Organoarsenic halides

Reaction of organoarsenic halides with metals or with metal hydrides gives diarsines as shown in equations 183 , 184 , 185 , 186 187 , 188 , 189 , 190 , 191 and 192 °°. These can be considered as reactions between the organoarsenic anionic species formed upon the reduction and the halides. 

Reaction of organoarsenic halides with metal anions... 

Sulfur nucleophiles react with organoarsenic halides or acids. Some examples are shown in equations 355 and 350 . ... 

There is considerable evidence for this type of reaction in organoarsenic chemistry and, indeed dissociation-equilibrium was believed to be the cause of racemization of arsonium halides which, for synthetic reasons, usually contained at least one alkyl substituent (often" the benzyl group) on the arsenic atom. In 1939, fractional crystallization was achieved of the diastereomers of the diarsonium picrate 3 . The individual diastereo-mers of the salt, racemic (R, R ) and meso (R, S ), were stable in boiling ethanol, a fact that should have dispelled concerns of dissociation equilibria in halide-free arsonium salts. In 1940, the tetrahedral structure of [AsPh4]I was established by X-ray crystallography. ... 

Reaction of organoarsenic anions with metal halides... 

Reaction of organoarsenic(V) halides or oxides with several nitrogen nucleophiles gives the corresponding nitrogen compounds. Several examples are shown in equations... 

The pyrolysis of organoarsenic compounds containing the arsenyl moiety has some limited preparative applications [arsenyl (As=0) by analogy with phosphoryl (P=0)]. The compounds are based on the arsonic acid RAs(0)(0H)2, the arsinic acid R2As(0)0H and the arsine oxide R3As=0 structures. The acids are in interesting contrast with the phosphorus series. The phosphonic and phosphinic esters are prepared from the phosphorus(III) precursors via the Arbuzov synthesis. This synthetic route fails with the arsenic analogues, and further, if an alkyl halide or a salt is added in the pyrolysis of arsonic or arsinic acid esters a retro-Arbuzov reaction takes place . ... 

Organoarsenic(III) halides are reduce d with hydride reagents to give primary and secondary arsines in good yields (equations 112, H3io5b,i33 114 " ). 

Reactions of organoarsenic compounds are summarized in Fig. 4.10. Alkyl-arsonic and dialkylarsinic acids can be prepared by the Meyer reaction. An alkyl halide or sulphate is treated with an alkali metal arsenite in aqueous solution. 

Apart from their use as pharmaceuticals (p. 142) organoarsenicals such as alkyl- or arylarsonic acids have found some application as herbicides, fungicides and bactericides. They are being superseded by the less toxic tin compounds. All arsenic compounds should be treated as poisonous. The halides cause severe burns on the skin which heal only with diflSculty. This property was put to evil use... 

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