Anions hydrosulphide

NaOH.Aq = Na2 S.Aq + H20. Here it must be supposed that the hydrogen of the hydrosulphide is present as an anion, and that it reacts with the hydroxyl of the caustic soda, forming water, while the sodium sulphide remains in solution in an ionised form, and can be recovered on evaporation in crystals with 9H20. Similar compounds exist with potassium. 

These iodonium salts are usually obtained directly from arenes or organometallics and an inorganic compound of iodine (III) or (V). Once formed, iodonium salts can exchange their anion with almost any other anion exceptions are hydrosulphide, sulphide and cyanide. For large-scale preparations one of the early methods is always useful and can be applied to arenes of various kinds, including those bearing electron-withdrawing substituents. 

The steric effect is shown by the successive decrease in ft31 found for the reaction of hydrosulphide and acetate ions, which reflects the smaller solid angle of the surface of the anion available for reprotonation. Molecular models show that, for example, the proton can only approach the acetate ion over about half its surface, which corresponds to the halving of the recombination rate compared with that for fluoride. 

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