Thallium(I) chloride

Thallium(I) chloride is the chemical compound with the formula TlCl. This colourless solid is an intermediate in the isolation of thallium from its ores. Typically, a sulfuric acid solution of thallium(I) is treated with HCl to precipitate insoluble TlCl. This solid crystallizes in the caesium chloride motif.

The low solubility of TlCl is exploited in chemical synthesis: treatment of metal chloride complexes with TlPF6, gives the corresponding metal PF6- derivative. The resulting TlCl precipitate is separated by filtration of the reaction mixture. The overall methodology is similar to the use of AgPF6, except that Tl+ is non-oxidizing.

Safety
Thallium compounds are highly toxic, comparable to the effects of lead and mercury. The usual antidote is Prussian Blue.