Pyridinium Hexachloroplumbate IV

Submitted by GEORGE B. KAUFFMAN, LEO KIM,f and DEAN F. MARINO t Checked by WILLIAM B. WITMER and JOHN H. TURNEY  

Only a few simple compounds of lead(lV) are known, for example, the acetate, fluoride, and chloride. Lead(IV) chloride, an unstable substance, may be prepared by treatment of one of the hexachloroplumbates mentioned above with cold concentrated sulfuric acid.1,11,14 

Twenty grams (0.0719 mol) of very finely powdered lead(ll) chloride is suspended in 400 mL of concentrated hydrochloric acid contained in an all-glass 500-mL gas washing bottle whose inlet tube terminates in a high-porosity fritted-glass cylinder. The bottle and contents are maintained at 10-15° by means of an ice bath, the suspension is magnetically stirred at a high rate, and a stream (2-3 bubbles/sec) of chlorine (Hood ) is introduced until all the lead(II) chloride has dissolved (2-3 hr). 

After excess chlorine has been removed by bubbling air through the pale lemon-yellow solution, it is cooled to 0°, and 10 mL (0.124 mole) of pyridine is added dropwise with rapid stirring. The resulting bright lemon-yellow precipitate is collected on a fine sintered-glass funnel, washed with five 10-mL portions of ice-cold ethanol, and air-dried. The powdered product is then dried at 50° for 1 hr. The yield is 18.4 g (44.1%). 

Pyridinium hexachloropIumbate(IV) is a lemon-yellow salt which is stable on exposure to air, being neither hydrolyzed nor losing chlorine, but it is hydrolyzed by water to give lead(IV) oxide and hydrochloric acid. Since it reacts with concentrated sulfuric acid to yield lead(lV) chloride, it is a convenient source of this unstable explosive compound. 

---

Pyridinium hexachloroplumbate (IV), which is more resistant to heat and moisture than the ammonium salt (larger, less polarized cation) may be prepared by substituting a solution of 12g of pyridine in 80ml of SM hydrochloric acid for the ammonium chloride solution used above. 

---