Platinum alkali metals

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

Single-bond cleavage with molecular hydrogen is termed hydrogenolysis. Palladium is the best catalyst for this purpose, platinum is not useful. Desulfurizations are most efficiently per-formed with Raney nickel (with or without hydrogen G.R. Pettit, 1962 A or with alkali metals in liquid ammonia or amines. The scheme below summarizes some classes of compounds most susceptible to hydrogenolysis. 

All the six platinum-group metals are highly resistant to corrosion by most acids, alkalis, and other chemicals. Their high nobility is the main factor determining their chemical resistance, and the formation of. complex ions in solution is principally responsible for their dissolution under certain conditions. 

The range of chemical reactivity of metals is wide, from the inertness of the platinum group to the extreme reactivity of some alkali metals. The order of metal reactivity follows essentially the order of the electrochemical series which is shown in Table 17.4 for the metals commonly deposited by CVD. 

M. Faraday was the first to observe an electrocatalytic process, in 1834, when he discovered that a new compound, ethane, is formed in the electrolysis of alkali metal acetates (this is probably the first example of electrochemical synthesis). This process was later named the Kolbe reaction, as Kolbe discovered in 1849 that this is a general phenomenon for fatty acids (except for formic acid) and their salts at higher concentrations. If these electrolytes are electrolysed with a platinum or irridium anode, oxygen evolution ceases in the potential interval between +2.1 and +2.2 V and a hydrocarbon is formed according to the equation... 

Dithiophosphato metal complexes are usually prepared by metathesis of metal halides with alkali metal or ammonium salts. A convenient method uses the redox reaction of his th iophosphory 1 )d is ulfanes (RO)2(S)PSSP(S)(OR)2, with metal species in low oxidation states resulting in the insertion of the metal into the sulfur-sulfur bond.24 Recently it was used for the synthesis of long alkyl chain, liquid platinum(II) dithiophosphates25 and for the synthesis of Ru (CO)2[S2P(OPr%]2 from Ru3(CO)i2 with (Pr 0)2(S)PSSP(S)(0Pr,)2.26... 

The production of sulphuric acid by the contact process, introduced in about 1875, was the first process of industrial significance to utilize heterogeneous catalysts. In this process, SO2 was oxidized on a platinum catalyst to S03, which was subsequently absorbed in aqueous sulphuric acid. Later, the platinum catalyst was superseded by a catalyst containing vanadium oxide and alkali-metal sulphates on a silica carrier, which was cheaper and less prone to poisoning. Further development of the vanadium catalysts over the last decades has led to highly optimized modem sulphuric acid catalysts, which are all based on the vanadium-alkali sulphate system. 

Palladium and platinum. These are resistant to chemical attack (Pt more than Pd). Both metals dissolve in fused alkali metal oxides and peroxides. Pt is attacked, at high temperature, by molten alkali and alkaline earth halogenides and by several compounds of B, Si, Pb, P, As, Sb, Bi. Pd dissolves slowly in oxidizing acids Pt is dissolved by aqua regia. 

Alkyl chlorides are with a few exceptions not reduced by mild catalytic hydrogenation over platinum [502], rhodium [40] and nickel [63], even in the presence of alkali. Metal hydrides and complex hydrides are used more successfully various lithium aluminum hydrides [506, 507], lithium copper hydrides [501], sodium borohydride [504, 505], and especially different tin hydrides (stannanes) [503,508,509,510] are the reagents of choice for selective replacement of halogen in the presence of other functional groups. In some cases the reduction is stereoselective. Both cis- and rrunj-9-chlorodecaIin, on reductions with triphenylstannane or dibutylstannane, gave predominantly trani-decalin [509]. 

The Kolbe reaction is earned out in an undivided cell with closely spaced platinum electrodes. Early examples used a concentrated, up to 50 %, aqueous solution of an alkali metal salt of the carboxylic acid and the solution became strongly alkaline due to hydrogen evolution at the cathode. Ingenious cells were devised with a renewing mercury cathode, which allowed removal of alkali metal amalgam. These experimental conditions have been replaced by the use of a solution of the carboxylic acid in methanol partially neutralised by sodium methoxide or trieth-... 

Fused alkalies, particularly potassium and barium hydroxides, are corrosive to platinum. In the presence of oxygen or oxidizing agents this corrosive action of fused alkalies increases. Also, cyanide and nitrates of alkali metals in fused state are corrosive to platinum. 

Antoine Baum , 1728-1804. French pharmacist and chemist. Author of a Chymie expenmentale et raisonnee in which he discussed chemical apparatus, chemical affinity, fire, air, earth, water, sulfur, gypsum, alum, clay, niter, gunpowder, borax, arsenic, glass, porcelain, and the common acids, alkalies, metals, and ores used m 1773. His hydrometer scale is still used. He was one of the first chemists to investigate platinum... 

Between these limiting cases, intermediate states are possible The same molecule can give off electrons to a metal with high electronic work function (e.g., H atoms to platinum) or receive electrons from a metal with low electronic work function (formation of hydrides between H atoms and alkali-metal surfaces). 

Reduction. Benzene can be reduced to cyclohexane [110-82-7], C5H12, or cycloolefins. At room temperature and ordinary pressure, benzene, either alone or in hydrocarbon solvents, is quantitatively reduced to cyclohexane with hydrogen and nickel or cobalt (14) catalysts. Catalytic vapor-phase hydrogenation of benzene is readily accomplished at about 200°C with nickel catalysts. Nickel or platinum catalysts are deactivated by the presence of sulfur-containing impurities in the benzene and these metals should only be used with thiophene-free benzene. Catalysts less active and less sensitive to sulfur, such as molybdenum oxide or sulfide, can be used when benzene is contaminated with sulfur-containing impurities. Benzene is reduced to 1,4-cydohexadiene [628-41-1], C6HS, with alkali metals in liquid ammonia solution in the presence of alcohols (15). 

The alkali-metal halide phosphors are produced by firing the corresponding alkali-metal halide and the activator in platinum or fused-silica crucibles under an inert atmosphere. 

Oxalo-niobates or niobo-oxalates correspond to the vanado-oxalates, and contain both oxalic acid and niobic add radicals in the complex anion. The only known series possesses the general formula 3R aO. Nb 205.6C203.a H20, where R stands for an alkali metal. The sodium, potassium and rubidium salts are prepared by fusing one molecular proportion of niobium pentoxide with three molecular proportions of the alkali carbonate in a platinum crucible. The aqueous extract of the melt jjs poured into hot oxalic add solution concentration and cooling, or addition of alcohol or acetone, then brings about precipitation of the complex salt. Comparison of the dectrical conductivity measurements of solutions of the alkali oxalo-niobates with those of the alkali hydrogen oxalates determined under the same conditions indicates that the oxalo-niobates are hydrolysed in aqueous solution, and that their anions contain a complex oxalo-niobic acid radical.6... 

The reaction commences at a temperature above 400° C., before the melting temperature is reached, and the fused product therefore always contains some arsenious oxide.1 When heated in hydrogen, the pentoxide is reduced first to arsenious oxide and then to free arsenic. Similar reduction occurs when it is heated with carbon or phosphorus with sulphur, arsenious sulphide is formed. Arsenic and metallic arsenides result when the pentoxide is heated with alkali metals,2 zinc, lead, iron or most other heavy metals mercury and silver react only at high temperature gold and platinum do not react. 

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