Alkanes and Alkylaromatics

Ru(Cl)2(PPh3)3] catalyzes the oxidation of alkanes and alkylaromatics with t-butylhydroper-oxides and peracetic acid, and an oxoruthenium(IV) active intermediate has been proposed. ... 

Aldehydes do not co-oxidize alkanes due to a huge difference in the reactivity of these two classes of organic compounds. Alkanes are almost inert to oxidation at room temperature and can be treated as inert solvents toward oxidized aldehydes [35]. Olefins and alkylaromatic hydrocarbons are co-oxidized with aldehydes. The addition of alkylaromatic hydrocarbon (R2H) to benzaldehyde (R1H) retards the rate of the initiated oxidation [36-39]. The rate of co-oxidation obeys the equation [37] ... 

The sulfoxidation of aliphatic hydrocarbons is the easiest method for the synthesis of alkylsulfonic acids. Their sodium salts are widely used as surfactive reactants in technology and housekeeping. Platz and Schimmelschmidt [1] were the first to invent this synthetic method. Normal paraffins (Ci4-Cig) are used for the industrial production of alkylsulfonic acids [2-4]. Olefins and alkylaromatic hydrocarbons do not produce sulfonic acids under the action of sulfur dioxide and dioxygen and retard the sulfoxidation of alkanes [5-9],... 

The nitration of alkanes and that of alkylaromatics at the side chain can be accomplished with nitric acid or nitrogen oxides in either the liquid or the vapor... 

Main reactions in CR processes are dehydrogenation of cyclohexane and alkylcylohexanes, cyclization of alkanes, isomerization of n-parafines, alkylcyclopentanes and alkylaromatics, and hydrocracking. Secondary reactions are the demethylation and cracking of cyclic compounds. 

Coke deposits were studied using mass spectra obtmed from the probe El and Cl analyses of the deactivated catalysts arising from the various feed streams. Alkane and alkene fragments were observed to dominate the individual mass spectra (particularly, m/z 57, 71 and 55, 69, respectively, in the El mode). Although alkylaromatics were evident for the catalyst from the tests with n-hexadecane and the n-hexadecane/phenanthrene mixture PACs are only present in trace quantities. Quinoline addition gave rise to much less intense ions from the deactivated catalyst due to its lower carbon content and the reduced sensitivity made it difBcult to observe the aromatic fragments. Indeed, the most intense peak was from quinoline itself (m/z 129 El, 130 Cl). 

Indirect electrochemical oxidative carbonylation with a palladium catalyst converts alkynes, carbon monoxide and methanol to substituted dimethyl maleate esters (81). Indirect electrochemical oxidation of dienes can be accomplished with the palladium-hydroquinone system (82). Olefins, ketones and alkylaromatics have been oxidized electrochemically using a Ru(IV) oxidant (83, 84). Indirect electrooxidation of alkylbenzenes can be carried out with cobalt, iron, cerium or manganese ions as the mediator (85). Metalloporphyrins and metal salen complexes have been used as mediators for the oxidation of alkanes and alkenes by oxygen (86-90). Reduction of oxygen and the metalloporphyrin generates an oxoporphyrin that converts an alkene into an epoxide. 

All the above reactions are reversible. Hence, at higher temperatures with zeolites, cleavages of olefins and isomerization and trans-alkylation of alkylaromatics can occur in the presence of alkenes and alkylaromatics as hydride acceptors, alkanes can also take part. 

Photo-oxidation has been reported at crude-oil spills. It results in depletion of n-alkanes below nCi5 and alkylaromatics such as Ci- and C2-substituted naphthalenes relative to unoxidized oil (Payne and Phillips, 1985). In terms of a material balance, photo-oxidation has been found to be a minor process (NRC, 1985) but does result in changes in the residual oil composition and can affect the subsequent behavior of an oil spill on the open ocean (Payne and Phillips, 1985). Autooxidation reactions of hydrocarbons in the absence of light have not been well studied. 

Alkanes can be simultaneously chlorinated and chlorosulfonated. This commercially useful reaction has been appHed to polyethylene (201—203). Aromatics can be chlorinated on the ring, and in the presence of a free-radical initiator alkylaromatic compounds can be chlorinated selectively in the side chain. King chlorination can be selective. A patent shows chlorination of 2,5-di- to 2,4,5-trichlorophenoxyacetic acid free of the toxic... 

Dehydrocyclization, 30 35-43, 31 23 see also Cyclization acyclic alkanes, 30 3 7C-adsorbed olefins, 30 35-36, 38-39 of alkylaromatics, see specific compounds alkyl-substituted benzenes, 30 65 carbene-alkyl insertion mechanism, 30 37 carbon complexes, 32 179-182 catalytic, 26 384 C—C bond formation, 30 210 Q mechanism, 29 279-283 comparison of rates, 28 300-306 dehydrogenation, 30 35-36 of hexanes over platintim films, 23 43-46 hydrogenolysis and, 23 103 -hydrogenolysis mechanism, 25 150-158 iridium supported catalyst, 30 42 mechanisms, 30 38-39, 42-43 metal-catalyzed, 28 293-319 n-hexane, 29 284, 286 palladium, 30 36 pathways, 30 40 platinum, 30 40 rate, 30 36-37, 39... 

