FORMATION FROM TOLUENE

The reaction of toluene formation from benzene and methyl alcohol can be represented by the following scheme ... 

As it is mentioned earlier, there is a significant change in selectivities of toluene and Cg+ aromatics with the addition of zinc. The preferential increase of toluene indicates the possibility of toluene formation from the direet dChydrocyclization/direct aromatization of n-heptane over the Zn/HZSM-5 (Kms), in addition to the cracking-and-oligomerization route (Kai). The direct dehydrocyclization of hydrocarbons (hexane and above) was also reported by Giannetto et al [49] from their studies over Ga-HZSM-5 catalyst. 

Table 5.1 gives a sample calculation of the NHVj for toluene, starting from the molar enthalpies of formation of the reactants and products and the enthalpies of changes in state as the case requires. 

As another example, the tropylium ion [3 ], which is stabilized by virtue of the 67t electrons spread over a heptagonal sp hybridized carbon framework [Hiickel s (4n 4- 2)v rule with = 1], is also unstable in the gas phase. Its formation from toluene or the benzyl cation has been a long-standing problem in organic mass spectrometry, and the reaction mechanism and energetics have recently been exhaustively discussed (Lif-shitz, 1994). It was, however, isolated as the bromide salt by Doering and Knox (1954, 1957), and was the first non-benzenoid aromatic carbocation. 

One synthesis approach that does not rely on CNT formation from the gas phase is molten salt synthesis. The reactor consists of a vertically oriented quartz tube that contains two graphite electrodes (i.e. anode is also the crucible) and is filled with ionic salts (e.g. LiCl or LiBr). An external furnace keeps the temperature at around 600 °C, which leads to the melting of the salt. Upon applying an electric field the ions penetrate and exfoliate the graphite cathode, producing graphene-type sheets that wrap up into CNTs on the cathode surface. Subsequently, the reactor is allowed to cool down, washed with water, and nanocarbon materials are extracted with toluene [83]. This process typically yields 20-30 % MWCNTs of low purity. 

Side-chain oxidations of alkyl aromatic compounds to aromatic carboxylic acids by electrogenerated and regenerated chromic acid have been studied extensively in the case of saccharin formation from o-toluene sulfonamide This... 

At 450°C the formation of coke compared to that of the other products is very slow. Whatever the reactant the main coke components are alkylpyrenes. However these alkylpyrenes result probably through different reaction paths one involving aromatics and alkene would be responsible for coke formation from the propene-toluene mixture and from propene, the other involving only reactions of aromatics would be responsible for coke formation from toluene [8]. The same coke molecules are formed through both paths because their size and their shape are imposed by the size and the shape of channel intersections. 

That migration of acetyl groups had not taken place during the formation of the D-galactose methylphenylhydrazone tetraacetates was shown by the isolation of two different p-toluene sulfonates from IX and X. This evidence shows therefore that even when oxide rings are present in (16) J. Compton and M. L. Wolfrom, J. Am. Ckem. Soc., 66, 1157 (1934). 

The alkylation of the naphthenic cation causes formation of complex aliphatic carbonium ions. Transformation of such intermediates according to Poustma [30] gives the molecules of light saturated hydrocarbons and aromatics. It is generally accepted that the formation of condensed aromatic rings being a coke precursors is difficult in the pores of ZSM-5 zeolite. The fact that the products of the toluene transformation reaction in all cases contained 1 - and 2-methylnaphthalene seems to prove their formation from the olefinic or naphthenic carbocations. Transformation of the naphthenic carbocations occuring in zeolite pores and on the external zeolite surface is the most probable source of methyinaphthalene isomers [23]. 

This coke profile can be used to explain why the maximum reaction rate for toluene formation shifted from the Inlet to the outlet. With the fresh catalyst, the greater the concentration of n-heptane, the greater the rate of toluene formation. This is represented by the curve at time t=0 In Figure 6. When the catalyst is deactivated by coke, the first section loses more activity than the others. Therefore, one point downstream of the first section has greater dehydrocyctization activity. Its toluene formation rate is the highest due to less deactivation compared to its upstream section, and to higher n-heptane concentration compared to its downstream section. 

Oxidations. Aromatic aldehydes are obtained by oxidation catalyzed with a Mn(IV) complex. A procedure for oxidation of alcohols which is organic solvent free and halide free employs 30% H Oj, Na2W04 dihydrate, and a quaternary ammonium hydrogensulfate. Under such conditions secondary alcohols are oxidized 4-5 times faster than primary alcohols. In toluene the conversion of benzylic alcohols to aldehydes or acids (depending on quantities of HjOj) is accomplished. A similar system is also effective for epoxidation of alkenes. Terminal epoxides are obtained in reactions mediated by a Mn(II) complex or Mg-Al-O-t-Bu hydrotalcite. The last catalyst is capable of inducing epoxide formation from other alkenes and enones. 

Figure 7(b) Variation of aromatic formation from heptane, and benzene formation from toluene, with W/F... 

Typically, there is less methane and ethylene present in the effluent of a reactor than would be expected from the benzene and toluene formation. Carbon monoxide is generally about 10mol% of the total carbon oxides. 

The Fina/Badger distillation section consists of three distillation columns. All the columns are designed to operate under vacuum to minimize temperature and polymer formation. The first column in the sequence splits the benzene and toluene byproducts from the unconverted EB and styrene product. The benzene and toluene mixture is typically sent to an integrated EB plant where it is further fractionated. In this case, the benzene by-product is ultimately consumed in the EB unit and the toluene becomes a by-product stream from the EB plant. 

Cycloheptatriene, Norbomadiene, Methylenecyclohexadienes (Isotoluenes) and Bicy-clof3.2.0/heptadienes. The gas-phase ion chemistry of ionized 1,3,5-cycloheptatriene is closely related to that of ionized toluene, in particular, and to that of norbomadiene and other non-aromatic ( yllx isomers. This extensive body of work will not be discussed here since a detailed review on this topic has been published by one of these authors in the context of the gas-phase chemistry of the alkylbenzene radical cations This chemistry pertains also to the well-known isomerization of the even-electron CvHv ions and to their formation from the respective parents, e.g. CyHs" " . A related, albeit chemically different held concerns protonated cycloheptatriene, i.e. the even-electron C7H9+ ions , and alkylcycloheptatrienes, which are closely related to protonated toluene and higher alkylbenzenium ions. A parallel review by one of these authors on protonated alkylbenzenes has been pubUshed, and recent investigations on protonated alkylcycloheptatrienes have highUghtened the complexity of this gas-phase ion chemistry 42 jp a minor extent, ionized and protonated fulvenes have also been investigated with respect to their interconversion to their (mainly arene-derived) isomers. 

The quantum yield for toluene formation is very low in solution but approaches unity in the gas phase at low pressures- . The toluene was suggested to be formed from vibrationally excited ground state molecules, following rapid internal conversion from the excited singlet state manifold, perhaps involving the intermediacy of norcaradiene... 

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