Arsonium salts

Arsonium salts have found considerable use in analytical chemistry. One such use involves the extraction of a metal complex in aqueous solution with tetraphenyiarsonium chloride in an organic solvent. Titanium(IV) thiocyanate [35787-79-2] (157) and copper(II) thiocyanate [15192-76-4] (158) in hydrochloric acid solution have been extracted using tetraphenyiarsonium chloride in chloroform solution in this manner, and the Ti(IV) and Cu(II) thiocyanates deterrnined spectrophotometricaHy. Cobalt, palladium, tungsten, niobium, and molybdenum have been deterrnined in a similar manner. In addition to their use for the deterrnination of metals, anions such as perchlorate and perrhenate have been deterrnined as arsonium salts. Tetraphenyiarsonium permanganate is the only known insoluble salt of this anion. 

Further organic storing materials Phenyl bromide [14], pyridine, 1 -picoline, 2,6-lutidine [15-17] Arsonium salts [18, 19] Phosphonium salts [20] Pyridinium bromides [21] Aromatic amines [22] Urotropin-bromine adduct [23] Pyridinium and sulfonium salts [24] Propionitril [25]... 

Horner has extended this reaction to the electrochemical reduction of optically active arsonium salts (68, X = As), which also undergo cleavage with retention of stereochemical configuration at arsenic M 65). This is a convenient synthetic route of optically active arsines of known configuration. 

This procedure is generally unsatisfactory for tetraphenyl-arsonium salts because of coprecipitation of tetraphenylarsonium triiodide. 

The Cu(I)-catalyzed cyclization for the formation of ethyl ( )-tetrahydro-4-methylene-2-phenyl-3-(phenylsulfonyl)furan-3-carboxylate 82 has been accomplished starting from propargyl alcohol and ethyl 2-phenylsulfonyl cinnamate. Upon treatment with Pd(0) and phenylvinyl zinc chloride as shown in the following scheme, the methylenetetrahydrofuran 82 can be converted to a 2,3,4-trisubstituted 2,5-dihydrofuran. In this manner, a number of substituents (aryl, vinyl and alkyl) can be introduced to C4 <00EJO1711>. Moderate yields of 2-(a-substituted N-tosyIaminomethyl)-2,5-dihydrofurans can be realized when N-tosylimines are treated with a 4-hydroxy-cis-butenyl arsonium salt or a sulfonium salt in the presence of KOH in acetonitrile. The mechanism is believed to involve a new ylide cyclization process <00T2967>. 

It was a result of demand from industry in the mid-1960s for an alternative to be found for the expensive traditional synthetic procedures that led to the evolution of phase-transfer catalysis in which hydrophilic anions could be transferred into an organic medium. Several phase-transfer catalysts are available quaternary ammonium, phosphonium and arsonium salts, crown ethers, cryptands and polyethylene glycols. Of these, the quaternary ammonium salts are the most versatile and, compared with the crown ethers, which have many applications, they have the advantage of being relatively cheap, stable and non-toxic [1, 2]. Additionally, comparisons of the efficiencies of the various catalysts have shown that the ammonium salts are superior to the crown ethers and polyethylene glycols and comparable with the cryptands [e.g. 3, 4], which have fewer proven applications and require higher... 

Urns-Epoxides. This unstable ylide (1), when generated as formulated above, reacts with an aliphatic aldehyde at —78° to give a fram-epoxide with almost complete stereoselectivity. The stereochemical selectivity is markedly dependent on the base and also on the counterion of the arsonium salt. Optimum selectivity for the trans-epoxide is obtained with conditions similar to those that induce cis-olefination in Wittig reactions.2 Stereoselection is not so high with aromatic aldehydes. The reagent also reacts with ketones to form trisubstituted epoxides. 

The trithiocarbonato complex anions [M(CS3)212 (M = Zn or Cd) have been isolated as their tetraphenyl-phosphonium and -arsonium salts.881 The trithiocarbonate is bidentate and forms four-membered chelate rings. 

The nature of the arsonium substituents also influences the course of the reaction. Gosney et al. (33) studied the reaction between arsonium salts of type 50 and benzaldehyde in THF using -butyllithium to generate the ylide. The results, summarized in Table IX, clearly show that electron-donating substituents at the arsenic atom promote the formation of al-kenes. At one extreme, the reaction of 0) gives a notable yield of stilbene almost to the exclusion of stilbene oxide, whereas at the other, the reaction of (a) yields predominantly stilbene oxide. Table IX shows that electron-donating substituents at arsenic increase the ratio of alkene to epoxide. 

Allen et at. found that high yields of the dissymmetric trans-2,3-diaryloxirans result from the reaction between semistabilized arsonium ylides derived from the benzyl salts of the enantiomers of racemic o-phen-ylenebismethyl phenylarsine and of methyl a-naphthyl-p-tolylarsine upon reaction with prochiral aromatic aldehydes. Optical yields of between 4.7 and 38% are obtained using optically active arsonium salts (2). 

Imidazole, phosphonium, arsonium salts and miscellaneous cationic entities... 

The existence of oxaarsetanes during an arsa-Wittig reaction has been proved by H and 170 NMR spectroscopy.40 75As NMR spectra were obtained from the corresponding arsonium salts and arsane oxides. It has been shown that the reaction mechanism of the arsa-Wittig reaction is identical with that of the phospha-Wittig reaction. 

Methylene trimethylarsorane (the term trimethylarsonium methylide is equally correct) had already been formulated in 1953 by Wittig and Torssell (104) who studied the reaction of tetramethylarsonium salts with organolithium compounds. Although this method cannot be used for the preparation of the salt-free material due to the strong complexation by the lithium cations, it is clear from reactions of the product mixture that the ylide is present in solution. The formation of arsonium salts upon addition of alkyl halides is a typical example ... 

As would be expected, the proton exchange is much slower than in tetra-methylphosphonium and -arsonium salts (12). 

Arsonium salts R4As+ can be cleaved with tlie ease of reduction in the following order ... 

Recently, the preparation of salts of the bis(tetrathiotungsto)nickelate (II) ion, Ni(WS4)J2, has been reported and the tetraphenylphosphonium and -arsonium salts isolated. The structure shown in Fig. 17 has been proposed for this anion196. ... 

Similar results were obtained in corresponding reactions with the substituted spiro-arsonium salt 144-1129). 

When arsonium salt 120-1 is treated with lithium aluminum hydride in tetra-hydrofurane at —70 °C copious evolution of hydrogen occurs and a red solution is obtained, whose color fades on warming to room temperature. Hydrolysis yields only 2-biphenylyl-2,2 -biphenylylenearsine (124). The same deep red solution and colorless hydrolysis product 124 are obtained when 2 -bromo-2-biphenylyl-2,2 -biphenylylenearsine (147) is first reacted with t-butyllithium in tetrahydrofurane... 

Figure 13. Symmetry of space groups of tetraphenylphosphonium and arsonium salts (4 7], crystallizing by forming parallel columns of cations and accommodating the anions in holes between the columns. The two frequent space groups in this family can be obtained by adding either a screw axis (group I-4) or a center of symmetry (group P4/n) to the point group of the cation.

Ammonium, phosphonium and arsonium salts may also possess a a LUMO and undergo PET bond cleavage reactions to provide products that depend largely upon the heteroatom nuclear hyperfine coupling constant [93]. 

Ammonium and phosphonium salts with relatively large nuclear hyperfine coupling constants for N and P provide only out-of-cage products, i.e., bibenzyl. While an arsonium salt, on the other hand, provides mainly in-cage radical coupling, i.e., rearrangement, due to a smaller nuclear hyperfine coupling constant... 

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