The calcined iron-grafted materials exhibit high selectivity as catalysts for oxidations of alkanes, alkenes and arenes with H2O2 as the oxidants [13a]. A similar method has been used by Tilley et al. to prepare a pseudotetrahedral (Co(II) [Co(4,4 -di Bu-bipy) OSi(0 Bu)3 2]) complex grafted onto the SBA-15 surface and subsequently use it in catalytic oxidation of alkylaromatic substrates with tert-butyl hydroperoxide [14]. Unfortunately, neither iron nor cobalt surface organometaUic compounds have been tested in the recycled catalytic system. 

VM, percentage matter volatilized in pyrolysis CHYDR, carbohydrates with pentose and hexose subunits PHLM, phenols and lignin monomers LDIM, lignin dimers LIPID, lipids, alkanes, alkenes, bound fatty acids, and alkylmonoesters ALKY, alkylaromatics NCOMP, mainly heterocyclic N-containing compounds STEROL, sterols PEPTI, peptides SUBER, suberin FATTY, free fatty acids in % of total ion intensity. 

For non-electrophilic strong oxidants, the reaction with an alkane typically follows an outer-sphere ET mechanism. Photoexcited aromatic compounds are among the most powerful outer-sphere oxidants (e.g., the oxidation potential of the excited singlet state of 1,2,4,5-tetracyanobenzene (TCB) is 3.44 V relative to the SCE) [14, 15]. Photoexcited TCB (TCB ) can generate radical cations even from straight-chain alkanes through an SET oxidation. The reaction involves formation of ion-radical pairs between the alkane radical cation and the reduced oxidant (Eq. 5). Proton loss from the radical cation to the solvent (Eq. 6) is followed by aromatic substitution (Eq. 7) to form alkylaromatic compounds. 

As noted above, Carlson et al. (1993) initially identified the presence of monocyclic/acyclic branched alkanes in the high molecular weight fractions. More recently Hsieh et al. (2000) noted the presence of alkylaromatic compounds in this fraction along with a wide variety of branched hydrocarbons, alkylcyclohexanes and alkylcyclopentanes. However, the need to document the identities of all the compounds completely cannot be over-emphasized. Physical properties of the branched hydrocarbons, particularly melting points, vary significantly with... 

The c-organyl complexes formed in oxidative addition [12] of alkanes, arenes as well as alkenes and monosubstituted acetylenes can be fairly stable and in many cases have been isolated. Thus, upon heating or photolysis, the complexes CP2WH2, Cp2 VCO,and CpjWHCHj give rise to a coordinatively unsaturated tungstocene species CpjW, which readily combines with aromatic or alkylaromatic hydrocarbons [13]. 

The mechanism via bromine atoms is supported by molecular bromine formation in the interaction of with Br in the absence of a hydrocarbon (Bf2 is apparently formed by bromine atom recombination). This mechanism is also consistent with the fact that bromide ions, while catalyzing the oxidation in the case of alkylaromatic compounds, are not particularly effective in the case of simple alkanes. This corresponds to the difference of bromine atom reactivity with respect to alkylaromatic and aliphatic hydrocarbons. The bond energy in the H-Br molecule (85 kcal mole ) is practically equal to the energy of the C-H bond in the n.-position to the aromatic ring, so that the reaction... 

In two papers by Walsh and Rollman [14-C]labelled hydrocarbons were used to study the origin of carbonaceous deposits on zeolites. With feeds composed of an aliphatic + an aromatic hydrocarbon, the initial reaction involved in the formation of coke was the alkylation of aromatics by the olefmic fragments of alkane cracking. Since ZSM-5 and mordenite have the same framework A1 content, it was possible to compare directly the coke yields of these zeolites. Under the same experimental conditions it was found that C deposition on mordenite was almost two orders of magnitude greater than on ZSM-5. The differences were explained in terms of pore size. In the smaller ZSM-5 pore, the alkylaromatics, once formed were prevented from reacting further to produce coke, because of the spacial constraints. 

The first examples of molecular shape-selective catalysis in zeolites were given by Weisz and Frilette in 1960 [1]. In those early days of zeolite catalysis, the applications were limited by the availability of 8-N and 12-MR zeolites only. An example of reactant selectivity on an 8-MR zeolite is the hydrocracking of a mixture of linear and branched alkanes on erionite [4]. n-Alkanes can diffuse through the 8-MR windows and are cracked inside the erionite cages, while isoalkanes have no access to the intracrystalline catalytic sites. A boom in molecular shape-selective catalysis occurred in the early eighties, with the application of medium-pore zeolites, especially of ZSM-5, in hydrocarbon conversion reactions involving alkylaromatics [5-7]. A typical example of product selectivity is found in the toluene all lation reaction with methanol on H-ZSM-5. Meta-, para- and ortho-xylene are made inside the ZSM-5 chaimels, but the product is enriched in para-xylene since this isomer has the smallest kinetic diameter and diffuses out most rapidly. Xylene isomerisation in H-ZSM-5 is an often cited example of tranSition-state shape selectivity. The diaryl type transition state complexes leading to trimethylbenzenes and coke cannot be accommodated in the pores of the ZSM-5 structure. 

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