Barium chromite

The most active forms contain barium chromite, which is incorporated by adding barium nitrate to the reaction mixture. The barium in the catalyst gives protection against sulphate poisoning and is said to stabilise the catalyst against reduction. 

Tishchenko (79), using a modified form of Raney nickel, obtained a 95.7 % yield of camphor from the dehydrogenation of borneol. Rutovskii, (80) received a 93.5% yield of camphor with Raney alloy. Reeves and Adkins (81), studying the dehydrogenation of primary alcohols, removed the hydrogen with ethylene. It was found that, though Raney nickel could be used for a catalyst for the reaction, the yields were low and, in general, the Raney nickel was inferior to a catalyst composed of copper, zinc, nickel, and barium chromite. 

Barium Chromite, BaO.CrjOj or Ba(Cr02)2, is a green crystalline powder, obtained by heating together potassium dichromate and barium chloride. By fusing a mixture of barium and chromium oxides in the electric furnace, very hard green crystals of composition Ba0.4Cr20g are obtained, the density of which is 5-4 at 15° C. 

Hydrogenolysis of an ester to the alcohol is a reversible reaction commonly obtained at high T and P however, with massive quantities of catalyst the reaction proceeds below 100°C. Noble metal catalysts are not effective for this purpose and hydrogenation to the alcohol usually is done over activated copper-barium-chromite in dioxane . 

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

This reaction is favored by moderate temperatures (100—150°C), low pressures, and acidic solvents. High activity catalysts such as 5—10 wt % palladium on activated carbon or barium sulfate, high activity Raney nickel, or copper chromite (nonpromoted or promoted with barium) can be used. Palladium catalysts are recommended for the reduction of aromatic aldehydes, such as that of benzaldehyde to toluene. 

Recommendations by the ACGIH are classified as threshold limit values (TLV) based on 8-h TWA. Chromium metal and alloys, Cr(II) compounds and Cr(III) compounds, including chromite ore, have a TLV of 0.5 mg/m Cr in air. Water-soluble Cr(VI) compounds have a TLV of 0.05 mg/m Cr. Certain water-insoluble Cr(VI) compounds, ie, the chromates of 2inc, barium, calcium, lead, strontium, sintered chromic acid, and processing chromite ores, also have a TLV of 0.05 mg/m as well as a human carcinogen designation (145). 

Copper chromite 14) and barium-promoted copper chromite (75,/7) have been used for acid reductions but very high temperatures (300 C) are required. The necessary temperature is sufficiently higher than that required foresters to permit selective reduction of half-acid esters to the hydroxy acid 23). The reverse selectivity can be achieved by reduction over H Ru4 CO)a PBu3)4 at I00-200 C and 1500-3000 psig. This homogeneous catalyst will reduce acids and anhydrides, but not esters (2). 

Reductions of 5//-dibenz[/j,/]azepines to their 10,11-dihydro derivatives have been accomplished in high yield with sodium in ethanol,29 133 with copper(II) chromite (2CuO Cr203) and barium carbonate,224 with 5 % palladium on charcoal29 or platinum(IV) oxide30 in ethanol, and with magnesium in methanol.225 4//-Thieno[3,2-/)][1]benzazepine is reduced similarly with hydrogen and palladium on charcoal in ethanol.137... 

Marinho EP, Souza AG, de Melo DS, Santos IMG, Melo DMA, and da Silva WJ. Lanthanum chromites partially substituted by calcium strontium and barium synthesized by urea combustion—Thermogravimetric study. J. Thermal Analysis Calorimetry 2007 87 801-804. 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

Phthalimide was hydrogenated catalytically at 60-80° over palladium on barium sulfate in acetic acid containing an equimolar quantity of sulfuric or perchloric acid to phthalimidine [7729]. The same compound was produced in 76-80% yield by hydrogenation over nickel at 200° and 200-250 atm [43 and in 75% yield over copper chromite at 250° and 190 atm [7730]. Reduction with lithium aluminum hydride, on the other hand, reduced both carbonyls and gave isoindoline (yield 5%) [7730], also obtained by electroreduction on a lead cathode in sulfuric acid (yield 72%) [7730]. 

Another commercial aldehyde synthesis is the catalytic dehydrogenation of primary alcohols at high temperature in the presence of a copper or a copper-chromite catalyst. Although there are several other synthetic processes employed, these tend to be smaller scale reactions. For example, acyl halides can be reduced to the aldehyde (Rosemnund reaction) using a palladium-on-barium sulfate catalyst. Formylation of aryl compounds, similar to hydrofomiylation, using HCN and HQ (Gatterman reaction) or carbon monoxide and HQ (Gatterman-Koch reaction) can be used to produce aromatic aldehydes. 

