Potassium dichromate and chromic acid

6 POTASSIUM DICHROMATE AND CHROMIC ACID The oxidation of the chromic ion  

Invariably the electrolysis medium contains sulphuric acid but the concentrations of both the acid and the chromium(III) vary widely depending on the source of the solution from the oxidation of organic compounds, a typical solution may contain 1 M Cr(III) and 3 M H2SO4, while from a plating bath to be conditioned, the chromium(III) may be as dilute as 0.02 M with 0.005 M H2SO4 and a large excess of chromium(VI). 

The old design of cell is based on a lead-lined tank filled with aqueous sulphuric acid, and the spent chromic acid solution in porous ceramic pots was placed in the tank. The anodes were lead rods dipped into the ceramic pots and the cathode was the lining to the tank. The plant was obviously operated totally as a batch process. More modern and economic cells are now available they are based on a bipolar filter press concept with lead alloy anodes, steel cathodes and a Nafion protonconducting membrane. The energy consumption and space time yields with such 

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W. D. Bancroft measured the oxidation potential of potassium dichromate and chromic acid respectively at 16°-18°, and in 0-2M-soln. with the following results stannous chloride and potash-lye, 1-37, and 1-70 volt stannous chloride and hydrochloric acid, 0-57, and 0-90 volt sodimn sulphide, 1-15, and 1-49 volt hydroxyl-amine and potash-lye, 1-12, and — volt hydroxylamine and hydrochloric acid, 0-43, and — volt chromous acetate, 0-70, and 1-03 volt chromous acetate and alkah-lye,... 

Manufacture The primary iadustrial compounds of chromium made directly from chromite ore are sodium chromate, sodium dichromate, and chromic acid. Secondary chromium compounds produced ia quantity include potassium dichromate, potassium chromate, and ammonium dichromate. 

Oxidation of secondary alcohols to ketones (Section 15.10) Many oxidizing agents are available for converting secondary alcohols to ketones. PDC or PCC may be used, as well as other Cr(VI)-based agents such as chromic acid or potassium dichromate and sulfuric acid. 

Trimethylacetic acid may be made by the hydrolysis of tert-butyl cyanide with weak hydrochloric acid at ioo0.1 It is also obtained by oxidation of trimethylpyroracemic acid with silver oxide or potassium dichromate and sulfuric acid,2 by oxidation of tertf-butylethylene with permanganate solution,3 or by oxidation of dimethyl 2,2-propanol with chromic acid.4 Schroeter reports the formation of trimethylacetic acid by rearrangement of the oxime of trimethylacetophenone to give the anilide of trimethylacetic acid, which can be hydrolyzed to give the acid.5... 

Baudet cell — This was a - chromic acid battery with zinc anodes, and a construction that the chromic acid solutions could be delivered from vessels containing solid potassium dichromate and sulfuric acid. 

Potassium Trichromate, EgCrgOio, obtained by dissolving the dichromate in nitric acid, of density 1-19, or by interaction of potassium dichromate with chromium trioxide or chromic acid, as red monoclinic crystals,of density 2-649, which melt at 250° C., and are decomposed by water with formation of dichromate and chromic acid. ... 

In 1873, it was first reported that cellulose that has been oxidized with chromic acid or potassium permanganate is weakened in alkaline solutions, and several years later these findings were confirmed. By 1899, it was known that cellulose that had been oxidized with nitric acid, or bromine in the presence of calcium carbonate, afforded oxidized celluloses from which D-glucoisosaccharinates were formed on suitable treatment with lime-water.Hydrocelluloses, alkaline-hypobromite oxycelluloses, and alkaline-hypochlorite oxycelluloses have no internal, alkali-sensitive links. Cellulose oxidized with neutral hypochlorite, acidic hypochlorite, potassium dichromate and sulfuric acid, potassium dichromate and oxalic acid, periodic acid, or metaperiodate gives products which are alkali-sensitive. Periodic acid oxycellulose and metaperiodate oxycellulose are much more alkali-sensitive than the others. ... 

