Sulfur elemental selenium

It is apparent from these equations that significant quantities of sulfur dioxide are generated. For selenium, the reaction shown for oxidation of elemental selenium reverses itself at the lower temperatures employed for water scmbbing, thus regenerating sulfuric acid. The tellurium dioxide remains in the sulfated slimes. 

Selenium and precious metals can be removed selectively from the chlorination Hquor by reduction with sulfur dioxide. However, conditions of acidity, temperature, and a rate of reduction must be carefliUy controlled to avoid the formation of selenium monochloride, which reacts with elemental selenium already generated to form a tar-like substance. This tar gradually hardens to form an intractable mass which must be chipped from the reactor. Under proper conditions of precipitation, a selenium/precious metals product substantially free of other impurities can be obtained. Selenium can be recovered in a pure state by vacuum distillation, leaving behind a precious metals residue. 

A number of substances, such as the most commonly used sulfur dioxide, can reduce selenous acid solution to an elemental selenium precipitate. This precipitation separates the selenium from most elements and serves as a basis for gravimetry. In a solution containing both selenous and teUurous acids, the selenium may be quantitatively separated from the latter by performing the reduction in a solution which is 8 to 9.5 W with respect to hydrochloric acid. When selenic acid may also be present, the addition of hydroxylamine hydrochloride is recommended along with the sulfur dioxide. A simple method for the separation and deterrnination of selenium(IV) and molybdenum(VI) in mixtures, based on selective precipitation with potassium thiocarbonate, has been developed (69). 

The fumes from the roaster are passed through a train of water-spray scmbbers and an electrostatic precipitator. In the scmbber, selenium dioxide [7446-08-4] reacts with sulfur dioxide (eq. 37) to produce elemental selenium, which is purified to provide a commercial product. 

Vol 12 PerfluorohaloorganiL Compounds of Main Group Elements Part 2 Compounds of Sulfur (Cuniinuanon) Selenium and Tellurium... 

Sulfur diamides (diaminosulfanes) are obtained by the action of sulfur chlorides with an aliphatic secondary amine (Eq. 10.10). ° The monoselanes Se(NR2)2 (R = Me, Et) have also been prepared. Polyselanes Scx(NR2)2 (x = 2 - 4, NR2 = morpholinyl x = 4, NR2 = piperidinyl) are formed in the reaction of elemental selenium with the boiling amine in the presence of Pb304. ... 

Very little is known about chalcogenide halides of Group IVB elements. Although the existence of sulfide chlorides (45, 274, 329, 365) and of a selenide chloride (329) of titanium was claimed in early publications, their true composition, and even their existence, remains doubtful. They have usually been obtained by the reaction of titanium chlorides with sulfur and selenium, respectively, or with hydrogen sulfide. The synthesis of a pure compound, TiSClj, was published in 1959 (113). It is an intermediate of the reaction of TiCU with HjS. 

The elements sulfur and selenium, which combine with the hydrogen evolved to give, respectively, H2S and H2Se. Little is known about this mechanism either. ... 

Elemental sulfur dissolves in boiling aqueous sodium sulfite solutions with the formation of sodium thiosulfate (Na2S203). The reaction proceeds quantitatively if sulfur and excess sodium sulfite are boiled for some time in weakly alkaline solutions. In the cold, however, practically no reaction occurs. Alternatively, thiosulfate can be produced quantitatively in solution phase by using organic solvents to first dissolve sulfur and then accomplish the reaction with aqueous sulfite. In a parallel reaction, elemental selenium dissolves in alkaline sulfite solution to produce selenosulfate, SeSO ... 

A method to circumvent the problem of chalcogen excess in the solid is to employ low oxidation state precursors in solution, so that the above collateral reactions will not be in favor thermodynamically. Complexation strategies have been used for this purpose [1, 2]. The most established procedure utilizes thiosulfate or selenosulfate ions in aqueous alkaline solutions, as sulfur and selenium precursors, respectively (there is no analogue telluro-complex). The mechanism of deposition in such solutions has been demonstrated primarily from the viewpoint of chemical rather than electrochemical processes (see Sect. 3.3.1). Facts about the (electro)chemistry of thiosulfate will be addressed in following sections for sulfide compounds (mainly CdS). Well documented is the specific redox and solution chemistry involved in the formulation of selenosulfate plating baths and related deposition results [11, 12]. It is convenient to consider some elements of this chemistry in the present section. 

Although the sulfur-gold bond has been most investigated, the Group 16 elements selenium and tellurium have also attracted attention and are discussed in detail here (polonium has not received attention due to its radioactivity). 

Compounds having divalent sulfur and selenium atoms bound to more electronegative elements react with alkenes to give addition products. The mechanism is similar to that in halogenation and involves of bridged cationic intermediates. 

The first examples of mononuclear disulfur and diselenium complexes of platinum have been described.330 Reduction of the sterically hindered complex trans- PtC 2( P M e2A r)2] (Ar = 2,4, 6-tris[bis(trimethylsilyl)methyl]phenyl, 2,6-bis[bis(trimethylsilyl)-methyl]-4-[tris(trimethylsilyl) methyl]-phenyl) with lithium naphthalide in THF solution affords the platinum(0) species [Pt(PMe2Ar)2]. Oxidative addition of elemental sulfur or selenium yields the dichalcogenatoplatinum(II) complexes of the type [PtE2(PMe2Ar)2] (E = S, Se) containing a unique PtE2 ring system. The complexes are stable to air in the solid state, but slowly decompose in solution after several days at room temperature. 

As in the case of phosphorus trihalides, the phosphorus atom in trialkyl phosphites will undergo addition reactions in which oxygen, sulfur, or selenium is added. The latter two react as elements, but a suitable source of oxygen is hydrogen peroxide. 

Use of diamines in the preparation of chalcogenofcamidophosphonic acids gives heterocyclic products for example, reaction of l,l -diaminoferrocene with RPC12 (R = tBu, Ph) and elemental sulfur or selenium gives the thio/ seleno-feamidophosphonic acid 33 (Equation 48).61... 

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