Alkylaromatics ethylbenzene

Alkylaromatic hydrocarbons, such as tetralin, ethylbenzene, and cumene, are oxidized in a solution of acetic acid in the presence of cobalt acetate by a different mechanism. In these... 

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. 

Kinetics of oxidation of toluene and cumene to the corresponding a-hydroxy compounds by stoich. trani-[Ru(0)(bpy)(tpy)] VCH3CN were reported a two-electron hydride-ion transfer step may be involved [672]. Electro-oxidation of side-chains in alkylaromatics by [Ru(0)(bpy)(tpy)] (generated electrochemicaUy in situ from [Ru(OH)(bpy)(tpy)] V BuOH/water pH 6.8/Pt electrodes/50°C) was effected toluene gave benzoic acid and ethylbenzene gave acetophenone (Table 4.1) [673]. 

Bragin and co-workers found that over platinum-on-carbon catalysts, both paraffins and alkylaromatics follow zero-order kinetics. Activation energy for C5-dehydrocyclization in which the new bond is formed between two sp3 hybridized atoms is substantially less than the activation energy of cyclization in which the new bond is formed between one sp3 hybridized atom and the sp2 hybridized carbon atom of the aromatic ring. Over one batch of platinum-on-carbon catalyst, Bragin and co-workers obtained 20 kcal/mol and 27.5 kcal/mol activation energies for the dehydrocyclization of paraffins and monoalkylbenzenes, respectively (6). Another batch of platinum on carbon (which differed only in some minor details of preparation from the first batch), gave 14 kcal/mol for the cyclization of l-methyl-2-ethylbenzene and isooctane, and 29 kcal/mol for the cyclization of secondary butylbenzene ( ) (Fig. 1). 

Depending on the alkene cation radical nature, open-chain oxygenation and epoxida-tion take place as well as the formation of other trivial ozonolysis products. Alkylaromatic compounds are also oxidized by ozone via the ion radical mechanism. Ethylbenzene, for example, undergoes ozone attack on the ring (80%) and on the alkyl group (20%). According to kinetic studies, the ozone consumption obeys the chain law (Galstyan et al. 2001). 

The materials showed some activity in the autoxidation of alkylaromatics such as ethylbenzene at 403 118 K, even though at these temperatures there is a considerable blank background reaction. The stability of a salicylidene imine under the conditions of high-temperature autoxidation is questionable in any event. 

A further useful application of SC-CO2 as a reaction medium is the free-radical side-chain bromination of alkylaromatics, replacing conventional solvents such as tetra-chloromethane or chlorofluorohydrocarbons having no abstractable hydrogen atoms [920]. For example, bromination of ethylbenzene in SC-CO2 at 40 °C and 22.9 MPa yields 95 cmol/mol (1-bromoethyl)benzene, with practically the same regioselectivity as obtained in conventional tetrachloromethane as the solvent. Even the classical Wohl-Ziegler bromination of benzylic or allylic substrates using A-bromosuccinimide (NBS) can be conducted in SC-CO2 [920]. Irradiation of a solution of toluene, NBS, and AIBN (as initiator) in SC-CO2 at 40 °C and 17.0 MPa for 4 hours gave (bromomethyl)-... 

In refining processes alkylation of isobutane with propene or butene is important in order to obtain all date which has a high octane number and a low vapour pressure. This process is not, however, directly relevant to the focus of attention of this paper and wifi therefore not be deah with in any detail It has been well reviewed recai% [36]. It is, however, worth noting that recent attempts to develop a zeolite as an ahemate to the currently used hydrofluoric or su huric acid do not appear to have been successful and it is now assumed that superacid catalysts are the most likely heterogeneous alternatives. For the petrochemical industry the alkylation of aromatics is an inportant route to the production of alkylaromatic such as ethylbenzene, xylenes, cume, alkylbenzoies, alky henol... 

The acetamidation of alkylaromatics has been partly discussed [Eq. (11)]. Methyl-substituted benzenes are particularly good substrates for side-chain acetamidation, and they have featured in numerous product and mechanistic studies [9-12,21-23,160-162] ethylbenzene and isopropylbenzene give other products predominantly [163]. Hexamethylbenzene has been a favored substrate for mechanistic investigations of acetamidation [160,164], and in this case there is evidence [165] that on the time scale of conventional cyclic voltammetry, proton loss is rapid from hexamethylbenzene radical cation but relatively slow from hexaethylbenzene. 

In spite of its topicality, the history of the industrial transition metal-catalyzed oxidation of alkylaromatic compounds dates back to the early 1920s with the continuous oxidation of ethylbenzene to acetophenone using manganese acetate as catalyst. This process was developed by the IG Farben at Uerdingen [2]. 

The reaction mechanism for a very strong one-electron donor centre in the dehydrogenation of alkylaromatic hydrocarbons is similar to that proposed by Krause for ethylbenzene dehydrogenation [reactions (5) and (6)]. The mechanism for n-propylbenzene transalkylation and cyclization on the radical pathway has been suggested. ... 

