Chromium trioxide solubility

Chromium trioxide is also solublized in dichloromethane in the form of complex chromates Q+[X(CrO,) ] by the addition of an appropriate tetra-n-butylammonium salt [9-14],... 

Fusion of polonium dioxide with a potassium chlorate/hydroxide mixture gives a bluish solid (colorless when hot) which is more soluble in water than the corresponding polonite (Po032 ) this presumably contains some potassium polonate. The trioxide may possibly be formed by strongly heating polonium dioxide and chromium trioxide in air (12). 

Dark, brownish-red needles, or rhombic prisms, very readily soluble in water. Chromium trioxide contains almost 100 per cent of Cr03. 

Chromic Acid. (Chromic Anhydride or Chromium Trioxide), [Chrom (Vl)-oxyd in Ger]. CrO, mw 100,01 (The name "chromic acid is in common use, although the true acid l CrO, exists only in soln). Dark purplish-red deliq crysts, mp 197° (dec), d 2.70 at 20° v sol in w sol in ale ether. Solubilities in w at different temps are given in Ref 2a, pl996- Can be prepd by treating Na dichromate with coned... 

Colourless crystals soluble in alcohol M.P. 159° (J. C. S., loc. tit.) M.P. 164-2° (Am. Soc., 13, 556). Oxidised with chromium trioxide in glacial acetic acid solution, yields anthxaquinone gives a diacetyl derivative on heating with acetic anhydride and pyridine (J. C. S., 117, 1335). 

Although Cr03 is soluble in some organic solvents, like tert-butyl alcohol, pyridine or acetic anhydride, its use in such solvents is limited, because of the tendency of the resulting solutions to explode.2,3 Nevertheless, acetone can safely be mixed with a solution of chromium trioxide in diluted aqueous sulfuric acid. This useful property prompted the development of the so-called Jones oxidation, in which a solution of chromium trioxide in diluted sulfuric acid is dropped on a solution of an organic compound in acetone. This reaction, first described by Jones,13 has become one of the most employed procedures for the oxidation of alcohols, and represents a seminal contribution that prompted the development of other chromium (VI) oxidants in organic synthesis. 

Chromium trioxide reacts with pyridine in a highly exothermic reaction, resulting in the formation of the complex Cr03 2Py, which is soluble in organic solvents. A solution of this complex in pyridine is called Sarett... 

The mixture of chromium trioxide with one equivalent of trimethylsilyl chloride, with no solvent added, results in the formation of an explosive red liquid that is soluble in dichloromethane or tetrachloromethane.428 It is suggested, with no spectroscopic evidence, that it consists of trimethylsilyl chlorochromate [Me3Si-0-Cr(0)2-Cl]. This compound, which can safely be used in organic solvents, is able to oxidize alcohols to aldehydes or ketones, and interacts with r-butyldimethylsilyl ethers producing deprotection, followed by oxidation of the liberated alcohol.138 Compounds analogue to trimethylsilyl chlorochromate are also able to oxidize alcohols, although they possess lesser reactivity. They can be prepared by reaction of chromium trioxide with dimethyldichlorosilane and diphenyldichlorosilane.428b... 

The oxidation of primary alcohols to aldehydes also suffers from the problem of overoxidation of the aldehyde to a carboxylic acid. Mild methods capable of stopping die oxidation at the aldehyde oxidation level are required if aldehydes are to be obtained. The most common and effective reagent for this purpose is pyridinium chlorochromate (PCC), produced by the reaction of pyridinium hydrochloride with chromium trioxide. This reagent is soluble in dichloromethane and smoothly oxidizes primary alcohols to aldehydes in high yields. Because of die mild, neutral reaction conditions and the use of stoichiomettic amounts of oxidant, the aldehyde product is not oxidized further. 

All these form corrosive dusts those from water-soluble chromates are particularly dangerous since they dissolve in nasal fluid and in perspiration. Long-term exposure can lead to ulceration and cancer. Chromium trioxide may cause sensitisation by skin contact. 

OSHA regulates chromium levels in the workplace air. The occupational exposure limits for an 8-hour workday, 40-hour workweek are 500 pg chromium/m3 for water-soluble chromic (chromium(HI)) or chromous [chromium(II)] salts and 1,000 pg chromium/m3 for metallic chromium (chromium(O)), and insoluble salts. The level of chromium trioxide (chromic acid) and other chromium(VI) compounds in the workplace air should not be higher than 52 pg chromium(VI)/m3 for any period of time. 

