The Compounds of Silver

Cuprous ion, Cu , is so unstable in aqueous solution that it undergoes auto-oxidation-reduction into copper and cupric ion  

Very few cuprous salts of oxygen acids exist. The stable cuprous compounds are either insoluble crystals containing covalent bonds or covalent complexes. 

When copper is added to a solution of cupric chloride in stong hydrochloric acid a reaction occurs that results in the formation of a colorless solution containing cuprous chloride complex ions such as CuCla  

This complex ion involves two covalent bonds, its electronic structure being 

Other cuprous complexes, CuCls and CuC, also exist. 

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Hyposulphite of soda, and other soluble salts of hyposulphurous acid, possess the remarkable property of dissolving all the compounds of silver, even the chloride, and the solution thus formed has a very intense sweet taste, with a metallic after-taste. This property has been made available in the dagaerreotype, for the purpose of dissolving the sensitive coating of iodide from the plate of eilver alter exposure to light, aud thus fixing the image already formed. For this purpose hyposulphite of soda is now prepared on a very considerable scale. 

Silver ion is an excellent antiseptic, and several of the compounds of silver are used in medicine because of their germicidal power. A compound of silver and protein is used in treating the eyes of new-bom infants to obviate the possibility of blindness from gonorrheal... 

They give, with caustic fixed alkalies, a brown precipitate with ammonia, a similar one, soluble in the slightest excess with hydrochloric acid, or any soluble chloride, the white curdy precipitate of chloride of silver, insoluble in water and acids, but soluble in ammonia and with sulphuretted hydrogen, a dark brown, nearly black precipitate of sulphuret. Silver and all its compounds are very sensitive to sulphuretted hydrogen, which blackens them. Most of the compounds of oxide of silver are very soluble in ammonia and all the compounds of silver are darkened by the actjon of light, a property which has lately been applied to useful purposes in the Daguerreot3ipe, Calotype, and other photographic methods. Oxide of silver is reduced to the metallic state from its solutions by copper, zinc, and several other metals. When mercury is used, there is formed a heautiful arborescent crystallisation of an alloy of silver and mercury, called Arbor Dianae. 

Silver ion is an excellent antiseptic, and several of the compounds of silver are used in medicine because of their germicidal power. 

The more noble metals (for example copper, mercury and silver) can form oxides, and exhibit variable oxidation state in such compounds (for example CU2O, CuO), but it is not easy to prepare such oxides by direct action of oxygen on the metal, and elevated temperatures are necessary. Moreover, in the case of silver and mercury, loss of oxygen from the oxide by heating is easy. The oxidesare, however, basic (for example Ag20 - Ag, CuO - Cu in acids). 

In ammoniacal solution (in which the ion [AgfNHjlj]" is formed) it is readily reduced to silver (see above) by many organic compounds. The use of silver nitrate for marking clothes depends on its reduction by the material to black silver. The reduction also occurs even when the neutral solution comes in contact with the skin, and a black stain is left. Thus solid silver nitrate rubbed on the skin leaves a black deposit and so is used in surgery as a mild caustic—hence the old name for silver nitrate of lunar caustic. 

The structure of compound A was established in part by converting it to known compounds Treat ment of A with excess methyl iodide in the presence of silver oxide followed by hydrolysis with dilute hydrochlonc acid gave a tnmethyl ether of D galactose Companng this trimethyl ether with known trimethyl ethers of D galactose allowed the structure of compound A to be deduced... 

Silver and sulfur combine even in the cold to form silver sulfide. The tendency of silver to tarnish is an example of the ease with which silver and sulfur compounds react. PoHshes that contain silver complexing agents, such as chloride ion or thiourea, are used to remove silver tarnish. 

