Arsenic acid, commercial

Arsenic trioxide may be made by burning arsenic in air or by the hydrolysis of an arsenic trihaUde. Commercially, it is obtained by roasting arsenopyrite [1303-18-0] FeAsS. It dissolves in water to a slight extent (1.7 g/100 g water at 25°C) to form a weaMy acidic solution which probably contains the species H AsO, orthoarsenous acid [36465-76-6]. The oxide is amphoteric and hence soluble in acids and bases. It is frequendy used as a primary analytical standard in oxidimetry because it is readily attainable in a high state of purity and is quantitatively oxidized by many reagents commonly used in volumetric analysis, eg, dichromate, nitric acid, hypochlorite, and inon(III). 

Arsenic Acids and the Arsenates. Commercial arsenic acid, corresponds to the composition, one mole of arsenic pentoxide to four moles of water, and probably is the arsenic acid hemihydrate [7774-41-6] H AsO O.5H2O. It is obtained by treatment of arsenic trioxide with concentrated nitric acid. Solutions of this substance or of arsenic pentoxide in water behave as triprotic acids with successive dissociation constants = 5.6 x 10 , ... 

As pointed out earlier, all U.S. cotton in commercial production is now harvested by machines. The application of harvest-aid chemicals to cause the plants to shed their leaves (defoliation) or to kill and dry the plant (desiccation) are common practices in many areas. Chlorates and organic phosphates are popular defoliant materials and arsenic acid is commonly used as a desiccant. 

Commercial arsenic acid is usually the orthoarsenic acid [7774-M1-6] corresponding to the above hemihydrate formula. The aqueous solution of this acid behaves as a triprotic acid the dissociation constants, Ki, K2 and K3 being 5.6x10-3, 1.7x10 and 3.OxlO-i, respectively. The meta and pyro forms... 

The commercial product is usually obtained either by adding arsenic acid to partly slaked lime containing sufficient quicklime to combine with the free water, thus yielding a dry product,9 or by heating a mixture of lime and white arsenic in the presence of an oxidising medium, such as oxygen,10 chlorine11 or nitrates.12 It is essential that the product... 

Commercial methods of producing copper arsenate consist in heating copper arsenite at 600° to 700° C. in an oxygen-enriched atmosphere,3 or in heating basic copper chloride with an arsenate or arsenic acid.4... 

Commercial lead arsenate usually consists mainly of the monohydrogen arsenate, but may also contain the normal arsenate. It is in great demand as an insecticide (see p. 301). Many methods of manufacture are described in the patent literature,14 some of the more recent being as follows (1) Metallic lead and arsenious oxide are added to a concentrated solution of arsenic acid containing nitric acid 15 lead arsenate is precipitated, the concentration of the arsenic acid remaining constant. At intervals the precipitate is removed and the arsenic acid solution again treated. (2) A solution of a soluble arsenate is treated... 

Phosphoric Add.—The commercial acid (D. 1-5) contains 65% H3P04 syrupy phosphoric acid contains about 90% H3P04. Usual impurities sulphuric acid, iron and arsenic acid. 

Before 1914, the US imported most metallic arsenic from Germany (e.g., Smith, 1945). From 1914 to about 1930, the bulk of the arsenic production in the US (marketed for commercial applications as As203, arsenic trioxide, or white arsenic) was derived as a metallurgical by-product of the smelting of copper, lead, and gold. Arsenic trioxide was used in the production of fertilizers, herbicides, and insecticides (Kirk-Othmer, 1992 Ullman s Encyclopedia, 1998), or if transformed to arsenic acid, used in the manufacture of CCA, a preservative of wood products (Mineral Commodity Summaries, 2004). Arsenic metal is also used for solders, ammunition, anti-friction additive to bearings, and in the computer and electronics industry for semiconductors (Mineral Commodity Summaries, 2004). 

Commercial phosphorus often contains a small quantity of arsenic. This on the treatment with nitric acid is oxidized to arsenic acid, which would contaminate the preparation of phosphoric acid unless removed by hydrogen sulphide. 

