Releasing Cyanide From Ferrocyanide by Carbon Monoxide Ligand Exchange in Alkaline and Hyperalkaline Aqueous Environments

Cyanide is believed to be an important compound for the origin of life. Early Earth was likely a liquid ocean in contact with iron and magnesium rich rocks, which dissolves iron atoms into the water. When cyanide encounters aqueous iron atoms, six cyanide atoms are captured by iron to form a ferrocyanide complex. Ferrocyanide can help concentrate cyanide, but because of the complex's stability, it is difficult to release cyanide from the complex to be used in downstream chemical reactions. One proposed mechanism is a meteor impact onto a bed of dried ferrocyanide salts. The heat from the impact would break apart the complex and when water is added back to the system, cyanide would be free to react. Alternatively, we have shown that in the presence of carbon monoxide, the carbon monoxide will replace cyanide in the complex forming ferrocyanocarbonyl complexes and releasing cyanide. This pathway could produce a regular source of cyanide under mild early Earth conditions. Further, the resulting ferrocyanocarbonyl complexes themselves may also be important for prebiotic chemical networks.