Alkali chromites

If calcium chromate be treated with a soln. of potassium sulphate, the calcium chromate is converted into calcium sulphate, which is precipitated, and potassium chromate, which remains in soln. Instead of leaching the calcium chromate with a soln. of potassium sulphate, W. J. Chrystal showed that if ammonium sulphate is used, a soln. of ammonium chromate is produced, and J. J. Hood found that if the soln. of potassium salt be treated with sodium hydrosulphate, potassium sulphate crystallizes from the soln., while sodium dichromate remains in soln. According to F. M. and D. D. Spence and co-workers, if a mixtiu-e of ammonia and carbon dioxide be passed into the aq. extract of the calcium chromate. Calcium carbonate is precipitated while ammonium and alkali chromate remain in soln. If the liquid be boiled, ammonia is given off, and sodium dichromate remains in soln. S. Pontius used water and carbon dioxide under press, for the leaching ptocess. J. Brock and W. A. Rowell purified alkali chromite by treating the soln. with strontium hydroxide, and digesting the washed precipitate with a soln. of alkali sulphate or carbonate W. J. A. Donald used calcium hydroxide or barium chloride as precipitant. A mixture of chromite with calcium carbonate and potassium carbonate was formerly much employed. Modifications of the process were described by W. J. A. Donald, A. R. Lindblad, C. J. Head, 8. G. Thomas, W. Gow, J. Stevenson and T. Carlile, L. I. Popoff,G. Bessa, P.Weise, P. N. Lukianoff,... 

C. F. Nagel, W. D. Bancroft, and N. G. Chatterji and N. R. Dhar showed that the colloidal oxide can be removed by the ultra-filter. W. Biltz and W. Giebel added that the colloidal soln. consists mainly of amicrons, only a small proportion of sub-microns are present. There has been some discussion as to whether the colloidal soln. contains alkali chromite. H. W. Fischer and W. Herz said that peptization, not dissolution, occurs. This is in agreement with hypothesis that the soln. is really the colloidal oxide and the observation of A. B. Northcote and A. H. Church that complete soln. occurs in the presence of 40 per cent, of ferric oxide 12-5, manganous oxide or 20 per cent, of either cobalt or nickel oxide, whereas complete precipitation occurs with 80 per cent, of ferric oxide 60, of manganous oxide or 50, of either cobalt or nickel oxide. Analogous observations were made by M. Prud homme, and M. Kreps. H. B. Weiser and G. L. Mack obtained an organosol in propyl alcohol. 

J. Heyrovsky inferred that soln. of alkali chromite are not true soln. but contain colloidal chromic hydroxide. The primary sodium metachromite, NaCr02, is formed with alkali-lye below lOiV-NaOH and sodium orthochromite, NagCrOs, above that cone. J. d Ans and J. Loffler obtained NaCr02 by the action of chromic oxide on sodium hydroxide. J. Heyrovsky obtained similar results... 

When produced by such dry methods it is frequently unreactive but, if precipitated as the hydrous oxide (or hydroxide ) from aqueous chromium(III) solutions it is amphoteric. It dissolves readily in aqueous acids to give an extensive cationic chemistry based on the [Cr(H20)6] ion, and in alkalis to produce complicated, extensively hydrolysed chromate(III) species ( chromites ). 

Preparation. Oxidation of the chromite ore by air in molten alkali gives sodium chromate, Na2Cr04 that is then converted to Cr203. The oxide is further reduced with aluminium or silicon to form chromium metal. Solutions suitable for electrolytic production of chromium (for plating) can be obtained from ore by oxidative roasting in alkali or by dissolution of chromite in H2S04 and especially by dissolving ferro-chromium in sulphuric acid. 

Pure decarbonylation typically employs noble metal catalysts. Carbon supported palladium, in particular, is highly elfective for furan and CO formation.Typically, alkali carbonates are added as promoters for the palladium catalyst.The decarbonylation reaction can be carried out at reflux conditions in pure furfural (165 °C), which achieves continuous removal of CO and furan from the reactor. However, a continuous flow system at 159-162 °C gave the highest activity of 36 kg furan per gram of palladium with potassium carbonate added as promoter. In oxidative decarbonylation, gaseous furfural and steam is passed over a catalyst at high temperatures (300 00 °C). Typical catalysts are zinc-iron chromite or zinc-manganese chromite catalyst and furfural can be obtained in yields of... 

