Arsonium ions

The salts (- -)-[AsAmylBnEtPh]Br ( —)-[AsBn(n-Bu)EtPh]Cl and (-h)-[AsBnEt(n-Pentyl)Ph]Br were reported to completely racemize over cu 1 h at 20 °C in chloroform. A dissociation-equilibrium between the salt and the tertiary arsine and alkyl halide was put forward as the mechanism of the racemization, where the alkyl halide was considered to attack the tertiary arsine from the side of the lone-pair (preferred) or from the side of the plane of the three substituents It was stated that the racemization would be facilitated by raising the temperature due to inversion of the tertiary arsine in line with earlier calculations . This notion of facile dissociation-equilibrium in arsonium salts, first suggested in 1921 and carried through until 1964 was finally put to rest in 1965, however, when it was shown that the salts ( —)-[AsBn(n-Bu)EtPh]X (where X = Cl or Br) in chloroform or ethyl acetate were completely stable for days. Moreover, 

The data collected on the racemization of arsonium ions are consistent with a mechanism involving Berry pseudorotation of a transient five-coordinate halogeno-arsenic(V) intermediate (equation 22). The more nucleophilic the halide the faster the racemization. 

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Curve 1 in Fig. 5 gives an example of the oscillation of membrane current observed with the liquid membrane system as in Eq. (3) by applying a constant AFwi-w2 of —0.48 V and measuring the time course of the current through the LM, /wi-w2- The cell used was the same as that used for the measurement of the potential oscillation, except a tetraphenyl-arsonium ion selective electrode [26,27], TPhAsE, was employed as a reference electrode in LM of NB ... 

Through the presence of aromatic or pseudoaromatic groups in the molecule (tetraphenylborate and related derivatives, the tetraphenyl-arsonium ion, cationic triphenylmethane dyes, complexes of o-phenanthroline with divalent nickel or ion, where the hydrophobicity is increased by further substitution by a hydrophobic group on the pseudoaromatic nucleus). 

As might be expected, it is violently explosive, as is the precursor triazidoarsine any other salts of this hitherto unknown arsonium ion may also prove so. 

Aqueous extracts of soil samples Arsenic Arsenite, arsenate, monomethyl arsonate dimethylarsenite, arsenbetaine, arsenocholine, tetramethyl arsonium ion Ion exchange (both cationic and anionic) Approximately 1 jug cnT1 Hansen et al. (1992)... 

Blais et al. [268] determined arsenobetaine, arsenocholine and tetramethyl arsonium ion in non saline waters in amounts, respectively, down to 13.3, 14.5 and 7.8pg by a procedure based on liquid chromatography-thermochemical hydride generation atomic absorption spectrometiy. 

DMA, AsB, arsenosugar B, and tetramethyl arsonium ion in anion-exchange chromatography (recommended for analyses of water and marine plants containing multiple arsenosugars)... 

Strong-acid protonation of t-alkyl- or arylarsines yields arsonium ions in solution ... 

The opening up of the various synthetic routes between resolved arsonium ions and arsines, particularly for simple non-cyclic compounds, and the laying down of firm stereochemical foundations for interconversions between them, marked the beginning of an era in which chiral tertiary arsines could be designed, synthesized and resolved for a variety of applications in organic synthesis and coordination chemistry. 

An optically active arsonium ion containing an allyl or a benzyl group is quantitatively reduced at a mercury electrode in water or ethanol with retention of configuration at arsenic (and liberation of toluene or propene) to give an optically active tertiary arsine, free of functional groups on the organic substituents (equation 3). 

In aqueous solution, determinations of half-wave potentials have indicated the following ordering of difficulty of removal of organic substituents from arsonium ions ... 

The absolute configurations of a number of arsonium ions and arsines have been correlated with one another on the basis of the stereospecificity of cathodic cleavage of the benzyl group from an arsonium ion and the quaternization of an arsine by benzyl and other alkyl halides, both of which occur with retention of configuration. Scheme 1 gives the connection between the stereochemistries of various optically active arsonium ions and arsines related to (S)-(+)-62. 

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