J. Thomsen, and J. Krutwig similarly treated silver chromate with hydrochloric acid. A. Mailfert found that chromium trioxide is formed when soln. of chromic salts or chromic oxide are treated with ozone. M. Prud homme and F. Binder observed that if barium chloride is added to a soln. of barium dichromate, normal barium chromate is precipitated, and potassium chloride and chromic acid remain in soln. In preparing chromic acid, V. V. Polyansky first obtained calcium chromate by addition of calcium hydroxide paste, followed by calcium chloride soln., to... 

G. Kriiss obtained the trichromate by evaporating over sulphuric acid a soln. of potassium dichromate in chromic acid F. A. H. Schreinemakers, and I. Koppel and E. Blumenthal studied the conditions of equilibrium, and the results are summarized in Figs. 36 to 41. Potassium trichromate furnishes deep red, prismatic crystals and F. Bothe reported that the monoclinic prisms have the axial ratios a 6 c=0-8437 1 0-8318, and j8=101° 0 the (OlO)-cleavage is distinct. F. Bothe gave 3-613 for the sp. gr. H. G. F. Schroder, 2-676-2-702 L. Pla air and J. P. Joule, 2-655 and E. Jager and G. Kriiss, 2-667 at 10°—crystallized from chromic acid—-and 2-648 at 11°—crystallized from nitric acid. The hardness is... 

A hot chromic-sulfuric acid cleaning solution prepared from potassium dichromate and sulfuric acid provides free oxygen for cleaning but has a tendency to leave residues, and the surface must be rinsed very thoroughly. Disposal of the waste material is also a problem. 

The primary Cr—O bonded species is cbromium (VT) oxide, CrO, which is better known as chromic acid [1115-74-5], the commercial and common name. This compound also has the aliases chromic trioxide and chromic acid anhydride and shows some similarity to SO. The crystals consist of infinite chains of vertex-shared CrO tetrahedra and are obtained as an orange-red precipitate from the addition of sulfuric acid to the potassium or sodium dichromate(VI). Completely dry CrO is very dark red to red purple, but the compound is deflquescent and even traces of water give the normal mby red color. Cbromium (VT) oxide is a very powerful oxidi2er and contact with oxidi2able organic compounds may cause fires or explosions. 

Terephthalic acid has been obtained from a great many /)-disubstituted derivatives of benzene or cyclohexane by oxidation with permanganate, chromic acid, or nitric acid. The following routes appear to have preparative value from />-toluic acid, />-methylacetophenone,2 or dihydro-/)-tolualdehyde by oxidation with permanganate from f>-cymene by oxidation with sodium dichromate and sulfuric acid from />-dibromobenzene or from /i-chloro- or -bromobenzoic acid by heating at 250° with potassium and cuprous cyanides and from />-dibromo-benzene, butyllithium, and carbon dioxide. ... 

Phenanthrenequinone has been prepared by treatment of phe-nanthrene with chromic acid in acetic acid 5 potassium dichromate in sulfuric acid 3-6 hydrogen peroxide in acetic acid 6 7 and selenium dioxide above 250°.8 It can also be prepared from benzil with aluminum chloride at 120° 9 and from biphenyl-2,2 -dialdehyde with potassium cyanide.10... 

Chromium trioxide in aqueous solution equilibrates with a number of species, and chromic acid, being the most abundant one under acidic conditions (see page 1). Thus, a mixture of chromium trioxide and sulfuric acid is often referred to as a chromic acid solution. Such solution can also be obtained by the action of sulfuric acid on sodium dichromate (Na2Cr207) or potassium dichromate (K2Cr207). 

A. (+)-lBomenthone. Into a 1-L, three-necked, round-bottomed flask equipped with a mechanical stirrer, condenser, thermometer and dropping funnel, are placed 54.6 g (0.35 mol) of (+)-isomenthol (Note 1) and 350 mL of ether. A solution of chromic acid, prepared by mixing 56.7 g (0.23 mol) of potassium dichromate and 31 S3 mL (0.58 mol) of 98% sulfuric acid and diluting to 200 mL with water, is added dropwise to maintain the reaction temperature at 25°C. The mixture is stirred for a further 2 hr. The ether layer is separated and the aqueous phase is extracted twice with 100-mL portions of ether. The combined ether extracts are washed with saturated sodium bicarbonate solution, dried over magnesium sulfate, and evaporated under... 

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