Applications with arsenic

In natural waters, arsenic may exist as one or more dissolved species, whose chemistry would depend on the chemistry of the waters. Over time, arsenic species dissolved in water may (1) interact with biological organisms and possibly methylate or demethylate (Chapter 4), (2) undergo abiotic or biotic oxidation, reduction, or other reactions, (3) sorb onto solids, often through ion exchange, (4) precipitate, or (5) coprecipitate. This section discusses the dissolution of solid arsenic compounds in water, the chemistry of dissolved arsenic species in aqueous solutions, and how the chemistry of the dissolved species varies with water chemistry and, in particular, pH, redox conditions, and the presence of dissolved sulfides. Discussions also include introductions to sorption, ion exchange, precipitation, and coprecipitation, which have important applications with arsenic in natural environments (Chapters 3 and 6) and water treatment technologies (Chapter 7). 

Mixing molten copper with other metals yields a variety of alloys, such as bronze when alloyed with tin, brass with zinc, and arsenical copper with arsenic (see Table 34 and text below). All these alloys have extremely good mechanical and working properties and have, therefore, been employed for applications requiring strength and hardness (West 1982). 

The introduction of the arsinic acid group into the aromatic nucleus is of great interest in connexion with the therapeutic application of arsenic compounds in combating certain infectious diseases (atoxyl = sodium arsanilate salvorsan). 

The synthehc applicability of arsenates is restricted by their toxicity that avoids the green aspect of the enzymatic processes. Wong et al. have shown that the use of inorganic borate buffer allows L-rhamnulose-l-phosphate aldolase (Rha-IPA) to accept DHA as substrate, although the of the reaction is about 50 times lower than with the natural substrate [10]. In spite of this fact, these authors have successfully used this approach for the one-step synthesis of L-fructose and L-rhamnulose, and for the facile two-step synthesis of several L-iminocyclitols. 

The liquid state of arsenic(III) fluoride and miscibility with many solvents and other liquids is an advantage permitting variation of the reaction conditions over a wide range. The first reported application of arsenic(III) fluoride as a fluorinating agent was the conversion of acetyl chloride into acetyl fluoride.3... 

In recent years use of the oxide as a constituent of cement has been advocated,1 especially in Sweden. Thus, a mixture of Portland cement (60 to 70 per cent.) and white arsenic (40 to 30 per cent.) heated to 200° to 250° C. affords a hydraulic cement of normal setting time and of less solubility than ordinary cement, so that lime liberation is inhibited and the resistance to water improved. Wooden structures exposed to the action of sea water may be protected by spraying with a concrete composed of white arsenic, cement and sand in the proportions 1 3 12. The arsenic makes the mixture elastic and helps the cement to adhere to the wood. There is, however, danger in the too widespread application of arsenic in the directions described above. 

Information on the pnictogens, like the chalcogens and halogens, rapidly decreases down the group Thus, the following discussion will mainly centre on the phosphorus. However, by analogy, the arguments will usually be applicable to arsenic and, with less certainty, to antimony and bismuth. 

As discussed earlier in Section 3.17, the excessive application of arsenic-bearing pesticides and phosphate fertilizers on agricultural lands, golf courses, and lawns may locally contaminate surface waters and ground-waters (Welch et al., 2000), (Lewis et al., 2002), 590. Phosphates desorb arsenic from mineral surfaces and readily interfere with the sorption and coprecipitation of arsenic onto iron (oxy)(hydr)oxides (Campos, 2002). Commercial phosphate fertilizers also frequently contain >13 mg kg-1 of arsenic impurities (Campos, 2002), which may further contribute to groundwater contamination. 

The tables and maps in this appendix list the locations of prominent areas with arsenic-contaminated groundwater, geothermal waters, and/or substantial arsenic-bearing rocks and mining wastes. Additionally, there are countless sites that have local waters, sediments, and soils that have been contaminated by arsenic from chemical manufacturing facilities, pesticide applications, and individual mines. These small-scale areas, which include hundreds of Superfund sites in the United States, are too numerous and poorly documented to list in this appendix. Appendix B in US Environmental Protection Agency (US EPA) (2002) lists the locations of Superfund sites where arsenic is a contaminant of concern. 

Silicon (Si) Silicon is a lustrous silvery gray material. Because silicon conducts electricity, but not as well as a metal, silicon is classified as a semimetal. Crystals of pure silicon that have been doped with arsenic or gallium are known as semiconductors and are used to fabricate computer chips. Silicone rubbers are polymers containing silicon, oxygen, and various hydrocarbon groups, and are used in applications ranging from sealants to breast implants. 

B. Syntheses and Applications of Arsenic Compounds Labelled with... 

The method is applicable for triorganoarsenic compounds bearing aryl or vinyl substituents (equations 76 , 77 and 78 ), while for the preparation of alkylarsenic halides this method has not been useful since only adduct formation and redox reactions have been reported between R3AS and AsXj (equations 79a and b) . Reaction of tris(trifluoromethyl) arsine with arsenic iodide, however, has been reported to afford a mixture of halides (equation 80) . In the reaction of unsymmetrically substituted compounds such as 4, cleavage of the aryl-arsenic bond is preferred to that of the alkyl-arsenic bond (equation 78 ). The cleavage of 4 by this method is in contrast to that of 3 in thermolysis (equation 75). 

A review is presented of product developments in the area of microbiocides, with details of new products and their targeted applications. Currently arsenic-based formulations account for 70% of the market, but researchers forecast a significant shift in consumption patterns, and anticipate that the demand for non-arsenic based formulations will rise by 10-20% per year. 

---