Aerobic selective oxidation of alkylaromatics, including cumene (CU), ethylbenzene (EtB), and cyclohexylbenzene (CyB), to the corresponding hydroperoxides (CHPs) represents a key step for several large-scale productions, including the Hock process for the synthesis of phenol (see Chapter 2) [15] and the Shell styrene monomer/propylene oxide (SM/PO) process for the production of propylene oxide (PO) and styrene monomer (SM) [16]. 

Oxidation of alkylaromatic hydrocarbons only affects the alkyl substituent, although benzene itself may be oxidized, Among substrates of this type oxidations of toluene, ethylbenzene and cumene by immobilized complexes of transition metals have been studied intensively [3]. 

The Cg alkylaromatics fraction is formed by ethylbenzene and the three xylene isomers. Ethylbenzene is used as a raw material to produce styrene by dehydrogenation, or oxidative dehydrogenation. Para-xylene and ortho-xylene are catalytically oxidized to give terephthalic and phthalic acid. The meta-xylene isomer can also be oxidized to give isophthalic acid. The major industrial source of these products is the catalytic reforming of naphthas. The Cyclar process, can also produce xylenes from propane and butane. However, using this process, xylenes are formed less selectively than toluene or benzene in the BTX. 

The mixtiue of the Q alkylaromatic isomers is separated by a combination of fractionation and crystallization, or molecular sieve adsorption. The ethylbenzene and ortho-xylene could be separated from each other and from the xylene stream by fractionation. The meta and para isomers, due to their very close boiling poipts, can not allow this type of separation and commercially is carried out by fractional crystallization or molecular sieve adsorption (165). The crystallization process can only recover 60% of the most valuable para isomer due to the formation of eutectics with other isomers which diminishes product piuity. However, by using the molecular sieve adsorption technique, practically 100% of the para-xylene in the feed can be recovered. 

Borosilicates have also being used to isomerize Cj alkylaromatics (186). These are active catalysts, and highly selective for ethylbenzene conversion (186-189). 

Synthesis of alkylaromatics. Alkylaromatics are widely used for production of styrene (ethylbenzene), phenol (isopropylbenzene), and long chain alkylated benzene for detergent intermediates. 

There is no further, destructive, oxidation as can be observed in cobalt-acetic acid systems, and the remaining unreacted ethylbenzene may be recycled. The reaction can be extended to a range of substituted ethylbenzenes. It may also be possible selectively to oxidise the side chain of other alkylaromatics, although toluenes are largely resistant to oxidation except under forcing conditions. 

Sixteen alkylaromatic compounds (e.g., o-xylene, ethylbenzene, n-amylbenzene, 1-ethylnaphthalene and 2-n-hexylnaphthalene) were chromatographed on a silica column (A = 254nm) using hexane and 0.5-2.0% dichloromethane, chloroform, carbon tetrachloride, or ethyl bromide as the mobile phase modifier [599]. For the stronger solvent modifiers (chloroform and dichloromethane) linear decreases in the reciprocal of the adjusted retention time (i.e., 1 /[(retention time) — (void volume)]) versus mole fraction of modifier in the mobile phases resulted. However, for the weaker modifiers (carbon tetrachloride and ethyl bromide) the plot was distinctly nonlinear at low mole fractions of modifier (0.01-0.02) and linear at higher mole fiactions of the modifier (>0.05). 

MA adducts of alkylaromatics have potential as monomers. Stevens claims chemical resistance of unsaturated polyesters when they contain adducts made from MA with toluene, p-xylene, ethylbenzene, and cumene. The adducts have also been proposed as intermediates for plasticizers, synthetic resins,and dye intermediates. 

Benzene/Toluene/Ethylbenzene/Xylenes (BTEX, Alkylaromatics)... 

Alkylaromatics form very stable molecular ions which can be detected with very high sensitivity (Figures 3.57-3.65). The tropylium ion occurs at m/z 91 as the base peak, which is, for example, responsible for the uneven base peak in the toluene spectrum (M - 92). The fragmentation of the aromatic skeleton leads to typical series of ions with m/z 38-40, 50-52, 63-67, 77-79 ( aromatic rubble ). Ethylbenzene and the xylenes cannot be differentiated from their spectra because they are isomers. In these cases, the retention times of the components are more meaningful. 

Microporous aluminum terephthalate MIL-53 for HPLC separation of xylenes and ethylbenzene, ethyl-toluenes, and cymenes was also reported by Alaerts et al. in 2008. Compared to the structurally similar MIL-47, the selectivities of alkylaromatics on MIL-53 are different. MIL-53 has the largest adsorption affinity for the orthoisomer among each group of alkylaromatic compounds. Separations of ortho-compounds from the other isomers were realized on a MIL-53-packed column using hexane as the mobile phase. As evidenced by Rietveld refinements, specific interactions of the xylenes with the pore walls of MIL-53 determine the selectivity. Alaerts et also... 

In previous work, some of the authors showed that metal organic frameworks could be successfully used as selective adsorbents for the industrially relevant separations of para-xylene (pX) versus meta-xylene (mX) and ortho-xylene (oX) versus ethylbenzene (eB) [8-10]. The separation of mixed C8 alkylaromatic compounds is one of the most challenging issues in the chemical industry, for example because of its direct link with PET production [11]. Among the various types of MOFs that have been tested, the MIL-47 material proved to be very successful. This MOF... 

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