Oxides of arsenic, antimony and bismuth

Bismuth(III) oxide occurs naturally as bismite, and is formed when Bi combines with O2 on heating. In contrast to earlier members of group 15, molecular species are not observed for Bi203, and the structure is more like that of a typical metal oxide. 

Arsenic(V) oxide is most readily made by reaction 15.125 than by direct oxidation of the elements. The route makes use of the fact that AS2O5 is the acid anhydride of arsenic acid, H3ASO4. In the solid state, AS2O5 has a 3-dimensional structure consisting of As—O—As linked octahedral AsOs and tetrahedral As04-units. 

Antimony(V) oxide may be made by reacting Sb203 with O2 at high temperatures and pressures. It crystallizes with a 3-dimensional structure in which the Sb atoms are octahed-rally sited with respect to six O atoms. Bismuth(V) oxide is poorly characterized, and its formation requires the action of strong oxidants (e.g. alkaline hypochlorite) on Bi203. 

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Oxides of arsenic, antimony and bismuth are very important as components of mixed metal oxides for oxidation of propene and butenes. However, the acid or base properties of the individual oxides have rarely been studied. 

Give an account of the oxides and the chlorides of arsenic, antimony and bismuth, including an explanation of any major... 

The majority of amides (or imides) of arsenic, antimony and bismuth (collectively designated as of M ), have M in the - -3 oxidation state, although several examples of As and Sb amides or imides have been reported but only three papers have dealt with Bi compounds. The imides considered to be within the scope of this chapter are those having trivalent nitrogen as, for instance, in [As(p-NR)X]2. There are very few examples of As —N compounds, such as the bis(imido)arsenic(I) cation 1," and only one of a thermally stable... 

Compare the acid-basic, reducing, and oxidizing properties of arsenic, antimony, and bismuth hydroxides. 

Although no organoelement(V) hydrides of arsenic, antimony and bismuth are known, primary and secondary arsines (oxidation state III) may be obtained by the reduction of organoarsenic(V) compounds (equations 4 and 5) ... 

A considerable number of organometallic species of arsenic, antimony and bismuth have been detected in the natural environment in different manners. A number of these are nonmethyl compounds which have entered the environment after manufacture and use [e.g. butyltin and phenyltin compounds for antifouling paints on boats, and arsanilic acid (Figure 2, 5) and phenylarsonic acids (Figure 2, 6-8) for animal husbandry]. Only a few methyl compounds are now manufactured and used (e.g. methyltin compounds for oxide film precursors on glass and methylarsenic compounds for desiccants or defoliants). 

The trioxides of arsenic, antimony and bismuth are of structural interest, showing a transition from the molecular lattice characteristic of covalent compounds to an ionic lattice. Arsenic oxide contains As Og molecules, similar in structure to P40g and based on the As tetrahedron. The cubic form of Sb Og is similar, but above 570° this is converted to the macro-molecular valentinite form containing infinite chains (Fig. 179). 

The halides of arsenic, antimony and bismuth illustrate the following trends down the Group (a) increasing metallic character of the elements (b) the inert pair effect—that is, the tendency towards an increased stability of the Group number minus two oxidation number (+3) (c) a tendency to higher coordination numbers. 

The washed slime is dried and melted to produce slag and metal. The slag is usually purified by selective reduction and smelted to produce antimonial lead. The metal is treated ia the molten state by selective oxidation for the removal of arsenic, antimony, and some of the lead. It is then transferred to a cupel furnace, where the oxidation is continued until only the silver—gold alloy (dorn) remains. The bismuth-rich cupel slags are cmshed, mixed with a small amount of sulfur, and reduced with carbon to a copper matte and impure bismuth metal the latter is transferred to the bismuth refining plant. 

The optimal reaction conditions for the generation of the hydrides can be quite different for the various elements. The type of acid and its concentration in the sample solution often have a marked effect on sensitivity. Additional complications arise because many of the hydrideforming elements exist in two oxidation states which are not equally amenable to borohydride reduction. For example, potassium iodide is often used to pre-reduce AsV and SbV to the 3+ oxidation state for maximum sensitivity, but this can also cause reduction of Se IV to elemental selenium from which no hydride is formed. For this and other reasons Thompson et al. [132] found it necessary to develop a separate procedure for the determination of selenium in soils and sediments although arsenic, antimony and bismuth could be determined simultaneously [133]. A method for simultaneous determination of As III, Sb III and Se IV has been reported in which the problem of reduction of Se IV to Se O by potassium iodide was circumvented by adding the potassium iodide after the addition of sodium borohydride [134], Goulden et al. [123] have reported the simultaneous determination of arsenic, antimony, selenium, tin and bismuth, but it appears that in this case the generation of arsine and stibene occurs from the 5+ oxidation state. 

The Ziervogel process can be worked with argentiferous copper mattes free from lead, arsenic, antimony, and bismuth. By roasting the matte in an oxidizing atmosphere, the iron is converted into sulphate. About 700° C. this substance is decomposed, the copper being converted into sulphate. At 840° to 850° C. the copper salt is converted into cupric oxide,8 and silver sulphate simultaneously formed. At this point the roasting is stopped, the silver sulphate is extracted with hot water, and the silver precipitated by means of metallic copper. These mattes are now usually worked for copper, and the silver separated electrolytically. 

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