Alkylaromatics toluene

As alkylaromatic hydrocarbon (toluene, p-xylene, etc.) is oxidized, aldehydes appear radicals and peracids formed from them play an important role. First, aldehydes react rapidly with the Co3+ and Mn3+ ions, which intensifies oxidation. Second, acylperoxyl radicals formed from aldehydes are very reactive and rapidly react with the initial hydrocarbon. Third, aldehydes form an adduct with primary hydroperoxide, which decomposes to form aldehyde and acid. 

Catalysts and reaction conditions used are generally similar to those used for olefin isomerization. Catalysts reported are sodium-organosodium catalysts prepared in situ by reaction of a promoter such as o-chloro-toluene or anthracene with sodium 19-24), alkali metal hydrides 20,21), alkali metals 22), benzylsodium 26), and potassium-graphite 26). These catalysts are strong bases that can react with alkylaromatics to replace a benzylic hydrogen [Reaction (2)]. 

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]. 

As alkylaromatic hydrocarbon (toluene, p-xylene, etc.) is oxidized, aldehydes appear radicals and peracids formed from them play an important role. First, aldehydes react rapidly... 

In addition to these rearrangements of more general importance, a number of isomerizations have been observed which apply only to specific cases. Some cycloolefines, like cyclooctatetraene and cycloheptatriene, are converted almost quantitatively to the alkylaromats styrene and toluene respectively 18). Of possible interest for preparative chemistry are ring-chain isomerizations which have been observed with certain nitrogen compounds 19). When pyrrole is subjected to a discharge it is largely converted to croton nitrile. 

The dimerization of toluene and substituted toluenes leads to diaryl-ethanes 2S.28.32) Electron-attracting substituents favour the reaction 32) while electron-donating groups reduce the yield. In alkylaromats with straight or branched alkyl groups it is almost always the weakest bond of the side chain which is broken 25 >28>. The resulting radicals combine to diarylethanes or substituted diarylethanes ... 

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)-... 

As previously discussed, removal of an electron from the 7r-system of alkylaromatic substrates leads to a dramatic increase in the acid strength of the C -H bonds, as clearly shown by the pA a between -11 and —13 estimated for the deprotonation of toluene radical cation in acetonitrile [130]. The presence of a positive charge on the aromatic ring can also influence, however to a much smaller extent, the acidity of groups which are further spaced from the aromatic ring such as OH and CO2H as... 

Therefore the catalysis of the oxidation of the alkylbenzenes to the corresponding aldehydes is kept alive by the formation of an excess of Co ", formed by the oxidation of the aldehydes with oxygen. In general, oxidation intermediates like aromatic aldehydes and peroxides, which are normally more reactive than the corresponding toluenes, can regenerate highly oxidized metal species. Besides the free-radical mechanism stoichiometric and ionic reaction pathways also play an important role in the oxidation of alkylaromatic compounds. This is shown with Co " as oxidant on the left-hand side of Scheme 2. 

In Table XVIII there are listed conditions for various transformations of alkylaromatics over crystalline aluminosilicate catalysts, many of which occurred under alkylation conditions. Toluene disproportionation, mainly to benzenes and xylenes over REX (43), occurred in low yield at 264° and 400 psig in the liquid phase severe aging occurred in this reaction, even under hydrogen pressure. o-Xylene isomerized to mixtures of m- and p-xylenes in liquid phase continuous flow reactions over H-mordenite at 200-600° (134) and over REX at 177-204° (43). 

There are two routes to the partial oxidation of alkylaromatic hydrocarbons - oxidation of the side chain or of the aromatic ring. In both cases the oxidation could proceed at different positions (except for the methyl group of toluene) and to different extents. Titanium silicalites were found to activate the oxidation of the secondary or tertiary saturated carbon atoms, the terminal methyl groups remaining unaffected [2,6-8]. This behaviour limits the number of the... 

Alkylation seems characteristic of the support acidity. Over NigHY2>7, the alkylaromatics distribution reveals 62 % toluene and 38 % Cg when dimethyldisulfide is used as a sulfiding agent, and shifts to 22 % C7-78 % C8 when diethyldisulfide is injected in place of DMDS. Therefore the alkylation reaction is mainly due to the presence of an alkyldisulfide. The initial formation of toluene is immediately followed by disproportionation, yielding xylenes. But product analysis also reveals that with the (benzene + DMDS) mixture, more methane is produced with HY2-7 catalyst where alkylation goes on, than over HY45 where no benzene conversion occurs. Thus, some of the methane may arise from a deep degradation of benzene, and such a reaction may also be considered as a minor source of alkylaromatics. 

Toluene. Lithiation of aromatic and alkylaromatic compounds is markedly catalyzed by chelating diamines. Toluene is metalated by organosodium reagents but is rather unreactive toward organolithium compounds in the absence of diamine catalysts. However in the presence... 

Nonacidic Catalysts. The hydrocracking of alkylaromatics over nonacidic catalysts is relatively simple and straightforward (5,39,42,46). Little or no isomerization occurs. Successive removal of methyl groups from the side chains is the principal reaction. The larger side chains are attacked first. For example, the reaction of p-ferf-butyltoluene over Rh on neutral alumina is reported to proceed sequentially as follows p-ferf-butyltoluene -> p-proplytoluene - p-ethyltoluene -> p-xylene — toluene benzene. In the hydrogenolysis of indane, the first reaction is the cleavage of the 1-2 (or 3-4) carbon-carbon bond of the five-... 

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