Hydrogen sulfide dissolves in water to give a solution c.a. 0.1 M at 1 atm. Its dissociation constants are
Owing to this small second dissociation constant, essentially only SH- ions are present in solutions of ionic sulfides, and S2- occurs only in very alkaline solutions(>8 M NaOH) as
The compounds H2S2 to H2S6 are generally known as sulfanes; they contain —S—S— to —SSSSSS— chains. They can be obtained by reactions such as
19-4 Halides and Oxohalides of Sulfur
Sulfur fluorides. Direct fluorination of S8 yields mainly SF6 and traces of S2F10 and SF4.
The tetrafluoride , SF4 (bp —300) is evolved as a gas when SCl2 is refluxed with NaF in acetonitrile at 78 to 80o
SF4 is extremely reactive, and instantly hydrolyzed by water to SO2 and HF It is a very selective fluorinating agent converting C=O and P=O groups smoothly into CF2 and PF2 and COOH and P(O)OH groups into CF3 and PF3 groups.
Sulfur hexafluoride is very resistant to chemical attack. Because of its inertness, high dielectric strength, and molecular weight, It is used as a gaseous insulator in high-voltage generators and other electrical equipment. The low reactivity is presumably due to a combination of factors including high S-F bond strength and the fact that sulfur is both coordinately saturated and sterically hindered It is due to kinetic factors and not to thermodynamic stability, since the reaction of SF6 with H2O to give SO3 and HF would be decidedly favorable (∆F =-460 kJ mol- 1).
Sulfur Chlorides. The chlorination of molten sulfur gives S2Cl2,an orange liquid of revolting smell. By using an excess of Cl2 and traces of FeCl3 or I2, as catalyst, at room temperature, an equilibrium mixture containing ca. 85% of SCl2 is obtained. The dichloride dissociates within a few hours: