Reduction platinum chloride

The most usual synthetic routes to the derivatives of platinum group metals are the exchange reactions of the complexes containing halide ligands with alkali metal alkoxides (method 5), alcoholysis of the same kind derivatives (usually by phenols, method 4), alcoholysis of hydroxide complexes (method 3), and redox reactions — reduction of chlorides or 0s04 in alcohol media (method 7) (Table 12.25). 

Flynn and Hulburt, however, went further into a study of the hydrogenation of ethylene by hydrogen when a stream of these gases was passed through a solution of ethylene platinum chloride. They found that ethylene inhibits the formation of platinum metal. This inhibition seems to indicate that the first step of the reduction is a dissociation of the complex with ethylene as one of its products. The platinum formed as a result of the initial dissociation and reduction would catalyze the reduction of the complex. Ethylene, however, still inhibits the reaction markedly in the presence of platinum. 

In our process we make use of a 10% solution of hydrochloroplatinic acid for preparation of our colloidal metal, and precipitate the activated metal in aU aqueous solution of gum arabic by reduction with hydrogen gas without first introducing any colloidal metal to promote the reduction of the platinum chloride solution. Skita used in many cases a promoter to stimulate the formation of colloidal metal (Impfmethode). This was prepared by reducing platinum solution with formaldehyde in alkaline solution. 

The mechanism proposed was confirmed by the work of Cariati et al. [43]. In addition to their studies on rhodium WGSR catalysis in acid media, Cheng and Eisenberg have also reported [27] that mixtures of platinum chloride and tin chloride are active WGSR catalysts in an acetic acid/HCl solvent system. They proposed the following mechanism (Scheme 7.2). The catalytic cycle appears to involve the Sn(ll)/Sn(IV) redox couple. The formation of H2 coincides with the oxidation of Sn(ll) to Sn(IV) and CO is oxidized to CO2 concurrent with reduction of Sn(IV) to Sn(II). 

Isobe started with hexyl-functionalized dibromo crysene 76, and accessed the metallocycle 78 via the diboronate 77 using platinum chloride and cesium fluoride. Reductive elimination with triphenylphosphine offered the hydrocarbon 79 cleanly. 

Zinc platinum chloride/hydrochloric acid Reductive aromatization... 

Dicyanocobyrinic acid heptamethyl ester (52) undergoes oxidation at the a-bridge by molecular oxygen in the presence of ascorbic acid to form the wew-hydroxy-lactone (53) the dicyanocobyrinic acid lactone (54a) can be transformed into a variety of /S-meso-substituted derivatives, e.g. (54b), and reduction of the bromo- and iodo-lactones (54b R = Br or I) led to dicyanocobyrinic acid heptamethyl ester (52)/ Nickel complexes of 5-methyl derivatives of 1,19-dimethyl-octadehydrocorrins have been prepared, and the synthesis of l,19-diethoxycarbonyl-octamethylplatinum(ll) tetradehydrocorrin bromide by oxidative ring closure of the corresponding 1,19-diethoxycarbonyl-bilatriene in the presence of platinum chloride has been reported. 

Sahs of metals whose oxides are reduced by formaldehyde are readily reduced w heu treated with formaldehyde and alkalies. However, gold and platinum chlorides are reported to undergo reduction even in strongly acid solution . Under these conditions, the metals separate as crystalline... 

The PGM concentrate is attacked with aqua regia to dissolve gold, platinum, and palladium. The more insoluble metals, iridium, rhodium, mthenium, and osmium remain as a residue. Gold is recovered from the aqua regia solution either by reduction to the metallic form with ferrous salts or by solvent-extraction methods. The solution is then treated with ammonium chloride to produce a precipitate of ammonium hexachloroplatinate(IV),... 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

Isoquinoline can be reduced quantitatively over platinum in acidic media to a mixture of i j -decahydroisoquinoline [2744-08-3] and /n j -decahydroisoquinoline [2744-09-4] (32). Hydrogenation with platinum oxide in strong acid, but under mild conditions, selectively reduces the benzene ring and leads to a 90% yield of 5,6,7,8-tetrahydroisoquinoline [36556-06-6] (32,33). Sodium hydride, in dipolar aprotic solvents like hexamethylphosphoric triamide, reduces isoquinoline in quantitative yield to the sodium adduct [81045-34-3] (25) (152). The adduct reacts with acid chlorides or anhydrides to give N-acyl derivatives which are converted to 4-substituted 1,2-dihydroisoquinolines. Sodium borohydride and carboxylic acids combine to provide a one-step reduction—alkylation (35). Sodium cyanoborohydride reduces isoquinoline under similar conditions without N-alkylation to give... 

Reduction of vanillin by means of platinum black in the presence of ferric chloride gives vanillin alcohol in excellent yields. In 1875, Tiemann reported the reduction of vanillin to vanillin alcohol by using sodium amalgam in water. The yields were poor, however, and there were a number of by-products. High yields of vanillin alcohol have been obtained by electrolytic reduction. 

Oxidation and chlorination of the catalyst are then performed to ensure complete carbon removal, restore the catalyst chloride to its proper level, and maintain full platinum dispersion on the catalyst surface. Typically, the catalyst is oxidized in sufficient oxygen at about 510°C for a period of six hours or more. Sufficient chloride is added, usually as an organic chloride, to restore the chloride content and acid function of the catalyst and to provide redispersion of any platinum agglomeration that may have occurred. The catalyst is then reduced to return the metal components to their active form. This reduction is accompHshed by using a flow of electrolytic hydrogen or recycle gas from another Platforming unit at 400 to 480°C for a period of one to two hours. 

Johnson and Whitehead have further shown that the reductive elimination of the pyrrolidine group from the pyrrolidine enamine of 2,4-dimethyl-cyclohexanone (16), which involved treating it with a mixture of lithium aluminum hydride and aluminum chloride (9), gave the trans isomer of 3,5-dimethyl-/l -cyclohexene (17) which on subsequent hydrogenation on a platinum catalyst led to the // onr-3,5-dimethylcyclohexane (18). 

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