Arsenite Meyer reaction

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 ... 

The Meyer reaction is intrinsically reversible. As the pH rises and arsenite becomes progressively dehydronated, it becomes an increasingly good nucleophile, whereas it becomes an increasingly good leaving group as the pH falls and the C—As bond can break (see 75, p. 987). 

When we required 3-arsonopyruvate, it was similarly necessary to make the labile -CO—CH2—As03H2 structure only at the last stage, and again we used periodate for this (68), as shown in Fig. 15. The pathway makes use of the recently emphasized (76) fact that when the Meyer reaction (Section VII,A,1) is performed with a 2-haloalcohol, the halide is not directly displaced by arsenite, but the alkali first causes formation of an epoxide, which is then opened by arsenite at its less hindered carbon. As with the arsonoacetaldehyde, the compound was not isolated from solution. 

Historically, the Meyer reaction, which consists of alkylating metal arsenites with alkyl halides, is the most widely used preparative method for alkylarsouic acid salts (equation 135). Subsequent alkylation of the alkylarsonic acid salt gives the alkylarsinic acid salt (equation 136). Excellent yields of alkylarylarsinic acid salts are obtained upon alkylating an arylarsonic acid salt. Aryl halides do not give satisfactory yields of the arylarsonic acid salts. 

Arsonic acids have been prepared from readily available compounds such as arsenic(III) oxide and arsenic trichloride. Reaction of sodium arsenite with alkyl halides has been named the Meyer reaction, and reaction with arenediazonium salts the Bart reaction. In addition, some modifications have been made for the preparation of arsonic acids. Some examples are shown in equations 326 and 327. ... 

Meyer reaction. Preparation of alkylstannonic acids byreacting alkali stannite with an alkyl iodide. When applied to alkali arsenites or plumbites, the reaction yields alkylarsonic and alkylplumbonic acids, respectively. 

Rosenmund reaction. Formation of aromatic arsonic acids by heating equimolar amounts of sodium or potassium arsenite with aryl halides in aqueous solution. The reaction is an extension of the Meyer reaction. 

The Meyer reaction is a general reaction particularly suitable for preparation of aliphatic arsonic acids 507,511 here an alkyl halide is treated with sodium arsenite ... 

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. 

Preparative aspects. Since bonds between carbon and arsenic, antimony and bismuth are stable to water they may be made in aqueous solution. Thus, alkyl arsonic adds RAs(OH)2 may be prepared by the Meyer reaction between sodium arsenite and alkyl halides ... 

The best-known route for making aliphatic arsonic acids is the Meyer (103) reaction, in which an alkyl halide reacts with alkaline arsenite by simple nucleophilic displacement ... 

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