Catalysts. Silver and silver compounds are widely used in research and industry as catalysts for oxidation, reduction, and polymerization reactions. Silver nitrate has been reported as a catalyst for the preparation of propylene oxide (qv) from propylene (qv) (58), and silver acetate has been reported as being a suitable catalyst for the production of ethylene oxide (qv) from ethylene (qv) (59). The solubiUty of silver perchlorate in organic solvents makes it a possible catalyst for polymerization reactions, such as the production of butyl acrylate polymers in dimethylformamide (60) or the polymerization of methacrylamide (61). Similarly, the solubiUty of silver tetrafiuoroborate in organic solvents has enhanced its use in the synthesis of 3-pyrrolines by the cyclization of aHenic amines (62). 

Discrimination between exposed and unexposed areas in this process requires the selection of thia zolidine compounds that do not readily undergo alkaline hydrolysis in the absence of silver ions. In a study of model compounds, the rates of hydrolysis of model /V-methyl thia zolidine and A/-octadecyl thiazolidine compounds were compared (47). An alkaline hydrolysis half-life of 33 min was reported for the /V-methyl compound, a half-life of 5525 min (3.8 days) was reported for the corresponding V/-octadecyl compound. Other factors affecting the kinetics include the particular silver ligand chosen and its concentration (48). Polaroid Spectra film introduced silver-assisted thiazolidine cleavage to produce the yellow dye image (49), a system subsequentiy used in 600 Plus and Polacolor Pro 100 films. 

The use of silver (II) salts, particularly argentic picolinate, as reagents for hydroxyl oxidation has also been disclosed recently. The reaction may be run in acid, neutral or basic media in aqueous or polar organic solvents at room or slightly elevated temperatures. Primary alcohols may be oxidized to aldehydes or acids depending on the conditions used. Amines and trivalent phosphorous compounds are more sensitive to oxidation with this reagent than are hydroxyl groups. 

Determination of silver as chloride Discussion. The theory of the process is given under Chloride (Section 11.57). Lead, copper(I), palladium)II), mercury)I), and thallium)I) ions interfere, as do cyanides and thiosulphates. If a mercury(I) [or copper(I) or thallium(I)] salt is present, it must be oxidised with concentrated nitric acid before the precipitation of silver this process also destroys cyanides and thiosulphates. If lead is present, the solution must be diluted so that it contains not more than 0.25 g of the substance in 200 mL, and the hydrochloric acid must be added very slowly. Compounds of bismuth and antimony that hydrolyse in the dilute acid medium used for the complete precipitation of silver must be absent. For possible errors in the weight of silver chloride due to the action of light, see Section 11.57. 

For many years, the chemistry of silver and gold was believed to be more similar than is now known to be the case [1-10]. In the Cu-Ag-Au triad, the stability of oxidation states does not follow the usual trend of increasingly stable high oxidation state on descending the group for copper, the +2 state is the most important, for silver it is the +1 state and, though oxidation states between -1 and +7 are claimed, for gold it is the +1 and +3 states that dominate its chemistry. The types of compound are summarized in Table 4.1. 

Stable compounds of silver(II) are found with N, O and F as donor atoms macrocycles are, as elsewhere, able to support the higher oxidation state. As a d9 system, Ag2+ imitates Cu2+ in displaying Jahn-Teller distortion. 

Organometallic compounds of silver [2(f), 6] are restricted to the silver(I) state and are usually light, air and moisture sensitive. Simple alkyls are unstable at room temperature though some fluoroalkyls are isolable. Therefore, perfluoroisopropylsilver is stable to 60°C as a MeCN adduct. Alkenyls... 

Silver(I) does not disproportionate in aqueous solution and, in almost all its compounds, silver has oxidation number +1. Apart from silver nitrate, AgN03, and silver fluoride, silver salts are generally only sparingly soluble in water. Silver nitrate is the most important compound of silver and the starting point for the manufacture of silver halides for use in photography. 

Under the chosen conditions aromatic compounds are nitrated to nitroaromatics [1]. The detection of rotenone [1] (see below) depends on the reduction of silver ions, incorporated into the layer, to metallic silver in the presence of ammonia [4]. The mechanism of the reaction of many substances leading to fluorescent derivatives has not yet been elucidated [2],... 

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