Preparation of Amalgams

The solubilities of various metals in mercury at 18° C. are noted in the accompanying table. Concentration of the saturated amalgam usually results in the precipitation of the dissolved solute as a mercuride, rarely in the form of the free metal. It should be noted that metals chemically and physically similar to mercury are characterized by high solubility. The farther removed in the Mendeleev periodic table the metals are from mercury the less soluble they become. Actually none of the metals except thallium is extremely soluble consequently, methods leading to the preparation of amalgams often give products 

Various methods have been employed for the preparation of amalgams.4 Each has certain advantages, and each is especially applicable in certain cases. They may be grouped into four general classes  

The first three are illustrated by specific examples in the syntheses that follow. Sodium amalgam (synthesis 4) is readily prepared by direct combination of the metal with mercury (illustrating method 1). Barium amalgam (synthesis 5) can be produced readily by the electrolysis of a saturated aqueous solution of barium chloride with a mercury cathode (illustrating method 2a). Barium amalgam is also easily obtainable by the action of sodium amalgam upon a concentrated aqueous solution of barium chloride (illustrating method 3). 

Methods of direct combination are especially desirable in those cases where the metal to be amalgamated is readily available. It is generally necessary to heat the two constituents together to effect solution and reaction. Where either the metal or the product is reactive, the preparation is carried out under an inert solvent, in an atmosphere of hydrogen or nitrogen, or by heating in a vacuum in a sealed glass tube or metal bomb. 

The electrolytic method is especially useful in those cases where the metals are not readily obtainable in the free state or where they are too active to permit use of the method of direct combination. Potassium, rubidium, 

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Preparation of amalgams electrochemical reduction on an Hg cathode According to Guminski (2002), the electrochemical reduction of metallic ions on an Hg cathode from aqueous or non-aqueous solvents (as well as from molten salts) allows the introduction of both soluble and insoluble metals into the Hg phase. Some amalgams may be prepared by simultaneous reduction of Hg2+ and Men+ from their solutions. On the other side, noble metal (Pd, Pt, Ag, Au) amalgams may by obtained by reduction of Hg2+ on noble metal electrodes. 

Aluminum fer/.-butoxide can be prepared by refluxing dry tert. -butyl alcohol with amalgamated aluminum 5l 6 or aluminum plus mercuric chloride.6 The method described is that of Adkins and Cox.0 The preparation of amalgamated aluminum has been described.3, 4 Aluminum isopropoxide can be prepared from dry isopropyl alcohol and aluminum,1 2 the method being essentially that described for aluminum ethoxide (Org. Syn. is, 82). 

Another general method for preparation of amalgams consists of the electrolysis of solutions ofthe respective metal salts in cells comprising an Hg cathode. The concentrations of the respective metals in the amalgam reach very high levels so that solid phases may separate. The method is applicable even to metals with extremely low solubility in Hg (for example, Fe) in this case, the method gives suspensions of the metal in Hg which exhibit behavior very similar to that of true amalgams (see Table 7). 

The preparation of amalgams of lanthanum, neodymium, and cerium by electrolysis of the anhydrous chlorides in alcoholic solution has already been described. The electrolysis of a rare earth chloride in water solution proves unsatisfactory because of the production of a precipitate of hydrous oxide at the cathode and the liberation of chlorine at the anode. 

If pure triphenylchloromethane and freshly prepared sodium amalgam are used, the yield of sodium triphenyl-methide should be almost quantitative but is usually 0 15 mol per htre (1). The reagent should be used as soon as possible after its preparation. 

Xanthhydrol. Prepare an amalgam from 9 0 g. of clean sodium and 750 g. (55 ml.) of mercury (Section 11,50,7, Method 1), and warm it to 50° in a 500 ml. Pyrex bottle. Add a cold suspension of 25 g. of xanthone in 175 ml. of rectified spirit, stopper the bottle and shake vigorously raise the stopper from time to time to release the pressure. The temperature rises rapidly to 60-70°, the sohd xanthone passes into solution, and a transient blue colour is developed. After about 5 minutes the alcoholic solution is clear and almost colourless. Shake for a further 10 minutes, separate the mercury, and wash it with 15 ml. of alcohol. Filter the... 

Electrolytic Preparation of Chlorine and Caustic Soda. The preparation of chlorine [7782-50-5] and caustic soda [1310-73-2] is an important use for mercury metal. Since 1989, chlor—alkali production has been responsible for the largest use for mercury in the United States. In this process, mercury is used as a flowing cathode in an electrolytic cell into which a sodium chloride [7647-14-5] solution (brine) is introduced. This brine is then subjected to an electric current, and the aqueous solution of sodium chloride flows between the anode and the mercury, releasing chlorine gas at the anode. The sodium ions form an amalgam with the mercury cathode. Water is added to the amalgam to remove the sodium [7440-23-5] forming hydrogen [1333-74-0] and sodium hydroxide and relatively pure mercury metal, which is recycled into the cell (see Alkali and chlorine products). 

Composition. The composition of powdered alloys used in preparing dental amalgams usually includes 66.7—75.5% silver 25.3—27.0% tin ... 

The photochemical or thermal reaction between petfluoroalkyl iodides and mercury-cadmium amalgams has been used for the synthesis of perfluoro-alkylmercury compounds [150] Functionalized analogues have been prepared similarly via this route [151, 152] (equation 117), and the preparation of bis(tri-fluoromethyl)mercury has been described [153]... 

Preparation of y -Bis-(4-Hydroxylphenyl)-Hexane- i -Diol A sodium amalgam is prepared containing 6 grams of sodium and 400 grams of mercury. The amalgam is covered with a solution of 20 grams of 4-hydroxypropiophenone in a mixture of 30 ml of 5 N sodium... 

Reduction of 16-keto-17(0i)-hydroxyestratrienol-3-methyl to 16,17-dihydroxyestratrienol-3-methyl ether A solution of 800 mg of the alpha ketol methyl ether in 100 cc of ethanol and 10 cc of acetic acid was carefully maintained at 40°C (water bath), and 200 g of freshly prepared sodium amalgam (2%) were added in small pieces with efficient swirling. Before all of the amalgam had been added, a precipitation of sodium acetate occurred, and at this point an additional 100 cc of 50% acetic acid were added. After all the reducing agent had been added, the mixture was transferred to a separatory funnel with ether and water. 

Fleischer1 prepared benzylaniline by heating aniline with benzyl chloride at i6o°. This reaction may be very violent and always leads to mixtures. Bernthsen and Trompetter 2 reduced thiobenzanilide with zinc and hydrochloric acid or sodium amalgam, while O. Fischer 3 reduced bcnzalaniline with sodium and alcohol, to benzylaniline. Knoevenagel4 obtained a 32 per cent yield of benzylaniline from benzyl alcohol and aniline in the presence of iodine. Ullmann5 describes the preparation of benzylaniline from benzyl chloride and excess of aniline at low temperatures. 

Silver was formerly extracted by cyanide solution of Ag2S, the resulting Ag(CN)2 being treated with zinc to afford the metal roasted ores could also be extracted with mercury to give silver amalgam. Presently much silver is extracted by workup of the anode slime from the preparation of non-ferrous metals (Pb, Cu) pure silver is obtained by electrolysis of AgN03. 

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