Arsonium compounds, quaternary

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 ... 

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... 

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. 

Univation Technologies - Maricet Infonnation, http //www.univation.com Friedrich, M.E.P., Marvel, C.S., The reaction between alkali metal alkyls and quaternary arsonium compounds, J. Am. Chem. Soc. 1930,52 376-384. 

Preparative oxidation of EtjAs and PhjAs or PhjSb in the presence of aromatic or heteroaromatic compounds leads to formation of quaternary arsonium or stibonium salts . The oxidations were carried out in nominally dry MeCN in the presence of an excess of the aromatic compound which, in the case of the arsines, were naphthalene, thiophene, pyridine and furan , and in the case of Ph3Sb were thiophene and toluene . ... 

Quaternary Arsonium and Stibonium Compounds. More recently, experimental work in this laboratory has revealed that quaternairy arsonium compounds (18) are extremely effective as latent accelerators for epoxy-anhydride resius. Surprisingly, it has also been found that quaternary stibonium compounds are very much less effective as accelerators than quaternary arsonium, phosphonium or ammonium compounds. In fact, the order of gelation reactivity of these compounds with epoxy-anhydride resins would appear to be as follows ... 

Historically, Bernard (1851, 1856) demonstrated that curare (from arrow poisons used by South American Indians) blocked nerve impulse transmission at the junction of the nerve and skeletal muscle. It was later shown that many alkaloids, such as morphine, atropine, nicotine, and even strychnine and brucine (the latter two normally causing convulsions), will become muscle relaxants when quaternized by methylation. It soon became apparent that a great many quaternary ammonium compounds qualitatively share the ability to produce neuromuscular blockade. In fact, the onium ion need not be a nitrogen atom. Thus sulfonium (/ 3S+), phosphonium (/ 3P+), and arsonium (/ 3As+) ions have been shown to be curariform , although of lesser activity than ammonium ions. 

Crum Brown and Fraser (6) in 1868 attributed curariform activity to the onium ion. Even at that early date, they suggested therapeutic possibilities of synthetic quaternary salts which could be prepared of constant purity and effectiveness. Boehm (7, 8) first showed that the active alkaloids of curare preparations are quaternary ammonium compounds. Since these discoveries, a great many quaternary compounds have been investigated, and even the simplest quaternary ammonium salts, as well as sul-fonium, phosphonium, arsonium, and stibonium salts, exhibit curare activity (9). Quaternary ammonium compounds widely varied in character have been found to exhibit curare activity. Hunt and Renshaw and collaborators (10, 11) have published a series of papers on onium compounds and their effects on the autonomic nervous system. In addition to curare action, they were shown to exhibit muscarinic and nicotinic actions in varying degrees. 

Often, the cationic component of the ion pair is formed by the protonation of a compound of appreciable basicity, most typically a nitrogen-containing base. Alternatively, the cation may be of the quaternary ammonium, phosphonium or arsonium type. 

The quaternary iodides are crystalline compounds, form platini-chlorides, and with chlorine yield iododicMorides of the type R4ASI.CI2. Some aliphatic-aromatic arsonium iodides combine with metallic salts such as mercwic halides, auric chloride, and cadmiumiodide, whilst iodoform also forms addition compounds with some derivatives. Treatment of the iodides with a boiling suspension of silver chloride replaces the iodine by chlorine, giving R4ASCI. The latter also results when hydrochloric add is added to hydroxides of the type R4AS.OH. The hydroxides are derived from the iodides by boiling the latter with a suspension of silver oxide in water or alcohol. It is not always possible to isolate a crystalline product from this reaction, and the syrups often isolated soon absorb carbon dioxide from the air. 

The stibonium compounds are the most difficult to prepare and are the least common. These quaternary salts, excepting the hydroxides, which are obtained as sirupy masses, are white crystalline compounds. The tetra-phenyl-phosphonium and -arsonium ions are useful for precipitating large anions such as ReO, CIO and complex anions of metals. Tetraphenyl-stibonium hydroxide has been shown55 to contain tbp molecules, with the OH group in an axial position. 

Many anion-selective ISEs are based on classic exchangers, complexes of 2-phenanthroline, and quaternary ammonium, phosphonium and arsonium salts. Not all of these possess the required selectivity, e.g. the electrodes based on dialkyltin(IV) compounds for HPO4" and H2PO4. ... 

Other Compounds. Horner and co-workers [129-131] have described the production of optically active phosphines and arsines in the cathodic cleavage of quaternary phosphonium and arsonium salts. This reaction, like its reverse quaternization reaction, takes place with retention of configuration. Shapoval, Skobets, and Markova [132, 133] have described the production of a. stereoregular isocyanate polymer during reduction at a nickel cathode in dimethyl-formamide. The formation of a stereoregular product evidently demonstrates the orienting effect of the electrode on the molecules of the monomer in the polymerization process. 

Quaternary ammonium, phosphonium, and arsonium salts serve cis sources of large lipophilic cations which may be employed in precipitation reactions. In addition, bis(triphenylphosphine)iminium salts, [(Ph3P>2N]X, have been employed for the precipitation of complex anions from aqueous solution.19 One advantage of the [(Ph3P)2N]+ cation is that it often combines with anionic complexes to form crystalline compounds suitable for analysis by X-ray diffraction. 

Such compounds find extensive use as metal ion extractants. Solutions of compounds such as Tri-butylphosphate (TBT) in cyclohexane or CCI4 enable salts such as U02(N03)2 and Th(N03)4 to be extracted because the TBT solvates the metal ion via its strongly basic oxygen, forming, e.g. U02(N03)2.2TBT. Phosphonium ions such as Tetraphenylphosphonium (1+) [PPh ] are used as ion-pairing cations for the extraction of anions such as CIO , ReO and SbCl . Quaternary ammonium salts and arsonium salts behave similarly. Some phosphoric acids have been proposed as metal ion precipitants. 

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