Chromic hydroxide, preparation

Bromo-pentammino-chromic Bromide, [Cr(NH3)3Br]Br2, is prepared by transforming ehloro-pentammino-chloride into aquo-pentammino-chromic hydroxide, [Cr(NH3)5H20](0H)3, by means of silver oxide, treating the mixture with dilute hydrobromic acid, filtering off silver bromide formed, and allowing the filtrate to evaporate to small bulk. It is then heated with an equal volume of concentrated acid, the precipitate formed, collected, washed with dilute acid and alcohol.1 It crystallises in violet-red octahedra, and in solution the salt decomposes like the chloro-pentammino-salt warming with water and a little aeicl transforms the salt into aquo-pentammino-broniide silver oxide and water convert it into aquo-pentammino-hydroxide. 

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. 

The ease with which the proton is removed can be judged by the fact that the hexaaquo ion (p fl 4) is almost as strong an acid as formic acid. Further deprotonation and polymerization can occur and, as the pH is raised, the final product is hydrated chromium(lll) oxide or chromic hydroxide . Formation of this is the reason why amine complexes are not prepared by simple addition of the amine base to an aqueous solution of By methods... 

Chromic Hydroxide. Chromium hydroxide, chromic oxide gel chromic oxide, hydrous. CrH3Oj mol wt 103.03. Cr 50.48%. H 2-93%, O 46.59%. Cr(OH)j. Occurs only as hydrates. Prepn Ruthroff, Inorg. Syn. 2, 190 (1946) Hein, Herzog in Handbook of Preparative Inorganic Chemistry vol. 2, G- Brauer, Ed, (Academic Press, New York, 2nd ed- 1965) pp 1345-1346. 

Since commercial chromic hydroxide always contains an appreciable percentage of carbonate, sodium hexahydroxochromate (III) is best prepared from an aqueous Cr(C104)3 solution obtained from CrsOa.aq. the NaC104 formed by reaction with NaOH is sufficiently soluble even in highly concentrated NaOH. 

CrzOs gels are prepared by decomposition of salts of Cr such as ammonium bichromate and chromic hydroxide. Chromic hydroxide can be prepared by neutralization of an aqueous solution of chromic nitrate with ammonia or urea, followed by washing and drying of the precipitate. Surface area is usually 1 — 10 m g , but it varies depending on the heat treatment. Heat treatment at 600 — 700 K causes transformation of chromia gel to a-Cr203. Molybdenum and tungsten oxides are prepared similarly. Preparation of Cr, Mo, and W oxides which are supported, impregnated and fixed on oxide surfaces may be referred to in the literature. ... 

Cr2 03 - 112 0, of indefinite composition occurs. This compound is commonly misnamed as chromic or chromium (ITT) hydroxide [1308-14-1], Cr(OH)2. A tme hydroxide, chromium (ITT) hydroxide trihydrate [41646-40-6], Cr(OH)2 3H20, does exist and is prepared by the slow addition of alkaU hydroxide to a cold aqueous solution of hexaaquachromium(III) ion (40). The fresh precipitate is amphoteric and dissolves in acid or in excess of hydroxide to form the metastable Cr(OH). This ion decomposes upon heating to give the hydrous chromium (ITT) oxide. However, if the precipitate is allowed to age, it resists dissolution in excess hydroxide. 

Methyl n-amyl ketone has been prepared by the hydration of heptine-x and of heptine-2 under various conditions,1 and by heating n-amyl propiolic acid with potassium hydroxide.2 It has also been obtained by the oxidation of methyl n-amyl carbinol with chromic acid.3... 

Azoxybenzene has been prepared by reduction of nitrobenzene with alcoholic potassium hydroxide,1 with sodium amalgam,2 with hydrogen in the presence of lead oxide,3 with methyl alcohol and sodium hydroxide,4 with sodium methylate and methyl alcohol,5 and by electrolytic reduction 6 by oxidation of azobenzene with chromic anhydride 7 by treatment of /9-phenylhydroxylamine with alkaline potassium permanganate,8 with nitrobenzene,9 with mineral adds,10 and with mercury acetamide,11 and by oxidation of aniline with hydrogen peroxide,12 and with acid permanganate solution in the presence of formaldehyde.13 The procedure described above is a slight modification of one described in the literature.14... 

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