Complexes of Silver Cyanide

Further confidence in these early experiments is gained by noting that the recalculated enthalpies of formation for liquid RNC with R = Me and Et are (123.5 4.2) and (113.6 9.2) kJ mol-1, while the currently suggested values8 are numerically rather close — (130.8 7.3) and (108.6 4.7) kJmol-1, respectively—indeed, the two sets of values are the same within error bars19. 

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Cyanide Complexes. Insoluble silver cyanide, AgCN, is readily dissolved in an excess of alkah cyanide. The predominant silver species present in such solutions is Ag(CN) 2) with some Ag(CN) 3 and Ag(CN) 4. Virtually all silver salts, including the insoluble silver sulfide, dissolve in the presence of excess cyanide because the dissociation constant for the Ag(CN) 2 complex is only 4 x 10 (see Cyanides). 

Sulfur Complexes. Silver compounds other than sulfide dissolve in excess thiosulfate. Stable silver complexes are also formed with thiourea. Except for the cyanide complexes, these sulfur complexes of silver are the most stable. In photography, solutions of sodium or ammonium thiosulfate fixers are used to solubilize silver hahdes present in processed photographic emulsions. When insoluble silver thiosulfate is dissolved in excess thiosulfate, various silver complexes form. At low thiosulfate concentrations, the principal silver species is Ag2(S203) 2j high thiosulfate concentrations, species such as Ag2(S203) 3 are present. Silver sulfide dissolves in alkaline sulfide solutions to form complex ions such as Ag(S 2 Ag(HS) 4. These ions are... 

Electroplating. Most silver-plating baths employ alkaline solutions of silver cyanide. The silver cyanide complexes that are obtained in a very low concentration of free silver ion in solution produce a much firmer deposit of silver during electroplating than solutions that contain higher concentrations. An excess of cyanide beyond that needed to form the Ag(CN)2 complex is employed to control the concentration. The silver is added to the solution either directly as silver cyanide or by oxidation of a silver-rod electrode. Plating baths frequently contain 40—140 g/L of silver cyanide... 

Silver(I) isocyanide complexes have been known for a long time and they were usually prepared by alkylation of silver cyanide.226 More recent reports include the study of steric effects of ligands... 

The development of more benign alternatives to cyanide for gold-leaching (see Section 9.17.3.1) such as thiourea, thiocyanate, or thiosulfate, which form stable complexes in water has prompted research to identify suitable solvent extractants from these media. Cyanex 301, 302, 272, Ionquest 801, LIX 26, MEHPA, DEHPA, Alamine 300 (Table 5) have been evaluated as extractants for gold or silver from acidic thiourea solutions.347 Whilst the efficacy of Cyanex 301 and 302 was unaffected by the presence of thiourea in the aqueous feed, the loading of the other extractants is severely depressed. Formation of solvated complexes of gold and of an inner-sphere complex of silver has been proposed.347... 

Reactions at o -Position. Many studies have been concerned with the reactions of alkyl halides with cyanide in the presence of various metal ions, and with the direct alkylation of cyanide complexes. The classic synthesis of isonitriles was accomplished by the use of silver cyanide, whereas the corresponding reaction of organic halogen compounds with alkali cyanides yields nitriles (Equations 40 and 41) (34,36). 

Complex Negative Ions. When an equivalent amount of sodium cyanide is added to a solution of silver nitrate, quantitative precipitation of silver cyanide takes place... 

Silver nitrate solution white precipitate of silver cyanide, AgCN, readily soluble in excess of the cyanide solution forming the complex ion, dicyano-argentate(I) [Ag(CN)2] (cf. Section III.6, reaction 7) ... 

Formation of Complex Ions.—In certain cases the solubility of a sparingly soluble salt is greatly increased, instead of being decreased, by the addition of a common ion a familiar illustration of this behavior is provided by the high solubility of silver cyanide in a solution of cyanide ions. Similarly, mercuric iodide is soluble in the presence of excess of iodide ions and aluminum hydroxide dissolves in solutions of alkali hydroxides. In cases of this kind it is readily shown by transference measurements that the silver, mercury or other cation is actually present in the solution in the form of a complex ion. The solubility of a sparingly soluble salt can be increased by the addition of any substance, whether it... 

