The Electrophilic Character of Bunsen's Cacodyl Disulfide, Me₂As(S)‐S‐AsMe₂, Towards Some Nucleophiles of Groups 15 and 16

Abstract

The reactivity of Bunsen's cacodyl disulfide, Me 2 As(S)-S-AsMe 2 , towards nitrogen, phosphorus(III), oxygen and sulfur(II) nucleophiles was evaluated with the aim at identifying its electrophilic atom. The nitrogen nucleophiles either did not react or bind or split the disulfide. All phosphorus(III) nucleophiles desulfurized it. Water, methanol and phenol did not react but thiophenol reacted IntroductionThe great experimental chemist Robert Bunsen [1] in 1843 prepared a compound Me 4 As 2 S 2 which he named cacodyl disulfide by reducing cacodylic acid, Me 2 AsO 2 H, with hydrogen sulfide. [2] Its structure was not the expected As III /As III bis(dimethylarsenic)disulfide (2) but the As V /As III dimethylarsino dimethyldithioarsinate [3,4 ] and mechanisms of its formation have been proposed. [4,5] Bunsen's cacodyl disulfide (1) is a remarkable chemical chameleon. When dissolved in non-basic solvents it equilibrates with 2 to the extent of approx. 10 %, thus showing an internal redox property. [6] Bunsen, apart from studying the behavior of his disulfide towards heat, HCl, H 2 SO 4 and HNO 3 , he found that it reacted with metal salts of the non-reducible metals Pb II , Sb III and Bi III giving the complexes (Me 2 AsS 2 ) x M (= L x M) [2] and we extended the list by preparing complexes with Zn II , Cd II and Ag I under conditions that afforded pure products. [7] With compounds of lighter metals like AlCl 3 , compound 1 was isomerized to 2, GaCl 3 and InCl 3 bound to 1, while Tl(AcO) 3 was reduced giving LTl. [8] Bunsen himself also found that the reducible Au III and Cu II gave the complexes LAu and LCu [2] and we [7] verified the production of LCu identifying some by-products. Pd II also produced L 2 Pd that was unstable and decomposed to unknown compounds, [9] but Hg II was not reduced. [7] It was proposed [7,8] that the electron for the reduction came from the bound Me 2 AsS 2 group and reasonable

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

“…2.0 ppm and the Me 2 As III protons in 1 and 2 at approx. 1.5 ppm,1,8 the Me 2 As protons of 3 resonated at 2.026 ppm in CDCl 3 and at 1.980 ppm in CD 3 OD (Figure 1). It should be noted that the iodide Me 2 As‐I ( 6 ) resonated at 2.016 (this work) or 2.019 in CDCl 3 , at 1.98 in CD 3 OD,6 at 2.00 as neat liquid,10 while it resonated in the expected region, i.e.…”

“…Tris(phenylthio)phosphine48 in CDCl 3 reacted slowly (>24 h) with 3 giving, by 31 P NMR, (PhS) 3 P=S (at δ = 93.1 ppm; literature value –91.1 ppm25) but most (PhS) 3 P had not reacted (δ = 133.1 ppm; literature value –130.5 ppm25). The overall reaction was complicated because the 1 H NMR spectra showed, that 2 was produced in 1 h but in 24 h had reacted and Me 2 As–SPh ( 10 ) was present at 1.353 ppm,1 arising by an unknown mechanism. The prominent singlet at 2.019 ppm could be due to { 3 and 6 }.…”

“…After 24 h at room temp., the 1 H NMR spectrum showed in the aromatic region (PhS) 3 As, absence of PhSSPh and presence of signals some of them attributable to Me 2 As–SPh ( 10 ). In the aliphatic region there was a singlet at 1.353 ppm due to 10 1 and another singlet of equal intensity at 2.021 ppm. 2 was not detected.…”

“…Bunsen's cacodyl disulfide ( 1 ) was prepared according to Zingaro et al2,8,50 The sources and purity of the nucleophiles (amines, phosphorus(III), arsenic(III), oxygen and sulfur(II) compounds) are described in a previous publication 1. Solvents were kept over 4 Å molecular sieves.…”

“…In a previous publication1 we summarized the nucleophilic (towards many heavy metal cations) and electrophilic (towards a variety of nucleophiles of group 15 and 16 of the periodic Table) reactions of Bunsen's cacodyl disulfide Me 2 As(S)‐S‐AsMe 2 ( 1 ). Metal cations split 1 giving complexes (Me 2 As(S)‐S) x M , whereas nucleophiles either bind or split or desulfurize 1 .…”