Alkali metal reactions

Pytlewski LL, Krevitz K, Smith AB. 1979. Conversion of PCBs and halogenated pesticides into non-toxic materials using a new type of alkali metal reaction. In Eleventh Mid-Atlantic Industrial Waste Conference, Pennsylvania State University, University Park, PA, July 15-17, 1979. University Park, PA Pennsylvania State University, 97-99. 

Whereas sulfolane is relatively stable to about 220°C, above that temperature it starts to break down, presumably to sulfur dioxide and a polymeric material. Sulfolane, also stable in the presence of various chemical substances as shown in Table 2 (2), is relatively inert except toward sulfur and aluminum chloride. Despite this relative chemical inertness, sulfolane does undergo certain reactions, for example, halogenations, ring cleavage by alkali metals, ring additions catalyzed by alkali metals, reaction with Grignard reagents, and formation of weak chemical complexes. 

The most simple way of preparing sodium caprolactam consists in dissolving the sodium metal in molten caprolactam. Although the solutions thus obtained are capable to induce a rapid polymerization, we meet with complications arising from the presence of reduction products formed such as hexamethyleneimine (53,69,80,81) and 6-aminohexanol (59,69). These by-products affect the course of the subsequent polymerization as they react with the active centers. The ratio neutralization/reduction in the alkali metal reaction with caprolactam depends strongly on the temperature. According to Hamann (41) and Yumoto (101) the reduction reaction takes place to 75% and 10—20% respectively. In order to suppress the reduction it is recommended to maintain the temperature during the dissolution of the sodium metal below 100° (42). 

The acidity of the hydroxyl group can be seen in the rapid proton-deuteron exchange that can take place when alcohols are dissolved in D O (Reaction I), alkali metals (Reaction II) and organometallic reagents (Reaction III and IV). 

Triorganotin salts of general formula [R3Sn] A+, A = alkali metal, are readily obtained from the reaction of the corresponding chlorotin compounds with the alkali metal. Reaction of these compounds with transition-metal halides is thus another useful salt-elimination reaction for the formation of tin-metal bonds. A representative selection of such reactions is illustrated in equation 72 -7448,49,232. 

There are three general types of metallation reactions (metal-hydrogen exchange) that are commonly used to synthesize organoalkali metal compoimds from organic molecules Direct reaction with an alkali metal, reaction with an alkali metal hydride, or reaction with an organo- or amido-alkali metal. Since these reactions involve acid/base equilibria, they are dependent on both the C-H acidity of the organic molecule and the basicity of the alkali metal source. 

The structural requirement described above places restrictions on the types of host lattices that are snitable for intercalation reactions. Nevertheless, many examples of one-, two-, and three-dimensional structures can be found with suitable properties. Studies of alkali metal reactions with Ceo see Carbon Fullerenes) have been discnssed in terms of intercalation in a host lattice of effectively zero dimensionahty. The different types of host lattice geometry are shown in Figure 1. 

TABLE 18.6 Selected Reactions of the Alkali Metals Reaction Comment... 

Reviews of alkali-metal reactions with conjugated organic substrates are B. J. McClelland, Chem. Rev., 64, 301 (1964) V. Kalyanaraman, M. V. George, J. Organomet. Chem., 47, 225 (1973). 

If too much organic halide is added to Na or K dispersions a sudden rise in T may occur accompanied by an uncontrolled reaction that may result in explosion if reaction mixture is pushed out of the reaction vessel into the atmosphere . For this reason and because of the fragility of the usual glass apparatus the customary apparatus for alkali-metal reactions should be contained within a second inert atmosphere, such as inside a glove box filled with N,. 

Table 23-4 summarizes some reactions of the alkaline earth metals, which, except for stoichiometry, are similar to the corresponding reactions of the alkali metals. Reactions with hydrogen and oxygen were discussed in Sections 6-7 and 6-8. 

Table A-3 Evaluation of the standard enthalpy of formation of alkali metal (Reactions 1 to 3) and alkaline earth metal (Reaction 4) selenides. The sources of the data are indicated.

The gas reactions listed in Table 2 have high rates at room temperature and emission occurs not too far in the infrared. These restrictions are due to limitations of the experimental method which may be overcome in the future. The table could be considerably enlarged by including alkali-metal reactions which have largely been studied by molecular beam methods. 21> Though much discussed, chemical lasers on alkali halides have not yet been realized experimentally. Other results, obtained for instance by flash photolysis/absorption studies, or by the study of combustion, are less detailed and axe not included here. But even in this limited form. Table 2 indicates that nonequilibrium distributions which can lead to molecular amplification are often found and are perhaps the rule rather than the exception in simple chemical reactions. 

For an up-to-date account of alkali metal reactions in the gas phase, the reader is referred to the article in the present series [147]. 

Generally in molecular beam studies, both beams have comparable velocities and intersect one another at 90°, and thus the CM velocity vector points at a wide angle intermediate between the two beams. Measurement of the displacement of the laboratory angular distribution of products from the centre-of-mass vector enables an estimate of the velocity of the products to be derived. Reaction products have been velocity analysed (e.g. see refs. 8 and 231) and the results support the view that the product relative translational energy is usually within ca. 1 kcal mole of the reactant relative translational energy. Most of the alkali metal reactions studied to date are exothermic, thus the products must be internally excited. It is believed [8] that, for most reactions, the internal excitation consists mainly of vibrational excitation however, the partition of the vibrational energy between, for example, KI and CH3 is as yet unknown. There are a few exceptions, e.g. the K + HBr reaction where KBr is rotationally excited rather than vibrationally excited [8], and the... 

There are alkali-metal reactions which have yet not been studied in any great detail by the molecular beam technique, e.g. M -1- F2. As outlined in Section 3.2.2, it is now experimentally possible to produce ntolecular beams from thermal up to thousands of eV translational energy. The effect of translational energy on both the reaction cross-section [145, 146] and angular reactive scattering has yet to be explored in detail. It would be hoped that an analogously diverse set of reaction mechanisms to those found for ion—molecule reactions [122] would be discovered. 

Since [1,4] migration of phenyl was a minor process in all the above reactions of 4-chloro-1,1,1-triphenylbutane with alkali metals, reactions of 4-chloro-l-p-biphenylyl-l,l-diphenylbutane were next studied (36) because of the expected superior migratory aptitude of p-biphenylyl over phenyl in anionic rearrangements. Reaction in THF with potassium or cesium at 65°C or with Cs-K-Na alloy at -75°C gave a high yield of 4-p-biphenylyl-l,l-diphenylbutyl anion (58) as deduced from the NMR spectrum of the anion and products of carbonation and protonation. 

Making Alkali Metal Reactions Safer Alkali metals, such as sodium and potassium, are excellent reducing agents but their high reactivity makes them dangerous to handle and store. Because of this, some commercial reactions have been developed to avoid using these metals, but the alternate synthetic pathways are often inefficient and wasteful. A method has been developed to incorporate reactive metals in porous metal oxides to form sand-like powders so that the metals can be used with greater control of their reactivity. Furthermore, these materials are safer to store and reduce waste disposal. 

These reactions resemble alkali metal reactions in their low inertia (as evident from the low activation energy and the resultant high effectivity of collisions). 

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