The hydroxide V(OH)3 is distinguished from the corresponding hydroxides of phosphorus, arsenic and antimony in that it is wholly basic. It is insoluble in alkalis, so that there do not exist any compounds of vanadium which would correspond to the phosphites, arsenites, and antimonites, or to the ferrites, aluminates, and chromites. 

CA 45, 2885(195lXHydrogenati°n of nitrocompds with Raney Ni treated with chloroplatinic acid and with alkali) p)J.A.Grand R.Miller, USP 2555333(1951) CA 45, 7337(1951XUse of Cu chromite as combustion catalyst in solid compressed fuel, such as mixt of NGu 75 GuN 25%) r)Anon, ChemEngrg 1951, June, p 183 (Catalytic process for waste disposal developed by D.V.Moses and put into operation at DuPont s Belle Plant, West Virginia, consists of vapor -phase catalytic destruction of organic wastes by oxidation to C02 H20. It was claimed that the method is more convenient than bio-oxidation... 

Elimination of chromite that makes the brick less susceptible to alkali attack in service... 

When pure chromium is required, the chromite is first treated with molten alkali and oxygen to convert the Cr111 to chromate(VI), which is dissolved in water and eventually precipitated as sodium dichromate. This is then reduced with carbon to Crm oxide ... 

If ignited too strongly, Cr203 becomes inert toward both acid and base, but otherwise it and its hydrous form are amphoteric, dissolving readily in acid to give aqua ions [Cr(H20)6]3+, and in concentrated alkali to form chromites. ... 

Acids do not attack chromite, but fusion with alkali hydrogen sulphates effects its decomposition. The Grecian ore, which occurs mainly in the Eastern Provinces and in the island of Skyros, is particularly refractory on account of the impurities it contains. Chrome iron ores containing some Fe203 may be regarded as mixtures of chromite and chromitite (p. 17). Platmiferous chromites are found in the Urals.1... 

Naphthalene is reduced to 1,4-dihydronaphthalene by sodium and alcohol. Isomerization of this product to 3,4-dihydronaphthalene occurs with sodamide in liquid ammonia. Tetrahydronaphthalene (tetralin) is formed from naphthalene by sodium in amyl alcohol or by reduction with nickel-aluminum alloy and aqueous alkali. Catalytic hydrogenation of naphthalene can be stopped at the tetralin stage over copper chromite, Raney nickel, or alkali metal catalysts. cis-Decahydronaphthalene is produced by high-pressure hydrogenation of tetralin over Adams catalyst, whereas a mixture of cis- and trans-decalins is obtained from naphthalene under the same conditions. ... 

The chromites of the alkali metals and of ammonium are presumably formed to some extent in solution, when chromic hydroxide dissolves in excess of the alkali hydroxide but it has been shown that these solutions are in large degree merely colloidal solutions of the hydroxide (see p. 36). By shaking chromic hydroxide, dried over sulphuric acid, with solutions of sodium hydroxide of different concentrations, Muller found that the amount of hydroxide dissolved depended on the time of agitation, rising to a maximum and then falling to an almost constant value. The solutions obtained w ere not colloidal. Fricke and Wind-hausen have prepared similar solutions, and by allowing solutions of potassium chromite to stand for some time, obtained needle-shaped crystals of composition CrjOj.SKjO.SHjO. 

Chromates are usually yellow or red in colour, and, except those of ammonium, the alkali metals, calcium, strontium, and magnesium, are practically insoluble in w ater. They are obtained by oxidation of chromites, by fusion of chromium sesquioxide with the appropriate base in presence of air or of an oxidising agent by oxidation of chromium salts in solution or by double decomposition. Normal, di-, and tri-clrromates, etc., are derived from one and the same acid oxide KaCrOj behaves like an alkali torvards CrOg, since it is quantitatively converted into dichromate. A large number of complex double chromates are known. 

