Hydrogen halides selenium oxide

Hydrides of variable composition are not only formed with pure metals as solvents. A large number of the binary metal hydrides are non-stoichiometric compounds. Non-stoichiometric compounds are in general common for d,f and some p block metals in combination with soft anions such as sulfur, selenium and hydrogen, and also for somewhat harder anions like oxygen. Hard anions such as the halides, sulfates and nitrides form few non-stoichiometric compounds. Two factors are important the crystal structures must allow changes in composition, and the transition metal must have accessible oxidation states. These factors are partly related. FeO,... 

The evidence supplied by the method of formation and the occurrence of isomerism as to analogous structures for the thiosulphates and selenosulphates, is amplified by the chemical behaviour of the potassium alkyl selenosulphates, obtained by treatment of potassium selenosulphates with alkyl halides.1 These, on electrolytic reduction and also on oxidation with hydrogen peroxide, yield the corresponding di-selenides (compare the thiosulphates, p. 203). The structure of the selenosulphates therefore involves a selenium atom directly attached to... 

Selenoxide elimination occurs under relatively mild conditions in comparison to the elimination reactions described above. Selenoxides undergo spontaneous yn-elimi-nation at room temperature or below and thus have been used for the preparation of a variety of unsaturated compounds. The selenide precursors can be obtained by displacement of halides or sulfonate esters with PhSeNa. Oxidation of the selenides with hydrogen peroxide or tert-huiyX hydroperoxide, sodium periodate, or peroxycar-boxylic acids furnishes the corresponding selenoxides. Their eliminations usually favor formation of the less substituted olefin in the absence of heteroatom substituents or delocalizing groups. Since selenium compounds are toxic, they should be handled with care. 

---