Platinum halogen compounds

The reactions of trifluoromethylthiosilver with cobalt- (p. 326), palladium-, or platinum-halogen compounds (p. 341) have already been discussed." The reaction of silver(i) oxide with (CFg)2S(0) NH and with CFa SOg NH SOjF in benzene provides a route to silver bis(trifluoro-methyl)sulphur oxyimine [(CFg)2S(0) NAg] and CF3-S0g-NAgS02F, respectively. Each gives the A methyl compound on treatment with methyl iodide, and (CF8)3S(0) NAg is readily converted into the iV-chloro-com-pound by chlorine. ... 

The most important of the tertiary phosphine complexes of platinum(IV) are Pt(QR3)2X4, generally prepared by halogen oxidation [174] of cis- or trans-Pt(QR3)2X2 (Q = P, As, R = alkyl Q = Sb, R = Me), since direct reaction of the platinum(IV) halides with the ligands leads to reduction. Once made, the platinum(IV) compounds are stable to reduction ... 

The most systematic study of reactions of transition metal atoms with halogen compounds has been the work of Klabunde on oxidation of nickel and palladium atoms. Some work has been done with copper, silver, gold, and platinum, but only scattered results have been reported for other metals. Klabunde s research has shown that perfluoroorgano-halides form isolable organometallic compounds on reaction with metal atoms much more commonly than nonfluorinated halides. The types of reactions observed with different classes of organic halides are considered next. 

Halogenated Hydrocarbons. A few halogenated hydrocarbons were studied by the usual procedure, using mixtures in air over the platinum filament. Neither dichlorodifluoromethane (CC12F2) nor 1,1-dichloro-ethene yielded a measurable ion current at temperatures up to 900°C. 1,1,1-Trichloroethane yielded a modest ion current, but the results were erratic and not reproducible. There was some indication that the halogen compounds changed the behavior of the filament. Consequently, no further experiments with halogenated compounds were conducted. This erratic behavior was in contrast with the very reproducible results with hydrocarbons. 

The nature of the cathode has been found to have major effect on the efficiency of electrochemical HDH of halogenated compounds. For instance, the HDH of 12 mM chlorobenzene at carbon cloth or lead cathodes gave conversions up to 95% with a current efficiency of 20%, lower conversion and efficiency (<5%) were observed using platinum, titanium or nickel cathodes (Zanaveskin et al. 1996). A 100% electrochemical HDH of 153 ppm 4-chlorophenol to phenol was achieved using a palladium-coated carbon cloth cathode (Balko et al. 1993). Unfortunately, several environmentally unacceptable materials, such as Hg and Pb, have also been used as cathodes (Bonfatti et al. 1999 Kulikov et al. 1996). 

Catalysts for the oxidation of volatile organic compounds (VOC) are generally supported platinum or palladium catalysts. Copper oxide, vanadium oxide and chromium oxide are suitable for the oxidation of halogenated compounds. 

Metal-based catalysts also were used for methane oxidation. Especially over metals such as platinum and palladium, trace amounts of methanol, formaldehyde, and formic acid can be found. Organic halides increased the yield of partial oxidation products and inhibited the complete combustion of methane [173]. Inhibition effects of dichloromethane was observed. Mann and Dosi [174] used a Pd/Al203 catalyst and found that the addition of halogen compounds reduced the conversion of methane in the following order ... 

Poly(56) and poly(57), which are functionalized with pyridinium groups, have been successfully polymerized by controlled potential oxidation to give films that show the reversible redox chemistry of the bipyridinium group [257,258]. This group was reduced at the expected potential in two one-electron steps. A film of poly(57) on platinum or on glassy carbon has been used to promote the reduction of aliphatic halogen compounds, dibromostilbene to stilbene [258] and hexachlo-roacetone to pentachloroacetone [259]. 

Catalytic Oxidation. Catalytic oxidation is used only for gaseous streams because combustion reactions take place on the surface of the catalyst which otherwise would be covered by soHd material. Common catalysts are palladium [7440-05-3] and platinum [7440-06-4]. Because of the catalytic boost, operating temperatures and residence times are much lower which reduce operating costs. Catalysts in any treatment system are susceptible to poisoning (masking of or interference with the active sites). Catalysts can be poisoned or deactivated by sulfur, bismuth [7440-69-9] phosphoms [7723-14-0] arsenic, antimony, mercury, lead, zinc, tin [7440-31-5] or halogens (notably chlorine) platinum catalysts can tolerate sulfur compounds, but can be poisoned by chlorine. 

Metals in the platinum family are recognized for their ability to promote combustion at lowtemperatures. Other catalysts include various oxides of copper, chromium, vanadium, nickel, and cobalt. These catalysts are subject to poisoning, particularly from halogens, halogen and sulfur compounds, zinc, arsenic, lead, mercury, and particulates. It is therefore important that catalyst surfaces be clean and active to ensure optimum performance. 

Condensation of ethyl acetoacetate with phenyl hydrazine gives the pyrazolone, 58. Methylation by means of methyl iodide affords the prototype of this series, antipyrine (59). Reaction of that compound with nitrous acid gives the product of substitution at the only available position, the nitroso derivative (60) reduction affords another antiinflammatory agent, aminopyrine (61). Reductive alkylation of 61 with acetone in the presence of hydrogen and platinum gives isopyrine (62). Acylation of 61 with the acid chloride from nicotinic acid affords nifenazone (63). Acylation of 61 with 2-chloropropionyl chloride gives the amide, 64 displacement of the halogen with dimethylamine leads to aminopropylon (65). ... 

The magnetic criterion is particularly valuable because it provides a basis for differentiating sharply between essentially ionic and essentially electron-pair bonds Experimental data have as yet been obtained for only a few of the interesting compounds, but these indicate that oxides and fluorides of most metals are ionic. Electron-pair bonds are formed by most of the transition elements with sulfur, selenium, tellurium, phosphorus, arsenic and antimony, as in the sulfide minerals (pyrite, molybdenite, skutterudite, etc.). The halogens other than fluorine form electron-pair bonds with metals of the palladium and platinum groups and sometimes, but not always, with iron-group metals. 

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