Estimation of Chromium.—In the analysis of chromites or of other substances containing chromium, such as leather ashes, pigments, etc., it is first necessary to obtain a solution. This is done by finely powdering the substance and heating it with a suitable flux in a crucible, preferably of nickel. Many fluxes have been employed, usually caustic alkali or alkali carbonates, but the one in most common use at present is sodium peroxide, whereby the chromium compound is rapidly converted to a chromate. - Excess of alkali is removed by boiling with ammonium carbonate, which also precipitates any iron present. The filtrate is then acidified with dilute sulphuric acid and the chromium estimated either by gravimetric or volumetric methods. 

The condensation of a, dicarbonyl compounds (49) with aj3-diamino compounds (50), which proceeds through the dihydropyrazine (51), has been much used for the synthesis of alkyl- and arylpyrazines (52). These reactions are usually carried out in methanol, ethanol, or ether in the presence of sodium or potassium hydroxide. The dihydropyrazines may be isolated, or oxidized directly to the pyrazine. Dehydrogenating agents that have been employed include oxygen in aqueous alkali (329), air in the presence of potassium hydroxide (330), sodium amylate in amyl alcohol (330a), alcoholic ferric chloride (24), and copper chromite catalyst at 300° (331) (see also Section 1). Pyrazines prepared by this method and modifications described below are listed in Table II.8 (2, 6, 24, 60, 80,195, 329-382) and some additional data are provided in Sections VI. 1 A, VlII.lA(l), and IX.4A(1). 

The dehydrogenation of piperazines to pyrazine was first achieved by Stoehr (32), who heated piperazine (87) or its hydrochloride with zinc dust or, better, zinc dust and lime to give a yield of approximately 10% pyrazine (88). Since that time a number of publications and patents has described the conversion of piperazines to pyrazines by heating at elevated temperatures with various catalysts usually containing copper chromite (464) but also with palladium-charcoal (465) and platinum on alkali-washed firebrick (466), and also with other reagents. Some of these preparations are summarized in Table II.11 (464-475). 

Only alkaline oxidative digestion is suitable for the industrial conversion of chromite to chromium chemicals. This results in alkali (sodium) chromates ... 

The diketone [lxxx] is soluble in alkali, probably as a result of enolization of the 9-keto group, but on catalytic reduction over copper chromite it yields an alkali-insoluble dihydro-derivative, and this reaction was first assumed to involve reduction of this keto group, The dihydro-derivative on hydrogenation over Raney nickel at room temperature affords a basic hexahydro-compound (giving a neutral diaoetyl-derivative) that on further reduction with hydriodio aoid and red phosphorus gives a basic dosoxy-oompound. The latter yields an... 

There are two other reasons why alkalis are important. First, in mineral processing, minerals such as chromite require fusing with an alkali to convert the element being extracted into a soluble form. Both sodium carbonate and potassium carbonate are used as fusion mixtures. Second, in the manufacture of glass, silica is fiised with either soda ash or potassium carbonate. In our view, ashes with a very high alkali content, such as those of banana wastes, can be used in place of the commercially-available alkalis. Some tests are under way to confirm this hypothesis. 

The catalyst for reaction 1 is an alcoholate formed by dissolving an alkali metal, such as sodium, in the starting alcohol. The hydrogenolysis reaction (eq.2) is carried out in either the gas or liquid phase using copper-based (preferably copper chromite) catalysts. 

Special multicomponent catalysts were necessary for N-aUcylation of sterically hindered anilines with alkoxy alcohols [9]. Doping Cu-chromite with Pd accelerated the hydrogenation of the imine intermediate this was found to be the rate-limiting step for all the catalysts. Alkali cations (Na and Ba ) increased the activity whereas acidic centers (e. g. Cr " " and Al ) favored hydrogenolysis of the ether bond. For N-alkylation with secondary alkoxy alcohols a Pt/Si02 catalyst doped with Sn + and Ca ions afforded the best performance. Yields of mono-alkylated anilines varied in the range 22-93 % depending on the steric hindrance in the reactants. 

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