Arsonous acids RAs

These As-O bonded species are related by the fact that they contain arsenic in the +3 oxidation state and have one organo substituent bonded to the arsenic. The general formulas are as follows arsonous acids, RAs(OH)2 arsonous acid anhydrides, RAsO arsonous acid esters, RAs(OR )2-... 

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 . ... 

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) ... 

Where X is Br or Q, the free acids may be obtained by acidification of the alkaline solution, but where X is I, the acids must be isolated as salts to avoid reduction of the arsonic acids by HI. Rather than using alkyl haUdes, alkyl or dialkyl sulfates or alkyl arenesulfonates can be used. Primary alkyl haUdes react rapidly and smoothly, secondary haUdes react only slowly, whereas tertiary haUdes do not give arsonic acids. AHyl haUdes undergo the Meyer reaction, but vinyl hahdes do not. Substituted alkyl haUdes can be used eg, ethylene chlorohydrin gives 2-hydroxyethylarsonic acid [65423-87-2], C2H2ASO4. Arsinic acids, R2AsO(OH), are also readily prepared by substituting an alkaU metal arsonite, RAs(OM)2, for sodium arsenite ... 

More extensive catenation occurs in the cyc/o-polyarsanes (RAs) which can readily be prepared from organoarsenic dihalides or from arsonic acids as follows ... 

Several methods are available for the synthesis of cycloarsoxanes (a) hydrolysis of organoarsenic(III) dihalides RASX2 (X = Cl, Br, I), (b) reduction of arsonic acids RAsO(OH)2 and (c) oxidation of primary arsines RASH2 or cyclopolyarsines (RAs) . The tetramer cyclo-(MeAsO)4 exhibits the boat-chair conformation, whereas the mesityl derivative cyclo-(MesAsO)4 adopts the crown conformation (Figure 11.24). The As-O bond distances are in the range 1.77-1.82 A, typical for single bonds. 

RAs(OH)2 for arsonic acids and R2A8—OH for arsinic adds. The neutral arsine oxides, R3As—>0, may be considered as derivatives in which all the hydroxyl groups have been replaced by organic residues. 

Arsonous acid general formula RAs(OH)2, where R is an alkyl or aryl group... 

It has already been noted that the esters of arsinous and arsonous acids disproportionate of heating. The formation of As(OR)3 in the pyrolysis of arsonic acid derivatives is thought to be the product of the secondary disproportionation reaction of the primary product RAs(OR)2-... 

Dodecyl-2-hydroxyphenyl)azo] phenyl]arsonic acid, D-01151 Eriochrome fast grey RAS Na salt, in E-00014... 

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