Reduction of benzene

C, b.p. 81"C. Manufactured by the reduction of benzene with hydrogen in the presence of a nickel catalyst and recovered from natural gase.s. It is inflammable. Used as an intermediate in the preparation of nylon [6] and [66] via caprolactam and as a solvent for oils, fats and waxes, and also as a paint remover. For stereochemistry of cyclohexane see conformation. U.S. production 1980 1 megatonne. 

It is prepared commercially by treating benzene diazonium chloride with sodium sulphite and then reducing the mixture with zinc dust and ethanoic acid. It can also be prepared by reduction of benzene diazonium chloride with SnCl. ... 

Another way to make cyclohexenes is by the partial reduction of benzene rings ( Birch reduction, described in Norman, p.553-557) such as ... 

The mechanism by which the Birch reduction of benzene takes place (Figure 118) IS analogous to the mechanism for the metal-ammonia reduction of alkynes It involves a sequence of four steps m which steps 1 and 3 are single electron transfers from the metal and steps 2 and 4 are proton transfers from the alcohol... 

This addition would correspond to a reduction of benzene by two electrons to give CfiHfi2. Do you expect these ions to be diamagnetic or paramagnetic ... 

Phenylhydrazine has been prepared by the reduction of benzene diazonium salts with sulfites 1 by the reduction of benzene diazonium chloride with stannous chloride 2 by the reduction of benzene diazonium hydrate with zinc or sulfur dioxide 3 by the reduction of sodium benzene diazotate with sodium stannite 4 by the reduction of diazoamino benzene 5 by the reduction of nitrosophenyl hydroxylamine or its methyl ether 6 and by the action of hydrazine hydrate on phenol.7... 

Hydrogenation over rhodium (5% on alumina) in acetic acid at room temperature and 3-4 atm of hydrogen was successfully used for reduction of benzene rings in compounds containing functions which would be hydrogen-olyzed over platinum or palladium catalyst [390], Palladium at low temperature usually does not reduce benzene rings and is therefore suited for hydro-genolysis of benzyl derivatives (pp. 150, 151). 

It is of interest to mention reduction of benzene and its homologs to the corresponding hexahydro derivatives by heating with anhydrous hydrazine. 

Most effort over the electrochemical reduction of benzene hydrocarbons has centred on finding a reaction medium, which is also a better solvent for the substrate than liquid ammonia. Aliphatic amines have proved useful solvents and they may be used in an undivided electrochemical cell. Base is generated at the cathode while an equivalent of acid is generated in the anode reaction so that mixing of the cel contents maintains a neutral solution. An alcohol is usually added as a proton donor to prevent the build-up of a localised highly basic environment. The simultaneous anode reaction is oxidation of the amine. Electrodes of platinum, aluminium or graphite have been used. Under these conditions, benzene [38] is converted... 

Cyclohexane. It can be prepared with high purity by distillation of a mixture of alkanes fi om petroleum refining or by reduction of benzene. 

Additional emission reductions of benzene, volatile organic compounds, and particulate matter... 

The highly hydrogenated derivative, C60H36 displays only one reversible reduction in THF, which appears to involve two electrons [87]. Reductions are observed at —3.24 and —3.18 V vs. Fc/Fc+ when the voltammetry is conducted at +14 and — 38°C respectively. These highly negative potentials approach the value for the reduction of benzene (see Table 10), and support the notion that as fullerene double bonds become saturated, reduction becomes more difficult. No oxidation was obtained in THF, but the compound oxidizes irreversibly in DCM and MeCN at +1.22 and +1.25 V vs. Fc/Fc+ at —47 and —28 °C respectively. 

Free radical attack at the pyridine ring is noted for its low selectivity and substituents have little effect. Arylation takes place at all three positions, but halogen atoms preferentially attack the a-, and alkyl radicals the a- and y-positions. Metals such as sodium and zinc transfer a single electron to pyridine to form anion radicals. These can dimerize by reaction at the a- or y-position to yield dipyridyls by loss of hydride ion. Thus, reduction of pyridine by chemical and catalytic means is easier than reduction of benzene. 

