An investigation of the structure of the so-called phenarsazine : Mass spectroscopical evidence for the thermal formation of phenarsazine

The structure of Wieland and Rheinheimer's “phenarsazine” has been reinvestigated. The proposed aromatic structure 3 is not correct, spectral and chemical evidence showing that this compound is 10,10′-bis(5,10-dihydrophenarsazinyl) 16. An attempt to synthesize phenarsazine 3 by base-induced hydrogen chloride elimination was unsuccessful. However, mass spectroscopic evidence indicates that phenarsazine is formed by thermal elimination of either hydrogen chloride or methanol from 10-chloro-5,10-dihydrophenarsazine 7 or 10-methoxy-5,10-dihydrophenarsazine 10, respectively.