The nature of the solutions of some inorganic halides in disulphuric acid
Tetrachlorides of selenium and tellurium form the pyramidal cation MCl3+ when dissolved in disulphuric acid. Tellurium tetrabromide disproportionates and phosphorus pentachloride forms PCl4+ ions, whereas phosphorus pentabromide forms phosphoryl bromide and iodine trichloride forms ICl2+. However, mono- and di-chlorides of sulphur and selenium disproportionate to give elements and tetrachloride. Trihalides of phosphorus are oxidised to phosphoryl halides which become protonated but trihalides of arsenic and antimony are solvolysed to form hydrogen sulphate.