Silver compounds mechanism

Environmental Fate. The factors governing the environmental fate of silver are not well characterized. While silver and its compounds are transported in the air, water, and soil, and are partitioned between these media, the mechanisms of transport and partitioning are not well-defined. No partition coefficients or constants have been determined for silver or its compounds. Little information was found in the available literature on transformation of silver in water or soil. Some microorganisms present in these media may be able to transform silver and silver compounds however, silver is not expected to be significantly transformed in the environment because it is toxic to microorganisms. Further information on the size and flux of environmental compartments and the transport and transformations of silver and silver compounds in the environment would be useful in defining pathways for potential human exposure. 

Silver compounds also have non-medical uses, several of which will be considered. In this short review, we shall trace their pedigree, describe their uses and discuss in depth their mechanisms of action and of bacterial resistance to them. 

Direct observations of the decompositions of a wide range of inorganic compounds [231—246], which are unstable in the electron beam, particularly azides and silver halides, have provided information concerning the mechanisms of radiolysis these are often closely related to the processes which operate during thermal decomposition. Sample temperatures estimated [234] to occur at low beam intensity are up to 470 K while, at higher intensity, 670 K may be attained. 

Sodium nitrite can be used to form nitro compounds with primary or secondary alkyl bromides or iodides, though the method is of limited scope. Silver nitrite gives nitro compounds only when RX is a primary bromide or iodide. Nitrite esters are an important side product in all these cases (10-33) and become the major product (by an SnI mechanism) when secondary or tertiary halides are treated with silver nitrite. 

Despite its synthetic importance, the mechanism of the copper-quinoline method has been studied very little, but it has been shown that the actual catalyst is cuprous ion. In fact, the reaction proceeds much faster if the acid is heated in quinoline with cuprous oxide instead of copper, provided that atmospheric oxygen is rigorously excluded. A mechanism has been suggested in which it is the cuprous salt of the acid that actually undergoes the decarboxylation. It has been shown that cuprous salts of aromatic acids are easily decarboxylated by heating in quinoline and that arylcopper compounds are intermediates that can be isolated in some cases. Metallic silver has been used in place of copper, with higher yields. ... 

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],... 

Above 140°C its exothermic decomposition to metal and carbon dioxide readily becomes explosive [1], A 1 kg batch which had been thoroughly dried at 50°C exploded violently when mechanical grinding in an end-runner mill was attempted [2], Explosions have been experienced when drying the oxalate as low as 80°C [6], It is a compound of zero oxygen balance. The explosion temperature of the pure oxalate is lowered appreciably (from 143 to 122°C) by application of an electric field [3], The salt prepared from silver nitrate with excess of sodium oxalate is much less stable than that from excess nitrate [4], Decomposition at 125°C in glycerol prevents explosion in the preparation of silver powder [5],... 

A study518 of the mechanism of oxidation of alcohols by the reagent suggested that a reversible, oriented adsorption of the alcohol onto the surface of the oxidant occurs, with the oxygen atom of the alcohol forming a coordinate bond to a silver ion, followed by a concerted, irreversible, homolytic shift of electrons to generate silver atoms, carbon dioxide, water, and the carbonyl compound. The reactivity of a polyhydroxy compound may not, it appears, be deduced from the relative reactivity of its component functions, as the geometry of the adsorbed state, itself affected by solvent polarity, exerts an important influence on the selectivity observed.519... 

Silver and its compounds have long been used as antimicrobial agents in medicine. The mechanisms of silver toxicity as they relate to human exposure to pharmaceuticals have been reviewed (328). Silver is active at low concentrations and has a low toxicity. The practice of instilling the eyes of infants with 1% of AgN03 solution immediately after birth is still common in some countries, for prevention of opthalmia neonatorum (329). Silver sulfadiazine 77 is clinically used as a topical antimicrobial and antifungal agent and applied as a cream to prevent bacterial infections in cases of severe burns. It is an insoluble polymeric compound and releases Ag(I) ions slowly. 

In addition, Wipf and co-workers104 have used silver(i)-catalyzed addition of zirconocenes to 3,4,6-tri-O-benzyl-D-glucal epoxide 93 for the stereoselective synthesis of a-C-glucosyl compounds 95 and 96 following a similar mechanism as in the reaction with organoaluminium and organoboron reagents (Scheme 32). 

Uses. The unalloyed metal cannot be directly used owing to its bad mechanical properties and its high oxidability. Several thallium alloys are used as semiconductors or ceramic compounds it may be used as additive to gold, silver or copper contacts in the electronic industries. Thallium is dangerously toxic. 

Aromatic cation-radicals can also react with NOj", giving nitro compounds. Such reactions proceed either with a preliminary prepared cation-radical or starting from nncharged componnd if iodine and silver nitrite are added. As for mechanisms, two of them seem feasible—first, single electron transfer from the nitrite ion to a cation-radical and second, nitration of ArH with the NOj radical. This radical is quantitatively formed when iodine oxidizes silver nitrite in carbon tetrachloride (Neelmeyer 1904). 

---