Trivalent chromium compounds, except for acetate, nitrate, and chromium(III) chloride-hexahydrate salts, are generally insoluble in water. Some hexavalent compounds, such as chromium trioxide (or chromic acid) and the ammonium and alkali metal (e.g., sodium, potassium) salts of chromic acid are readily soluble in water. The alkaline metal (e.g., calcium, strontium) salts of chromic acid are less soluble in water. The zinc and lead salts of chromic acid are practically insoluble in cold water. Chromium(VI) compounds are reduced to chromium(III) in the presence of oxidizable organic matter. However, in natural waters where there is a low concentration of reducing materials, chromium(VI) compounds are more stable (EPA 1984a). For more information on the physical and chemical properties of chromium, see Chapter 3. 

Cardiovascular Effects. Information regarding cardiovascular effects in humans after inhalation exposure to chromium and its compounds is limited. In a survey of a facility engaged in chromate production in Italy, where exposure concentrations were 0.01 mg chromium(VI)/m3, electrocardiograms were recorded for 22 of the 65 workers who worked in the production of dichromate and chromium trioxide for at least 1 year. No abnormalities were found (Sassi 1956). An extensive survey to determine the health status of chromate workers in seven U.S. chromate production plants found no association between heart disease or effects on blood pressure and exposure to chromates. Various manufacturing processes in the plants resulted in exposure of workers to chromite ore (mean time-weighted concentration of 0-0.89 mg chromium(ni)/m3) water-soluble chromium(VI) compounds (0.005-0.17 mg chromium(VI)/m3) and acid-soluble/water-insoluble chromium compounds (including basic chromium sulfate), which may or may not entirely represent trivalent chromium (0-0.47 mg chromium/m3) (PHS 1953). No excess deaths were observed from cardiovascular diseases and ischemic heart disease in a cohort of 4,227 stainless steel production workers from 1968 to 1984 when compared to expected deaths based on national rates and matched for age, sex, and calender time (Moulin et al. 1993). No measurements of exposure were provided. In a cohort of 3,408 individuals who had worked in 4 facilities that produced chromium compounds from chromite ore in northern New Jersey sometime between 1937 and 1971, where the exposure durations of workers ranged from <1 to >20 years, and no increases in atherosclerotic heart disease were evident (Rosenman and Stanbury 1996). The proportionate mortality ratios for white and black men were 97 (confidence limits 88-107) and 90 (confidence limits 72-111), respectively. 

The intermediate inhalation MRL derived from the Lindberg and Hedenstierna (1983) study is primarily based on effects in the nose due to direct contact with irritating properties of soluble chromates. Furthermore, the likelihood for environmental exposure to chromium trioxide and other soluble chromium(VI) compound mists is less than the likelihood for environmental exposure to particulate chromium(VI) compounds. Therefore, it is also appropriate to derive an inhalation MRL for particulate chromium(VI) compounds. 

A better reagent for the limited oxidation of primary alcohols to aldehydes is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HC1. PCC oxidizes most primary alcohols to aldehydes in excellent yields. Unlike most other oxidants, PCC is soluble in nonpolar solvents such as dichloromethane (CH2C12), which is an excellent solvent for most organic compounds. PCC can also serve as a mild reagent for oxidizing secondary alcohols to ketones. 

Silver chromate is almost insoluble in water, glacial acetic acid, and in solutions of potassium chromate, but soluble in those of ammonia, caustic alkalies, nitrates, and in dilute acetic acid. A concentrated solution of ammonium nitrate is a good crystallising medium for silver chromate. With chlorine, above 200° C., silver chloride, chromium trioxide, and oxygen are produced. The solution in ammonia contains the compound Ag2Cr04.4NH3, which forms crystals isomorphous with the corresponding ammoniacal sulphate. ... 

Hexavalent chromium compounds soluble in organic solvents are pyr-idinium chromate [597] and pyridinium dichromate [603], Pyridinium chromate is prepared by adding 2 mol of pyridine to 1 mol of chromium trioxide adsorbed on silica gel. 

Pyridinium dichromate, prepared from chromium trioxide in a minimum amount of water and pyridine, forms a bright-orange solid and is soluble in water, dimethylformamide, dimethyl sulfoxide, and dimethyl-acetamide sparingly soluble in dichloromethane, chloroform, and acetone and almost insoluble in hexane, toluene, ether, and ethyl acetate. Allylic secondary alcohols are oxidized more rapidly than their saturated analogues. Oxidations are carried out in dichloromethane solutions at 25 °C, and ketones are obtained in high yields (equation 251) [603. ... 

Properties Brown or yellowish-brown powder. Variable composition. (Pure cobaltous chromate is CoCr04, gray-black crystals.) Soluble in mineral acids and solutions of chromium trioxide insoluble in water. 

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