Reactions with aromatic hydrocarbons

The Friedel-Crafts Reaction, in which an aromatic hydrocarbon reacts with an alkyl halide under the influence of aluminium chloride ... 

Aromatic hydrocarbon resins. The polymerization procedure and variables in the reactions of the aromatic hydrocarbon resins are similar to those for the coumarone-indene resins. However, the Cg feedstreams used in the polymerization of the aromatic hydrocarbon resins do not contain significant amounts of phenols or pyridine bases, so they are submitted directly to fractional distillation. Distillation produced more byproducts than light coal-tar oils. The aromatic hydrocarbon resins obtained have softening points between liquid and 125°C and Gardner colour of 6 to 11. By changing distillation conditions, aromatic hydrocarbon resins with softening points between 65 and 170°C and Gardner colour of 5 to 10 can also be obtained. 

In contrast to saturated hydrocarbons, the unsaturated hydrocarbons react with atomic fluorine by two pathways, i.e. (atomic fluorine addition at >C=C< double bond and hydrogen substitution by fluorine atoms. The reaction of fluorine with aromatic hydrocarbons proceeds with the formation of F-derivatives and hydrogen atoms break off ... 

Solid Catalysts. Nafion-H is an active catalyst for acylation with aroyl halides and anhydrides.60,61 The reaction is carried out at the boiling point of the aromatic hydrocarbons. Yields with benzoyl chloride using 10-30% Nafion-H for benzene, toluene, and p-xylene are 14%, 85% and 82%, respectively. Attempted acylation with acetyl chloride, however, led to HC1 evolution and ketene formation. Nation resin-silica nanocomposite materials containing a dispersed form of the resin within silica exhibits significantly enhanced activity in Friedel-Crafts acylations.62,63... 

Thus if we axe interested only in the relative values of equilibrium or rate constants for closely similar reactions, we need only concern ourselves with changes in delocalization energy. This of course is a useful simplification. A good illustration is provided by the protonation of aromatic hydrocarbons. Aromatic hydrocarbons react with strong acids to form salts. These are now known4 to be arenonium ions thus benzene is converted to benzenonium ion (I) by strong acids ... 

Many chlorine-substituted compounds and some aromatic hydrocarbons react with 0 T ions this type of reaction is discussed later. Adduct formation, involving a halide ion, leads to negative ions under some circumstances. There are also a few addition reactions of specialized reagents that will lead to negative ions. 

Sulfones are often produced as by-products in the sulfonation of aromatic hydrocarbons (method 540). Aromatic hydrocarbons react with sulfonic acids less readily than with sulfuric acid. The success of the reaction depends upon the removal of the water as it is formed. An automatic water separator is used in the conversion of a refluxing mixture of benzene and sulfuric acid to diphenyl sulfone (80%). A similar technique has been employed in the preparation of unsymmetrical sulfones. 

From Aliphatic Acids.—By the introduction of an aryl radical into an aliphatic acid we may obtain side-chain carboxy acids in which the side chain is the same as in the aliphatic acid. This reaction is effected by the Friedel-Craft reagent, aluminium chloride, with the aromatic hydrocarbon together with a halogen aliphatic acid. 

Table 6.4 shows the principal photoreactions of aromatic compounds that we discuss in this chapter. Upon irradiation, aromatic compounds, such as benzenes, naphthalenes and some of their heterocyclic analogues, undergo remarkable rearrangements that lead to some non-aromatic highly strained products, such as benzvalene and Dewar benzene (entry 1), which can be isolated under specific conditions. Quantum and chemical reaction yields are usually low however, photochemistry may still represent the most convenient way for their preparation. While bulky ring substituents usually enhance the stability of those products, aromatic hydrocarbons substituted with less sterically demanding substituents exhibit ring isomerization (phototransposition) (entry 2). 

A number of aromatic hydrocarbons react with pyridine when oxidized either with iodine or anodically. N-Arylpyridinium ions arc formed and the reaction is called pyridination. The reactive species is... 

VI. THEORETICAL CALCULATION OF THE RELATIVE RATES OF REACTION OF AROMATIC HYDROCARBONS COMPARISON WITH EXPERIMENTAL DATA... 

Electron transfer initiations can also result from reactions of alkali metals with aromatic hydrocarbons or with aromatic ketones that result in formations of radical ions ... 

For this reaction the use was recommended of a hydrocarbon solvent (such as benzene, xylene, decahydronaphthalene, cyclohexane or a petroleum ether (with preference for an aromatic hydrocarbon)) mixed with diethyl ether. Thus the dangers of large-scale use of the extremely risky ether were largely suppressed. 

Benzene—the most common aromatic hydrocarbon. The benzene molecule has six carbon atoms connected in a ring. Each carbon atom has four bonding sites available in benzene, three are used and one is free. The three bonds are covalent the fourth can be shared by all six carbon atoms. This creates a donut-shaped cloud or aromatic ring. Reactions with benzene are substitution and not addition. 

The measurement of the electronic absorption spectra of the anions of aromatic hydrocarbons together with the interpretation given also contributed appreciably to a better understanding of the structure of the products of the reaction of alkali metals with hydrocarbons. The anions all give rise to a strong absorption in the visible range. On the basis of a quantum... 

A method ) has been recommended for the determination of benzene in the presence of its homologues. It is based on nitration of a mixture of aromatic hydrocarbons, extraction with ether of the nitro-compounds formed from the reaction mixture, evaporation of the solvent, oxidation with chromic acid and dissolution of the residue in acetic acid. 

Electron transfer is the rate-determined step, and collapse of the intermediate species gives a o-complex. Radical cations of polycyclic aromatic hydrocarbons react with nucleophiles and radicals to yield substituted compounds. The oxidation of anthracene to 9,10-anthraquinone involves the reaction of radical cations with water followed by one-electron transfer and deprotonation ... 

Cobalt.—Aromatic hydrocarbon hydrogenations with a discrete metal complex have now been achieved for the first time. Thus hydrogenation of benzene to cyclohexane proceeds slowly at 25 °C and < 760 mmHg pressure in the presence of [Co( y -C3HB)- P(OMe)3)3]. Alkylbenzenes are converted into alkylcyclohexanes, anisole into methoxycyclohexane, and ethylbenzoate into ethyl cyclohexenylcarboxylate. The suggested mechanism of reaction is summarized in Scheme 14. ... 

Another metallocene, namely, decamethylosmocene, (Mc5C5)20s (catalyst 1.2), turned out to be a good precatalyst in a very efficient oxidation of alkanes with hydrogen peroxide in acetonitrile at 20 — 60 °C [9]. The reaction proceeds with a substantial lag period that can be reduced by the addition of pyridine in a small concentration. Alkanes, RH, are oxidized primarily to the corresponding alkyl hydroperoxides, ROOH. TONs attain 51,000 in the case of cyclohexane (maximum turnover frequency was 6000 h ) and 3600 in the case of ethane. The oxidation of benzene and styrene afforded phenol and benzaldehyde, respectively. A kinetic study of cyclohexane oxidation catalyzed by 1.2 and selectivity parameters (measured in the oxidation of n-heptane, methylcyclohexane, isooctane, c -dimethylcyclohexane, and trans-dimethylcyclohexane) indicated that the oxidation of saturated, olefinic, and aromatic hydrocarbons proceeds with the participation of hydroxyl radicals. 

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