Liquid sodium amalgam

The action of liquid sodium amalgam on trimethylchlorosilane (34a, 34b) or -bromosilane (207) at room temperature results in the exclusive formation of bis(trimethylsilyl)mercury, [(CH3)3Si]2Hg, which is relatively stable to heat. This compound, however, undergoes decomposition on heating at 100°-160° C for a day to give hexamethyldisilane in quantitative yield (9, 34a, 34b, 207). 

Because they possess an odd number of valence electrons the elements of this group can only satisfy the 18-electron rule in their carbonyls if M-M bonds are present. In accord with this, mononuclear carbonyls are not formed. Instead [M2(CO)s], [M4(CO)i2] and [M6(CO)i6] are the principal binary carbonyls of these elements. But reduction of [Co2(CO)g] with, for instance, sodium amalgam in benzene yields the monomeric and tetrahedral, 18-electron ion, [Co(CO)4] , acidification of which gives the pale yellow hydride, [HCo(CO)4]. Reductions employing Na metal in liquid NH3 yield the super-reduced [M(CO)3] (M = Co, Rh, Ir) containing these elements in their lowest formal oxidation state. 

The same analytical methods as for liquid sodium have been applied. Distillation separates and concentrates the impurities prior to analysis. Amalgamation has poor recovery value for oxygen compared to distillation (Table 1). ... 

Interaction of sodium and mercury to form sodium amalgam is violently exothermic, and moderation of the reaction with an inert liquid, or by adding mercury slowly to the sodium is necessary. Even so, temperatures of 400°C may be attained. 

In most cases, the reaction requires external stimulation in which a catalytic amount of electrons is injected into the solution. Solvated electrons in liquid ammonia, sodium amalgam in the same solvent71 light,66-68 electrodes1167 and... 

Sodium Amalgam.—Mercury and sodium react with violence, sparks and flames being produced the amalgam must therefore be made inside a fume chamber and goggles must be worn. In a mortar of moderate size 300 g. of mercury are warmed to 30°—40° and the sodium (6 5 g. in all), cut into small cubes, is introduced on the point of a glass rod about 30 cm. long the pieces are pushed under the surface of the liquid in rapid succession. A porous plate is used as a cover for the mortar in order to provide protection against spurt-... 

Sodium amide has been prepared by the action of gaseous 2 or liquid3 ammonia on sodium, by the action of ammonia on alloys of sodium,4 and by the electrolysis of a solution of sodium cyanide 5 in liquid ammonia with a sodium amalgam electrode. A summary of the chemistry of alkali amides is given by Bergstrom and Fernelius.1... 

It is logical to consider the nncleophile, Nu-, as a source of the electron to be transferred onto the snbstrate molecnle, RX. However, in most cases, the nucleophile is such a poor electron donor that electron transfer from Nn- to RX is extremely slow, if it is possible at all. These reactions reqnire an external stimulation in which a catalytic amount of electrons is injected. Such kinds of assistance to the reactions from photochemical and electrochemical initiations or from solvated electrons in the reaction mediums have been pointed out earlier. Alkali metals in liquid ammonia and sodium amalgam in organic solvents can serve as the solvated electron sources. Light initiation is also used widely. However, photochemical initiation complicates the reaction performance. 

Sodium and sodium amalgam may be used for reduction of amides but the yields of amines are generally very low. Primary aromatic amides (benz-amides) were reduced at the carbonyl function with 3.3 equivalents of sodium in liquid ammonia and ethanol while in tert-butyl alcohol reduction took place in the aromatic ring giving 1,4-dihydrobenzamides [984. ... 

A number of other routes are available for the syntheses of diquaternary salts of 4,4 -bipyridines. One method that has been extensively studied involves reaction of a 1-alkylpyridinium salt with sodium amalgam (or sodium in liquid ammonia) to form the 1,1 -dialkyl-1,1, 4,4 -tetrahydro-bipyridine, which is readily oxidized to the corresponding l,l -dialkyl diquaternary salt. This reaction is analogous to the synthesis of 4,4 -bipyridine by the action of sodium on pyridine, followed by oxidation of the intermediate tetrahydrobipyridine. " The reduction may be achieved electrolytically or by reaction with zinc or magnesium. Various oxidizing agents have been used to assist the conversion to the di-quaternary Another synthesis of diquaternary salts of... 

Cyclobutyl phenyl sulfides are reduced with sodium in liquid ammonia,150 while cyclobutyl phenyl sulfones are reduced either by sodium amalgam,SI -152 or sodium in ethanol.153 In the latter case, an alkene results if the sulfonyl group has a neighboring acetyl group, i.e. reduction of li , 2/ , 3S )-l-(l-acetoxy-2-methylpropyl)-2,3-dimethyl-1-phenylsulfonylcyclobutane gave lram -l,2-dimethyl-3-(2-methylpropylidene)cyclobutane (16).153... 

As a safety precaution against EXPLOSION (in case the purification has been insufficiently thorough) at least a quarter of the total volume of ether should remain in the distilling flask when the distillation is discontinued. To minimize peroxide formation, ethers should be stored in dark bottles and, if they are liquids, they should be left in contact with type 4A Linde molecular sieves, in a cold place, over sodium amalgam. The rate of formation of peroxides depends on storage conditions and is accelerated by heat, light, air and moisture. The formation of peroxides is inhibited in the presence of diphenylamine, di-tert-butylphenol, or other antioxidant as stabilizer. 

The pK.d values of TV-methyltrifluoromethanesulfonamide (TfNHMe = 7.5) and TV-meth-yltoluenesulfonamide (TosNHMe= 11.7) have been examined and it was found that these sulfonamides are applicable to the Mitsunobu reaction conditions. 80 A modified Mitsunobu reaction has been used for the synthesis of A7"-alkyl amino acid esters 81,82 this method is only applicable to amino acid esters and not to the free acids. Thus, TV-Tos amino acid esters are condensed with MeOH, EtOH, or iPrOH in the presence of TPP and DEAD. The Tos group is deprotected by sodium in liquid ammonia or with sodium amalgam. 83 The deprotection of the Tos group has also been achieved electrochemically under mild conditions and in good yields. 84 ... 

Compounds related to aniline, either directly or by oxidation, and to nitrobenzene by reduction, are numerous and important. When nitrobenzene is reduced in the presence of hydrochloric acid by tin or iron, the product is aniline (colorless liquid in die presence of water by zinc, the product is phenylhydroxylamine (white solid) in the presence of methyl alcohol by sodium alcoholate 01 by magnesium plus ammonium chloride solution, the product is azoxybenzene (pale yellow solid) by sodium stannitc, or by water plus sodium amalgam, the product is azobcnzcnc (red solid) in the presence of sodium hydroxide solution by zinc, the product is hydrazobenzene (pale yellow solid). The behavior of other nitrocompounds is similar to that of nitrobenzene. 

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