Arsenic Medical and Biological Effects of Environmental Pollutants (1977) / Chapter Skim
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2 Chemistry of Arsenic
2 Chemistry of Arsenic
Pages 4-15
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The commercial use and production of inorganic and organic arsenic compounds have raised local concentrations of this element in the environment much above the natural background concentrations.
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Other commercially useful organic and inorganic arsenic derivatives are prepared from it. Arsenic trioxide has been reported to exist in three allotropic modifications.
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Condensation of the vapors on a surface at temperatures above 250° C forms the glassy modification, which slowly changes to the crystalline, monoclinic form.32 ARSENIC PENTOXIDE Oxidation of elemental arsenic or arsenic trioxide by nitric acid, followed by evaporation of the resulting mixture and dehydration of the residue, yields white hydroscopic crystals of arsenic pentoxide. Thermal decomposition of the pentoxide converts it to the trioxide with concurrent loss of oxygen.
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From page 7... ...
, chromium, and aluminum readily absorb arsenous acid.32 o-Arsenic acid, H3As04, can be prepared in the form of a white crystalline solid, H3AsO4 /HO. This is the product formed when arsenic trioxide is dissolved in nitric acid and the solution is evaporated.
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An Eh-pH stability diagram has been published (Figure 2-1~. However, the ratios found in ocean water393 were in the range 0.1: 1 to 10: 1.
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~ ~ ~ an; ~ ESTERS OF ARSENOUS AND ARSENIC ACIDS Neutral esters of arsenous acid or arsenic acid, such as triorganyl arsenite and triorganyl arsenate, can be prepared, provided that the reaction products are protected from the action of moisture and acidic compounds.745 The arsenic-oxygen-carbon bond also has considerable hydrolytic instability. Esters of these acids are therefore not stable in aqueous media.
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From page 10... ...
The arsenic trisulf~de and pentasulfide are formed when hydrogen sulfide reacts with trivalent or pentavalent inorganic arsenic compounds in the presence of hydrochloric acid. Saturated solutions in distilled water contain sulfide at approximately 4 x 10-6 mol/liter.
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From page 11... ...
Se, NR Y = 0, S Se, Te, NR X= halogen Arsonic acid Diorganylarsinic acid The organic arsenic compounds that have environmental importance are those that contain methyl groups, the aromatic arsenic derivatives used as feed additives and in veterinary medicine, and a few others that may be important in biologic cycles.
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From page 12... ...
56 Differential thermal analysis of disodium methanearsonate showed that complete combustion was achieved at 660° C.42~ Arsonic acids can be mistermed with alkanols and dials under anhydrous conditions. The esters are very easily hydrolyzed.
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From page 13... ...
The arsenic-carbon bonds are very stable, but are cleaved by heating with solid sodium hydroxides or chromium trioxide.~7 The acid has a pKa value of 6.2.4 In strongly acidic solution, cacodylic acid exhibits basic properties and forms adducts with mineral acids.396 The reactions of cacodylic acid are summarized in Figure 2-3. It has been pointed out that cacodylic acid reacts with (CH3)
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From page 14... ...
ALKYLARSINES AND DIALKYLARSINES Alkylarsines and dialkylarsines have been detected as products formed by the reduction and methylation of inorganic and methylarsenic acids. They have also been used in experiments to elucidate their effects on biologic systems.383 Methylarsine is a gas at room temperature.
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From page 15... ...
If thiol groups are present in enzymes, trivalent arsenic compounds can form stable bonds with them, thus preventing the enzymes from functioning properly. The likely reaction between lipoic acid, a building block of the enzyme pyruvate oxidase, and a trivalent alkyldihaloarsine is the following: o E NH C (CH2 )
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