Another common catalyst prepared by coprecipitation is copper-chromium oxide, also known as "copper chromite" or Adkins catalyst.23 This catalyst is prepared by the addition of copper nitrate to a solution of ammonium dichromate in ammonia giving a precipitate copper ammonium dichromate. This precipitate is filtered, dried and then calcined at 650°-800°C, or more commonly, heated with a flame to induce a thermal reaction (Eqn. 13.5). The resulting fine powder is washed with acetic acid and dried to give the copper chromite catalyst.23 A more active catalyst is prepared by adding 10% barium nitrate by weight of copper before precipitation.24,25 Copper chromite catalysts containing calcium and were found to be less effective than those having a barium promoter.25... 

Copper chromite (Lazier catalyst). Supplier Harshaw (CU-0202P 556-002). For preparation of the catalysC an aqueous solution of barium nitrate and cupric nitrate trihydrate is stirred during addition of a solution of ammonium chromate, prepared from ammonium dichromate and aqueous ammonia. The reddish brown precipitate of copper barium ammonium chromate is washed and dried and decomposed by heating in a muffle furnace at 350-450 . The ignition residue is pulverized, washed with 10% acetic acid, dried, and ground to a fine black powder. 

Copper chromite has been made by the ignition of basic copper chromate at a red heat and by the thermal decomposition of copper ammonium chromate. The procedure given here is a modification of the latter method in which barium ammonium chromate is also incorporated. Copper-chromium oxide hydrogenation catalysts have also been prepared by grinding or heating together copper oxide and chromium oxides, by the decomposition of copper ammonium chromium carbonates... 

In a steel reaction vessel (Note i), capable of withstanding high pressures with an adequate safety factor (Note 2) and having a capacity of 400 cc. or more, are placed 252 g. (1.25 moles) of ethyl adipate (b.p. i44-i45°/29 mm.) (Org. Syn. 17, 32) and 20 g. of copper chromite catalyst, prepared either with or without the addition of barium (p. 31). The reaction vessel is closed, made gas tight, and secured in a suitable agitating device. After connection is made with the hydrogen supply, hydrogen is introduced until a pressure of 2000 to 3000 lb. per sq. in. is reached (Note 2). 

A solution of ammonium chromate is prepared by dissolving 126 g. (0.5 mole) of c.p. ammonium dichromate in 600 cc. of distilled water and adding 150 cc. of 28 per cent aqueous ammonia (sp. gr. 0.9) (Note 3). The warm solution of the nitrates is stirred (hand stirring is adequate) while the ammonium chromate solution is poured into it in a thin stream. The stirring is continued for a few minutes, after which the reddish brown precipitate of copper barium ammonium chromate is collected (Note 4) and pressed in a i6-cm. Buchner funnel, and dried at 110°. This dry precipitate is placed in a loosely covered nickel pan (Note 5), or one or two small porcelain casseroles covered with watch glasses, and heated in a muffle furnace for one hour at 350-450° (Note 6). At this point the yield of chromite should be about 160 g. The ignition residue is pulverized in a mortar to break up any hard lumps that may be present (Note 7) and... 

Barium has been included as a catalyst component on account of its protective action against sulfate poisoning and its reported stabilization of the catalyst against reduction. Alternatively, the above procedure may be used for the preparation of a copper chromite catalyst containing no barium. In this case the barium nitrate is omitted and 242 g. (i mole) of copper nitrate is used. All other details are the same as given above. 

Moreover, the catalysts promoted by alkaline or alkaline-earth species are more stable than the unpromoted CuCr. For example, barium impregnated on copper chromite increases the stability of the active CuCr02 phase (13). Furthermore, the presence of barium or calcium on copper chromite catalysts influences strongly the selectivity to the methylation of amines N-alkylation/N-methylation. 

In our laboratory, we have shown that copper chromite doped with barium, calcium or manganese can lead selectively to dimethyldodecylamine from lauronitrile, ammonia, hydrogen and methanol but not to methyldidodecylamine (14). 

The catalyst used in this study was a copper chromite doped with barium (YPl). The other solids were prepared from that catalyst by impregnation with alkaline salts from Prolabo (LiNOj, KOH, CsNOs). After impregnation, the catalysts were dried in a sand-bath (120°C), and then calcinated at 350°C for 4 hours under a dry air stream. 

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