Ores of silver native silver, argentite, cerargyrite (horn silver). Metallurgy of silver cyanide process, amalgamation process, Parkes process. O mpoimds of silver silver oxide, silver chloride, silver bromide, silver iodide, silver ammonia complex, silver cyanide complex, silver thiosulfate complex, silver nitrate. 

Silver (Ag, at. mass 107.87) occurs in its compounds in the (I)- oxidation state. So far, silver(II) is only of limited value in spectrophotometry. Silver(I) -sulphide and -halides are sparingly soluble. Ammine, cyanide, and thiosulphate complexes of silver are formed. In the presence of excess of Cf or SCN , traces of silver form soluble complexes. 

General properties of Raman spectra of silver cyanide complexes 285... 

The chemistry of the silver cyanide bath is determined by a variety of silver cyanide complexes existing in the solution. The following equilibria for 25°C, are known in the literature [4, 5] ... 

Furthermore we discussed the possibility that the observed splitting of the CN" vibrations resulted from differences in the density of charge in respect to a variety of silver cyanide complexes. In an early paper Otto et al. [7] explained the trend... 

To obtain isocyanides Gautier heated silver cyanide with 0.5-1.0 equivalent of alkyl iodide for several hours on a steam-bath for low-boiling alkyl iodides a pressure vessel is used. The mixture should not become brown in this reaction. The isocyanide is precipitated as a complex with silver cyanide, which, after removal of the excess of alkyl iodide by distillation, is decomposed by addition of a concentrated solution of potassium cyanide. The isocyanide can then be isolated by distillation. 

The mechanism of electroreduction of silver cyanide complexes in aqueous electrolytes—11. Interpretation of SERS data. Electrochim. Acta, 42 (9), 1345-1350. 

Baltrunas, G. (1984) Chemical limitations of electroreduction of silver cyanide complexes. Vilnius University, PhD Thesis. Vilnius. 

The Ag+ cation yields a white precipitate of silver cyanide or of silver cyanosilver-(I) Ag[Ag(CN)2], whose structure consists of the silver salt of the anion complex cyanosilver(I) [Ag(CN)2]. Silver cyanosilver(I) is easily soluble in an excess of cyanide ions through the formation of higher cyanosilver complexes. Likewise, it is soluble in ammonia and thiosulfate solutions through the formation of the silverammine and thiosulfatosilver complexes already encountered. 

In certain cases, the formation of a complex increases the soluhihty of a sparingly soluble salt. When potassium cyanide is added to a solution of sparingly soluble silver cyanide, soluhihty of silver cyanide increases due to complex formation. 

Silver is formed in nature as argentite. AgjS and horn silver. AgCl. The extraction of silver depends upon the fact that it very readily forms a dicyanoargentate(I) complex, [Ag(CN)2] (linear), and treatment of a silver ore with aqueous cyanide ion CN extracts the silver as this complex. The silver is then displaced from the complex by zinc ... 

The conversion of primary alcohols and aldehydes into carboxylic acids is generally possible with all strong oxidants. Silver(II) oxide in THF/water is particularly useful as a neutral oxidant (E.J. Corey, 1968 A). The direct conversion of primary alcohols into carboxylic esters is achieved with MnOj in the presence of hydrogen cyanide and alcohols (E.J. Corey, 1968 A,D). The remarkably smooth oxidation of ethers to esters by ruthenium tetroxide has been employed quite often (D.G. Lee, 1973). Dibutyl ether affords butyl butanoate, and tetra-hydrofuran yields butyrolactone almost quantitatively. More complex educts also give acceptable yields (M.E. Wolff, 1963). 

Silver Cyanide. Silver cyanide, AgCN, forms as a precipitate when stoichiometric quantities of silver nitrate and a soluble cyanide are mixed. Sdver(I) ion readily forms soluble complexes, ie, Ag(CN) 2 01 Ag(CN) 2> die presence of excess cyanide ion. 

Silver Iodide. Silver iodide, Agl, precipitates as a yellow soHd when iodide ion is added to a solution of silver nitrate. It dissolves in the presence of excess iodide ion, forming an Agl2 complex however, silver iodide is only slightly soluble in ammonia and dissolves slowly in thiosulfate and cyanide solutions. 

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