D. A. Hrovat, J. H. Hammons, C. D. Stevenson, and W. T. Borden, Calculations of the Equilibrium Isotope Effects on the Reductions of Benzene-dg and Cyclooctatetraene-dg, J. Am. Chem. Soc. 1997,119, 9523. B3LYP/6-31+G calculations on the title compounds and on the radical anions formed from them show that the very large difference between the equilibrium isotope effects, found by Stevenson, is due to an inverse isotope effect on the planarization of the COT ring. This explanation was subsequently confirmed by KIE measurements, carried out by C. D. Stevenson, E. C. Brown, D. A. Hrovat, and W. T. Borden, Isotope Effects on the Ring Inversion of Cyclooctatetraene, J. Am. Chem. Soc. 1998, 120, 8864. 

Fig. 9.25. (a) Tafel plots of numerous reactions reduction of benzene, oxidation of Cu in solid electrolyte, reduction of NOj in molten salt, reduction of Fe CNJg,... 

Plappert, U., Barthel, E. Seidel, H.J. (1994) Reduction of benzene toxicity by toluene. Environ, mol. Mutag., 24, 283-292... 

Adams platinum oxide catalyst is readily prepared from chloroplatinio acid or from ammonium chloroplatinate, and is employed for catalytio hydrogenation at pressures of one atmosphere to several atmospheres and from room temperature to about 90°. Reduction is usually carried out with rectified spirit or absolute alcohol as solvents. In some cases (e.g., the reduction of benzene, toluene, xylene, mesitylene, cymene and diphenyl ), the addition to the absolute alcohol solution of 2-5 per cent, of the volume of rectified spirit which has been saturated with hydrogen chloride increases the effectiveness of the catalyst under these conditions chlorobenzene, bromobenzene, o-, m- and p-bromotoluenes, p-dichloro- and p-dibromo-benzene are reduced completely but the halogens are simultaneously eliminated. Other solvents which are occasionally employed include glacial acetic acid, ethyl acetate, ethyl acetate with 17 per cent, acetic acid or 8 per cent, of alcohol. In the actual hydrogenation the platinum oxide Pt02,H20 is first reduced to an active form of finely-divided platinum, which is the real catalyst allowance must be made for the consumption of hydrogen in the process. 

It is possible to hydrogenate aromatics in the superacids HF-TaF5, HF-SbF5, or HBr-AlBr3 in the presence of hydrogen. The reduction of benzene was shown to give an equilibrium mixture of cyclohexane and methylcyclopentane.243 244 Reduction was postulated to proceed via initial protonation of benzene followed by hydride transfer ... 

Krapcho and Bothner-By made additional findings that are valuable in understanding the Birch reduction. The relative rates of reduction of benzene by lithium, sodium and potassium (ethanol as proton donor) were found to be approximately 180 1 0.5. In addition, they found that benzene is reduced fourteen times more rapidly when methanol is the proton donor than when (-butyl alcohol is used. Finally, the relative rates of reduction of various simple aromatic compounds by lithium were determined these data are given in Table 1-2. Taken together, the above data show that the rate of a given Birch reduction is strikingly controlled by the metal... 

Reduction -of benzene [BENZENE] (Vol 4) -dehydrogenase-catalyzed [ENZYMES IN ORGANIC SYNTHESIS] (Vol 9) -m dyes manufacture pYES AND DYE INTERMEDIATES] (Vol 8) -of esters pSTERS, ORGANIC] (Vol 9) -maleic anhydride [MALEIC ANHYDRIDE, MALEIC ACID AND FUMARIC ACID] (Vol 15) -microbial transformations [MICROBIAL TRANSFORMATIONS] (Vol 16) -of mtrophenols [AMINOPHENOLS] (Vol 2) -of terphenyls [BIPHENYL AND TERPHENYLS] (Vol 4)... 

In view of the mechanism suggested above for the ethanol-sodium reaction, it seems likely that reduction of aromatic compounds by solutions of alcohols and alkali metals in liquid ammonia proceeds by a general mechanism involving a steady-state concentration of ammonium ion. Krapcho and Bothner-By (29) observed that the reduction of benzene and several substituted benzenes in lithium-alcohol-ammonia solutions,... 

Fig. 3. Distribution of formal charge in the anionic intermediate of the Birch reduction of benzene calculated (a) by the Huckel method, (b) by the Pople method.

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