The following method of preparation of the acid is said to give a 20 to 30 per cent, yield in a fairly pure state 56-4 c.c. of commercial arsenic acid (density 1-88) are added to 1500 c.e. of aniline in a 2000 c.e. flask placed in an oihbath. The mixture is aerated when the temperature reaches 100° C., and the bath maintained at 230° C. until about 1200 C.C. of aniline have distilled over. The mass is then cooled and 200 c.c. of 8N sodium hydroxide added, the whole well shaken, allowed to settle, and the aqueous layer drawn off. The extraction is repeated using a further 100 c.c. of alkali and the combined extract shaken with 5 to 10 grams of infusorial earth, then filtered through hardened filter-paper. The acid is precipitated as a gummy mass by acidification... 

Resorcinol, 110 grams, and 171 grains of commercial arsenic acid (75° B6., or about 88 per cent.), are heated on the water-bath for several... 

If mode fix>m arsenical phosphorus, and commercial phoaphonis is usually arsenical, it is contaminated with arsenic acid, whose presence may be recognized by Alursh s test (q. v.). Tbe acid should not respond to the indigo and ferrous sulphate testa for HNO,... 

Although fuctisine is obtainable by a great variety of methods, those industrially uscil are Uniited to modifications of two the oxidation of commercial aniline by arsenic acid, or by a mixture of nitro-benzene, hydrochloric acid, ami iron filings and the purification of the pnxluct, after combination with an nchl, by repeated recrystnlUzationa... 

Figure 1 Oxidation states of volatile and soluble arsenic transformed by biological systems. pKi represents the equilibrium between the protonated cation and neutral forms of the hydroxyl group of dimethylarsinic acid. pKj represents the equilibrium between the neutral form and anionic form (2). Occasionally referred to as arsenous acid (2). HO—As=0 has also been referred to as arsenious acid (52). The term arsenite often refers to any of the As(lll) oxides. The species will be a function of the solute and the pH. Given that the pKa of arsenious acid is 9.2 (52), the protonated form is most likely the predominant form in aqueous environmental and physiological samples below pH 9. Structure commonly used when discussing arsenite in biological transformations, but is most likely not the predominant form in aqueous solutions. Monosodium methane arsonic acid (MSMA) is the commercially available sodium salt.

Arsine is formed when any inorganic arsenic-bearing material is brought in contact with zinc and sulfuric acid. The arsenides of the electropositive metals are decomposed with the formation of arsine by water or acid. Calcium arsenide [12255-53-7] Ca2As2, treated with water gives a 14% yield of arsine. Better yields (60—90%) are obtained by decomposing a solution of sodium arsenide [12044-25-6] Na As, in Hquid ammonia with ammonium bromide (14,15). Arsine may be accidentally formed by the reaction of arsenic impurities in commercial acids stored in metal tanks, so that a test should be made for... 

Arsenic Oxides and Acids. The only arsenic oxides of commercial importance are the trioxide and the pentoxide. These are readily soluble in alkaline solution, forming arsenites and arsenates, respectively. 

The Bart reaction is successful with a wide variety of aromatic and heterocycHc amines. A variation in which an aromatic amine, in the presence of arsenic trichloride, is dia2oti2ed in an organic solvent (the ScheUer reaction) has also found wide appHcation. Both arsonic and arsinic acids can be prepared by the ScheUer reaction which often gives better yields than the Bart reaction with electron-attracting substituents on the aromatic ring. For the commercial preparation of 4-aminophenylarsonic acid [98-50-0] (arsaniUc acid), C HgAsNO, and 4-hydroxyphenylarsonic acid [98-14-6] C H AsO, the Bnchamp reaction is used ... 

Three commercial processes that use these various hot carbonate flow arrangements are the promoted Benfield process, the Catacarb process, and the Giammarco-Vetrocoke process (26—29). Each uses an additive described as a promoter, activator, or catalyst, which increases the rates of absorption and desorption, improves removal efficiency, and reduces the energy requirement. The processes also use corrosion inhibitors, which aHow use of carbon—steel equipment. The Benfield and Catacarb processes do not specify additives. Vetrocoke uses boric acid, glycine, or arsenic trioxide, which is the most effective. 

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