Benzene-, nickel

Upon treatment with suitable cobalt complexes, methylbutynol cyclizes to a 1,2,4-substituted benzene. Nickel complexes give the 1,3,5-isomer (196), sometimes accompanied by linear polymer (25) or a mixture of tetrasubstituted cyclooctatetraenes (26). 

Nickel(O) triphenylphosphine species have been used to convert allyl halides to 1,5-hexadiene [332], for the reductive coupling of ethylene with aryl halides to give 1,1-diaryl-ethanes [333], and for the coupling of aryl halides and alkenes to prepare substituted olefins [334], In addition, l,2-bis[(di-2-propylphosphino)benzene]nickel(0) has been used for the reductive coupling of aryl halides [335], and l,2-bis[(diphenylphosphino)ethane]-nickel(O) has been employed to synthesize biphenyl from bromobenzene [336] and to prepare benzoic acid from bromobenzene in the presence of carbon dioxide [337]. 

Electrocatalytic reductive coupling of aryl chlorides to afford biphenyls can be accomplished with dichloro(l,2-bis(di-propylphosphino)benzene)nickel(II) in yields as high as 96% with 2 mol % of the catalyst in polar, coordinating solvents (55). Similar couplings can also be achieved with nickel-2,2 -bipyridyl and Pd(PPh3)2Cl2 as catalysts (56, 57). Indirect electrochemical reduction of vicinal dibromides to alkenes occurs efficiently with iron and cobalt porphyrins as mediators (58). Vitamin B12 is a mediator for the indirect electrochemical reduction of a-halo acids (59). 

Skin sensitizer May cause an allergic skin reaction 1 Warning Human evidence of skin sensitivity in a substantial number of persons or positive animal testing Pentadecylcatechol (poison ivy allergen), formaldehyde, epichlorohydrin, 2,4-dinitrochloro-benzene, nickel... 

The National Institute of Health in the USA estimates that asbestos, arsenic, benzene, nickel, chromium and petroleum fractions account for between 23% and 38% of total cancer mortality. This estimate is based, in part, on studies of American shipyard workers who were exposed to higher levels of asbestos dust than most other workers in the same industry. 

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. 

The higher iodides, however, tend to be unstable and decomposition occurs to the lower iodide (PI5 -> PI3). Anhydrous chlorides and bromides of some metals may also be prepared by the action of acetyl (ethanoyl) halide on the hydrated ethanoate (acetate) in benzene, for example cobalt(II) and nickel(II) chlorides ... 

Cyclization with various nickel complex catalysts gives up to 97% selectivity to a mixture of cyclooctatetraene derivatives, with only 3% of benzene derivatives. The principal isomer is the symmetrical l,3,5,7-cyclooctatetraene-l,3,5,7-tetramethanol (29). 

Cuprous salts catalyze the oligomerization of acetylene to vinylacetylene and divinylacetylene (38). The former compound is the raw material for the production of chloroprene monomer and polymers derived from it. Nickel catalysts with the appropriate ligands smoothly convert acetylene to benzene (39) or 1,3,5,7-cyclooctatetraene (40—42). Polymer formation accompanies these transition-metal catalyzed syntheses. 

Hydrogenation Reactions. Hydrogen over a nickel, platinum, or paladium catalyst can partially or totally saturate the aromatic ring. Thermal hyrogenolysis of toluene yields benzene, methane, and biphenyl. 

Benzene Cast Iron Cast Iron Carbon Steel Nickel Moly. Ring Cast Iron Mall. Iron ... 

Carcinogens Cancer-producing agents Skin Respiratory Bladder/urinary tract Liver Nasal Bone marrow Coal tar pitch dust crude anthracene dust mineral oil mist arsenic. Asbestos polycyclic aromatic hydrocarbons nickel ore arsenic bis-(chloromethyl) ether mustard gas. p-naphthylamine benzidine 4-am i nodi pheny lam ine. Vinyl chloride monomer. Mustard gas nickel ore. Benzene. 

Monomer-oligomer equilibria. [Ni(Me-sal)2], mentioned above as a typical planar complex, is a much studied compound. In pyridine it is converted to the octahedral bispyridine adduct (/zsoo = 3.1 BM), while in chloroform or benzene the value of is intermediate but increases with concentration. This is ascribed to an equilibrium between the diamagnetic monomer and a paramagnetic dimer, which must involve a coordination number of the nickel of at least 5 a similar explanation is acceptable also for the paramagnetism of the solid when heated above 180°C. The trimerization of Ni(acac)2 to attain octahedral coordination has already been referred to but it may also be noted that it is reported to be monomeric and planar in dilute chloroform solutions. 

Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

Raney cobalt is generally less effective than Raney nickel, but may be of use when the rupture of other bonds must be avoided. The important use of Raney nickel desulfurization for the structure determination of thiophenes and for the determination of the absolute configuration of optically active thiophene and benzene derivatives has been stressed earlier. 

Some generalizations that pertain are (1) Terminal olefins are more rapidly reduced than internal olefins (2) conjugated olefins are not reduced at 1 atmosphere (3) ethylene is not hydrogenated. Rates of reduction compare favorably with those obtained by heterogeneous catalysts such as Raney nickel or platinim oxide. In fact, the hydrogenation of some olefins may be so rapid that the temperature of the solution (benzene) is raised to the boiling point. 

Aziridines, like oxiranes, undergo hydrogenolysis easily with or without inversion of configuration, depending on the catalyst, reaction parameters, and various additives 65aJ08). For example, hydrogenolysis of 2-methyl-2-phenylaziridine in ethanol occurs mainly with inversion over palladium but with retention over platinum, Raney nickel, or Raney cobalt. Benzene solvent or alkali favor retention over palladium as well. 

---