Methylarsinous acid

Methylarsinic acid and dimethylarsinic acid are the two organoarsenic compounds that are most likely to be encountered in the environment. 

Methylarsinic acid salts are moderately toxic and do not accumulate in animals. The acute oral of MSMA for albino rats is 900 mg/kg, that of DSMA 1800 mg/kg. The dietary no-effect level of the acid is 100 mg/kg. Practically, the two active substances are barely toxic to fish, LC,o (48 h) being for bluegill more than 1000 mg/kg, though the addition of surfactants increases this toxicity. 

H Yamauchi, Y Yamamura. Metabolism and excretion of orally administered di-methylarsinic acid in the hamster. Toxicol Appl Pharmacol 74 134-140, 1984. 

Methylarsinic acid is formed. In methylarsine and methyldiiodoarsine, arsenic is at oxidation state +III, and both hydrogen atoms and both iodine atoms bound to arsenic atom must be considered at oxidation state —I. Some other organic arsenicals must be mineralized before their arsenic content can be determined (see Sect. 18.10.7). 

Abbreviations As(III) arsenite As(V) arsenate DMA dimethylarsinic acid MA methylarsinic acid AC arsenocholine AB arsenobetaine ... 

Good yields of phenylarsine [822-65-17, C H As, have been obtained by the reaction of phenylarsenic tetrachloride [29181-03-17, C H AsCl, or phenyldichloroarsine [696-28-6], C3H3ASCI25 with lithium aluminum hydride or lithium borohydride (41). Electrolytic reduction has also been used to convert arsonic acids to primary arsines (42). Another method for preparing primary arsines involves the reaction of arsine with calcium and subsequent addition of an alkyl haUde. Thus methylarsine [593-52-2], CH As, is obtained in 80% yield (43) ... 

Methylarsine, trifluoromethylarsine, and bis(trifluoromethyl)arsine [371-74-4] C2HAsF, are gases at room temperature all other primary and secondary arsines are liquids or solids. These compounds are extremely sensitive to oxygen, and ia some cases are spontaneously inflammable ia air (45). They readily undergo addition reactions with alkenes (51), alkynes (52), aldehydes (qv) (53), ketones (qv) (54), isocyanates (55), and a2o compounds (56). They also react with diborane (43) and a variety of other Lewis acids. Alkyl haUdes react with primary and secondary arsiaes to yield quaternary arsenic compounds (57). 

A large number of polymeric substances, (RAs) or (ArAs), are also known (113). They are usually prepared by the reduction of arsonic acids with hypophosphorous acid (100,114) or sodium dithionite (115). Most of these polymers have not been well characterized. An insoluble, purple material, poly(methylarsinidene) [26403-94-1], (CH As), prepared by the interaction of methylarsine and a dihalomethylarsine, however, has been shown by an x-ray investigation to have a ladderlike polymeric stmcture in which the inter-mng distances correspond to one-electron bonds (116) ... 

Marine algae transform arsenate into nonvolatile methylated arsenic compounds such as methanearsonic and dimethylarsinic acids (Tamaki and Frankenberger 1992). Freshwater algae and macrophytes, like marine algae, synthesize lipid-soluble arsenic compounds and do not produce volatile methylarsines. Terrestrial plants preferentially accumulate arsenate over arsenite by a factor of about 4. Phosphate inhibits arsenate uptake by plants, but not the reverse. The mode of toxicity of arsenate in plants is to partially block protein synthesis and interfere with protein phosphorylation — a process that is prevented by phosphate (Tamaki and Frankenberger 1992). 

The compounds MMA, DMA, and TMAO are reduced in acidic aqueous media by borohydride solutions to methylarsine (MeAsH2, bp 2°C), dimethylarsine (Me2AsH, bp 35°C), and trimethylarsine (Me3As, bp 55°C), respectively. These products are useful derivatives for speciation analysis of arsenic because they are readily separated from complex sample matrices and may be further separated from each other by distillation (41) or by gas chromatography (42) prior to their determination by element-specific detectors. Consequently, arsine generation techniques are the most commonly used methods for determining MMA, DMA, and TMAO in marine samples. 

Methyldiiodoarsine has been prepared in a variety of ways treatment of an alcoholic solution of methylarsenic oxide, CH3AsO, with an excess of hydriodic acid,1 passing methylarsine into an alcoholic solution of iodine,2 the action of sulfur dioxide on methylarsenic tetraiodide,3 the action of methyl iodide on arsenic,4 and treatment of a solution of disodium methanearsonate and potassium iodide with hydrochloric acid and sulfur dioxide.6 The following directions are essentially the last method combined with the preparation of the disodium methanearsonate in situ.6,7 The use of an alcoholic medium greatly facilitates the reaction between sodium arsenite and methyl iodide. 

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

Methylarsine, CHg.AsHj, may be prepared either by the reduction of. sodium methylarsinate with amalgamated zinc dust in alcoholic hydrochloric acid solution, the operation being conducted in a hydrogen atmosphere, or by the reduction of methyidichloroarsine. 

Sulphur. liquid sulphur dioxide. Sulphur dichloride. Cacodyl sulphide or disulphide, [(CHjj.AsLS or [(c4)3As]A Cacodyl disulphide, methylarsine sulphide, (CH,AsS), tri-methylarsine sulphide, (CHs)3A, oacodyliu acid. Cacodyl chloride, sulphur, hydrogen sulphide. 

Two hundred grains of sodium methylarsinate, 250 grams of potassium iodide, and 500 grams of water, containing T50 grams of hydrochloric acid, are saturated in the cold with sulphur dioxide. i... 

Calcium methylarsinate, CH3AsO.O2Ca.H2O, crystallises from its solution in dilute acetic acid after neutralisation with ammonium hydroxide. ... 

Yohimbine methylarsinate.— Prcj)arcd from 130 parts of acid and 368 parts of yoliimbine melts at l t0° C. ... 

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