Rubidium catalysts

Hydrogenation of dibenzofuran over a platinum catalyst in acetic acid at 50°C and moderate pressure affords perhydrodibenzofuran. At higher temperatures and pressures with platinum or palladium catalysts the product is 2-biphenylol. When dibenzofuran is hydrogenated in ethanol over Raney nickel at 190°C and 200 atm for 23 h, the products isolated were perhydrodibenzofuran (36%), trans-2-cyclohexylcyclohexanol (27%), cis-2-cyclohexylcyclohexanol (20%), and dicyclohexyl (3%). When the hydrogenation, under these conditions, was terminated after the absorption of only 3 mol equiv of hydrogen, the only product detected was perhydrodibenzo-furan. ° Hydrogenation of dibenzofuran over a sodium-rubidium catalyst,... 

The hydrogenation of phenanthridine at 250 °C under pressure in the presence of a sodium-rubidium catalyst in benzene is reported to give octahydrophenanthridines. Acridine similarly forms a variety of reduction products (71JOC694). 

Rubidium-87 emits beta-particles and decomposes to strontium. The age of some rocks and minerals can be measured by the determination of the ratio of the mbidium isotope to the strontium isotope (see Radioisotopes). The technique has also been studied in dating human artifacts. Rubidium has also been used in photoelectric cells. Rubidium compounds act as catalysts in some organic reactions, although the use is mainly restricted to that of a cocatalyst. 

Starting with a ceramic and depositing an aluminum oxide coating. The aluminum oxide makes the ceramic, which is fairly smooth, have a number of bumps. On those bumps a noble metal catalyst, such as platinum, palladium, or rubidium, is deposited. The active site, wherever the noble metal is deposited, is where the conversion will actually take place. An alternate to the ceramic substrate is a metallic substrate. In this process, the aluminum oxide is deposited on the metallic substrate to give the wavy contour. The precious metal is then deposited onto the aluminum oxide. Both forms of catalyst are called monoliths. 

In a series of reports between 1991 and 1997 Yamaguchi showed that rubidium salts of L-proline (9) catalysed the conjugate addition of both nitroalkanes [29, 30] andmalonates [31-33] to prochiral a,p-unsaturated carbonyl compounds in up to 88% ee (Scheme 1). Rationalisation of the selectivities observed involved initial formation of an iminium ion between the secondary amine of the catalyst and the a,p-unsaturated carbonyl substrate. Subsequent deprotonation of the nucleophile by the carboxylate and selective delivery using ion pair... 

Hanessian described the facile addition of cyclic and acyclic nitroalkanes to cyclic a,P-unsaturated ketones using L-proline 58 as the catalyst (3-7 mol%) in the presence of 2,5-dimethylpiperazine [100], The reactions proceeded efficiently at room temperature and consistently provided adduct 59 with increased levels of enantioselectivity when compared with the rubidium prolinate method disclosed by Yamaguchi [29] (Scheme 24). The presence of trace amounts of water in the reaction was found to be essential, suggesting a hydrolytic step is involved in the catalytic... 

Rubidium chloride is used in preparing rubidium metal and many rubidium salts. Also, it is used in pharmaceuticals as an antidepressant and as a density-gradient medium for centrifugal separation of viruses, DNA, and large particles. Other applications are as an additive to gasoline to improve its octane number and as a catalyst. 

Rubidium hydroxide is used as a catalyst in oxidative chlorination. It also may be used as a powerful base, stronger than caustic potash, in many preparative reactions. The compound holds promising apphcations as an electrolyte in storage batteries for use at low temperatures. 

In the vapor phase, perfluoro-2-azopropene has been oxidized at high temperatures with oxygen using rubidium fluoride as a catalyst to produce IV-nitrosobis(trifluromethyl)amine, b.p. -3°C to -4°C [34] (Eq. 5). 

A unique feature of azoles amongst five membered heterocycles is that they can act both as the carbon or the heteroatom donor during the bond formation. This possibility is frequently exploited in synthetic transformations. Pyrrole, for example, coupled effectively with bromoarenes in the presence of palladium based catalysts (6.67.), The use of PBuj as ligand and rubidium carbonate as base allowed for the reduction of catalyst loading to 1% without significant deterioration of the yield"... 

The addition of chlorine monofluoridc across the C = 0 bonds in difluorophosgene, per-fluoroacyl fluorides, and perfluoroketones with the formation of hypochlorites occurs only in the presence of the catalysts potassium fluoride, rubidium fluoride, cesium fluoride80,81 or the strong Lewis acids hydrogen fluoride, boron trifluoride, or arsenic(V) fluoride.82 The cesium fluoride catalyzed reactions are carried out in an autoclave for 2-3 hours at — 20"C or left overnight.80... 

