Sodium/mercury amalgam

Recently it has been shown that the oxides of the platinum metals can have a higher corrosion resistance than the metals themselves , and have sufficient conductivity to be used as coatings for anodes, e.g. with titanium cores. Anodes with a coating of ruthenium dioxide are being developed for use in mercury cells for the electrolysis of brine to produce chlorine , since they are resistant to attack if in contact with the sodium-mercury amalgam. 

Owing to the rocking of the box, the sodium mercury amalgam will pass into the centre compartment, where... 

Although commercially available (Aldrich), polymeric tungsten tetrachloride is routinely prepared by McCarley s method,7,15 which is given below. Tungsten hexachloride and tungsten hexacarbonyl (Strem) are used without further purification. Sodium-mercury amalgam (0.5 wt%) is prepared in a 500-mL two-necked round-bottomed flask equipped with a N2 gas inlet and a stopper, by adding 6.83 g (297 mmol) of sodium metal in small pieces ( 0.1-0.2 cm3) to 100 mL of mercury. 

Most useful of the demercuration procedures reported is the use of alkaline sodium borohydride244 or sodium-mercury amalgam.243 246 Reduction with UAIH4 affords the corresponding amines.24 ... 

Alkaline sodium borohydride is the preferred demercuration reagent, but sodium-mercury amalgam in D2O is best for stereospecific reduction with retention.268... 

The demercuration of (3-alkoxymercurials is usually best effected using alkaline sodium borohydride. Few rearrangements during this free radical reduction process have been observed 429 When the mercury moiety is positioned a to a carbonyl group, alkaline H2S430,431 or 1,3-propanedithiol316 provide alternatives that afford complementary stereochemical results (equation 262). The use of sodium-mercury amalgam is also useful for stereospecific reduction.432 433... 

A second method uses the Kellner-Solvay cell. Saturated sodium chloride solution is electrolyzed between a carbon anode and a flowing mercury cathode. In this case the sodium is produced at the cathode rather than the hydrogen because of the readiness of sodium to dissolve in the mercury. The sodium-mercury amalgam is then exposed to water and a sodium hydroxide solution is produced. 

Primary cells (known as the electrolyser) where sodium chloride is electrolysed to sodium and chlorine. Sodium combines with mercury to form sodium-mercury amalgam. 

The sodium-mercury amalgam is treated with water outside the cell to produce sodium hydroxide and hydrogen gas. 

In a similar fashion, Pelkey et al. demonstrated that 1,2-bis(phenylsulfonyl) indole (84) would undergo nucleophilic addition by methyl cuprate to form 3-methyl-2-(phenylsulfonyl)indole (86) [41]. The phenylsulfonyl group can be removed by treatment with sodium-mercury amalgam to produce skatole (88). Other simple cuprates such as butyl cuprate add to 84 to form 3-butyl-2-(phenyl-sulfonyl)indole (89) [8]. The presumed intermediate with a C-2 anion could be trapped by addition of methyl iodide shortly after the addition of methylcuprate to 77 to yield 2,3-dimethyl-l-(phenylsulfonyl)indole (90) in 70% yield [8]. 

Samarium iodide can also be used as an alternative to sodium/ mercury amalgam for the reductive elimination of 1,2-acetoxy-sulfones in the Julia-Lythgoe olefination. The alkene is generated in a two-step process that first involves DBU or LDA treatment to generate a vinyl sulfone that is then reductively cleaved with samarium iodide (eq 44). The diastereoselectivity of both transformations is usually quite good and the method is compatible with the synthesis of monoalkenes as well as dienes and trienes. 

Figure 21.17 Mercury cell used In the chlor-alkall process. The cathode contains mercury. The sodium-mercury amalgam Is treated with water outside the cell to produce sodium hydroxide and hydrogen gas.

Keck GE, Savin KA, Weglarz MA. Use of samarium diiodide as an alternative to sodium mercury amalgam in the Julia-Lythgoe olefination. J. Org. Chem. 1995 60(10) 3194-3204. 

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