Colloidal alkali metals

Reactions involving other alkali metals are not as numerous. The properties of colloidal alkali metals have been known for many years but they remain unexploited in synthesis due to the difficulties associated with their preparation. Luche and co-workers observed that small lumps of potassium could be dispersed in a few minutes by sonication in toluene or xylene at 10 °C in a cleaning bath [83], The colloid generated was used in a number of reactions for instance, a Dieckman cyclization could be effected within 5 min (Scheme 40). 

An emulsifying agent generally produces such an emulsion that the liquid in which it is most soluble forms the external phase. Thus the alkali metal soaps and hydrophilic colloids produce O/W emulsions, oil-soluble resins the W/O type (see emulsion). 

The sonochemistry of the other alkali metals is less explored. The use of ultrasound to produce colloidal Na has early origins and was found to greatly facilitate the production of the radical anion salt of 5,6-benzo-quinoline (225) and to give higher yields with greater control in the synthesis of phenylsodium (226). In addition, the use of an ultrasonic cleaning bath to promote the formation of other aromatic radical anions from chunk Na in undried solvents has been reported (227). Luche has recently studied the ultrasonic dispersion of potassium in toluene or xylene and its use for the cyclization of a, o-difunctionalized alkanes and for other reactions (228). 

T. Svedberg 33 prepared colloidal solns. of the alkali metals in ethyl ether, and he gives Table Y showing the colours of coarse and fine ethylethersols, as well as... 

The ordinary tellurates of colourless metallic radicals are colourless substances. The salts of the alkali metals are soluble in water but have no definite solubility. In many respects these salts resemble colloids, many of the basic and so-called acid salts which have been described having been shown to be adsorption compounds.7 When the alkali tellurates are heated, they decompose with the formation of tellurites, and they are generally more easily reducible than the latter salts. 

Micellar systems (i.e.,. Shenoy 1984 Ohlendorf Brunn) as well as other colloidal systems (polyphosphates (Hunston), tri-n-butyl-tin-fluoride, e.g. Dunn Evans) come under the heading surfactants . It is necessary to differentiate soaps into anionic, cationic, and non-ionic types. Among the anionic types one can find, for instance, alkali metals and ammonium salts consisting of various fatty acids, which were... 

At high neutralization levels with alkali metal ions, many ionomers spontaneously form colloidal suspensions in water when stirred vigorously at 100—150°C under pressure. Depending on solids content and acid level, the dispersions range in viscosity from water-like to paste-like. These provide convenient methods for applying thin coatings of ionomers to paper and other substrates. 

Ikeda, T., Nakahara, J., Sasaki, M., and Yasunaga, T. (1984). Kinetic behavior of alkali metal ion on zeolite 4A surface using the stopped-flow method. J. Colloid Interface Sci. 97, 278-283. 

Alkaline-earth metals. Of these metals, Ca, Sr, and Ba, only calcium is produced commercially in appreciable quantities. These three metals are more difficult to produce than the alkali metals since the chlorides of the alkaline-earth metals melt at relatively high temperatures. Furthermore, when these metals are liberated at the cathode, they tend to become colloidally dispersed throughout the molten electrolyte. Accordingly, it is necessary to design the electrolytic cells in such manner to permit the immediate collection of the elemental metal. The type of cell used in the production of calcium serves as a suitable illustration. Molten calcium chloride is placed in a cylindrical vessel around... 

As was mentioned in the previous section, the nature of the substrate is extremely critical in obtaining the maximum enhancement. For visible Raman excitation, the noble metals, such as Ag and Au, and the alkali metals are the substrates of choice. For other regions, other substrates are more suitable (e.g., Ge or Pt in the IR region). Probably the most common substrates used for SERS are the colloidal suspensions of silver or gold particles ( 5-20nm in diameter), and electrochemically roughened silver electrodes. 

The reactants tin(IV) chloride, alkali-metal base, and colloidal silica (Ludox-HS40) were thoroughly mixed at room temperature, according to the ratios 2-5M20 Sn02 4-10SiO2 8O-IOOH2O, for each synthesis [47], Cabosil (fumed silica) and sodium stannate were also used as reactants. 

But it was not to be. Try as we might, the difference in scattering lengths between the 6Li and 7Li isotopes was too small to permit us to measure the lithium ion distribution in the swollen state. We had to content ourselves with the results for the crystalline phase, where the behavior of the lithium ions is different from that of the larger alkali metal cations [27], Potassium and cesium ions bind directly to vermiculite clay surfaces rather than hydrating fully. Because only lithium-substituted vermiculites of the alkali metal series will swell macroscopically when soaked in water, it seems that interlayer cations must form fully hydrated ion-water complexes if the particles are to expand colloidally. This conclusion has since been supported... 

Cupric hydroxide, Cu(OH)2.—The hydroxide has been prepared in crystalline form by the action of a solution of caustic alkali on a basic cupric nitrate 2 and a basic cupric sulphate,3 and also by other methods.4 A hydrogel of varying composition is precipitated by addition of alkali to solutions of cupric salts.5 Unlike the colloidal form, the blue crystalline variety is stable at 100° C. A solid, colloidal variety has been obtained 6 as blackish-blue, brittle lamellae which dissolve in water to form the original solution. An amorphous modification is precipitated from ammoniaeal copper solutions by the action of alkali-metal hydroxides.7... 

In qualitative analysis copper is detected by precipitation as cupric sulphide from hydrochloric-acid solutions of its salts. To prevent the formation of a colloidal precipitate, the solution should be hot, and should contain excess of the acid. The sulphide is soluble in hot, dilute nitric acid, and in potassium-cyanide solution, but almost insoluble in solutions of alkali-metal sulphides. It dissolves to some extent in ammonium-sulphide solution. Other aids in the detection of copper are the blue colour of solutions of cupric-ammonia salts the reddish-brown precipitate of cupric ferrocyanide, produced by addition of potassium ferro-cyanide to cupric solutions the formation of an intense purple coloration by the interaction of hydrogen bromide and cupric salts, a very delicate reaction2 the formation of a bluish-green borax bead and the ready isolation of the metal from its compounds by the action of reducers. 

In initiation by alkali metal, an electron is transferred from the metal to the monomer (the metal is usually charged as a solid or colloid). Sodium-initiated butadiene polymerization provides an example [74,75] ... 

The chromites of the alkali metals and of ammonium are presumably formed to some extent in solution, when chromic hydroxide dissolves in excess of the alkali hydroxide but it has been shown that these solutions are in large degree merely colloidal solutions of the hydroxide (see p. 36). By shaking chromic hydroxide, dried over sulphuric acid, with solutions of sodium hydroxide of different concentrations, Muller found that the amount of hydroxide dissolved depended on the time of agitation, rising to a maximum and then falling to an almost constant value. The solutions obtained w ere not colloidal. Fricke and Wind-hausen have prepared similar solutions, and by allowing solutions of potassium chromite to stand for some time, obtained needle-shaped crystals of composition CrjOj.SKjO.SHjO. 

Introduction. The object of this experiment is to illustrate a number of general reactions of carboxylic acids. Salt formation is a characteristic property of the carboxyl group. The salts of the alkali metals as a rule are soluble. The higher, sparingly soluble, fatty acids form salts which give colloidal dispersions. The soluble salts are prepared by neutralization of the acid with alkali, or by boiling with an excess of the metallic carbonate and evaporating the solution. 

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