Methylated arsenic methylation

Arsenic (but not antimony) forms a second hydride. This is extremely unstable, decomposing at very low temperatures. Replacement of the hydrogen atoms by methyl groups gives the more stable substance tetramethyldiarsane, cacodyl, (CH3)2As -AsfCHj), a truly foul-smelhng liquid. 

If, for example, methyl iodide is added to a solution of arsenic trioxide in an... 

Arsenic. Arsenic is under consideration for inclusion as an essential element. No clear role has been estabHshed, but aresenic, long thought to be a poison, may be involved in methylation of macromolecules and as an effector of methionine metaboHsm (158,160). Most research has focused on the toxicity or pharmaceutical properties of arsenic (158). 

Organomineral peroxides of antimony arsenic, boron, magnesium, tin, cadmium, lead, silicon, and 2inc have been prepared by autoxidation and some are Hsted in Table 3 (33,44,60,93,115). For example, dimethyl cadmium reacts with oxygen to form methylperoxy methyl cadmium [69331-62-0] and bis(methylperoxy) cadmium. 

Trimethyl arsine [593-88-4] C H As, has been identified as the toxic volatile arsenical, once known as "Gosio gas," produced by the reaction of certain molds that grow on wallpaper paste and react with inorganic arsenic compounds present in the paper. A number of microorganisms can methylate arsenic trioxide and other arsenic-containing compounds to yield trimethylarsine. These microorganisms include Scopulariopsis brevicaulis Candida humicola and Gliocladium roseum (72). 

Inorganic arsenic plus methylated metabolites in End of workweek 35 pg/g As/I B... 

From a practical point of view, saturation of elimination has important consequences. If the metabolism becomes saturated, the duration of the action of the compound is prolonged. In such a case, correct timing for collection of biological monitoring samples also becomes difficult to assess. Furthermore, saturation of metabolism may also have qualitative effects. For example, it has been argued (but not yet proved) that arsenic compounds cause cancer at high doses at which methylation of inorganic arsenic becomes saturated. ... 

In a 30 minute test the results obtained should not differ by more than 1 minute using different lots of paper. On being exposed to nitric oxide fumes, these papers slowly turn green, followed by a salmon pink coloration Methyl Violet Paper Test (Field Test for Pro pint Powders). This method of testing proplnts using 0.1N methyl violet paper directly in the containers in which the powder is stored, was developed at Picatinny Arsenal in 1928—29 (Refs 1 2), and was adopted by the Ordnance Dept to replace the Observation Test about 1931... 

If the proplnt is double-base, it has been observed that even the most stable propints bleach methyl violet paper in much shorter periods than one year. Investigations conducted by P.F. Macy at Picatinny Arsenal (Ref 4) showed that diphenylamine-stabilized doublebase proplnts in service storage at about 30°, may be considered of satisfactory stability if they do not cause complete bleaching of 0.1 N methyl violet paper in one month or less. Such proplnts always show satisfactory stability when subjected to the 65.5° Surveillance Test. It was observed at the same time, that double-base proplnts which had deteriorated, but were not yet hazardous, took from 11 to 24 days to bleach methyl violet paper at 30°... 

Later tests at Picatinny Arsenal revealed that methyl violet paper very often faded in shorter time periods than described above, even for perfectly stable powders, as detd by the 65.5°... 

This applied particularly to double-base propints, although some single-base propints also gave erratic results. For these reasons, work was undertaken at Picatinny Arsenal to find an indicator that would be more reliable than methyl violet. About 60 commercially available dyes were examined by S. Helf (Ref 5) in exptl indicator paper tests, of which only three were found to be superior to methyl violet benzoazurine, trypan red and ethyl violet. Laboratory and surveillance testing showed that papers prepd with a 0.1% soln of benzoazurine did not change in color after one year when used with stable double-base propint, while methyl violet paper was bleached in nearly every case. The other two indicators mentioned above, trypan red and ethyl violet, were not as satisfactory as benzoazurine, although they were better than methyl violet. 

The biological cycle of arsenic in the surface ocean involves the uptake of arsenate by plankton, the conversion of arsenate to a number of as yet unidentified organic compounds, and the release of arsenite and methylated species into the seawater. Biological demethylation of the methyl-arsenicals and the oxidation of arsenite by as yet... 

The next eight chapters will be devoted to the ecotoxicology of groups of compounds that have caused concern on account of their real or perceived environmental effects and have been studied both in the laboratory and in the field. These are predominantly compounds produced by humans. However, a few of them, for example, methyl mercury, methyl arsenic, and polycyclic aromatic hydrocarbons (PAHs), are also naturally occurring. In this latter case, there can be difficulty in distinguishing between human and natural sources of harmful chemicals. 

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. 

Methyl arsenic, like methyl mercury, is generated from inorganic forms of the element by methylation reactions in soils and sediments. However, the mechanism is evidently different from that for mercury, depending on the attack by a methyl car-bonium ion rather than a methyl carbanion (Craig 1986, Crosby 1998). Methylation... 

FIGURE 8.6 Methylation of arsenate (after Environmental Health Criteria 18). 

Mercury, tin, lead, arsenic, and antimony form toxic lipophilic organometallic compounds, which have a potential for bioaccumulation/bioconcentration in food chains. Apart from anthropogenic organometallic compounds, methyl derivatives of mercury and arsenic are biosynthesized from inorganic precursors in the natural environment. 

Both alkyl and aryl metals have been studied, but not a very wide range of compounds. Several studies of triphenylarsene and triphenylstibine have been done. Methyl and ethyl compounds of arsenic, germanium, mercury, bismuth, and lead essentially complete the list. In virtually all cases the results have been clouded by difficulties in effecting chemical separation without altering the product distribution. The results do, nonetheless, lead to valid and important conclusions. 

Bentley R, TG Chasteen (2002) Microbial methylation of metalloids arsenic, antimony and bismuth. Microbiol Mol Biol Rev 66 250-271. 

Dermal Effects. Skin irritation was noted in wildlife officers at the RMA after they handled sick or dead ducks without gloves (NIOSH 1981). Although the investigators concluded that diisopropyl methylphosphonate contributed to the local effects, a number of other compounds were present. Analysis of the pond water indicated the presence of a number of organic and inorganic contaminants, including diisopropyl methylphosphonate (11.3 ppm) aldrin (0.368 ppm) dieldrin (0.0744 ppm) dicyclo-pentadiene, bicycloheptadiene, diethyl benzene, dimethyl disulfide, methyl acetate, methyl isobutyl ketone, toluene, and sodium (49,500 ppm) chloride (52,000 ppm) arsenic (1,470 ppm) potassium (180 ppm) fluoride (63 ppm) copper (2.4 ppm) and chromium (0.27 ppm). Because of the presence of numerous compounds, it is unclear whether diisopropyl methylphosphonate was related to the irritation. 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

Conversion of a nontoxic molecule to one that is toxic, or a molecule with low potency to one that is more potent. Examples include the formation of the phenoxy herbicide 2,4-D from the corresponding butyrate, formation of nitrosamines, and methylation of arsenicals to trimethylarsine. 

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