Alkylaromatic hydrocarbon

The scope of oxidation chemistry is enormous and embraces a wide range of reactions and processes. This article provides a brief introduction to the homogeneous free-radical oxidations of paraffinic and alkylaromatic hydrocarbons. Heterogeneous catalysis, biochemical and hiomimetic oxidations, oxidations of unsaturates, anodic oxidations, etc, even if used to illustrate specific points, are arbitrarily outside the purview of this article. There are, even so, many unifying features among these areas. 

Hydroperoxides were proved to be the only primary molecular product of the oxidation of aliphatic and alkylaromatic hydrocarbons [79-84], When the hydrocarbon is oxidized under mild conditions, in which the formed hydroperoxide is a stable product, the amount of produced ROOH was found to be nearly equal to the amount of consumed dioxygen [45,80,82],... 

Opeida proposed the following empirical equation for the rate constant of the peroxyl radical reaction with C—H bonds of alkylaromatic hydrocarbons [34] ... 

IA Opeida. Cooxidation of Alkylaromatic Hydrocarbons in the Liquid Phase. Doctoral Dissertation, Institute of Chemical Physics, Chernogolovka, 1982, pp 1-336 [in Russian]. 

As in the case of the reaction of hydroperoxide with the rr-bond of the olefin, the reaction of ROOH with the rr-bond of the aromatic ring occurs more rapidly than the attack of ROOH on the C—H bond of alkylaromatic hydrocarbon. 

When alkylaromatic hydrocarbon is oxidized, acids catalyze the decomposition of hydroperoxide with production of phenolic compounds [57,58],... 

In addition, phenols are formed by the reaction of hydroxyl radical addition to the aromatic ring of oxidized alkylaromatic hydrocarbon [56]. 

The reactivity of tertiary peroxyl radicals of different structures is very close, as it was evidenced by measuremets of Howard and Ingold [55,56]. The rate constants (L moR1 s-1) of four tertiary peroxyl radicals with a few alkylaromatic hydrocarbons (T = 303 K) are presented below. 

The addition of hydroxyl radicals to benzene ring of alkylaromatic hydrocarbon gives phenolic compounds. Phenols retard oxidation, terminating the chains (see Part II). 

Catalysis by nitroxyl radicals in hydrocarbon oxidation was discovered and studied recently [82-89], The introduction of /V-hydroxyphthalimide into oxidized alkylaromatic hydrocarbon was found to accelerate the oxidation. The formation of the stable phthalimide-/V-oxyl (PINO) radical was evidenced by the EPR method [90]. The following kinetic scheme was put forward to explain the accelerating effect of PINO on the chain oxidation of hydrocarbons [82-84]. 

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] ... 

We see that the triplet repulsion in the case of aliphatic amines increases Ee0 to 2.7 kJ mol-1. It is less than that of alkylaromatic hydrocarbons where A/fe0 = 5.9 kJ mol-1. So, one can conclude that the pair of p-electrons of nitrogen interacts with TS not so strongly as TT-electrons of the aromatic ring. 

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... 

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. 

This catalyst makes the increase in the oxidation rate of alkylaromatic hydrocarbons possible due to the intense participation of the catalyst itself (Co2+, Co3+, Br, and Br ) in chain propagation. 

Finally, it makes possible the oxidation of hydrocarbon to a significant depth, and when the RH molecule contains several methyl groups, the catalyst allows all these groups to be transformed into carboxyls. This last specific feature is insufficiently studied so far. Perhaps, it is associated with the following specific features of oxidation of alkylaromatic hydrocarbons. The thermal decomposition of formed hydroperoxide affords hydroxyl radicals, which give phenols after their addition at the aromatic ring... 

E0 = 40 kJ mol-1 at AH=0) is substituted by a few consecutive fast reactions with electron transfer. Russel [284-291] studied a few reactions of oxidation of alkylaromatic hydrocarbons in the presence of strong bases. He proved the chain mechanisms of these reactions. One of them includes a few stages with addition of dioxygen to carbanion. Another includes the electron transfer from carbanion to dioxygen. 

Hence, the peculiarities of emulsion oxidation of alkylaromatic hydrocarbons can be formulated as follows. 

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],... 

VF Tsepalov. The Study of Elementary Stages of Liquid-Phase Oxidation of Alkylaromatic Hydrocarbons. Doctoral Thesis, Institute of Chemical Physics, Chemogolovka, 1975, pp. 1-42 [in Russian]. 

Neuzil, R.W. and Antos, G.J. (1994) Use of a fluro-aromatic desorbent in a process for adsoptive separation of para-alkylaromatic hydrocarbons. Can. Patent 1322175. 

The side chain alkylation of alkyl benzenes is usually performed with alkenes as alkylating agents in the presence of strong-acid catalysts (256,257). The use of highly basic catalysts such as alkali metals, their hydrides, and sodium and potassium complexes for alkylation of alkylaromatic hydrocarbons has also been reported (256,257). The reaction mechanism proposed by Pines et al. (258) involves the addition of a benzylic carboanion to the alkene (Scheme 41). 

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