The Other Face of Bunsen's Cacodyl Disulfide,Me2As(S)‐S‐AsMe2: The Lewis‐Base Behaviour Towards Heavy Metal Cations

The reaction of Bunsen's cacodyl disulfide, Me₂As(S)‐S‐AsMe₂, with heavy metal cations in methanol produces insoluble salts (complexes) of dimethyldithioarsinic acid, Me₂AsS₂H, and dimethyl arsenium ion, Me₂As:⁺. This arsenium ion prefers to react with Me₂As(S)‐S‐AsMe₂, when in excess, compared to AcO^? or MeOH/H₂O and it is also reactive towards sulfur (S_x, x = 1‐8) producing the stabilized dimethylarsino sulfenium cation, . The complexes (Me₂AsS₂)_xM (x = 1 or 2) are unstable in the presence of their own heavy metal cations decomposing to colored solids. In an attempt to prepare salts of Me₂AsSH, the reactions of (Me₂AsS₂)_xM with triphenylphosphine and trimethyl phosphite gave the metal sulfide and Me₂As‐S‐AsMe₂ instead.