Stibonium salts

Tetraalkyl and tetraaryl compounds, R SbX, are well-known and are often referred to as stibonium salts. There is evidence, however, that most of the tetraaryl compounds contain pentacovalent antimony. The perchlorate [(C3H3)4Sb](ClO, however, is ionic (186). The tetraalkyl haUdes are readily prepared by quaternization of the corresponding tertiary stibiaes ... 

Reactions of trimethylstibine sulfide with alkylindium halides are quite different from those with organotin compounds described above (30). As shown in the following equation, reaction of R InX with (CH3)3SbS gives stibonium salts ... 

Electrochemical studies of quaternary arsonium and stibonium salts have mostly been carried out in aqueous or bufiered aqueous solution using polarographic methods, i.e. reduction at a dropping mercury electrode . A few studies in polar aprotic solvents have been carried out. 

All of the quarternary arsonium salts are reduced in a chemically irreversible two-electron process at mercury electrodes in aqueous solution and thereby resemble the analogous phosphonium salts " . In contrast, the stibonium salts, with the exception of the tetramethylstibonium ion, are reduced in two distinct one-electron steps at mercury electrodes . The arsonium salts are in aqueous solution reduced at potentials which are shifted approximately 300 mV in the positive direction compared with those of the corresponding phosphonium salts , whereas the first electron transfer to the stibonium salts takes place at a further 0.5-1.0 V in the positive direction cf Table 1. 

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... 

For the reduction of stibonium salts at mercury electrodes two slightly differing mechanisms have been proposed ... 

The second mechanism was proposed based on a study of the series of stibonium salts of the composition Ph Me4 Sb mentioned above . 

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 . ... 

The yields of arsonium salts were reported to be 77-80%, based on the stoichiometry 2RjAs +ArH R3AsAr +R3AsH + 2e , R = Ph, Et, whereas the yields of the stibonium salts were lower (46-51%) based on the stoichiometry Ph3Sb + ArH + PO4 " - PhaSbAr +HP04 " +2e. ... 

Cyclopropane derivatives have been prepared similarly from dibromo compounds, Br2CXCOOR, where X is another electron-withdrawing group, and conjugated alkenes, R CH=CHY (Y = electron-withdrawing group), in the presence of tributylstibine and again formation of a stibonium salt as an intermediate is postulated (equation 51) . ... 

Use Stibonium salts, cocatalyst in converting trienes to aromatics and hydro aromatics, reacts with nitric-sulfuric acid to give trinitro derivatives, polymerization inhibitor, lubricating-oil additive. 

Stibonium salts and ylides (a) A. Baba, H. Matsuda, Yuki Gosei Kagaku Kyokaishi 1989, 47, 102. (b) Y.-Z. Huang, Acc. 

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. 

Methylstibolane (89) is prepared in a more direct manner (Scheme 33). Here, the intermediate distibine cyclizes on thermolysis to give the stibolane in very good yield. Interestingly, condensation of the dimethylstibylsodium with 1,4-dibromobutane gives the stibolane directly in 63% yield without any need for thermolysis. The pathway probably involves quaternization of the initially formed 1 1 adduct to give a cyclic stibonium salt that is subsequently demethylated by another equivalent of dimethylstibylsodium <76JOM(ilO)i83>. 

Hazardous Decomp. Prods. Heated to decomp., emits toxic fumes of Sb Uses Stibonium salts cocatalyst in converting trienes to aromatics and hydroaromatics reacts with nitric-sulfuric acid to give trinitro derivatives polymerization inhibitor lubricating oil additive Manuf./Distrib. Aldrich http //www.sigma-aidrich.com] Fluka http //www.sigma-aidrich.com] Sigma... 

The ionic liquids discussed in this section are collected in Table 11.20. The crystal structures of protic ionic liquids derived from carboxylic acids have already been brought together in Table 11.6 and discussed in Section 11.4.1. Of the 67 salts listed in Table 11.20. only 11 are not formally the result of the reaction of a base and a carboxylic acid. The only crystal structure for a stibonium salt with a mpt. < 100°C is that of [SbMe4][(PhC02)2H], reported to melt at 80-82°C [327]. The structure of l-(hydroxycarbonylmethyl)-l-methylmorpholinium salicylate (mpt. 104-105°C) is noted [491]. 

Arsonium and stibonium salts have properties consistent with their ionic constitution. The hydroxides are strong alkalis like quaternary ammonium hydroxides. The tetrahedral structures of their cations have been confirmed in some instances by X-ray analysis. Of the few bismuthonium salts known, the tetraphenylborate Ph4Bi BPh4 (from Ph5Bi+Ph3B) is among the more stable. The halides readily lose halobenzene, e.g. 

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