Alkaline earth metal amalgam

CARBON, activated 1392 40 ALKALINE EARTH METAL AMALGAMS... 

The speed of the reaction depends both on the metal and on the alcohol, increasing as electropositivity iacreases and decreasiag with length and branching of the chain. Thus sodium reacts strongly with ethanol, but slowly with tertiary butyl alcohol. The reaction with alkaU metals is sometimes carried out ia ether, ben2ene, or xylene. Some processes use the metal amalgam or hydride iastead of the free metal. Alkaline earth metals and aluminum are often covered with an oxide film which hinders the reaction. 

Strontium [7440-24-6] Sr, is in Group 2 (IIA) of the Periodic Table, between calcium and barium. These three elements are called alkaline-earth metals because the chemical properties of the oxides fall between the hydroxides of alkaU metals, ie, sodium and potassium, and the oxides of earth metals, ie, magnesium, aluminum, and iron. Strontium was identified in the 1790s (1). The metal was first produced in 1808 in the form of a mercury amalgam. A few grams of the metal was produced in 1860—1861 by electrolysis of strontium chloride [10476-85-4]. 

Hydrogen can be prepared by the reaction of water or dilute acids on electropositive metals such as the alkali metals, alkaline earth metals, the metals of Groups 3, 4 and the lanthanoids. The reaction can be explosively violent. Convenient laboratory methods employ sodium amalgam or calcium with water, or zinc with hydrochloric acid. The reaction of aluminium or ferrosilicon with aqueous sodium hydroxide has also been used. For small-scale preparations the hydrolysis of metal hydrides is convenient, and this generates twice the amount of hydrogen as contained in the hydride, e.g. ... 

In many instances electrogravimetry must be preceded by a separation between metals suitably this can be an electroseparation by means of constant-current electrolysis as previously described, but more attractively an electroseparation by means of controlled-potential electrolysis at a mercury pool or sometimes at an amalgamated Pt or brass gauze electrode. In this way one can either concentrate the metal of interest on the Hg or remove other metals from the solution alternatively, it can be a rougher separation, i.e., the concentration of a group of metals such as Fe, Ni, Co, Cu, Zn and Cd on the Hg whilst other metals such as alkali and alkaline earth metals, Be, Al, Ti and Zr remain in solution151. In all these procedures specific separation effects can be... 

Up till now anionic mercury clusters have only existed as clearly separable structural units in alloys obtained by highly exothermic reactions between electropositive metals (preferably alkali and alkaline earth metals) and mercury. There is, however, weak evidence that some of the clusters might exist as intermediate species in liquid ammonia [13]. Cationic mercury clusters on the other hand are exclusively synthesized and crystallized by solvent reactions. Figure 2.4-2 gives an overview of the shapes of small monomeric and oligomeric anionic mercury clusters found in alkali and alkaline earth amalgams in comparison with a selection of cationic clusters. For isolated single mercury anions and extended network structures of mercury see Section 2.4.2.4. 

The only directly accessible metal fulminates are those of mercury(II) and silver(I), very dangerously exposive solids obtained by the action of nitric acid and ethanol on the metals or their salts. Most modern preparations of fulminato complexes involve the conversion of a known amount of mercury fulminate into aqueous sodium fulminate by the action of sodium amalgam and ice-cold water the sodium fulminate solution is then allowed to react with the appropriate amount of a transition metal salt, and the resulting complex fulminato ion is precipitated as the salt of a large cation, most frequently Ph4As+ or R4N+ these are not explosive,4,35 Alkali and alkaline earth metal salts containing complex fulminato anions may be isolated from aqueous solutions, but they are reported to be as exposive as the binary silver and mercury fulminates, and are therefore usually avoided. 

Compounds in which hydrogen is bonded to the alkali and alkaline-earth metals except beryllium are prepared by direct synthesis from the metals or amalgams. Beryllium hydride is prepared by pyrolysis or reduction of organic derivatives. 

All the arsinic acids dealt with in the following pages arc crystalline solids. Some of tlie primary acids, when heated above their melting-points, eliminate water and form anliydrides. The acids are very stable but may be reduced by amalgamated zinc dust and hydrochloric acid, or by electrolysis in aqueous alcoholic hydrochloric acid, to arylarsines, RAsIIs- An exception to tlie above-mentioned stability is the case of benzylarsinic acid, which is decomposed by mineral adds, and differs from all other members of this series in its reactions. The salts formed with alkali and alkaline earth metals show that the acids are dibasic. Esters may be formed by heating the silver salts of tlie acids in ethereal solution under reflux with the calculated amount of alkyl iodide, but excess of the latter must be avoided or alkyi-arylarsenites are formed ... 

Electrodes of the second kind are available for many anions. In the case of cations, one may use the pure metal or the metal amalgam. The latter choice is convenient for reactive metals such as the alkali and alkaline earth metals. Of course, amalgams containing very reactive metals such as sodium also react with water. However, special techniques have been worked out so that activity coefficient measurements can also be carried out with amalgams involving these metals [5]. 

Reaction of a 1,3-Diketone with a Metal. This procedure is usually carried out in an anhydrous inert medium. It has been used for obtaining derivatives of the alkali metals, 13,45,46 alkaline earth metals,13 copper (in the presence of air),47 aluminum (as an amalgam),48 and lead.40... 

For metals which are soluble in mercury (e.g. the alkali and alkaline earth metals) the polarographic half-wave potential Ey is a function of (i) the standard electrode potential of the metal-metal ion couple, (ii) the solubility of the metal in mercury and (iii) the free energy of amalgamation, (ii) and (iii) are independent of the nature of the solvent. 

The response of Thuringer glass to alkali and alkaline earth metals prompted Triimpler (1 ) to propose the glass electrode as a means of determining normal potentials via the use of amalgams. He found a value of 2.72 V for sodium. 

Matthias and Warhurst 34) report that the preparation of organic complexes of the alkaline earth metals Mg and Ca succeeded only with the aid of the amalgams of the metals. This may be caused by a lower ionization potential of the metal alloy as compared with that of its components. 

Several other rather novel methods for the separation of the lanthanides are discussed in the above text. Eu, Yb, and Sm can be reduced by amalgams of the alkali or alkaline earth metals to either the metal or the divalent ions which can be precipitated as sparingly soluble sulfates, RSO4. Electrolytic reduction at a mercury cathode can be used to separate the above three elements. A number of... 

The reaction requires the use of a catalyst for the alkaline earth metals, rare earth metals and aluminium. The most common approaches are the use of (in the laboratory practice only) the salts of mercury(II) such as HgC or Hg(OAc)2. Very small portions of these salts cause amalgamation of the metal surface (and thus clean it from the oxide layer) and facilitate the reaction with alcohols. The larger scale synthesis (and thus the industrial one—in the scope of pollution danger) uses the initial addition of solid iodine (1 g or less per 1(X) g ofalkoxide to be prepared). Formation of metal iodide serves both for cleaning the surface and increases also slightly the acidity of alcohols via formation of solvate complexes. In the case of barium, the application of dry ammonia gas has been reported for this purpose (Caulton, 1990 Drake, 1992). The major factor facilitating the reaction ofmetals with alcohols is the solubility of the alkoxides formed. Insoluble alkoxides form a protective layer on the surface of the metal and it hinders the reaction. Even the reaction of sodium with BuOH in toluene may be almost stopped by the formation of poorly soluble NaO Bu. 

---