Reactions with Other Alkali Metals

Interestingly, solvent effects appear to be extremely marked. Luche and co-workers noted that dispersion could not be effected in THF and other reports suggest that the process is extremely sluggish in benzene [106]. Similarly, sodium could only be dispersed in xylene and lithium could not be persuaded to disperse in either of the three solvents tried. Ley et al. have also observed this whilst attempting to form sodium phenylselenide by reaction of sodium with diphenyl diselenide [107]. Using solid sodium, the reaction time was halved when using xylene in place of THF (Table 4). 

Luche has suggested that the ease with which metals can be dispersed is related to the lattice energy of the metal. This would explain why 

Treatment of 4-bromo-2-sulpholenes with UDP results in deprotonation at C5. The product isolated is the bicyclic sulphone (16) [111] which pre- 

Primary cleavage of the C—Br bond followed by intermolecular abstraction of HBr was ruled out on the basis that the overall conversion of (15) 

Solutions of LN in non-ethereal solvent cannot be prepared by thermal means, but the reaction can be brought to completion within 2h using ultrasound. Solutions of the reagent in TMEDA or TMDAP/benzene were used to promote the dimerisation of isoprene [118] or its reaction with secondary amines [119]. However, the advantages over using a standard solution of the reagent in THE appear to be slight. 

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The synthesis of aliphatic nitro compounds from the reaction of alkyl halides with alkali metal nitrites was discovered by Kornblum and co-workers and is known as the modified Victor Meyer reaction or the Kornblum modification. The choice of solvent in these reactions is crucial when sodium nitrite is used as the nitrite soiuce. Both alkyl halide and nitrite anion must be in solution to react, and the higher the concentration of nitrite anion, the faster the reaction. For this reason, both DMF and DMSO are widely used as solvents, with both able to dissolve appreciable amounts of sodium nitrite. Although sodium nitrite is more soluble in DMSO than DMF the former can react with some halide substrates.Urea is occasionally added to DMF solutions of sodium nitrite to increase the solubility of this salt and hence increase reaction rates. Other alkali metal nitrites can be used in these reactions, like lithium nitrite,which is more soluble in DMF than sodium nitrite but is also less widely available. 

Cesium salts of substituted pyridine-3,5-dicarboxylic acids were used first by Krui-zinga and Kellogg for the synthesis of macrocyclic lactones [51]. Kellogg obtained the bis-lactone 46 in a one-pot reaction of the cesium carboxylate 44 and the dibro-mo compound 45 in 85 % yield without application of high dilution conditions [1]. By comparison with other alkali metal carbonates he proved the yield-increasing effect of the cesium ions ... 

Crown ethers. The dicesium salts of catechol, resorcinol, and salicylic acid react with dibromopolyethylene glycols in DMF to afford crown ethers. Similar reactions employing other alkali metal salts proceed less cleanly in significantly lower yield. 

Lithium metal may react with acidic hydrocarbons to give organolithiums. This reaction also occurs with other alkali metals, more commonly with the heavier group-IA metals potassium and Cs (see 5.5.3.2.4). Usually, deprotonation of acidic hydrocarbons ( 5.5.2.3.2) is the method of choice for organolithiums from acidic hydrocarbons, but in special cases where contaminants must be avoided, the direct reaction with Li metal can be useful. 

The principal commercial source of rubidium is accumulated stocks of a mixed carbonate produced as a byproduct in the extraction of lithium salts from lepidohte. Primarily a potassium carbonate, the byproduct also contains ca. 23 wt.% rubidium and 3 wt.% cesium carbonates. The primary difficulty associated with the production of either pure rubidium or pure cesium is that these two elements are always found together in nature and also are mixed with other alkali metals because these elements have very close ionic radii, their chemical separation encounters numerous issues. Before the development of procedures based on thermochemical reduction and fractional distillation, the elements were purified in the salt form through laborious fractional crystallization techniques. Once pure salts have been prepared by precipitation methods, it is a relatively simple task to convert them to the free metal. This is ordinarily accomplished by metallothermic reduction with calcium metal in a high-temperature vacuum system in which the highly volatile alkali metal is distilled from the solid reaction mixture. Today, direct reduction of the mixed carbonates from lepidolite purification, followed by fractional distillation, is perhaps the most important of the commercial methods for producing rubidium. The mixed carbonate is treated with excess sodium at ca. 650 C, and much of the rubidium and cesium passes into the metal phase. The resulting crude alloy is vacuum distilled to form a second alloy considerably richer in rubidium and cesium. This product is then refined by fractional distillation in a tower to produce elemental rubidium more than 99.5 wt.% pure. 

