Ammonium Plumbichloride, (NH₄)₂PbCl₆

Ammonium Plumbichloride, (NH₄)₂PbCl₆, has been prepared in several ways. It is obtained when cold hydrochloric acid acts on lead dioxide, and ammonium chloride is added to the resulting solution; by treating lead dichloride with fuming hydrochloric acid and chlorine under pressure, and then adding ammonium chloride; by adding ammonium chloride to the solution of hydrochloroplumbic acid obtained by electrolysis, or to a solution of lead tetra-acetate in hydrochloric acid; and by the interaction of lead dichloride and ammonium persulphate in hydrochloric acid solution, thus:

(NH₄)₂S₂O₈ + PbCl₂ + 4HCl = (NH₄)₂PbCl₆ + 2H₂SO₄.

Ammonium plumbichloride crystallises in citron-yellow octahedra, isomorphous with (NH₄)₂SnCl₆ and (NH₄)₂PtCl₆. It is stable in the air, and may be heated to 115° C. without perceptible decomposition; it decomposes, however, at 225° C. This salt has been employed for chlorinating aromatic hydrocarbons and their derivatives.

Potassium, rubidium, and caesium plumbichlorides resemble the ammonium salt; K₂PbCl₆ decomposes at 190° C., Rb₂PbCl₆ and Cs₂PbCl₆ at about 280° C. The quinoline and pyridine salts, (C₉H₇NH)₂PbCl₆ and (C₅H₅NH)₂PbCl₆, respectively, have been prepared.

A number of plumbichlorides have been prepared by Gutbier and Wissmuller by mixing hydrochloroplumbic acid with solutions of metallic or substituted ammonium chlorides. These salts are anhydrous, being X₂PbCl₆ or (R.NH₃)₂PbCl₆, and are obtained in minute yellow or red crystals. Compounds of the alkali metals, and derivatives of the pyridine and quinoline series, are stable; aliphatic ammonium compounds tend to decompose in the air, evolving chlorine.

Lead tetrachloride forms compounds with ammonia and organic bases.