Benzene and Its Derivatives

Reduction of arenes by catalytic hydrogenation was described m Section 114 A dif ferent method using Group I metals as reducing agents which gives 1 4 cyclohexadiene derivatives will be presented m Section 1111 Electrophilic aromatic substitution is the most important reaction type exhibited by benzene and its derivatives and constitutes the entire subject matter of Chapter 12... 

During our discussion of benzene and its derivatives it may have occurred to you that cyclobutadiene and cyclooctatetraene might be stabilized by cyclic rr electron delocal ization m a manner analogous to that of benzene... 

In the preceding chapter the special stability of benzene was described along with reac tions in which an aromatic ring was present as a substituent Now we 11 examine the aromatic ring as a functional group What kind of reactions are available to benzene and Its derivatives What sort of reagents react with arenes and what products are formed m those reactions ... 

CharactenshcaUy the reagents that react with the aromatic nng of benzene and its derivatives are electrophiles We already have some experience with electrophihc reagents particularly with respect to how they react with alkenes Electrophihc reagents add to alkenes... 

Ozone can be used to completely oxidize low concentrations of organics in aqueous streams or partially degrade compounds that are refractory or difficult to treat by other methods. Compounds that can be treated with ozone include alkanes, alcohols, ketones, aldehydes, phenols, benzene and its derivatives, and cyanide. Ozone readHy oxidizes cyanide to cyanate, however, further oxidation of the cyanate by ozone proceeds rather slowly and may require other oxidation treatment like alkaline chlorination to complete the degradation process. 

The range of preparatively useful electrophilic substitution reactions is often limited by the acid sensitivity of the substrates. Whereas thiophene can be successfully sulfonated in 95% sulfuric acid at room temperature, such strongly acidic conditions cannot be used for the sulfonation of furan or pyrrole. Attempts to nitrate thiophene, furan or pyrrole under conditions used to nitrate benzene and its derivatives invariably result in failure. In the... 

Aromatie eompounds are benzene and its derivatives and eompounds that resemble benzene in their behaviour in a ehemistry dominated by ionie substitution. Benzene has the formula C6H6 eommonly written as the ring ... 

Partial fluorination [50] and perfluorination [5/] of aromatic systems can be accomplished electrochemically. A number of other reagents add fluorine to benzene and its derivatives, as elaborated in equation 5 [52, 53, 54, 551... 

Arenas such as benzene and its derivatives can form complexes precisely analogous to ferrocene and related species. Though particularly exciting when first recognized as rj complexes in 1955 these compounds introduce no new principles and need only be briefly considered here. Curiously, the first such compounds were made as long ago as 1919 when F. Hein reacted CrCL with PhMgBr to give compounds which he formulated as polyphenylchromium compounds [CrPh ]°- + (n = 2, 3, or 4) their true nature... 

A difficulty arises when we attempt to represent the bonding in benzene and its derivatives. We might write... 

Reactions of the type shown in (ii) and (34) are called substitution reactions. The substitution reaction is the characteristic reaction of benzene and its derivatives and is the way in which a multitude of compounds are prepared by the organic chemist. By this means he is able to introduce functional groups, which can then be... 

Two soluble nanocatalysts have been investigated in partial hydrogenation. The results obtained by Einke or Dupont s catalysts are unsatisfactory but prove that nanoparticles are a potential catalyst for this reaction, hi summary, partial hydrogenation of benzene and its derivatives is still a challenge but will be the focus of future research. 

The photoaddition of water, alcohols, and acids to benzene and its derivatives has also been extensively investigated(87 91) ... 

Likewise it is possible to differentiate between substituted and unsubstituted alicycles using inclusion formation with 47 and 48 only the unbranched hydrocarbons are accommodated into the crystal lattices of 47 and 48 (e.g. separation of cyclohexane from methylcyclohexane, or of cyclopentane from methylcyclopentane). This holds also for cycloalkenes (cf. cyclohexene/methylcyclohexene), but not for benzene and its derivatives. Yet, in the latter case no arbitrary number of substituents (methyl groups) and nor any position of the attached substituents at the aromatic nucleus is tolerated on inclusion formation with 46, 47, and 48, dependent on the host molecule (Tables 7 and 8). This opens interesting separation procedures for analytical purposes, for instance the distinction between benzene and toluene or in the field of the isomeric xylenes. 

Reaction with Aromatic and Heteroaromatic Compounds 4.1 Benzene and its Derivatives... 

Copper-catalyzed cyclopropanation of benzene and its derivatives by a diazoacetic ester yields a norcaradiene 230 which undergoes spontaneous ring opening to cyclo-heptariene 231. At the temperatures needed for successful cyclopropanation, sigma-tropic H-shifts leading to conjugated isomers of cycloheptatriene carboxylates cannot be avoided. The situation is complicated by the formation of regioisomers upon cyclopropanation of substituted benzenes, and separation of the cycloheptatriene isomers may became tedious if not impossible. 

