Sodium Metal Method

Support a small Pyrex test tube in a vertical position using a clamp whose jaws have either an asbestos liner or none at all the jaws must not be lined with materials such as rubber or plastic (Fig. 25.1). Place a clean cube of sodium metal about 3-4 mm on an edge in the tube and heat it gently with a microburner flame until 

Preparation Sign in at www.cengage.com/login to read the MSDSs for the chemicals used or produced in this procedure. 

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A modification of the K-R reaction was introduced by Mozingo. This method involved reacting an o-hydroxyacetophenone with an ester in the presence of metallic sodium to form a 1,3-diketone. Treatment of the diketone with an acid then delivered the chromone via an intramolecular cyclization reaction. This method was applied to the preparation of 2-ethylchromone (21). 0-hydroxyarylketone 22 was allowed to react with ethyl propionate (23) in the presence of sodium metal.The resulting sodium enolate was then quenched with acetic acid to deliver the 1,3-diketone 24. Upon heating 24 in glacial acetic acid and hydrochloric acid, 2-ethylchromone (21) was delivered in 70-75% overall yield. 

Acetylenes are sufficiently acidic to react with sodium metal to generate acetylides, useful nucleophiles in the formation of carbon-carbon bonds. The reaction is classically carried out in liquid ammonia, which is a good solvent for alkali metals but which is troublesome to handle. Two convenient modifications of the acetylide generation reaction overcome this difficulty and are discussed below along with the classical method. 

To remove any metallic Au, the reaction mixture is evaporated to dryness and subsequently passed over a commercial terra infusorii column in a minimal volume of solvent. Crystallization may be performed by slow diffusion of a two-layer system. Yields are low (10-60%). The metal evaporation technique (see 8.2.1.2) gives higher yields than the sodium borohydride method. 

C21-0090. The first commercially successful method for the production of aluminum metal was developed in 1854 by H. Deville. The process relied on earlier work by the Danish scientist H. Oersted, who discovered that aluminum chloride is produced when chlorine gas is passed over hot aluminum oxide. Deville found that aluminum chloride reacts with sodium metal to give aluminum metal. Write balanced equations for these two reactions. 

Actually, the formation of an F-center is more complicated than this. Although F-centers can be formed by severed methods, the best way to do so is by exposing a sodium chloride ciystal to sodium metal vapors. In that case, the following defect reactions have been observed to take place ... 

Another important reductive coupling is the conversion of esters to a-hydroxyketones (acyloin condensation).267 This reaction is usually carried out with sodium metal in an inert solvent. Good results have also been obtained for sodium metal dispersed on solid supports.268 Diesters undergo intramolecular reactions and this is also an important method for the preparation of medium and large carbocyclic rings. 

Another general method of preparation involves the reaction of cyclopentadiene with sodium metal or sodium hydride in tetrahydrofuran (THF). Addition of iron(ll) chloride to this solution forms the complex dicyclopenta-dienyliron ... 

Sodium metal is produced by both electrolytic and chemical reduction processes. All commercial processes employed today are based on electrolytic methods. Such processes are in wide use since Davy prepared the metal the first time in 1807. 

I. Sodium. Probably the best known active hydrogen remover is sodium. When used outside a vacuum system, for instance as sodium wire to dry solvents, the sodium is little more than a support for a skin of sodium hydroxide. Inside a vacuum system, however, one can prepare films of sodium metal and one can prepare really clean sodium which will give a colourless solution of sodium ethoxide (see Section 5.2.1.). The method of making sodium films for the removal of acidic compounds from liquid reagents will be described and also a very much less well-known method involving sodium vapour and colloidal sodium. 

Other Methods. Other reductants like hydrazine, sodium metal, etc. can be used for the reduction of metal ions. Decomposition of metal salts or complexes by heat treatment is sometimes used for synthesis of fine particles as well. In this case the valence of metals in the fine particles should be carefully examined. Recently, irradiation of ultrasonic wave was applied to the synthesis of colloidal dispersions of metal fine particles. 

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. 

A. 2-Hydroxymethylenecyclohexanone, Method 1. A mixture of 23 g. (1 g.-atom) of sodium metal cut in approximately 1-cm. cubes, 2 1. of dry ether, 98 g. (103 ml., 1 mole) of redistilled cyclohexanone, and 110 g. (120 ml., 1.5 moles) of ethyl formate is placed in a 5-1. three-necked flask equipped with a stirrer, stopper, and vent tube. The reaction is initiated by the addition of 5 ml. of ethyl alcohol to the stirred mixture, which is then placed in a cold water bath. Stirring is continued for 6 hours. After standing overnight, 25 ml. of ethyl alcohol is added, and the mixture is stirred for an additional hour. After the addition of 200 ml. of water, the mixture is shaken in a 3-1. separatory funnel. The ether layer is washed with 50 ml. of water, and the combined aqueous extracts are washed with 100 ml. of ether. The aqueous layer is acidified with 165 ml. of 6N hydrochloric acid, and the mixture is extracted twice with 300 ml. of ether. The ether solution is washed with 25 ml. of saturated sodium chloride solution and then is dried by (he addition of approximately 30 g. of an-... 

A useful method of forming carbon-carbon bonds involves reduction of esters with sodium metal in aprotic solvents such as ether or benzene and is called the acyloin reaction ... 

D. Logie (83) described a new analytical separation technique by applying ion-exchange membranes, which can be used for the determination of boron in sodium metal. By treatment with water, the Na is converted to NaOH, borate being formed from the boron. When the solution is introduced in the anode chamber of a two-cell apparatus fitted with a negative membrane, the Na+ ion is transported to the cathode chamber, whereas the borate anion remains in the anode chamber. In general this method can be applied, if the trace element yields an ion with a charge which opposite to that of the main component. 

A long established method for the preparation of alkanes involves heating an alkyl halide with sodium metal (the Wurtz synthesis). 

The fully delocalized n electron system of the benzene ring remains intact during electrophilic aromatic substitution reactions. However, in the Birch reduction, this is not the case. In the Birch reduction, benzene, in the presence of sodium metal in liquid ammonia and methyl alcohol, produces a nonconjugated diene system. This reaction provides a convenient method for making a wide variety of useful cyclic dienes. 

The conversion of levoglucosan derivatives to phenol in reasonable yields has been reported (168-175). This affords the possibility of also obtaining phenol from the cellulose portion of renewable resources. The reaction is carried out in liquid ammonia with sodium metal and thus probably is impractical on a commercial scale. But further research might lead to simpler, less costly, and more efficient methods for this conversion. 

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