Arsonium compounds

Other methods for preparing tertiary arsiaes have been employed, but they have limited usefiilness. These methods include the cleavage of quaternary arsonium compounds (68), the cyclodehydrohalogenation of haloarsines (69), the reaction of dia2onium salts with arsenic trichloride in the presence of a metal such as 2inc or iron (70), and the disproportionation of halo- or dihaloarsines (71). 

Of the quaternary arsonium compounds, methyltriaryl derivatives are important as precursors of arsonium ylides, e.g. 

Such ylides are unstable and react with carbonyl compounds to give both the Wittig product (p. 545) as well as AsPh3 and an epoxide. However, this very reactivity is sometimes an advantage since As ylides often react with carbonyl compounds that are unresponsive to P ylides. Substituted quaternary arsonium compounds are also a useful source of heterocyclic organoarsanes, e.g. thermolysis of 4-(1,7-dibromoheptyl)trimethylarsonium bromide to l-arsabicyclo[3.3.0]octane ... 

Reaction of adsorbed inhibitors In some cases, the adsorbed corrosion inhibitor may react, usually by electro-chemical reduction, to form a product which may also be inhibitive. Inhibition due to the added substance has been termed primary inhibition and that due to the reaction product secondary inhibition " . In such cases, the inhibitive efficiency may increase or decrease with time according to whether the secondary inhibition is more or less effective than the primary inhibition. Some examples of inhibitors which react to give secondary inhibition are the following. Sulphoxides can be reduced to sulphides, which are more efficient inhibitorsQuaternary phosphonium and arsonium compounds can be reduced to the corresponding phosphine or arsine compounds, with little change in inhibitive efficiency . Acetylene compounds can undergo reduction followed by polymerisation to form a multimolecular protective film . Thioureas can be reduced to produce HS ions, which may act as stimulators of... 

The toxicity of arsenicals conforms to the following order, from greatest to least toxicity arsines > inorganic arsenites > organic trivalent compounds (arsenoxides) > inorganic arsenates > organic pentavalent compounds > arsonium compounds > elemental arsenic. 

Uptake experiments have also been conducted with other forms of arsenic. M. edulis exposed separately to a number of organoarsenic compounds in seawater were found to be selective in their arsenic uptake (85). They did not accumulate arsenic when it was present as MMA, DMA, TMAO, or DMAE. When exposed to the three quaternary arsonium compounds (arsenobetaine, arsenocholine, and TeMA), however, the mussels accumulated substantial quantities of arsenic, with arsenobetaine being the most efficiently accumulated (Table VII). The chemical form of the accumulated arsenic was also examined. Mussels... 

Tetramethylarsonium iodide, (CH3)4AsI.— The double compound of the iodide with arsenic tri-iodide is formed when powdered arsenic and methyl iodide are heated together at 160° to 200° C. If this reaction is carried out at ordinary temperatures or on the w ater-bath, the principal products are methyldi-iodoarsine and tetramethylarsonium iodide arsenic tri-iodide and a small quantity of cacodyl iodide arc also produced. When methyl iodide is ded to sodium arsenide in an atmosphere of carbon dioxide, the mixture on distillation gives cacodyl and tetramethylarsonium iodide, Cacodyl and methyl iodide react with evolution of heat, yielding the arsonium compound and cacodyl iodide according to the equation ... 

Alloys of arsenic with zinc and cadmium are also capable of giving the arsonium compound when heated at 160° to 180° C. with methyl iodide. It may be produced from its components, trimcthylarsinc and methyl iodide, or by heating methylarsine with an excess of methyl iodide for eight hours in a carbon dioxide atmosphere at 110° C. Arsenomethane, when heated at 100° C. with methyl iodide, ves tetramethylarsonium iodide ajvd methylarsine di-iodide see cyclo-pentamethylpenta-arsine, p. 33. 

Triphenylmethylarsonium iodide, Cj]il5)3As(CH j)I.— Triphenyl-arsine is heated for a long time with an excess of methyl iodide on die water-bath, when addition takes place. The arsonium compound crystallises in yellow plates, M.pt, 176° C., readily soluble in alcohol, less soluble in hot water, insoluble in ether. When treated with chlorine... 

Heating with alkyl iodides at 100° C. gives arsonium compounds, e.g. triphenylarsine di-iodide is converted by methyl iodide into triphenyl-methylarsonium tri-iodide. When the dihalides contain aliphatic and aromatic groupings, decomposition may occur as follows on heating ... 

In 1902, the unsuccessful fractional crystallization of (— )-aspartate and (-I- )-tartrate salts of the ethylmethyl(a-naphthyl)phenylarsonium ion was reported and, in 1912, the failure to resolve allylbenzylmethylphenylarsonium iodide by seeding solutions of the racemate with crystals of the corresponding optically active ammonium salt was reported . The first evidence of optical activity in arsonium compounds was published... 

Whereas the lithium aluminium hydride reduction of an optically active benzylphos-phonium salt in tetrahydrofuran leads to a racemic or highly racemized tertiary phosphine and toluene, the reduction of (—)-benzyl(n-butyl)methylphenylarsonium bromide (68) or (S)-(-(-)-benzylmethylphenyl(n-propyl)arsonium bromide, (S)-(-I-)-64, with this reagent affords (—)-n-butyImethylphenylarsine, ( —)-12, or (S)-(-l-)-methyl-phenyl(n-propyl)arsine, (S)-(-)-)-65, of similar optical purity to the products obtained by cathodic reduction of the respective arsonium compounds (Table 4) . Moreover,... 

The mechanism of reduction at mercury apparently changes dramatically when As is replaced by Sb. This is seen in the shift from one two-electron process to two one-electron processes, where the potential of the first reduction is shifted at least 0.5 V in the positive direction relative to the single reduction process for the analogous arsonium salt. The potential of the second reduction process remains close to that for the arsonium compound cf Table 1. The main difference between the arsonium and the stibonium salts is their tendency to adsorb on the mercury electrode. From electrocapillary measurements, in which the drop time (t) of the mercury electrode is measured as a function of potential ( ) in the absence and in the presence of the stibonium ions, it appears that the t/ relationship is severely effected by the presence of the stibonium ions the effect is the greater, the larger... 

Quaternary arsonium compounds are in general reduced at potentials 0.3 V less negative than those of the corresponding phosphonium salts [207]. The ease of cleavage of the different groups is mostly similar to that in the phosphonium compounds, but some differences are found. 

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