Dimethyl arsenic acid

The anti-plant agents favoured in Vietnam were 2,4-dichlorophenoxy-acetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), dimethyl-arsenic acid (cacodylic add) and 4-amnito-3,5,6-trichloropicolinic acid (picloram). The formulation in which they were used is set out in Table 5.1. 

Dimethyl arsenic acid yields predominantly dimethylarsine, while methylarsonic acid yields predominantly methylarsine and trimethylarsine oxide yields predominantly trimethylarsine. 

Figure 11.5. Chromatogram of 100 gg each of As(IU), DMAA (dimethyl arsenic acid), MMAA (monomethyl arsenic acid), As(V) species for standard test of species in drinking water, by standard IC and ICP-MS detection. Column ANl (Cetac Technologies, Omaha, NE). Eluent 2 mM PBS/0.2 mM EDTA, pH 6.0 at 1 mL/min. Chromatography courtesy of T. Matsuda, HP-Japan, 1999.

Sample digestion must yield 80% or greater recovery of added (dimethyl arsenic acid) and 90% or greater recovery of added As(III), As(V). 

Synonyms CAS 75-60-5 agent blue BOLLSEYE CHEXMATE dimethyl arsenic acid ERASE SALVO Cadmium... 

Arsenite, arsenate, dimethyl arsenic acid in 4 min EKC WATER Ground water FASI 10 mmol L phosphate buffer, 0.35 mmol L" TTAB (pH 9.0) UV, 185 nm 0.1-0.5 mgL 234... 

Arsenic can be found in two primary forms organic and inorganic. Organic species of As are mainly found in food, such as shellfish, and include forms as monomethyl arsenic acid (MMAA), dimethyl arsenic acid (DMAA) and arseno-sugars. Inorganic arsenic (i-As) occurs in two valence states, arsenite (As(III)) and arsenate (As(V)). In natural waters, As(III) species consist primarily of arsenious acid (H3ASO3) and As(V) species is predominantly present as H2AsO and HAsO ... 

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. 

Finally, particular chemical species can be determined in some cases, as when arsenic content is separated into As(III), As(V), monomethyl arsonic acid, and dimethyl arsinic acid using ion-exchange chromatography. Chemical speciation is sometimes possible but is often very difficult. If the metals... 

For instance in the synthesis of dimethyl arsinic acid (cacodylic acid) trivalent arsenic is isomerised to the pentavalent state... 

Inorganic arsenic complexes based on oxygen ligands is scarce. Simple esters of arsenic acid, As(0)(0R)3 (R = Me, Ft, n-Pr, n-Bu, CeHn) have tetragonal structures. Reaction of the diol ligand 2,4-dimethyl-2,4-pentanediol with AsCfr affords an arsenic chloride complex in which the As atom is part of a six-membered ring (37). ... 

Sorption of monomethyl arsonic acid (MMAA), dimethyl arsinic acid (DMAA), and arsenate on anaerobic bottom sediments from the Menominee River, Wisconsin are described by Langmuir Isotherms. These results were Incorporated Into a kinetic model of arsenic species transforamtlon which takes sorption Into account. Model predictions were found to be sensitive to the sediment water content and r, the adsorptive capacity of the sediment. Demethylatlon of MMAA and DMAA was observed In sediment Incubation experiments. The predictions of the sorption/kinetic model were In good agreement with the results of the Incubation experiments. 

When all the dimethyl sulphate has been added, the flask is fitted with a reflux condenser and the contents boiled for 2 hours. The sodium salt of methyl arsenic acid is obtained. It is allowed to cool and a small amount of potassium iodide is added, after which a current of sulphur dioxide is passed through the liquid until it is saturated (about 6 hours). The mixture is again boiled under reflux for about an hour during this period, an oily substance consisting of methyl arsenious oxide deposits at the bottom of the flask, where it is saturated with a current of gaseous hydrochloric acid, while the flask is cooled externally. On attaining complete saturation, the flask is connected with a Liebig s condenser and the liquid distilled. Much hydrochloric acid is evolved at first later a mixture of hydrochloric acid and methyl dichloroarsine distils over. The distillation is continued until no more oily liquid condenses. The distillate is placed in a separatory funnel and the oily layer separated and distilled. 