Although the chromium compound is the best known, other metals form similar complexes with benzene and its derivatives. 

When starting this chapter we promised ourselves and the reader not to consider benzene and its derivatives. Cyclooctatetraene [or more properly (Z,Z,Z,Z)-l,3,5,7-cyclooctatetra-ene, 147] is generally recognized as a polyene and so this latter compound would appear to belong here. How can we do one and not the other Therefore, in this concluding section of the chapter, we briefly discuss the enthalpies of formation of some of the... 

Since its initial discovery by Michael Faraday in 1825,58 benzene (C6H6) has been recognized as an extraordinary substance. The spectacular properties of benzene and its derivatives (particularly the aniline dyes discovered by W. H. Perkin) initiated dramatic growth of the pharmaceutical, dyestuff, and munitions industries in the mid nineteenth century. The famous puzzle of the chemical structure of benzene was solved in 1865 by August Kekule in terms of two alternative six-membered-ring formulas ... 

At present, the efficient partial hydrogenation of benzene and its derivatives has been rarely described with well-defined soluble nanoparticles catalysts. Nonetheless, this remains an interesting area for research, with promising future applications. 

It has been known since the 1950s that benzene and its derivatives can be oxidized to the corresponding cyclohexadienols in the presence of Pseudomonas putida (see Scheme 8-4 for an example). 

The initial electron transfer to form the anion radical species seems to be reversible. For example, Allred et al. investigated the ac polarography of bis(trimethylsilyl)benzene and its derivatives which showed two waves in di-methylformamide solutions [71] the first one is a reversible one-electron wave, and the second one corresponds to a two-electron reduction. Anion radicals generated by electrochemical reduction of arylsilanes have been detected by ESR. The cathodic reduction of phenylsilane derivatives in THF or DME at — 16° C gives ESR signals due to the corresponding anion radicals [5] (See Sect. 2.2.1). 

A bis(dithia-dication) dimer has been proposed" " as an intermediate in the remote oxygen migration reactions of l,4-bis(methylthio)benzene and its derivatives (see... 

Feng et al. (1986) performed quantum-chemical calculations of aromatic nitration. The resnlts they obtained were in good accordance with the IPs of N02 and benzene and its derivatives. The radical-pair recombination mechanism is favored for nitration whenever the IP of an aromatic molecule is much less than that of N02. According to calculations, nitration of toluene and xylene with N02 most probably proceeds according to ion-radical mechanism. Nitration of nitrobenzene and benzene derivatives with electron-acceptor substituents can proceed through the classical polar mechanism only. As for benzene, both mechanisms (ion-radical and polar) are possible. Substituents that raise the IP of an aromatic molecule to a value higher than that of N02 prevent the formation of this radical pair (one-electron transfer appears to be forbidden). This forces the classical mechanism to take place. It shonld be nnderlined that a solvent plays the decisive role in nitration. 

Benzene and its derivatives are used widely throughout the chemical industry as solvents and raw materials. Mono-, di-, and trichlorobenzenes are used directly as pesticides for their insecticidal and fungicidal properties. Benzene, toluene, and chlorobenzene are used as raw materials in the synthesis of at least 15 pesticides, although their main use is as a carrier solvent in 76 processes. Additional priority pollutant aromatics and chlorinated aromatics exist as impurities or as reaction byproducts because of the reactions of the basic raw materials and solvent compounds. 

Zub M Reactivity of the white blood cell system to toxic actions of benzene and its derivatives. Acta Biol Cracoviensia 21 163-174, 1978... 

Many fully unsaturated heterocyclic compounds are described as aromatic, and some have a close similarity to benzene and its derivatives. For example, pyridine (azabenzene) is formally derived from benzene through the replacement of one CH unit by N. As a result, the consti-... 

Additions to Aromatic Hydrocarbons. A variety of photochemical additions to aromatic hydrocarbons have been reported. Benzene and its derivatives add to maleic anhydride74-76 as well as to simple olefins,77-80 isoprene,81 acetylene derivatives,79,82 and alcohols.83 The mechanism of the maleic anhydride-benzene reaction is discussed in Section IV. A.4. Naphthalene forms a photoadduct with dimethyl acetylenedicarboxylate62 and with acrylonitrile8211 while anthracene behaves similarly with maleic anhydride84 and with 1,2-benzanthracene.85 The photoaddition of several aromatic amines to anthracene has been reported to proceed via a charge transfer complex86,87 in fact, the majority of these addition reactions may proceed in this manner. 

Alkyl halides, alcohols, epoxides, carboxylic acid and its derivatives, and benzene and its derivatives. 

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