10% acetophenone, 5—7% 1-phenylethanol, and <1% organic acids. EBHP is concentrated to 30—35% by distillation. The overhead ethylbenzene is recycled back to the oxidation reactor (170—172). 

PO—SM Coproduction. The copioduction of propylene oxide and styrene (40—49) includes three reaction steps (/) oxidation of ethylbenzene to ethylbenzene hydroperoxide, (2) epoxidation of ethylbenzene hydroperoxide with propylene to form a-phenylethanol and propylene oxide, and (3) dehydration of a-phenylethanol to styrene. 

Future Methods. A by-product stream containing 60—80% PEA can be obtained from the catalytic air oxidation of ethylbenzene [100-41-4] (100). Perfumery-grade material can be isolated from this stream by complexing the PEA with a metal haUde (such as CaCl2), separation of the adduct, and thermal decomposition followed by distillation. 

Recently, Nam, Fukuzumi, and coworkers succeed in an iron-catalyzed oxidation of alkanes using Ce(IV) and water. Here, the generation of the reactive nonheme iron (IV) 0x0 complex is proposed, which subsequently oxidized the respective alkane (Scheme 16) [104]. With the corresponding iron(II) complex of the pentadentate ligand 31, it was possible to achieve oxidation of ethylbenzene to acetophenone (9 TON). 0 labeling studies indicated that water is the oxygen source. 

A mononuclear diastereopure high-spin Fe alkylperoxo complex with a pen-tadentate N,N,N,0,0-ligand 33 (Scheme 17) was reported by Klein Gebbink and coworkers [109, 110]. The complex is characterized by unusual seven-coordinate geometry. However, in the oxidation of ethylbenzene the iron complex with 33 and TBHP yielded with large excess of substrate only low TON s (4) and low ee (6.5%) of 1-phenylethanol. 

In an earlier series of experiments, Cullis and Ladbury examined the kinetics of the permanganate oxidation of hydrocarbons in acetic acid solution. Initial attack on toluene occurs at the methyl group and a total order of two was found. Electron-withdrawing agents reduced the rate of oxidation. However, the effects of added salts were complex and the authors believe that lower oxidation states of manganese are responsible for the oxidation. The oxidation of ethylbenzene produced acetophenone, the process being second-order with... 

Another recent patent (22) and related patent application (31) cover incorporation and use of many active metals into Si-TUD-1. Some active materials were incorporated simultaneously (e.g., NiW, NiMo, and Ga/Zn/Sn). The various catalysts have been used for many organic reactions [TUD-1 variants are shown in brackets] Alkylation of naphthalene with 1-hexadecene [Al-Si] Friedel-Crafts benzylation of benzene [Fe-Si, Ga-Si, Sn-Si and Ti-Si, see apphcation 2 above] oligomerization of 1-decene [Al-Si] selective oxidation of ethylbenzene to acetophenone [Cr-Si, Mo-Si] and selective oxidation of cyclohexanol to cyclohexanone [Mo-Si], A dehydrogenation process (32) has been described using an immobilized pincer catalyst on a TUD-1 substrate. Previously these catalysts were homogeneous, which often caused problems in separation and recycle. Several other reactions were described, including acylation, hydrogenation, and ammoxidation. 

NM Emanuel, D Gal. Oxidation of Ethylbenzene. Moscow Nauka, 1984 [in Russian]. 

Oxidation of ethylbenzene catalyzed by the Cu(II) complex with o-phenanthroline was found to occur with the rate depending on the dioxygen concentration [170]. 

As the reaction temperature increases, the equilibrium constant diminishes, since complex formation is accompanied by heat liberation. Sterically hindered phenols form loose complexes because of the impeding effect of voluminous alkyl substituents in the ortho-position. Hydrogen bonding reduces the activity of phenols, which was first observed in the studies of the effects of cyclohexanol and butanol on the inhibitory activity of a-naphthol in cyclohexane [9]. This phenomenon was investigated in detail with reference to the oxidation of methylethylketone [10]. The k7 values for some inhibitors of the oxidation of ethylbenzene and methylethylketone are given below (333 K) [10,46] ... 

The H202 + AmO (TEMPO) + HA (citric acid) system also exhibits an extremely high inhibiting effect [45,46]. The data presented below demonstrate how the individual components of this system and the whole system influences the rate of the chain oxidation of ethylbenzene (343 K, p02 = 105 Pa, = 5.21 x 10-7 mol L-1 s-1 [44]). 

These reactions produce free radicals, as follows from the fact of consumption of free radical acceptor [42]. The oxidation of ethylbenzene in the presence of thiophenol is accompanied by CL induced by peroxyl radicals of ethylbenzene [43]. Dilauryl dithiopropionate induces the pro-oxidative effect in the oxidation of cumene in the presence of cumyl hydroperoxide [44] provided that the latter is added at a sufficiently high proportion ([sulfide]/[ROOH] > 2). By analogy with similar systems, it can be suggested that sulfide should react with ROOH both heterolytically (the major reaction) and homolytically producing free radicals. When dilauryl dithiopropionate reacts with cumyl hydroperoxide in chlorobenzene, the rate constants of these reactions (molecular m and homolytic i) in chlorobenzene are [42]... 

