Chromium compounds, catalytic

Chromium compounds as catalysts, 188 Chromium oxide in catalytic converter, 62 Chromium oxide catalysts, 175-184 formation of active component, 176,177 of Cr-C bonds, 177, 178 propagation centers formation of, 175-178 number of, 197, 198 change in, 183, 184 reduction of active component, 177 Clear Air Act of 1970, 59, 62 Cobalt oxide in catalytic converter, 62 Cocatalysts, 138-141, 152-154 Competitive reactions, 37-43 Copper chromite, oxidation of CO over, 86-88... 

Catalytic elfects on the thermal decomposition and burning under nitrogen of the nitrate were determined for ammonium dichromate, potassium dichromate, potassium chromate, barium chloride, sodium chloride and potassium nitrate. Chromium(VI) salts are most effective in decomposition, and the halides salts during burning of the nitrate [1]. The effect of chromium compounds soluble in the molten nitrate, all of which promote decomposition of the latter, was studied (especially using ammonium dichromate) in kinetic experiments [2],... 

Sodium chromate is produced as part of the process for obtaining Cr203, and it is probably the most important chromium compound. Although there are other oxides of chromium, Cr203 is very important because of its catalytic properties. One way to obtain this oxide is by the decomposition of ammonium dichromate,... 

A great effort is dedicated to the development of methodologies for the oxidation of alcohols, involving catalytic quantities of chromium compounds, which are re-oxidized with other oxidants present in excess.406 Using chromium compounds in catalytic amounts is environmentally sound, and often facilitates the work-ups. 

Chromium compounds used in catalytic amounts for the oxidation of alcohols to aldehydes and ketones include ... 

Table 1.4. Lists the combinations of catalytic chromium compounds and oxidants (used in excess) employed in the oxidation of alcohols to...

Catalytic chromium compound Oxidant used in excess Molar ratio chromium compound/oxidant in excess/alcohol Observations References... 

Although the oxidations using catalytic chromium compounds are industrially attractive, none of them has found a widespread use in organic synthesis, because its versatility and efficiency in complex substrates have not been demonstrated. 

Intramolecular Nozaki reaction. The addition of a vinyl-chromium compound to an aldehyde (12, 137 14, 96) is useful for macrocyclization, particularly if the CrCl2 reagent is activated by a catalytic amount of Ni(acac)2. Under these conditions, the vinyl iodide with a w-formyl group (1) cyclizes to (+ )-brefeldin C 12) and the 4-epimer as a 1 4 mixture in 60% yield.1... 

Investigation of the nature and activity of catalytic species in copper(i) chloride-promoted dimerisation of acetylene indicates that the mechanism either involves insertion of a C2H unit into a copper-chlorine bond, or the reaction of CgH with two copper atoms to give a 3-centre, 2-electron-bonded species. Cyclic oligomerisation of diphenylacetylene in the presence of AlPha proceeds through ir-complexes as intermediates benzyne intermediates are suggested, on the basis of observed products, in oligomerisation of but-2-yne and of oct-4-yne in the presence of n-butyl- or /7-tolyl-chromium compounds. 

Isotactic 1,2-polybutadiene has so far only been obtained using catalyst systems composed of aluminum alkyls and soluble chromium compounds such as Cr(acac)3, Cr(C=NPh)6, Cr(CO)6, and Cr(CO)3Py3. In all of these cases, high Al Cr ratios and ageing of the catalytic system are crucial to obtain prevalently isotactic polymer otherwise, syndiotactic polymer is produced. This behavior indicates that the catalytic species actually responsible for the isotactic polymerization are formed by reduction of the initial Cr complex by the alkylaluminum reagent. 

In the presence of RhCU -xHzO, Mel, an organic base and chromium compounds, methyl acetate is carbonylated to acetic anhydride. The rate is first order in rhodium, Mel, and, at low concentrations, the base chromium compounds have less influence on the rate but reduce the induction period remarkably. " Catalytic carbonylation of nitrocompounds has been reviewed. " ... 

Subsequently, hydrogen co-ordinates to the chromium prior to transfer to, and thus reduction of, the diene. Some preliminary observations on photochemical catalytic hydrogenation of conjugated dienes in the presence of Cr(CO)e or of Cr(CO)4(nor) have been published. Deuterium tracer experiments have shown that hydrogen (deuterium) transfer from alkyl-chromium compounds to dienes takes place intermolecularly, from the -position of the alkyl group. ... 

Another method of abating tail gas from ammonia-oxidation processes that normally do not exceed 2000 ppm nitrogen oxides is selective catalytic reduction (SCR). The term selective is used because the ammonia fuel only reacts with the nitrogen oxides and not with the oxygen first as in other abatement systems. Catalyst materials include vanadia/ titania and iron-chromium compounds. 

Butane-Naphtha Catalytic Liquid-Phase Oxidation. Direct Hquid-phase oxidation ofbutane and/or naphtha [8030-30-6] was once the most favored worldwide route to acetic acid because of the low cost of these hydrocarbons. Butane [106-97-8] in the presence of metallic ions, eg, cobalt, chromium, or manganese, undergoes simple air oxidation in acetic acid solvent (48). The peroxidic intermediates are decomposed by high temperature, by mechanical agitation, and by action of the metallic catalysts, to form acetic acid and a comparatively small suite of other compounds (49). Ethyl acetate and butanone are produced, and the process can be altered to provide larger quantities of these valuable materials. Ethanol is thought to be an important intermediate (50) acetone forms through a minor pathway from isobutane present in the hydrocarbon feed. Formic acid, propionic acid, and minor quantities of butyric acid are also formed. 

Jacobsen et al. took an important step towards the development of a more general catalytic enantioselective cycloaddition reaction of carbonyl compounds by introducing chiral tridentate Schiff base chromium(III) complexes 15 (Scheme 4.15)... 

The major developments of catalytic enantioselective cycloaddition reactions of carbonyl compounds with conjugated dienes have been presented. A variety of chiral catalysts is available for the different types of carbonyl compound. For unactivated aldehydes chiral catalysts such as BINOL-aluminum(III), BINOL-tita-nium(IV), acyloxylborane(III), and tridentate Schiff base chromium(III) complexes can catalyze highly diastereo- and enantioselective cycloaddition reactions. The mechanism of these reactions can be a stepwise pathway via a Mukaiyama aldol intermediate or a concerted mechanism. For a-dicarbonyl compounds, which can coordinate to the chiral catalyst in a bidentate fashion, the chiral BOX-copper(II)... 

The obvious next step was oxidation of the tris(pyrazolyl)borate chromium alkyls to the catalytically active -t-III oxidation state. However, cyclic voltammetry experiments did not show a reversible oxidation in any case, and all attempts to prepare complexes of the type [Tp Bu,Meci-R]+X by chemical oxidation failed, yielding [Tp Cr(THF)n] X instekl. TTie reasons for the apparent instability of TpCr alkyls are not clear, and we arc continuing our efforts to isolate related compounds,... 

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