Sodium hexachloroplatinate, solubility

When a solution of hexachloroplatinic(TV) add is boiled for some time with NaOH, all the chloride ions are replaced by hydroxide ions. The resulting sodium hexahydroxoplatinate(IV). Na2PttOH),s. is soluble in the basic solution, but it can be precipitated as hexaliydroxoplatinic(lV) acid, H2Pt(OH)6, by tire addition of acetic acid. The hydroxide ions of the salt are replaced by the corresponding ions of mineral acids when the compound is dissolved in acid. Hexahydioxoplatinic acid can be dehydrated to yield compounds corresponding to the tri-, di-, and monohydrate of platinum(IV) oxide. The last water molecule cannot be removed without some destruction of the dioxide. 

None of the accepted preparative methods12 for disodium hexa-chloroplatinate(IV), Na2[PtCl6], is entirely suitable for routine use, because these procedures require reaction of a mixture of solid sodium chloride and platinum metal with chlorine gas at temperatures near 500°. However, a preparation of the desired compound is described below which yields a product of very high purity and which is much more convenient than those previously reported since only solution chemistry is involved. Unlike the corresponding ammonium and potassium salts, disodium hexachloroplatinate(IV) exhibits high solubility in water and in several nonaqueous solvents, including ethanol, methanol, and Ar,/V-dimethylformamide—a fact which enables one to extend the range of studies of the chemistry of hexachloroplatinate(IV). 

Since few salts are sparingly soluble in water, there are few precipitation reactions of the aqueous ions. Generally the larger the M+ ion, the more numerous are its insoluble salts. Thus sodium has very few the mixed Na—Zn and Na—Mg uranyl acetates [e.g., NaZn(U02)3(CH3C02),-6H20], may be precipitated almost quantitatively under carefully controlled conditions from dilute acetic acid solutions. The perchlorates and hexachloroplatinates of K, Rb, and Cs are rather insoluble in water and virtually insoluble in 90% ethanol. These heavier ions may also be predpitated by the ion [Co(N02)6]3 and various other large anions. Sodium tetra-phenylborate Nal QHs), which is moderately soluble in water, predpitates the tetraphenylborates of K, Rb, and Cs from neutral or faintly acid aqueous solutions. 

The sodium salt of the hexachloroplatinate(IV) ion, Na2PtCl6, was prepared in the same manner as the potassium salt, except that NaCl was added instead of KCl. Furthermore, due to solubility differences, the product was washed only with 95 % ethanol. 

---