Studies in organoarsenic chemistry

Abstract

The proton NMR spectra of dimethylarsinodimethyl-dithioarsinate (I) in various solvents are inconsistent with both the solid-state structure, (CH₃)₂As(S)SAs(CH₃)₂, and the formulation (CH₃)₃AsSSAs(CH₃)₂. The intensities of the observed resonance peaks are dependent upon the solvent, concentration, time, and temperature. The spectrum of a freshly prepared solution of (CH₃)₂As(S)SAs(CH₃)₂ at 37° showed three sharp singlets. The low field peaks at 2.14-1.83 ppm were assigned to the pentavalent unit of I. These peaks were of approximately equal intensity in most of the nine solvents examined. The high field peak at about 1.36 ppm was associated with the methyl hydrogens attached to the As(III) atom of I. These were found to vary widely depending upon the solvent used. The spectrum was investigated over the temperature range -70 to 120° using methylene chloride and 1, 1, 2, 2-tetrachloroethane as solvents. At higher temperatures, a steady increase in the intensity of the up-field peak and the concurrent decrease in the intensities of the downfield peak was noted. The spectral behavior has been interpreted in terms of an equilibrium between (CH₃)₂As(S)SAs(CH₃)₂ and (CH₃)₂AsSSAs(CH₃)₂. The interpretation is supported by infrared data. The infrared spectrum was also investigated as a function of temperature. At higher temperatures the relative intensity ratios of v(As=S) to v(As-S) changed in favr of v(As-S)..