Alkali metals solutions

Some molecular solvents (such as ammonia, aliphatic amines, hexamethyl-phosphortriamide) dissolve alkali metals solutions with molalities of more than 10 mol kg-1 are obtained. Ammonia complexes M(NH3)6 analogous... 

Abe S, Choi P- K (2008) Effect of frequency on sonoluminescence spectrum from alkali-metal solutions. Nonlinear acoustics- Fundamentals and applications. AIP Confer Proc 22 189-192... 

Polyether complexation. The solution of the above problem is to add a suitable crown ether or cryptand to the alkali metal solution. This results in complexation of the alkali cation and apparently engenders sufficient stabilization of the M+ cation for alkalide salts of type M+L.M" (L = crown or cryptand) to form as solids. Thus the existence of such compounds appears to reflect, in part, the ability of the polyether ligands to isolate the positively charged cation from the remainder of the ion pair. 

Both macrocyclic and macrobicyclic ligands allow preparation of alkali metal solutions, but the former yield mainly M-, whereas solvated electrons are obtained with the [2]-cryptates (162,163). The enhancement of anion reactivity should also useful for activating anionic polymeriza-... 

D. Fluorocarbon Polymers. Four different fluorocarbons account for the bulk of the laboratory applications polytetrafluoroethylene, Teflon PTFE po-ly(chlorotrifluoroethylene), KEL-F tetrafluoroethylene-hexafluoropropylene copolymer, Teflon FEP and tetrafluoroethylene-perfluorovinyl ether copolymer, PFA. These polymers are inert with most chemicals and solvents at room temperature and exceptionally inert with oxidizing agents. They also have an exceptional resistance to temperature extremes. However, they are decomposed by liquid alkali metals, solutions of these metals in liquid ammonia, and carban-ion reagents such as butyllithium. Teflon retains some of its compliance at liquid hydrogen temperature. The maximum temperature which is recommended for continuous service is 260°C for Teflon PTFE and PFA, and about 200°C for Kel-F and Teflon FEP. 

Although seven-eighths of the current is carried by electrions, this process is not the same as that by which a current is carried in a metal. The low value of the conductance (about 900) of the electrion in dilute solution shows clearly that in its motion, the electron interacts with solvent molecules in such a way as to reduce its mobility. The existence of such interaction between the electron and ammonia is confirmed by the magnetic resonance and optical properties of alkali metal solutions. 

The dependence of the shape, intensity, and energy of the absorption band on temperature was investigated using a 2.83 X 10 AM solution of sodium in liquid ND8. The spectrum of this solution at several temperatures is shown in Figure 6b. A plot of the energy of the absorption maximum vs. temperature is shown in Figure 7, and a least squares treatment of these data indicates that the temperature dependence of the band maximum is — 14.3/cm./deg. Values of —9.7/cm./deg. for sodium (6), —9.1/cm./deg. for potassium (2), and — 12.7/cm./deg. for the alkali metal solutions (9) in liquid ammonia have been reported. No detectable decomposition of the solution occurred during the four hours required to take the measurements between —69° and —31° C. The intensity of the band, as measured by both the absorbance (1.48 0.04)... 

We have recently reported a new photochemical reaction, in which faded alkali metal solutions in ethylamine are regenerated by UV ir-... 

As early as 1969, Pedersen was intrigued by the intense blue colour observed upon dissolution of small quantities of sodium or potassium metal in coordinating organic solvents in the presence of crown ethers. Indeed, the history of alkali metal (as opposed to metal cation) solution chemistry may be traced back to an 1808 entry in the notebook of Sir Humphry Davy, concerning the blue or bronze colour of potassium-liquid ammonia solutions. This blue colour is attributed to the presence of a solvated form of free electrons. It is also observed upon dissolution of sodium metal in liquid ammonia, and is a useful reagent for dissolving metal reductions , such as the selective reduction of arenes to 1,4-dienes (Birch reduction). Alkali metal solutions in the presence of crown ethers and cryptands in etheric solvents are now used extensively in this context. The full characterisation of these intriguing materials had to wait until 1983, however, when the first X-ray crystal structure of an electride salt (a cation with an electron as the counter anion) was obtained by James L. Dye and... 

Fig. 12. Infrared optical absorption bands observed in ethylenediamine solutions (A) spread in band shape of er observed by pulse radiolysis, (B) spread in band shape observed in alkali metal solutions. [Adapted with permission from W. A. Seddon and J. W. Fletcher, Journal of Physical Chemistry, 84, 1104 (1980). Copyright 1980 American Chemical Society.]...

The latter process seems to be very selective against alkali metal cations in the initial stages of exchange and is critically dependent on alkali metal solution phase concentration. Sometimes ion-exchange processes can be described as ion sieving when a particular cation (hydrated or unhydrated) is too large to enter all, or part of, the zeolite internal structure. 

In 1864, W Weyl also observed the blue color of alkali metals solutions in ammonia, methylamine and ethyl amine and found that the resulting solutions had reducing properties, when used in chain synthesis. However, W Weyl did not discover the nature of these blue solutions. Nowadays, it is known that the blue color is due to the solvated electron, as alkali metals dissolved in amine solvents give the metal cation and a solvated electron as in the case of sodium ... 

From the first observations of the blue color of alkali metal solutions in ammonia, the major characteristic of the solvated electron is its optical properties. 

U TLC cellulose Alkali metal solutions Fluorimetry, photo-1 ppm metry 277)... 

The alkalide compounds are synthesized in an H-cell using vacuum line and drybox techniques . Measured amounts of the alkali elements (2 mol) are introduced into one side of the cell by means of a drybox. The metals are then sublimed to form a glass on the inside of the cell. Alternatively, the alkali metal is prepared by dissolution in liquid NH3 followed by evacuation to dryness. The chelate (1 mol for the crypt, 2 mol for the crown ethers) is placed into the other side of the cell. Dimethyl ether is then condensed into both sides. After complete dissolution of the reagents the alkali metal solution is decanted into the chelate solution through a frit separating the two sides of the cell. This solution is allowed to stand for 12 h before further manipulation. After the two solutions have been combined the temperature must be kept below — 20°C to prevent decomposition. Crystalline samples are obtained by slow cooling after addition of dimethylamine or by slow evaporation of the dimethyl ether solution. 

The solubility of alkali metals in most of the solvents used in anionic polymerization is exceedingly low. Liquid ammonia and hexamethylphosphoric-triamide are exceptional in this respect relatively high concentrations of the metals can be attained in these media. Several distinct species co-exist in alkali metal solutions. A minute but constant concentration of unionized atoms, Met, is maintained when a solvent is kept in contact with solid alkali metal. These in turn are in equilibrium with the products of their ionization ... 

The extremely high reactivity of alkali metal solutions calls for the utmost care in their handling. They must not be exposed to the air indeed, solutions such as potassium in hexamethylphosphoric-triamide are pyrophoric. Moisture and other adsorbed impurities have to be meticulously removed from all surfaces that come in contact with these reagents. A relatively simple technique to achieve this goal is described elsewhere1415. 

Alkoxide formation is responsible for the slow destruction of alkali-metal solutions in ethers. For example,... 

Since the first preparation of alkali-metal intercalates by the liquid ammonia technique, many preparation methods have been proposed. The most commonly used fall into four main groups (i) use of alkali-metal solutions in liquid ammonia, (ii) use of organometallic reagents, (iii) solid-state techniques and (iv) electrochemical processes. 

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