Sodium Dispersions

At temperatures above 97.5°, a mixture of sodium metal and a saturated hydrocarbon constitutes a binary system of mutually insoluble liquids that can be emulsified in much the same manner as oil and water. When this sodium-in-oil emulsion is permitted to cool below this temperature, the sodium solidifies as microscopic spheres suspended in the hydrocarbon. Addition of certain surface-active agents1 such as oleic acid, prior to cooling, assists in keeping the sodium in suspension. Such a formulation is known as a sodium dispersion. 

Caution. All work with sodium and sodium dispersions should be planned and conducted carefully. Face shield, rubber apron, and rubber gloves should be worn in order 

The condenser is immediately reattached to the flask, and the contents of the flask are heated to ca. 105° to melt the sodium. The stirrer is started, slowly at first but with increase to maximum speed in 1 to 2 minutes. Stirring is continued at this speed for approximately 15 minutes, the temperature being maintained in the range 105 to 125°. 

The resulting uniformly gray suspension is allowed to cool to room temperature without further agitation. The yield is quantitative. 

The cooled dispersion is either poured from the creased flask into a suitable container for further use or utilized directly in the dispersion flask (sodium hydride, synthesis 3). 

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Sodium Dispersions. Sodium is easily dispersed in inert hydrocarbons (qv), eg, white oil or kerosene, by agitation, or using a homogenizing device. Addition of oleic acid and other long-chain fatty acids, higher alcohols and esters, and some finely divided soHds, eg, carbon or bentonite, accelerate dispersion and produce finer (1—20 -lm) particles. Above 98°C the sodium is present as Hquid spheres. On cooling to lower temperatures, soHd spheres of sodium remain dispersed in the hydrocarbon and present an extended surface for reaction. Dispersions may contain as much as 50 wt % sodium. Sodium in this form is easily handled and reacts rapidly. For some purposes the presence of the inert hydrocarbon is a disadvantage. 

The organic layer is then dried, filtered and evaporated. The oily residue is distilled in vacuo, yielding 1,600 parts dl-N-formyI-N-[(ethoxycarbonyl)methyl] -1 -phenylethylamine (boiling point 160°C to 170°Cat 0.8 mm pressure). 30 parts of a sodium dispersion, 50% in paraffin oil are added to 450 parts tetrahydrofuran and the whole is slowly heated to a temperature of 40°C, while stirring. While maintaining this temperature (cooiing on a water bath is necessary) there are added portionwise 30 parts ethanol. 

Cyclohexane (Phillips 99+ mole %) was purified by stirring over H SO then distilled from a sodium dispersion. Tetrahydrofuran (Fisher) was distilled from a sodium/benzophenone complex. 

Our initial studies (23) were performed in toluene, and Table I shows the results from the polymerization of a number of representative monomers. The data reported in Table I are for direct addition of the monomer to the sodium dispersion. Inverse addition often leads to higher molecular weights, although the overall polymer yields are usually lower (15,23). The results in Table I show that, under these reaction conditions, a bimodal molecular molecular weight distribution is normally obtained. Furthermore, it is obvious that the crude polymer yields drop precipitously as the steric hindrance in the monomer increases. 

Polydiorganosilane copolymers were synthesized by adding 2.2 moles of a sodium dispersion in a light oil (Aldrich) at a constant rate (320 meq/min) into a toluene solution which contained a total of 1 mole of diorganodichlorsilane monomers. 

The reaction of these monomers with sodium dispersion at 70-90°C under a nitrogen atmosphere afforded poly[p-diethyldimethyldi-silanylenejphenylene] (10) and poly[p-(1,2-dimethyldiphenyldisilanyl-enejphenylene] (11), respectively, in good yields. 

The first stage of a reaction involved the addition of sodium dispersed in toluene to a solution of adipic ester in toluene. The subsequent addition of iodomethane (b.p. 42°C) was too fast and vigorous boiling ejected some of the flask contents. Exposure of sodium particles to air caused ignition, and a violent toluene-air explosion followed [ 1 ]. When a reagent as volatile and reactive as iodomethane is added to a hot reaction mixture, controlled addition, and one or more wide-bore reflux condensers are essential. A similar incident involving benzene was also reported [2]. 

In the preparation of triphenylphosphine from chlorobenzene, phosphorus trichloride and sodium dispersed in toluene or xylene, the possibility of explosion is avoided by adding about 1 mol% of a lower alcohol, based on sodium usage. 

After storage for 16 years in a tin, a sealed bottle originally holding sodium dispersed in xylene was found to contain a yellow/white solid layer in place of the expected supernatant xylene. Scraping the solid out caused a violent explosion. The force of the explosion leads to a suspicion of peroxide formation, but there is no obvious explanation. Reactive materials like alkali-metal dispersions in volatile solvents should not be stored indefinitely, but clearly labeled after receipt or preparation to show the disposal date. Disposal of such dispersions by binning is recommended. Sodium dispersed in toluene might behave in the same way. 

The reduction as described is applicable to small as well as large scale operations provided safety precautions necessary for handling molten sodium and sodium dispersion are observed. 

Sodium hydride is prepared by passing hydrogen gas into molten sodium metal dispersed in oil. Alternatively, the hydride can be made by passing hydrogen into sodium dispersed over the surface of an inert solid, such as, hydrocarbon above 200° C... 

Sodium aceiylide has also been prepared from acetylene and a sodium dispersion in an inert solvent at elevated temperatures [38]. This method seems more suitable for industrial application, since preparation of a sufficiently fine dispersion is not easily realized with the usual laboratory means. 

We have recently synthesized and characterized a variety of soluble, substituted polysilane homopolymers by the condensation of appropriately substituted methylsilyl dichlorides with sodium dispersion as shown below and in Table I... 

The polymers were produced in yields which ranged from 8-55%. It was observed in most cases that the highest molecular weights were obtained when the sodium dispersion was added to the monomer in toluene (4 1 toluene/monomer) in what we term "inverse addition." Normal addition (i.e., addition of the monomer to the sodium) usually resulted in slightly improved yields of lower molecular weight material. In either case, it is advantageous to avoid a large excess of sodium in the reaction mixture, since this usually results... 

THF was distilled from a blue solution of benzophenone ketyl obtained by refluxing THF in the presence of a sodium dispersion in paraffin and benzophenone. 

All of the polysilanes used in this study were prepared by the modified Wurtz-type coupling of substituted dichlorosilanes by sodium dispersion in an inert aromatic solvent as previously described (23.24). Poly(di-n-hexylgermane) was similarly prepared from di-n-hexyldichlorogcrmane (16). All of the polymer samples... 

The yield of cyclotetrasilene 51 is much improved using tris(tert-butyl-dimethylsilyl)silyl-substituted dibromochlorosilane 90 as a precursor for 51 the reductive dehalogenation of 90 using sodium dispersion in toluene at room temperature (rt) provides 51 in 64% yield 24... 

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