Chromium naturally occurring

Sulfates of sodium are iadustriaUy important materials commonly sold ia three forms (Table 1). In the period from 1970 to 1981, > 1 million metric tons were consumed aimuaHy ia the United States. Siace then, demand has declined. In 1988 consumption dropped to 890,000 t, and ia 1994 to 610,000 t (1,2). Sodium sulfate is used principally (40%) ia the soap (qv) and detergent iadustries. Pulp and paper manufacturers consume 25%, textiles 19%, glass 5%, and miscellaneous iadustries consume 11% (3). About half of all sodium sulfate produced is a synthetic by-product of rayon, dichromate, phenol (qv), or potash (see Chromium compounds Fibers, regenerated cellulosics Potassium compounds). Sodium sulfate made as a by-product is referred to as synthetic. Sodium sulfate made from mirabilite, thenardite, or naturally occurring brine is called natural sodium sulfate. In 1994, about 300,000 t of sodium sulfate were produced as a by-product another 300,000 t were produced from natural sodium sulfate deposits (4). 

Chromium in the crystalline form is a steel-gray, lustrous, hard metal characterized by an atomic weight of 51.996, an atomic number of 24, a density of 7.14 g/cm3, a melting point of 1857°C, and a boiling point of 2672 C. Four chromium isotopes occur naturally Cr-50 (4.3%), -52 (83.8%), -53 (9.6%), and -54 (2.4%), and seven are man-made. Elemental chromium is very stable but is not usually found pure in nature. Chromium can exist in oxidation states ranging from -2 to +6, but is most frequently found in the environment in the trivalent (+3) and hexavalent (+6) oxidation states. The +3 and +6 forms are the most important because the +2, +4, and +5 forms are unstable and are rapidly converted to +3, which in turn is oxidized to +6 (Towill et al. 1978 Langard and Norseth 1979 Ecological Analysts 1981 USPHS 1993). 

Naturally occurring fatty alcohols used in the fragrance industry are produced principally by reduction of the methyl esters of the corresponding carboxylic acids, which are obtained by transesterification of natural fats and oils with methanol. Industrial reduction processes include catalytic hydrogenation in the presence of copper-chromium oxide catalysts (Adkins catalysts) and reduction with sodium (Bouveault—Blanc reduction). Unsaturated alcohols can also be prepared by the latter method. Numerous alcohols used in flavor compositions are, meantime, produced by biotechnological processes [11]. Alcohols are starting materials for aldehydes and esters. 

The amino acids believed to be involved in GTF are the constituents of the naturally occurring tripeptide glutathione (256). Anderson et al. have reported a complex of glutathione/nicotinic acid and chromium(III) to be particularly active in their in vitro assay.1198 The complex was described as being purified by HPLC, but the details of the preparation are not available. 

Chromium is a naturally occurring element found in rocks, animals, plants, soil, and in volcanic dust and gases. Chromium is present in the environment in several different forms. The most common forms are chromium(O), trivalent (or chromium (HI)), and hexavalent (or chromium(VI)). Chromium(III) occurs naturally in the environment and is an essential nutrient... 

Chromium is a naturally occurring element found in animals, plants, rocks, and soil and in volcanic dust and gases. Chromium has oxidation states (or "valence states") ranging from chromium(-II) to chromium(VI). Elemental chromium (chromium(O)) does not occur naturally. Chromium compounds are stable in the trivalent state and occur in nature in this state in ores, such as ferrochromite. The hexavalent (VI) form is the second-most stable state. However, chromium(VI) rarely occurs naturally, but is usually produced from anthropogenic sources (EPA 1984a). 

The catalyzed complete combustion of individual hydrocarbons has been investigated by Todes in an attempt to establish the combustion characteristics of these hydrocarbons (220), while other workers have attempted to improve the techniques of catalyzed combustion (457). At the Power Institute Ravich has been working on the development of catalysts promoting complete combustion of gaseous and solid fuels with the aid of naturally occurring and synthetic minerals containing oxides of iron, chromium, nickel, potassium, aluminum, and manganese (317,-318,319). Industrial application of this process has been mentioned. 

High concentrations of chromium may occur naturally in groundwater in areas with mafic or ultramafic volcanic or metamorphic rocks (i.e. rocks that consist mainly of ferromagnesian minerals with no quartz). 

Workers come in contact with a large number of chemical substances in work areas, as does the general public. The commonly found chemical carcinogens are grouped under (1) polycyclic aromatic hydrocarbons (PAHs), (2) nitroso compounds, (3) halogenated hydrocarbons (solvents e.g., carbon tetrachloride, chloroform, trichloroethylene, and methylene chloride), (4) inorganic metals and minerals (beryllium, cadmium, nickel, cobalt, chromium, asbestos and arsenic), and (5) naturally occurring chemical substances (aflatoxins). 

Building on their earlier research into S-endo cyclisations of Sml2-generated ketyl-type radicals, Molander and co-workers [107,108] developed this process as a key step in the syntheses of several naturally occurring lignans of the dibenzocyclooctadiene type. For example, they prepared the biaryl-chromium tricarbonyl complex 128 containing orffio-formyl and butenolide... 

Sugar acetylene reacted with a Fisher chromium carbene complex to give a phenol derivative, a possible intermediate for naturally occurring aryl-C-glycoside antibiotics (O Scheme 34) [55]. 

There are four naturally occurring isotopes of chromium chromium-50, chromium-52, chromium-53, and chromium-54. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element s name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. 

Of the four naturally occurring isotopes, one (chromium-50) is radioactive. Seventeen radioactive isotopes of chromium have also been made in the laboratory. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive. 

Data for chromium s four naturally occurring isotopes is provided in the table below. Calculate chromium s atomic mass. 

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