Lead Tetrachloride, PbCl₄

Complex salts of the type M'₂PbCl₆ were prepared before the tetrachloride itself was isolated. First it was observed that lead dioxide can be dissolved in cold concentrated hydrochloric acid without the evolution of chlorine; also that a solution of sodium chloride saturated with chlorine can dissolve a considerable quantity of lead dichloride, and that hydrochloric acid itself maybe employed in place of sodium chloride. These facts indicate the probable existence in solution of complex ions containing quadrivalent lead; and the ammonium salt (NH₄)₂PbCl₆ was obtained in an impure state from such solution by Nikoljukin. The tetrachloride itself was first isolated by Friedrich, who prepared ammonium plumbichloride by passing chlorine into hydrochloric acid containing lead dichloride in suspension, and then adding ammonium chloride to the liquid. When the separated ammonium complex salt was added to well-cooled sulphuric acid there was a vigorous reaction, with evolution of hydrogen chloride gas, and the separation of a yellow liquid, which was lead tetrachloride.

Lead tetrachloride is a yellow, mobile, refractive liquid, having a density of 3.18 at 0° C.; it solidifies at -15° C. to a yellowish, crystalline mass. It is fairly stable under concentrated sulphuric acid, but fumes in moist air and decomposes into lead dichloride and chlorine; at 105° C. it decomposes explosively.

With a little water it forms an unstable hydrate, but with much water it is decomposed into lead dioxide and hydrochloric acid. With a little well-cooled, concentrated hydrochloric acid it yields yellow crystals which are probably hydrochloroplumbic acid, H₂PbCl₆. A yellow solution of this acid is obtained when concentrated hydrochloric acid is electrolysed with a lead anode.