Potassium Dodecatungstocobaltate Trihydrate: K₅CoW₁₂O₄₀×3H₂O

Introduction

Heteropolyoxometalates as stable inorganic porphyrins have attracted much attention in the last two decades. The versatility of these catalysts has been demonstrated in various organic transformations due to their weak super-acidicity, redox properties, low toxicity, stability, inexpensiveness, water tolerance and reusability. [¹] Potassium dodecatungstocobaltate (PDTC) is apparently a perfect outer-sphere one-electron oxidant, due to the presence of a sheath of chemically inert oxygen atoms, which protects the central ion from undesired inner-sphere substitution reactions. [²] For this reason, electron transfer with PDTC typically leads to selective reactions and clean chemistry.

Habibi et al. introduced this reagent for the acetylation, formylation, tetrahydropyranylation of alcohols, and detetrahydropyranylation of ethers. [³] Further PDTC was ­successfully used in various organic transformations including esterification and transesterification, regeneration of carbonyl compounds from oximes, and synthesis of substituted 3,4-dihydropyrimidin-2(1H)-ones, quinolines, dihydroquinolines, pyridines, imidazoles and xanthenes.

For the preparation of PDTC, cobaltous acetate and sodium tungstate were initially treated with acetic acid and water at pH ˜7 to give sodium tungstodicobalt(II)ate. The sodium salt was then converted into the potassium salt by treatment with potassium chloride. Finally, the cobalt(II) complex was oxidized to the cobalt(III) complex by potassium persulfate in sulfuric acid. Crystallization in MeOH yielded PDTC as light blue solid. [²] [5]

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