The resulting products, such as sulfenic acid or sulfur dioxide, are reactive and induce an acid-catalyzed breakdown of hydroperoxides. The important role of intermediate molecular sulfur has been reported [68-72]. Zinc (or other metal) forms a precipitate composed of ZnO and ZnS04. The decomposition of ROOH by dialkyl thiophosphates is an autocata-lytic process. The interaction of ROOH with zinc dialkyl thiophosphate gives rise to free radicals, due to which this reaction accelerates oxidation of hydrocarbons, excites CL during oxidation of ethylbenzene, and intensifies the consumption of acceptors, e.g., stable nitroxyl radicals [68], The induction period is often absent because of the rapid formation of intermediates, and the kinetics of decomposition is described by a simple bimolecular kinetic equation... 

In contrast, a similarly doped Co(salen) aerogel (Figure 5.10) was slow in catalysing the oxidation of ethylbenzene to acetophenone despite showing quantitative conversion of ethylbenzene, a yield not possible with a similar heterogenized system obtained by conventional impregnation when a drastic reduction in activity is observed after 50% conversion.21... 

Write the equation for the indirect oxidation of ethylbenzene to propylene oxide and styrene. 

The greatest advantage of the above catalytic system was the elimination of the unweleome induetion period which otherwise occurs commonly for cobalt(II)-based oxidation catalysts. This has been possible because through direct use of a eobalt(III)-based heterogeneous system it has been possible to eliminate the time required to ehange Co(II) to Co(III). The isolated yield of acetophenone was found to be 70% at 94% seleetivity during aerobie oxidation of ethylbenzene under atmospheric liquid phase eonditions. 

Figure 24. Aerobic oxidation of ethylbenzene catalyzed by Co(III)-CMS4.

Catalytic oxidation of ethylbenzene by using air as the oxidant and Co(III)-CMS 1 as the catalyst has been mentioned earlier in this chapter. Although the nature of the metal complex involved remained unknown at the time, it is now reasonably justified to state in view of our recent results that a eubane complex of cobalt(III) could be involved in the eatalyzed process. This belief is confirmed by our studies using Co(III)-CMS4 as the eatalyst for the aerobie oxidation of ethylbenzene under liquid phase conditions that do not call for the use of any solvents. 

Figure 25. Oxidation of ethylbenzene with air under atmospheric pressure using Co(III)-CMS4.

Oxidation of various alkylaromatics, including toluene, ethylbenzene, and cumene, by trans-[Ru (0)2(N202)] in MeCN also has large kinetic isotope effects k-alk-o = 16 for ethylbenzene), indicating C—bond cleavage in the transition state. The second-order rate constants for ethylbenzene and cumene are similar but are substantially higher than that for toluene. " Representative kinetic data for the oxidation of ethylbenzene, cumene, and toluene are collected in Table 10. 

Table 10 Representative kinetic data for the oxidation of ethylbenzene, cumene, and toluene by ruthenium...

The dibenzoate chirality rule 155, 156 extends the application of the exciton chirality method to molecules containing no suitable chromophore, but, rather two hydroxy groups which can be converted to benzoates or cinnamates. For example, the dibenzoate 1, obtained by benzoy-lation of the ra-diol, from microbial oxidation of ethylbenzene, displays a negative exciton Cotton effect and is hence assigned the 1 S.2R configuration157. 

Figure 11 Photocatalytic oxidation of ethylbenzene cofed with TCE. (From Ref. 17.)...

The induction period in the oxidation of ethylbenzene catalyzed by cobalt and sodium bromide in the presence of 2,6-di-fert-butyl-p-cresol indicates that the direct initiation is negligible compared with the rate of initiation by the cobalt-catalyzed decomposition of hydroperoxide. 

A mixed oxide of ruthenium, copper, iron and alumnium has been developed as a catalyst for the synthesis of aldehydes and ketones from alcohols.258 Oxidation of chiral secondary 1,2-diols with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone under ultrasound wave promotion leads to the selective oxidation of benzylic or allylic hydroxyl group. The configuration of the adjacent chiral centre is retained.259 The kinetics of oxidation of ethylbenzene in the presence of acetic anhydride have been studied.260... 

Representative Kinetic Data for the Oxidation of Ethylbenzene, Cumene, and Toluene by Ruthenium Oxo Complexes... 

For oxidation of ethylbenzene in FeCl3-catalysed reaction with ferf-butyl hydroxyperoxide isotope effect fcHn//C id = 2.02(4) was found in analysis of deuterium content in ethylbenzene at natural abundance. Mixture of ethylbenzene and 1,1-dideuteroethylbenzene (45 55) was used for the determination of (hh/ fcDD = 5.0(1). Isotope effects KIEr- = 3.5(2) and KIE2- = 1.41(6) were calculated from formulas (26). The value of primary isotope effect is consistent with a C-H bond breakage in the rate-limiting step, but its value does not allow distinguishing among a hydrogen radical abstraction, C-H insertion or a hydride abstraction processes. Secondary isotope effect is consistent with formation of benzylic radical. 

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