No abstract

The behaviour of Bunsen's cacodyl disulfide, Me 2 As(S)-S-AsMe 2 towards Lewis bases of group 15 of the Periodic Table was studied mainly by 1 H NMR. While Ph 3 N did not react, 4dimethylaminopyridine and triethylamine isomerized the disulfide to Me 2 AsSSAsMe 2 . Ph 3 P, (PhO) 3 P, (MeO) 3 P, (EtO) 3 P and Ph 3 As desulfurized the disulfide to Me 2 AsSAsMe 2 . (PhS) 3 P also desulfurized the disulfide but Me 2 As-S-SPh was also produced. Me 2 As-S-SPh was the main product with (PhS) 3 As nucleophile. In most sys-2077 tems, cationic and anionic species were formed. The results are best interpreted by initial attack of the nucleophile on the electrophilic AsϭS sulfur.

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 (Sx, x = 1‐8) producing the stabilized dimethylarsino sulfenium cation, $\rm Me_{2}As- {\mathop{\rm{S}}\limits^{.}_{\ddot{}}} ^{+} \longleftrightarrow Me_{2}\mathop{\rm{A}}\limits^{+}_{} s=\mathop{\rm{S}}\limits^{.}_{\ddot{}}$. 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.

No abstract

Bunsen's cacodyl disulfide, Me2As(S)‐S‐AsMe2 (1), reacted with iodine giving the novel dimethylarsinosulfenyl iodide, Me2As‐S‐I (3) although theoretical calculations indicated that the AsV compound Me2As(S)‐I (4) was more stable in the gas phase. The oily product was stable neat and as a solution in CDCl3 at +4 °C and –20 °C for at least 15 d. Light, H2O, H2O2, and Zn dust, but not NaI or Ag, decomposed it. Compound 3 did not interact with Ph3N, with Ph2NH and PhNH2 it interacted but not reacted. 3 was decomposed by piperidine, with pyridine and 4‐dimethylaminopyridine it interacted and produced Me2As‐SS‐AsMe2 (2) and I2 that formed charge transfer complexes Base·I2, whereas Et3N decomposed 3, and 3Et3N·2I2 was isolated. 3 was desulfurized by Ph3P and (Me2N)3P completely, and by (PhO)3P and (PhS)3P partially. The reactions of 3 with (Me2N)3P, (PhS)3P, and (EtO)3P were complicated. From the AsIII nucleophiles, only Ph3As was bound, while (PhS)3As reacted slowly in a complicated manner with 3. No interaction of 3 with MeOH or PhOH was observed but NaOH, Ag2O, and PhONa decomposed it. Thiophenol produced traces of Me2As‐SPh (10) and sodium thiophenolate attacked mainly at AsIII of 3. Thus, externally stabilized sulfenium ions of the type Me2As‐S‐Nu+I– were not obtained.