The Reaction of Bunsen's Cacodyl Disulfide, Me₂As(S)‐S‐AsMe₂, with Iodine: Preparation and Properties of Dimethylarsinosulfenyl Iodide, Me₂As‐S‐I

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.

The Reaction of Diethylthiophosphinyl Iodide, Et2P(S)I, with Nucleophiles

“…While diphenylamine and Me 2 As–S–I ( A ) under a 2:1 stoichiometry in CDCl 3 did not react, this amine showed some reactivity towards 2 in the presence of diphenylamine, pyridine, or triethylamine. The 31 P NMR spectra showed the presence of 3 and 6 but their chemical shifts showed some variance.…”

“…However, impurity 1 was not reactive towards the nucleophiles studied. The iodide 2 was a dark red oil [while Me 2 As–S–I ( A ) was a red orange oil] and on TLC runs above 1 with very little hydrolysis, although in moist air it hydrolyzes . Very small amounts of 2 were produced when 1 and I 2 were stirred in dry dichloromethane for 2.5 d. The mechanism of the reaction probably involves a 4‐center transition state although the bond lengths of 1 (P–P 22.2 pm) do not exactly match those of Cl–Cl (9.9 pm), Br–Br (11.4 pm), and I–I (13.3 pm).…”

“…The easier hydrolysis of impure 3 may be due to the presence of HI, which can protonate the anhydride probably at the oxygen atom thus facilitating its hydrolysis. Comparing the rate of hydrolysis of Me 2 As–S–I ( A ) (in CD 3 OD) by excess water with that of 2 (in Me 2 C=O), the former is faster and gave exclusively the acid Me 2 As(S)–OH via Me 2 As(S)–O–As(S)Me 2 , whereas 2 gave a mixture of the acid 4 and the anhydride 3 (predominating) plus an unknown compound.…”

“…We did not try the reaction of 2 with triphenylamine because triphenylamine is unreactive towards inorganic acids and Me 2 As–S–I ( A ) …”

“…Recently, by reacting Bunsen's cacodyl disulfide, Me 2 As(S)–S–AsMe 2 , with iodine we prepared a compound, Me 2 AsSI, which can be formulated as the As III compound dimethylarsinosulfenyl iodide [or (iodothio)dimethylarsane)], Me 2 As–S–I ( A ), or as the isomeric As V compound dimethylthioarsinyl iodide (or dimethylarsinothioic iodide), Me 2 As(S)–I ( B ) . Theoretical calculations showed that in the gas phase the arsinyl iodide B was more stable by 45.14 kJ · mol –1 than the sulfenyl iodide A .…”