Aurocyanides

Cyan-essigsaure, /. cyanoacetic acid, -gas, n. cyanogen gas. -gold, n. gold cyanide, -gold-kalium, n. potassium auri- or aurocyanide, potassium cyanoaurate. 

Some disadvantages stem from the same phenomena impeded diffusion reduces the maximum practical rate of plating to well below that possible with aquocation baths. The cyanide ion is not entirely stable both oxidation and reduction products accumulate, including carbonate. Carbonate is also formed in the alkaline cyanide baths (all cyanide baths are alkaline except some based on aurocyanides) by absorption of COj from the air, and it is necessary either to replace or purify baths periodically. Much has been made of the toxicity of cyanides, but the other process solutions used in plating are generally extremely toxic and corrosive or caustic, and it is necessary to treat them all with respect. 

Atomic spectroscopy, 1, 231-234 Atropisomers, 1,200 Aurintricarboxylic acid beryllium(II) complexes, 2, 482 Aurocyanides dissolution, 6,784 Autotrophic bacteria... 

Graham, G.G., Whitehouse, M.W. and Bushell, G.R. (2008) Aurocyanide, dicyano-aurate (1), a pharmacologically active metabolite of medicinal gold complexes. Inflammopharmacology, 16, 126-123. 

In another study, it was shown that the activity of hydrochlorination catalysts made by impregnation of activated carbon with tetrachloroaureate is due to the adsorption of [AuCy anions on the activated carbon [423]. Similar studies, dealing with the adsorption of aurocyanide, [Au(CN)2] , onto activated carbon, have revealed that aurocyanide does not convert to metallic gold up to temperature of about 240°C [424, 425]... 

An example of chemical destruction of an anionic species is the elution of aurocyanide from an anion-exchange resin with thiourea, a neutral ligand that reacts with gold cyanide in the presence of acid to form a cationic complex. The elution reaction can be described by the following equation ... 

In the extraction process, the aurocyanide complex plus other metal cyanide complexes that are common in cyanide leach liquors (e.g. Fe(CN) 4-, Fe(CN)63-, Zn(CN)42-, Ni(CN)42-, Cu(CN)43-and Co(CN)63-) load onto the resin by simple ion exchange ... 

Thiocyanate can be recovered and recycled from this solution by the precipitation of iron as iron(III) hydroxide.366 Aurocyanide can also be eluted from a strong-base resin by chemical conversion of the gold to a cationic complex with the thiourea ligand, as shown above (equation 98). This method of gold elution is favoured in the Soviet Union, but suffers from the drawback that elution of the other metal cyanide complexes is generally poor, and multi-elution procedures are necessary. 

The elution of aurocyanide and other anions from a weak-base resin is achieved by neutralization of the amine functional groups (equation 96). The method is cheap and very effective 366 this is a major factor favouring the use of weak-base resins, particularly since recent research has shown that modem weak-base resins extract "aurocyanide efficiently from cyanide leach liquors that have undergone minimal adjustment of pH.358 368... 

A further series of five experiments was made to determine the ratio of the electrochemical equivalents of gold and silver, by passing the same quantity of electricity through solutions of potassium aurocyanide,... 

Aurous sulphide, Au2S.—The pure sulphide can be prepared7 by saturation of a solution of potassium aurocyanide with hydrogen sulphide, and precipitation of the salt by acidifying the solution with hydrochloric acid. It is not produced by the action of hydrogen sulphide on a hot solution of auric chloride, as supposed by Berzelius.8 The moist substance has- a steel-grey colour when dried, it becomes brownish black. When freshly prepared, the sulphide dissolves in water to a colloidal solution, from which it is reprecipitated by addition of hydrochloric acid. The sulphide is unaffected by dilute acids, but is decomposed by powerful oxidizers such as aqua regia and chlorine. It is readily dissolved by solutions of polysulphides,0 and less readily by those of monosulphides. It also dissolves in a solution of potassium... 

Double decomposition of ammonium sulphate and potassium aurocyanide yields ammonium aurocyanide, NH4Au(CN)2. This substance begins to decompose at 100° C. into aurous cyanide, hydrogen cyanide, and ammonia.7 Sodium aurocyanide, NaAu(CN)2, resembles the corresponding potassium salt in both preparation and properties. Salts of the aurocyanic radical, Au(CN)2, with other metals are also known.8 The compound HAu(CN)2 has not been isolated, since it decomposes readily with production of hydrogen cyanide. 

Gold salts modify a variety of cellular and humoral immune responses their mode of action is not understood but may relate to the formation of aurocyanide in areas of inflammation. Sodium aurothiomalate by deep i.m. injection or auranofin by mouth are available but oral gold is less effective and is rarely used as initial therapy. 

Here we summarize the key developments with emphasis on the post-1985 period and the role of the carbon surface. Bansal et al. [35] have grouped the postulated mechanisms as follows (1) reduction theory (2) ion-pair adsorption theory (3) aurocyanide anion adsorption theory and (4) cluster compound formation theory. 

Davidson [258] noted that gold recovery increased with decreasing pH in the pre.sence of spectator Na and Ca ions and postulated that both the hydro,xide and aurocyanide anions are competing for active adsorption sites on the charcoal surface the author did not identify these sites, however. The presence of Ca- cations was more beneficial than that of Na" cations, and the author speculated that the adsorbed calcium aurocyanide complex is. . . more stable than the sodium aurocyanide complex. ... 

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