As the formation of the ethyl arsenic acid and the succeeding chlorination of the ethyl arsenious oxide takes place in add conditions, hydriodic acid, which is present in considerable quantity, can form ethyl diiodoarsine. In order to prevent this happening, the iodine is removed as methyl iodide by addition of dimethyl sulphate, which reacts, as discovered by Wieland Ber., 1905, 38, 2327), in the following manner ... 

Arsenic is an ubiquitous element which occurs in the form of various chemical species in the environment. In biological tissues, the main species identified is arsenobetaine which is considered to be non-toxic and present at more than 90% in fish tissues but does not exceed 50% in mollucs [128], Other species such as arsenocholine, tetramethylarsonium ion, trimethylarsenoxide, dimethyl-arsinic acid and arsenosugars have also been identified [129-132]. 

Trivalent monomethylated and dimethylated arsenic species have also been reported in lake water (58,68,69). These arsenicals are probably methylarsonous acid and dimethylarsinous acid, although their precise chemical structures in natural waters have not been demonstrated. Most analytical methods for determining arsenic species in water samples convert the original arsenic species into volatile hydrides, which then serve as the analytes. Since the trivalent methylated arsenicals generate the same analyte as their respective pentavalent analogues, they must be separated before the hydride generation step so that they can be determined independently. Solvent extraction has been used to effect this separation (58). Possibly, the presence of these trivalent methylated arsenicals has been underestimated because few studies include a solvent separation step. However, in one smdy at least, dimethylarsenic in estuarine and coastal waters, as determined by hydride generation techniques, was shown to be present solely as the pentavalent dimethylarsinate species in three out of the four samples tested (50). 

Lipid arsenic compounds also occur in marine animals (34,110). The compounds originally present in the lipid fraction were subjected to base and/or acid hydrolysis, and the water-soluble products identified by HPLC-ICPMS. In this way, phosphatidylarsenocholine (see Fig. 2, compound 18) and a phosphatidyl-arsenosugar (see Fig. 2, compound 5) were identified in the digestive gland of lobster (34), and evidence was presented for the presence of lipids containing arsenocholine and dimethylated arsenic moieties in shark tissues (110). 

What about ascending fronts If a front were to propagate upward, then the hot polymer-monomer solution in the reaction zone could rise because of buoyancy, removing enough heat at the polymer-monomer interface to quench the front. With a front that produces a solid product, the onset of convection is more complicated than the cases that we considered in Chapter 9, because the critical Rayleigh number is a function of the velocity (Volpert et al., 1996). Bowden et al. (1997) studied ascending fronts of acrylamide polymerization in dimethyl sulfoxide. As in the iodate-arsenous acid fronts, the first unstable mode is an antisymmetric one followed by an axisymmetric one. Unlike that system, in the polymerization front the stability of the front depends on both the solution viscosity and the front velocity. The faster the front, the lower the viscosity necessary to sustain a stable front. 

WAUCHOPE, D. 1976. Acid dissociation constants of arsenic acid, methylarsonic acid (MAA), dimethyl-arsinic acid (cacodylic acid), and N-(phosphono-methyl)glycine (glyphosate). J. Agric. Food Chem. 24 717-721. 

Reproductive system Environmental arsenic exposure can impair male fertility. A case-control study in China concluded that elevated inorganic arsenate (Asi(V)) exposure is associated with arsenic-induced male infertility. The mechanism of toxicity by arsenic species may involve oxidative stress and sexual hormone disruption measured by biomarkers including acylcamitines, aspartic acid and hydroxyestrone, which were negatively associated with infertility, and uridine and methylxanthine, which were positively associated [44 ]. Arsenic exposme is also correlated to a decrease in human semen quality as reported in a reproductive-age Chinese cohort. The study demonstrated significant association of dimethyl arsenic species (DMA) concentration with low sperm concentrations [45 -]. 

Arsenic Acid 70+ 275 Carbon Dioxide (Dry) I50f 275 Dimethyl Phthaiate ... 

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