Copper(II) catalysis in cyanide conversion into ethyl carbamate in spirits and relevant reactions

The role of copper(II) species in the oxidation of inorganic cyanide to cyanate and in the conversion of cyanate or urea into ethyl carbamate was investigated. The oxidation process has been shown to be independent from the dissolved oxygen. Elemental analysis and infrared spectroscopy have shown the formation of a mixed copper carbonate/hydroxide in the process of oxidation of cyanide to cyanate in water/ethanol. The complexation to Cu-II of cyanate formed upon cyanide oxidation makes the former more susceptible to nucleophilic attack from ethanol, with conversion into ethyl carbamate. Comparatively, urea has a minor role with respect to cyanide in the formation of ethyl carbamate. Therefore, the urea present in some samples of Brazilian sugar cane spirit (cachaca) has been shown to have almost no influence on the ethyl carbamate content of cachacas, which comes essentially from cyanide. Fe-II,(III) affords results similar to those found with Cu-II. Some suggestions are presented to avoid ethyl carbamate formation in spirits during distillation.