Arsenic compounds arsonates

Concerning anthropogenic sources, methyl arsenic compounds such as methyl arsonic acid and dimethylarsinic acid have been used as herbicides, and were once a significant source of environmental residues. Dimethyl-arsinic acid (Agent Blue) was used as a defoliant during the Vietnam War. 

Cullen et al. (1994) have proposed a possible mechanism of arsenic methylation after the study in which arsenite, arsenate, monomethyl-arsonate or dimethylarsinic acid were added to the growth medium in the presence of the unicellular alga Polyphsa peniculus. Evidence of arsenic biomethylation by the micro-organism Apiotrichum humicola in the presence of L-methionine-methyl-d3 has come from the same laboratory (Cullen et al., 1995). Their findings point to the role of S-adenosylmethionine, or a related sulfonium compound as possible methyl donors. Arsenic biomethylation and biotransformation has also been demonstrated in a freshwater environment (Kuroiwa et al., 1994). 

Three methods for the preparation of aromatic arsonic adds are de- scribed in this review. By far the most widely applicable of these is the Bart reaction, which involves the interaction of a diazonium salt with an inorganic arsenic compound. In the original Bart process 1 and most of its modifications an alkali arsenite is used, as shown in the following equation. 

Jacobs WA, Heidelberger M (1919) Aromatic arsenic compounds. II. The amides and alkylamides of N-arylglycine arsonic acids. J Am Chem Soc 41 1809-1821... 

A very closely related type of spiro-oxyarserane, (102-106j7nas been synthesized124 by an extension of the known reactions of tetracoordi-nated arsenic compounds, namely, the reaction of arsenic and arsonic acids and esters with glycols.128... 

SYNS (2-CHLOROETHENYL) ARSONOUS DICHLORIDE P-CHLOROVINYLBICHLOROARSINE 2-CHLOROVINYLDICHLOROARSINE (2-CHLOROVINYL)DICHLOROARSINE DICHLORO(2-CHLOROVINYL)ARSINE n LE STSITE n LEWISITE (ARSENIC COMPOUND)... 

Arsenicals have received some attention because of their therapeutic significance. Both inorganic and organic arsenic compounds display an As(III)-As(V) redox equilibrium in the body. This is shown with the arsine-arsine oxide and arsenoxide-arsonic acid equilibria (reactions 3-A and 3-B and reactions 4-B and 4-C, respectively). Another reaction of interest is the oxidation of arseno compounds to arsenox-ides (reaction 4-A),a reaction of importance in the bioactivation of a number of chemotherapeutic arsenicals. 

The present account of Ion-exchange Chromatography with Detection by Atomic Absorption began with exemplification of the applicability of this method by taking up the example of determination of constituents of the mentioned mixture of several arsenic compounds. The results of this determination are illustrative of the sensitivity that the method can show in certain cases of analysis of mixtures which may be amenable to resolution and analysis by this technique. In the case cited, the method has a sensitivity of at least 3 ng/ml and 20 ng/ml respectively for the arsonate and the arsenate derived from methane. 

In 1863 at the University of Strasbourg, Pierre Jacques Antoine Bechamp (1816-1908) prepared an arsenic compound by heating aniline with aniline arse-nite [24] that entered the literature as Bechamp s anilide or the anilide of arsonic acid (Fig. 7.3a). 

Although Lewisite is only slightly soluble in water (0.5 g L j [123], hydrolysis is rapid and results in the formation of the water-soluble dihydroxy arsine (2-chlorovinyl arsonous acid). In basic solution, the traws-Lewisite isomer is cleaved by the hydroxyl ion to give acetylene and sodium arsenite this occurs even at low temperatures [79, 123]. ds-Lewisite must be heated to over 40°C to react with NaOH to yield vinyl chloride, sodium arsenite and acetylene. In aqueous solution, the ds-isomer undergoes a photoconversion into the tr zws-isomer. In water and in the presence of oxidizers naturally present in the environment, the toxic trivalent arsenic of Lewisite oxide is oxidized to the less toxic pentavalent arsenic [124]. Regardless of the degradation pathway, arsenical compounds will ultimately be formed. 

Arsonic and Arsinic Acids. The arsonic acids, compounds of the type RAsO(OH)2, are among the most important organic arsenicals. The ahphatic arsonic acids are generally prepared by the Meyer reaction ie, heating an alkyl haUde with As O in alkaline solution ... 

Inorganic arsenicals such as arsenic trioxide, sodium arsenite, lead arsenate, calcium arsenate and Paris Green have been used for many years as soil sterilants. Organic arsenical herbicides, in which the organic group is bonded directly to the arsenic atom, have been used extensively for post-emergence control of weeds in cotton. Several of the more important herbicides are sodium cacodylate (monosodium dimethylarsenic acid) and sodium salts of methane arsonic acid. The latter compounds exist in two principal forms the monosodium salt (MSMA) at pH6.4 and the disodium salt (DSMA) at pH10.2. 

Because arsenic(V) (as arsonic or arsinic acids) is readily reduced to arsenic(III) by sulfur dioxide in concentrated HX,102,103 this makes chloroarsines much more readily accessible than the corresponding phosphine compounds. This is shown in equation (31),104... 

Lewisite 1 per se is never found in the environment. Figure 18 shows that this compound hydrolyzes rapidly on contact with moisture to 2-chlorovinyl arsonous acid, which in turn slowly dehydrates to lewisite oxide (syn. 2-chlorovinyl arsenous oxide) (16). Both 2-chlorovinyl arsonous acid and lewisite oxide are nonvolatile. The most frequently used method for the identification of CWC-related chemicals is based on gas chromatography (GC) in combination with mass spectrometry (GC/MS). Indirect GC/MS analysis of lewisite 1 requires sample preparation, which involves conversion of lewisite oxide to 2-chlorovinyl arsonous acid in an acidic environment, followed by derivatization (12). The obtained species is both volatile and thermally stable, and thus amenable to GC analysis. Often, a mercaptan reagent is used as a derivatization agent. The reaction with 3,4-dimercaptotoluene is shown in Figure 19. 

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