Benzene discovery

Let s begin by tracing the history of benzene its origin and its structure Many of the terms we use including aromaticity itself are of historical origin We 11 begin with the discovery of benzene... 

Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

Because of the number of citations, only selected imidazoquinolines are described, and biological activity is mentioned only briefly. The largest increase in the number of citations was caused by the discovery of the antibacterial properties of nalidixic acid type drugs. Efforts to prepare the bioisosters, for example of oxolinic acid, intensified in the early 1970s, and the discovery of the carcinogenic properties of 2-aminoimidazoquinolines followed in the early 1980s. These azoloquinolines can be considered as benzene-separated deazapurines. 

Another issue important to the success of this chiral titanium reagent 31 was the discovery of a marked solvent effect. When the fumaric acid derivative is reacted with isoprene in the presence of 10 mol% of the titanium reagent 31 in toluene, poor optical purity results (36-68% ee). Interestingly the optical purity of the adduct greatly increased in the order benzene, toluene, xylenes, and mesitylene, with 92% ee obtained in the last. Mesitylene is difficult to remove, because of its high boiling point, and other solvents were screened in detail. As a result, the mixed solvent system toluene petroleum ether (1 1) was discovered to be very effective. 

Anticoagulant therapy was developed with the adventitious discovery of dicoumarol (8). A fuller discussion of the rationale for the use of such compounds is found in the chapter on Five-Mem-bered Heterocycles Fused to One Benzene Ring. The reader s attention is directed, however, at the fact that dicoumarol is a polycarbonyl compound containing a very acidic hydrogen. A series of similarly acidic 1,3-indandiones have been found to constitute an additional class of anticoagulant agents. 

Robert Curl, Richard Smalley, and Harold Kroto were awarded the Nobel prize in chemistry in 1996 for the discovery of the soccer-ball-shaped molecule C60. This fundamental molecule was the first of a new series of molecular allotropes of carbon. The enthalpy of combustion of C60 is —25 937 kj-mol, and its enthalpy of sublimation is +233 kj-mol There are 90 bonds in C60, of which 60 are single bonds and 30 are double bonds. Like benzene, C60 has... 

This discovery was quite unexpected, since iron oxide has been never reported as an active catalyst in either partial or full oxidation. The studies of two simplest reactions, i.e. O2 isotopic exchange and N2O decomposition, revealed a dramatic change of Fe properties in the ZSM-5 matrix compared to Fe203 [4]. Fe atoms lose their ability to activate O2 but gain remarkably in their ability to activate N2O. It gives rise to a great effect of the oxidant nature in the reaction of benzene oxidation over the FeZSM-5 zeolite (Table 1). Thus, in the presence of N2O benzene conversion is 27% at 623 K, while in the presence of O2 it is only 0.3% at 773 K. And what is more, there is a perfect change of the reaction route. Instead of selective phenol formation with... 

For some important insect pests there are still no satisfactory chemical controls. Such problems should be given due consideration in the development program. Many of these problems appeared to be solved with the discovery of DDT, benzene hexachlo-ride (hexachlorocyclohexane), and some of the more recent insecticides. Further studies of the toxicity of some of these products to warm-blooded animals have raised the important question of the advisability of continuing their use where food and feed products are concerned. Considerable attention is being centered on finding safer analogs, such as TDE and methoxychlor, and new and better insecticides. 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

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 ... 

There are several examples of the concerted mechanism. However, no report of an insertion of a carbon—carbon triple bond into a metallacyclopentadiene had appeared prior to discovery of this reaction. At low temperatures, during the reaction of zirconacyclopentadienes with DMAD, the formation of trienes (79) is observed upon hydrolysis. This clearly indicates that the benzene formation involves the insertion (addition) reaction of DMAD. As shown in Eq. 2.50, the alkenyl copper moiety adds to the carbon—carbon triple bond of DMAD and elimination of Cu metal leads to the benzene derivatives 72. Indeed, a copper mirror is observed on the wall of the reaction vessel. 

Accidently, using hexafluoro-p-xylene with the contaminated copper wire obtained from the precursor method experiments, a polymer film was deposited on the silicon substrates. Obviously, some dibromotetrafluoro-p-xylene from the precursor method that adhered to, or reacted with, the metal could somehow initiate this VDP process. However, a complete explanation of these results is not yet available. As an extension of this discovery, commercially available 1,4-bis(trifluoromethyl)benzene in conjunction with a catalyst/initiator has proved to be a potential alternative by which to deposit poly(tetrafluoro-p-xylylene) film successfully.23... 

We might expect that the reaction would lead to the formation of tetraphenylmethane from benzene and carbon tetrachloride in the presence of aluminium chloride, but this is not so. In this case the fourth Cl-atom remains in the reaction product. Triphenylchloromethane (C6H5)3CC1 has acquired extraordinary importance because, when applied in the Wurtz reaction, it made possible the discovery of the first free organic radicle (Gomberg, 1900). Compare p. 352. 

This view was given further support by the discovery of "tautomerism," that is, that some compounds behave as if they have two different structures simultaneously. Peter Laar suggested in 1886 that this can best be explained as the result of continual oscillation of a hydrogen atom between two positions within a single molecule, 109 a hypothesis influenced by Kekule s suggestion that the peculiarities of benzene are the result of an oscillation of atoms in benzene and that "equivalence" or valence is "the relative number of contacts which occur in a unit of time between atoms." 110... 

In 1899, Lowry discovered the change in the rotatory power over time of a solution of nitrocamphor in benzene, an effect previously encountered only with aqueous solution of sugars. He named this effect "mutarotation," and its discovery was taken as a prominent achievement for Armstrong s laboratory research group. 50 Lowry ascribed the phenomenon to tautomeric conversion (from a CH-N02 form to a C = NO-OH form), that is, the shift of a hydrogen atom and the shift of a double bond. In 1909, he and Desch concluded that this reversible transformation occurs very quickly because they could not find an ultraviolet absorption spectral band characteristic of either isomer. 51 But what triggered this reversible transformation ... 

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