The strongly anionic alkali metal naphthalene compounds produced very large amounts of 1.2 (or 3.4) structure. The remainder of the polymer was 1.4-trans. No 1.4-cis polymer was produced. Increasing anionic catalysts such as rubidium and cesium produce even larger amounts of 1.4-trans-polybutadiene. 

A detailed study of the rearrangement of heptafluoro-2-phenylbut-1-ene (11) to but-2-ene 12 and the E,7. equilibration of 12 showed that lithium and sodium fluorides do not catalyze the rearrangement. Cesium, rubidium, and potassium fluorides are effective catalysts, in that order of decreasing reactivity.25... 

Silver alone on a support does not give rise to a good catalyst (150). However, addition of minor amounts of promoter enhance the activity and the selectivity of the catalyst, and improve its long-term stability. Excess addition lowers the catalyst performance (151,152). Promoter formulations have been studied extensively in the chemical industry. The most commonly used promoters are alkaline-earth metals, such as calcium or barium, and alkali metals such as cesium, rubidium, or potassium (153). Using these metals in conjunction with various counter anions, selectivities as high as 82—87% were reported. Precise information on commercial catalyst promoter formulations is proprietary (154—156). 

The synthesis of NH- and N-vinyltetrahydroindoles (1,2) is successfully performed with the cyclohexanone oxime/acetylene molar ratio 1 (2-5) at 90-140°C with bases (alkali metal hydroxides and alkoxides) taken in amounts of 10-50% of cyclohexanone oxime mass, serving as reaction catalysts. The reaction is catalyzed by potassium, rubidium, and tetrabu-tylammonium hydroxides (78MIP1). 

The reaction was carried out in dioxane, HMPA, and sulfolane as well as in mixtures of dioxane-DMSO (5 1 by volume) and water-DMSO (1 2) at 100-140°C with alkali metal (Li, Na, K, Rb, Cs) hydroxides, tetrabu-tylammonium hydroxide, and rubidium chloride examined as catalysts. All tests were run in an autoclave (1 L) at an initial acetylenic pressure of 12 atm. The most significant effect on the yield of 1-ethynylcyclo-hexanol (110) is that of the catalyst and the solvent. According to their diminishing efficiency, the catalysts examined are arranged as follows KOH RbOH > (Bu4)NOH > LiOH RbCl failed to catalyze the reaction and in the presence of CsOH, resinification was observed. The alcohol 110 is formed most readily in aqueous DMSO, dioxane being next in efficiency (with account for the yield based on the oxime consumed). Addition of DMSO to dioxane does not improve the yield of 110, and only trace amounts of this compound were obtained in HMPA and sulfolane. 

Another interesting example was reported by Yamaguchi et al. by using a simple L-proline rubidium salt 27 (Scheme 8D. 15) [32], A reversible iminium salt formation, involving the amine moiety of the catalyst and the carbonyl group of an enone, was proposed as the key intermediate. 

D ee achieved by Yamaguchi et al. using rubidium prolinate as catalyst (refs. 25,26). 

The conversion of phenanthridine into an unspecified octahydro-derivative by hydrogenation over a sodium metal-rubidium carbonate catalyst has been reported.334 Hydrogenation of the tetrahydro-phenanthridine (231) over platinum in acetic acid gave, rather surprisingly, the octahydrophenanthridine (232) with loss of meth-oxyl.173... 

One other point should be made with respect to the alkali metal cases, and that is that Foster and Binder (12) find that the molecular weight of the polymer decreases as the metal catalyst becomes more electropositive. Thus, all rubidium and cesium polymers have been of very low molecular weight and appear to be unsuitable for industrial development. 

Metal fluoroborates are produced either from fluoroboric acid and metal salts or by reactions of boric acid and hydrofluoric acid with metal salts. Fluoroborates of alkali metals and ammonium ions tend to crystallize as hydrates and are water soluble except for those of potassium, rubidium, and cesium. The major use for these compounds is as a high-temperature flux. Transition metal and other heavy metal fluoroborates are not as well known and well characterized. They are usually prepared from fluoroboric acid and an appropriate salt and are sold as 40-50% water solutions. Some fluoroborates from metals such as tin, lead, copper, and nickel are prepared by electrolysis of fluoroboric acid. The transition and other heavy metal fluoroborate solutions are used primarily as plating solutions and catalysts. 

The only system which seems to be promising for industrial application is ruthenium promoted with rubidium on graphite as carrier (see Section 3.6.2.3). Further information on structure, activity and reaction mechanism of non-iron catalysts is given in [102], [172]-[175], Specific references vanadium [176], uranium [177], molybdenum [178]-[180], tungsten [181]. 

From the early days of ammonia production to the present, the only catalysts that have been used have been iron catalysts promoted with nonreducible oxides. Recently, a ruthenium-based catalyst promoted with rubidium has found industrial application. The basic composition of iron catalysts is still very similar to that of the first catalyst developed by BASF. 

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