Chromium salts, oxidation

Chromium(VI) oxide is acidic, and the corresponding salts are the chromates and dichromates, containing the ions CrO and Cr207 . i.e. [Cr04 -I- CrOj] ". The oxidation state of chromium is -f6 in each ion (cf sulphur in and 8207 ). 

For metal compound categories (e.g.,chromiumcompounds), report releases of only the parent metal. Forexample, a user of various inorganic chromium salts would report the total chromium released in each waste type regardless of the chemical form (e.g., as the original salts, chromium ion, oxide) and exclude any contribution to mass made by other species in the molecule. 

Chromi-nydroxyd, n. chromic hydroxide, chro-mium(III) hydroxide, -oxyd, n. chromic oxide, chromium(III) oxide, -rhodanwasser-stoffsMure, /. chromithiocyanic acid, thio-cyanatochromic(III) acid, -salz, n. chromic salt, chromium(III) salt, -suifat, n. chromic sulfate, chromium(III) sulfate, -suifocyan-saure, /. chromithiocyanic acid, thiocyana-tochromic(III) acid, -verbindung,/. chromic compound, chromium(III) compound. 

ChromsMure, /. chromic acid, -anhydrid, n. chromic anhydride, chromium(VI) oxide, emisch, n. chromic acid mixture. -Ibsung. /. chromic acid solution, -salz, n. salt of chromic add, chromate. 

Various experimental conditions have been used for oxidations of alcohols by Cr(VI) on a laboratory scale, and several examples are shown in Scheme 12.1. Entry 1 is an example of oxidation of a primary alcohol to an aldehyde. The propanal is distilled from the reaction mixture as oxidation proceeds, which minimizes overoxidation. For secondary alcohols, oxidation can be done by addition of an acidic aqueous solution containing chromic acid (known as Jones reagent) to an acetone solution of the alcohol. Oxidation normally occurs rapidly, and overoxidation is minimal. In acetone solution, the reduced chromium salts precipitate and the reaction solution can be decanted. Entries 2 to 4 in Scheme 12.1 are examples of this method. 

The catalytic process is also achieved in the Pd(0)/Cr(II)-mediated coupling of organic halides with aldehydes (Scheme 33) [74], Oxidative addition of a vinyl or aryl halide to a Pd(0) species, followed by transmetallation with a chromium salt and subsequent addition of the resulting organo chromate to an aldehyde, leads to the alcohol 54. The presence of an oxophile [Li(I) salts or MesSiCl] allows the cleavage of the Cr(III) - 0 bond to liberate Cr(III), which is reduced to active Cr(II) on the electrode surface. 

Chromate conversion coatings for aluminum are carried out in acidic solutions. These solutions usually contain one chromium salt, such as sodium chromate or chromic acid and a strong oxidizing agent such as hydrofluoric acid or nitric acid. The final film usually contains both products and reactants and water of hydration. Chromate films are formed by the chemical reaction of hexavalent chromium with a metal surface in the presence of accelerators such as cyanides, acetates, formates, sulfates, chlorides, fluorides, nitrates, phosphates, and sulfamates. 

Technically important dyes are salicylic acid derivatives that function as chrome mordant dyes for wool. Thus Cl Mordant Blue 1 (6.187) is made by the aldehyde synthesis from 2,6-dichlorobenzaldehyde and 2-hydroxy-3-methylbenzoic (o-cresotinic) acid in concentrated sulphuric acid. Oxidation of the leuco base is achieved by the addition of sodium nitrite. On wool the product, which is isolated as the sodium salt, is a dull maroon colour, changing to a bright blue on treatment with a chromium salt. Some dyes of this type, such as Cl Mordant Violet 1 (6.188), also contain a basic group. This compound is also prepared by the aldehyde route. 

Figure 9.1 compares the synthesis of acetophenone by classic oxidation of 1-phenylethanol with stoichiometric amounts of chromium oxide and sulphuric acid, with an atom efficiency of 42%, with the heterogeneous catalytic oxidation with O2, with an atom efficiency of 87%, and with water as the only by-product. This is especially important if we consider the environmental unfriendliness of chromium salts the potential environmental impact of reactions can be expressed by the environmental quotient (EQ), where E is the E-factor (kg waste/kg product) and Q is the environmental unfriendliness quotient of the waste. If Q is... 

Prepare a chromite solution using for this purpose the smallest possible amount of a sodium hydroxide solution, and boil it. What happens Which salt hydrolyzes more—one of chromium(III) oxide or sodium chromite Why How can the hydrolysis of chromium(IH) chloride be brought to the end ... 

Reduction of Ammonium Dichromate. Chromium(III) oxide can be obtained by thermal decomposition of ammonium dichromate. Above ca. 200 °C, a highly voluminous product is formed with elimination of nitrogen [3.48]. The pigment is obtained after addition of alkali salts (e.g., sodium sulfate) and subsequent calcination [3.49]. 

In our attempts to synthesize nano structured or even nanoporous chromium (III) oxide we used a great variety of surfactants (amines, polyethylen oxides, carboxylates, sulfates, phosphates and quartemary alkylammonium salts) and Cr3+ precursors (nitrate, acetate, acetylacetonate and iso-propyl ate) to obtain the desired materials [19]. Different kinds of interaction are established throughout the structure-directing process such as electrostatic (S+... 

The Phillips Cr/silica polymerization catalyst is prepared by impregnating a chromium compound onto a wide pore silica and then calcining in oxygen to activate the catalyst. This leaves the chromium in the hexavalent state, monodispersed on the silica surface. Chromium trioxide (Cr03) has been impregnated mast commonly, but even a trivalent chromium salt can be used since oxidation to Cr(VI) occurs during calcining. 

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