How aqua regia overcomes the chemical inertness of cinnabar: a thermodynamic analysis in light of long-term knowledge about a reaction that has been of interest for centuries

Abstract

AbstractWith the rise of the Swiss-born alchemist Paracelsus in the 16th century, the dissolution of cinnabar (red HgS) in aqua regia has repeatedly appeared in the chemical literature. This article reviews the relevant history and takes a thermodynamic approach to shed new light on the dissolution. The conclusions reveal that the reaction in which the sulfide ion is oxidized by nitric acid is the most thermodynamically favorable step in the dissolution. The importance of the role of hydrochloric acid in the dissolution, when it provides complexation, was also observed. Further, it was found that the overall effect of nitric acid is much greater than that of the aqua regia by-product elemental chlorine.