Selenium oxyhalides

Contact with elemental selenium does not injure the skin. Selenium dioxide, however, upon contact with water, sweat, or tears, forms selenous acid, a severe skin irritant. Selenium oxyhalides are extremely vesicant and cause bums when in contact with human skin (91,92). Hydrogen selenide affects the mucous membranes of the upper respiratory tract and the eyes (93). 

Tellurium Halides. Tellurium forms the dihalides TeCl and TeBi, but not Tel2. However, it forms tetrahalides with all four halogens. Tellurium decafluoride [53214-07-6] and hexafluoride can also be prepared. No monohalide, Te2X2, is believed to exist. Tellurium does not form well-defined oxyhalides as do sulfur and selenium. The tellurium halides show varying tendencies to form complexes and addition compounds with nitrogen compounds such as ammonia, pyridine, simple and substituted thioureas and anilines, and ethylenediamine, as well as sulfur trioxide and the chlorides of other elements. 

Selenium forms several oxyhalides, e g.. SeOb2. SeOCL. and SeOBr2, the first two being liquids and the last a crystalline solid, nip 41.6°C. Selenium also forms tetraselenium tetranitride, Se4N4. 

Chemically, thionyl chloride can function as either a Lewis acid (sulfur is the acceptor atom) or a Lewis base (oxygen is the usual electron donor atom). It behaves in the same manner as other oxyhalides of sulfur and selenium with regard to hydrolysis, and the reaction can be shown as... 

Nitrogen bromide, sulfur, and many selenium halides and oxyhalides result in explosive reactions when mixed with white phosphoms (NFPA 1997). 

According to the different donor properties found in this group of solvents a distinction may be made between (a) oxyhalides with low donor numbers including carbonyl chloride, nitrosyl chloride, thionyl chloride, sulphuryl chloride, acetyl and benzoyl halides and (b) oxyhalides with medium donor numbers, namely phosphorus oxychloride, selenium oxychloride and phenyl phosphonic halides, the latter having donor properties approaching those of water or of the ethers. 

In the oxyhalides discussed so far the donor properties at the 0-atoms are too small to be considered in connection with the formation of anionic complexes and their capacities for solute-dissolution are poor. Solvents of higher donor number allow a wider range of solubilities, since more energy is provided by the interactions with acceptors, such as metal ions. Selenium oxychloride , phosphorus oxychloride and phenylphosphonic dichloride are much better donor-solvents than the oxyhalides discussed above. Coordination chemistry in their solutions may be explained in terms of competing reactions between the donor solvent molecules and the competitive ligands towards the acceptor molecules or acceptor ions ... 

Carbonyls. As has already been discussed, TMS-Br may be used as a source of bromine. In this case, TMS-Br, when mixed with a second reagent, may be used to introduce a bromine atom at either a benzylic position or alpha to an aldehyde or ketone. In one example of this type selenium(IV) oxyhalides (eq 34) are generated in situ from selenium dioxide and TMS-Br. 

The noncatenated halides include the relatively inert sulfur hexafluoride and the highly reactive tetrafluorides of sulfur, selenium, and tellurium. SFg( ) is useful in insulators and pressurized athletic equipment. SF4( ) is an important fluorinating agent. Two important oxyhalides are thionyl and sulfuryl chloride. The former is particularly useful in preparing anhydrous metal halides. 

The electrical conductivities of arsenic, antimony, bismuth, vanadium, selenium and tellurium oxides and of antimony, bismuth and vanadium oxyhalides have been determined in chlorosulfonic acid. Arsenic, antimony and bismuth oxides in chlorosulfonic acid yield the corresponding oxychlorosulfonates as shown (Equation 9). 

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