Alkali-Metal-Silver Compounds

In contrast to the other elements of group 13, thallium is considered a soft acid in Pearson s soft/hard acid classification (see Hard Soft Acids and Bases).This makes the element and its derivatives unique, and leads to its potentially most outstanding feature the properties of thallium are a subtle blend of some of the most desirable properties of numerous other metals (e.g. heavy alkali metals, silver, mercury, and lead). Thallium compounds are stable in both oxidation states (-1-1 and -1-3). The trivalent cation is quite a strong oxidation reagent, since it is reduced to T1+ easily (standard redox potential E°(TP+ — Tl" ") = -1.25 V). The ease of this reduction is utilized in certain organic reactions. 

For elements which form diatomic molecules A2 with single bonds, Da-a is equal to the energy of dissociation. This applies to H2, the halogens, the alkali metals, silver and copper. A few other elements form homoatomic molecules A . In the P4—AS4—and Sb4-molecules, for instance, each element is bonded to three other atoms, as in compounds of type AB3. As there are six A—A bonds in the A4-molecules, the bond energy Da-a is one sixth of the energy of dissociation for the reaction... 

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

A number of compounds of the types RBiY2 or R2BiY, where Y is an anionic group other than halogen, have been prepared by the reaction of a dihalo- or halobismuthine with a lithium, sodium, potassium, ammonium, silver, or lead alkoxide (120,121), amide (122,123), a2ide (124,125), carboxylate (121,126), cyanide (125,127), dithiocarbamate (128,129), mercaptide (130,131), nitrate (108), phenoxide (120), selenocyanate (125), silanolate (132), thiocyanate (125,127), or xanthate (133). Dialkyl- and diaryUialobismuthines can also be readily converted to secondary bismuthides by treatment with an alkali metal (50,105,134) ... 

Fluorinated olefins, such as chlorotritluoroethylene, hexafluoropropene, per-fluoroisobutylene, and hexafluorocyclobutene, react with silver trifluoroacetate in the presence of alkali metal fluondes to give perfluoroalkylsilver compounds [270] (equation 186)... 

The elements that form only one cation are the alkali metals (group IA), the alkaline earth metals (group IIA), zinc, cadmium, aluminum, and most often silver. The charge on the ions that these elements form in their compounds is always equal to their periodic table group number (or group number minus 10 in the newest labeling system in the periodic table). 

Nonpolar molecular compounds dissolve in nonpolar solvents. Polar molecular compounds and ionic compounds may dissolve in polar solvents. Metals dissolve in other molten metals. These can range from copper, silver, gold, alkali metals dissolving in mercury at room temperature, to chromium, molybdenum, and tungsten dissolving in molten iron. 

Unlike boron, aluminum, gallium, and indium, thallium exists in both stable univalent (thallous) and trivalent (thallic) forms. There are numerous thallous compounds, which are usually more stable than the corresponding thallic compounds. The thallium(I) ion resembles the alkali metal ions and the silver ion in properties. In this respect, it forms a soluble, strongly basic hydroxide and a soluble carbonate, oxide, and cyanide like the alkali metal ions. However, like the silver ion, it forms a very soluble fluoride, but the other halides are insoluble. Thallium(III) ion resembles aluminum, gallium, and indium ions in properties. 

Univalent halides—e.g. NH l.AgCl CsCl.CuCl 2KCl.CuCl etc. The halides of the alkali metals do not often unite together to form stable complexes. Univalent copper, silver, and gold form double chlorides with the alkali halides, while the corresponding double bromides of silver and gold and the double iodide of silver have not been made. The facts can be summarized in the form of a scheme due to P. Pfeiffer (1902), where the hyphens represent compounds which have not yet been prepared ... 

Humphry Davy s process for the isolation of the alkali metals by the aid of the electric current is now regarded as the foundation of dry electrometallurgy, and justly so in spite of the fact that M. van Marum 4 had previously reduced several compounds by subjecting them to the electrical discharge. These methods were described in M. van Marum s pamphlet Experiences, qui font voir, qu il y a de la calorique dans la fluid ilectrique (Haarlem, 1795). He noted that in the reduction oxygen gas is evolved, and he credited the decomposition to the heating effect of the electric current. A few years later, J. W. Ritter decomposed silver salts by the discharge from a small electrical machine. 

The alkaline earth metals yield compounds of the type R2M(CNS)4, where R is an alkali metal or silver these are of interest since double halides of this type containing alkali and alkaline earth metals are not known. 

CARBIDES. A binary solid compound of carbon and another element. The most familiar carbides are those of calcium, tungsten, silicon, boron, and iron (cemcntitc) Two factors have an important bearing on the properties of carbides (1) the difference in electronegativity between carbon and the second elemenl. and (2) whether the second element is a transition metal. Saltlike carbides of alkali metals are obtained by reaction with acetylene. Those ohlained from silver, copper, and mercury sails are explosive. See also Carbon and Iron Metals, Alloys, and Steels. 

The tetraalkylammonium halides formed by complete alkylation of amines are ionic compounds that resemble alkali-metal salts. When silver oxide is used to precipitate the halide ion, tetraalkylammonium halides are converted to tetraalkylammonium hydroxides, which are strongly basic substances similar to sodium or potassium hydroxide ... 

Electrochemical Process. Several patents claim that ethylene oxide is produced in good yields in addition to faradic quantities of substantially pure hydrogen when water and ethylene react in an electrochemical cell to form ethylene oxide and hydrogen (206—208). The only raw materials that are utilized in the ethylene oxide formation are ethylene, water, and electrical eneigy. The electrolyte is regenerated in situ, ie, within the electrolytic cell. The addition of oxygen to the ethylene is activated by a catalyst such as elemental silver or its compounds at the anode or its vicinity (206). The common electrolytes used are water-soluble alkali metal phosphates, borates, sulfates, or chromates at ca 22—25°C (207). The process can be either batch or continuous (see Electrochemical processing). 

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