Arsenic: Not So Evil After All?

The Composition of Ehrlich's Salvarsan: Resolution of a Century‐Old Debate

“…[1,2] Ehrlich synthesized the compound by the reaction of 3-nitro-4-hydroxyphenylarsonic acid with dithionite. [3] This simultaneously reduced the NO 2 group to NH 2 and As V to As I to give a material of formula 3-H 2 N-4-HOC 6 H 3 As (Scheme 1).…”

“…Although As = As bonds are now known to be found only in sterically crowded molecules, [6] the As=As form is repeatedly cited, with textbooks and reviews still giving structure 1. [1,2] Various suggestions for the true structure of salvarsan have been proposed, including large polycyclic molecules [7] and polymers, [8] but lack strong supporting data.…”

“…[15] This was earlier assumed to give rise to what was originally formulated as the oxide (RAs = O), but is undoubtedly RAs(OH) 2 or a condensation product thereof. [12] In essence, salvarsan (RAs) n appears to serve as a slow-release source of RAs(OH) 2 . This oxidation process was confirmed by our ESI MS results.…”

“…This oxidation process was confirmed by our ESI MS results. Peaks at m/z 218 and 200 can be assigned to [RAs(OH) 2 + H] + and [RAs(OH)] + , respectively ( Figure 1). As the sample was exposed to air, these signals increased in intensity at the expense of those from the various [(RAs) n + H] + species, until after a few hours they completely dominated the spectrum.…”

The Composition of Ehrlich's Salvarsan: Resolution of a Century‐Old Debate

“…There is a significant peak ([R 2 As] + ) which connotes a fragmentation product of the cyclic polyarsines (see below). Peaks corresponding to [RAs(OH) 2 + H] + and [RAs(OH)] + arise from complete oxidative cleavage of As-As bonds.…”