Lithium-metal reactions

Polymers prepared by the above procedure have molecular weights up to 80,000. It is also possible to start with diphenoxysiloxane and catalyze the reaction with sodium or lithium metals. Reactions of cyclic silazanes with arylene disalanols yield polymers with molecular weights as high as 900,000 ... 

Compound (12) can also be obtained by dissolving metal reactions through treatment with an excess of lithium—hquid ammonia in tert-huty alcohol (54). 

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Economic Aspects. Lithium metal is available commercially in ingots, special shapes, shot, and dispersions. Ingots are sold in 0.11-, 0.23-, 0.45-, and 0.91-kg sizes. Special shapes include foil, wire, and rod. Lithium is available in hermetically sealed copper cartridges and in sealed copper tubes for use in treating molten copper and copper-base alloys. Shot is sold in 1.19—4.76 mm (16—4 mesh) sizes. Lithium dispersions (30% in mineral oil) of 10—50-p.m particle size are used primarily in organic chemical reactions. Dispersions in other solvents and of other size fractions can be suppHed. 

Uses. The largest use of lithium metal is in the production of organometaUic alkyl and aryl lithium compounds by reactions of lithium dispersions with the corresponding organohaHdes. Lithium metal is also used in organic syntheses for preparations of alkoxides and organosilanes, as weU as for reductions. Other uses for the metal include fabricated lithium battery components and manufacture of lithium alloys. It is also used for production of lithium hydride and lithium nitride. 

Lithium Amide. Lithium amide [7782-89-0], LiNH2, is produced from the reaction of anhydrous ammonia and lithium hydride. The compound can also be prepared by the removal of ammonia from solutions of lithium metal in the presence of catalysts (54). Lithium amide starts to decompose at 320°C and melts at 375°C. Decomposition of the amide above 400°C results first in lithium imide, Li2NH, and eventually in lithium nitride, Li N. Lithium amide is used in the production of antioxidants (qv) and antihistamines (see HiSTAMlNE AND HISTAMINE ANTAGONISTS). 

Lithium Iodide. Lithium iodide [10377-51 -2/, Lil, is the most difficult lithium halide to prepare and has few appHcations. Aqueous solutions of the salt can be prepared by carehil neutralization of hydroiodic acid with lithium carbonate or lithium hydroxide. Concentration of the aqueous solution leads successively to the trihydrate [7790-22-9] dihydrate [17023-25-5] and monohydrate [17023-24 ] which melt congmendy at 75, 79, and 130°C, respectively. The anhydrous salt can be obtained by carehil removal of water under vacuum, but because of the strong tendency to oxidize and eliminate iodine which occurs on heating the salt ia air, it is often prepared from reactions of lithium metal or lithium hydride with iodine ia organic solvents. The salt is extremely soluble ia water (62.6 wt % at 25°C) (59) and the solutions have extremely low vapor pressures (60). Lithium iodide is used as an electrolyte ia selected lithium battery appHcations, where it is formed in situ from reaction of lithium metal with iodine. It can also be a component of low melting molten salts and as a catalyst ia aldol condensations. 

Lithium Nitride. Lithium nitride [26134-62-3], Li N, is prepared from the strongly exothermic direct reaction of lithium and nitrogen. The reaction proceeds to completion even when the temperature is kept below the melting point of lithium metal. The lithium ion is extremely mobile in the hexagonal lattice resulting in one of the highest known soHd ionic conductivities. Lithium nitride in combination with other compounds is used as a catalyst for the conversion of hexagonal boron nitride to the cubic form. The properties of lithium nitride have been extensively reviewed (66). 

C. It can be obtained from its hahde-free solutions in cyclohexane and ethylether by vacuum distUlation to remove the ether. The usual preparative method is by reaction of chloro- or bromobenzene and lithium metal in ethyl ether or in a mixture of ethyl ether and cyclohexane. 

Lithium metal in tetrahydrofuran can also be used as the coupling reagent, and unsymmetrical ditins can be prepared when the reaction is conducted in stages (162,163). 

As soon as the receiver containing the methyl 11 thiurn solution has been removed and stoppered, the residual solids in the reaction flask and the filtration apparatus should be rinsed Into another receiver with anhydrous ether under an atmosphere of argon or nitrogen. The ether slurry of solids, which may contain some unchanged lithium metal, should be treated cautiously in a hood with t-butyl alcohol to consume any residual lithium metal before the mixture is discarded. 

An ethereal solution approximately 2.5 molar in methyllithium is prepared from 17 ml of methyl iodide and 4 g of lithium metal in 200 ml of anhydrous ether. A mixture consisting of 150 ml anhydrous ether, 3 g (10 mmoles) of 3jS-hydroxy-5a-androstane-ll,17-dione and 60 ml (0.15 moles) of the above methyllithium solution are stirred at room temperature for 40 hr. The reaction mixture is diluted with 100 ml of water and the ether is removed by distillation. Filtration of the chilled aqueous phase yields 2.6 g (77%) of 1 la,17a-dimethyl-5a-androstane-3a,l l/ ,17j5-triol mp 149-154°. Recrystallization from acetone-hexane yields pure material mp 164-166° [a] —5° (CHCI3). 

Heptafluoro-2-naphthyllithiuni prepared by metalation reaction can thermally decompose to a hexafluoro-l,2-naphlhalyne by elimination of lithium fluoride [36, 37] In this organolithium compound, fluorine elimination can occur from either position 1 or 3, however, no evidence for fluorine elimination from position 3 IS observed... 

Many other kinds of organometallic compounds can be prepared in a manner similar to that of Grignard reagents. For instance, alkyllithium reagents, RLi, can be prepared by the reaction of an alkyl halide with lithium metal. Alkyllithiums are both nucleophiles and strong bases, and their chemistry is similar in many respects to that of alkylmagnesium halides. 

For lithium metal in 1 Af HC1, the observed facts are that the metal dissolves spontaneously and a gas bubbles out of the solution. From Appendix 3 we select the two half-reactions (notice that the half-reactions are already balanced in both charge and number of atoms) ... 

Both of these half-reactions show production of electrons. But we know there must be an electron used for each produced, so one of the equations must be reversed. Experiment shows us it is the second because hydrogen gas is evolved from the solution. The first equation is correct as written. Lithium metal dissolves and is converted to ions. Thus,... 

Dilithium phthctlocyanine (PcLi2) can be prepared by the method of Linstead.59 Lithium metal is added to pentan-l-ol and heated to dissolve the metal. Then, the phthalonitrile is added and the mixture is refluxed for some hours. Due to its lability toward water and acid, both have to be excluded during the reaction and purification.79131132... 

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