Silver Cyanide Itself

We start with AgCN as the archetype of the species of interest and merely accept its crystalline phase enthalpy of formation6 of 146.0 kJmol-1. Similar to reaction 3, we 

The corresponding reaction for copper-containing organometallics16 has a comparable endothermicity, and so reaction 7 is thermoneutral. 

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When nitrosyl cyanide adduct 1 is reacted with ( , )-l,4-diphenyl-1,3-butadiene in refluxing benzene, the expected cycloadduct 2 is obtained with total diastereoselectivity, whereas by reaction with nitrosyl cyanide itself, prepared from nitrosyl chloride and silver cyanide, only 3-chloro-4-nitro-1,4-diphenyl-l-butene and l-nitro-l,4-diphenyl-l,3-butadiene are recovered in low yield34,35. 

An especially difficult acylation of the resin-bound, stericaUy hindered D-Piz(Z) derivative 3 (Scheme 3) was achieved by using silver cyanide as additive. While Fmoc-Ile-Cl itself led to a yield of only 50%, the efficiency was increased when the reaction was carried out in the presence of silver cyanide. The exact mechanism of silver cyanide catalysis is not clear, but it was shown that silver cyanide effects conversion of the acid chloride to the oxazol-5(4//)-one. Although the hydrogen cyanide formed during this process may catalyze the reaction of the oxazol-5(4//)-one, the results of separate hydrogen cyanide catalyzed coupling of preformed oxazol-5(4//)-one did not match exactly the silver cyanide catalyzed reaction of the acid chloride. ... 

Silver has little tendency to formally lose more than one electron its chemistry is therefore almost entirely restricted to the + 1 oxidation state. Silver itself is resistant to chemical attack, though aqueous cyanide ion slowly attacks it, as does sulphur or a sulphide (to give black Ag S). hence the tarnishing of silver by the atmosphere or other sulphur-containing materials. It dissolves in concentrated nitric acid to give a solution of silver(I) nitrate. AgNOj. 

Gold ores can be concentrated by froth flotation, the resulting concentrate being roasted at 600-800°C to oxidize off sulphur and arsenic as their oxides. The product is extracted with cyanide under oxidizing conditions (using either peroxide or air itself) before displacement with powdered zinc. More reactive metals (silver etc.) can be removed by chlorination of molten gold. 

Electrophilic catalysis of the departure of halogens in the century-old Koenigs-Knorr reaction is implicit in the use of heavy metal bases such as silver oxide and mercuric cyanide, but the first demonstration of electrophilic catalysis in water (in the hydrolysis of the p-glucoside of 8-hydroxyquinoline by first-row transition metals (Cu Np > C")) was by Clark and Hay in 1973. The observations were expanded to the more conveniently followed (because more labile) benzaldehyde methylacetals or tetrahydropyranyl derivatives of 8-hydroxyquinoline, whose hydrolysis is now known to give solvent-equilibrated oxocarbenium ions (Figure 3.19). Surprisingly, however, the observation of electrophilic catalysis of glycoside hydrolysis itself was not picked up by paper... 

As already stated, the water used in the television experiment was only similar to the Tisza water in its concentration of cyanide. The pollution, in fact, came from a gold mine. In a gold mine, metals that are above gold in the periodic table (silver and, mainly, copper) are also present. So the pollution that was ealled a cyanide spill in the press actually contained a number of additional eomponents. The presence of copper itself would have not been a problem, but its interaetion with cyanide ions fundamentally altered the ehentieal properties. Even among ehemists, heated debates followed among those who were not aware of all important facts. 

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