The solvent for the reaction with the alkali metal, metal hydride, and so on, is often the alcohol itseh. However, on occasion, such as when the alcohol is not a liquid or when other functional groups with which the alkoxide anion might react are present, ethers or hydrocarbons are used as solvents. Commercially available butyllithium reagents are sold as solutions in hydrocarbon solvents. 

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). 

Anhydrous halogen derivatives of metals can be converted into metal alkoxides via reaction with either alkali metal alkoxides or with alcohols in the presence of ammonia. The reaction is usually carried out in other solvents than alcohols (hydrocarbon or ether ones) on cooling and with the amoimts of alcohols only slightly exceeding the stoichiometry. The reason is that oxo-alkoxides or oxo-alkoxide halides can otherwise be formed as impurities. This approach can be used successfully for synthesis of, for example, alkoxides of Sn(IV) [87], Bi (III) [114], and Fe(III) [82] ... 

A number of compounds of the types RBiY2 or R2BiY, where Y is an anionic group other than halogen, have been prepared by the reaction of a dihalo- or halobismuthine with a lithium, sodium, potassium, ammonium, silver, or lead alkoxide (120,121), amide (122,123), a2ide (124,125), carboxylate (121,126), cyanide (125,127), dithiocarbamate (128,129), mercaptide (130,131), nitrate (108), phenoxide (120), selenocyanate (125), silanolate (132), thiocyanate (125,127), or xanthate (133). Dialkyl- and diaryUialobismuthines can also be readily converted to secondary bismuthides by treatment with an alkali metal (50,105,134) ... 

Electron transfer reactions involving alkali metals are heterogeneous, and for many purposes it is desirable to deal with a homogeneous electron transfer system. It was noticed by Scott39 that sodium and other alkali metals react rapidly with aromatic hydrocarbons like diphenyl, naphthalene, anthracene, etc., giving intensely colored complexes of a 1 to 1 ratio of sodium to hydro-... 

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

Sodium is, like all other alkali metals, a very strong reducing agent (more reactive than lithium), which has extremely violent reactions with numerous compounds. It causes a large number of accidents. Sodium peroxide is a very reactive oxidant, which has violent interactions with reducing agents. Carbonates, and especially sodium hydroxide, are bases which react with acids (the reaction is aggravated by the formation of carbon dioxide). 

Reaction with cold water is of moderate vigour, but violent with hot water, and the liberated hydrogen may ignite [1], The powdered metal reacts explosively with water [2], The reactivity of lithium and other alkali metals with various forms of water has been discussed in detail. Prolonged contact with steam forms a thermally insulating layer which promotes overheating of the metal and may lead to a subsequent explosion as the insulating layer breaks up [3],... 

Rowley, A. T. et al., Inorg. Chem. Acta, 1993, 211(1), 77 Preparation of metal oxides by fusing metal halides with lithium oxide in a sealed tube leads to explosions if halide hydrates are employed, particularly lanthanide trihalide hydrates. The preparation succeeds with anhydrous halides. This will be purely a question of vapour pressure above an exothermic reaction the question is whether the vapour is water, or metal halide, and the reaction oxide formation, or hydration of lithium oxide. Like other alkali metal oxides, hydration is extremely energetic. 

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). 

There is a limited number of examples of preparations involving the reaction of stannyl-alkali metal compounds with a substituted heteroarene, for example, Equations (58)-(60).88,197,198 Some of these reactions (e g Equation (58)) occur only with photoirradiation, showing that they involve SRN1 processes, but others may be straightforward nucleophilic heteroaromatic substitutions. 

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