Lithium dispersions

The use of alkaU metals for anionic polymerization of diene monomers is primarily of historical interest. A patent disclosure issued in 1911 (16) detailed the use of metallic sodium to polymerize isoprene and other dienes. Independentiy and simultaneously, the use of sodium metal to polymerize butadiene, isoprene, and 2,3-dimethyl-l,3-butadiene was described (17). Interest in alkaU metal-initiated polymerization of 1,3-dienes culminated in the discovery (18) at Firestone Tire and Rubber Co. that polymerization of neat isoprene with lithium dispersion produced high i7j -l,4-polyisoprene, similar in stmcture and properties to Hevea natural mbber (see ELASTOLffiRS,SYNTHETic-POLYisoPRENE Rubber, natural). 

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. 

There are some indications that the situation described above has been realized, at least partially, in the system styrene-methyl methacrylate polymerized by metallic lithium.29 29b It is known51 that in a 50-50 mixture of styrene and methyl methacrylate radical polymerization yields a product of approximately the same composition as the feed. On the other hand, a product containing only a few per cent of styrene is formed in a polymerization proceeding by an anionic mechanism. Since the polymer obtained in the 50-50 mixture of styrene and methyl methacrylate polymerized with metallic lithium had apparently an intermediate composition, it has been suggested that this is a block polymer obtained in a reaction discussed above. Further evidence favoring this mechanism is provided by the fact that under identical conditions only pure poly-methyl methacrylate is formed if the polymerization is initiated by butyl lithium and not by lithium dispersion. This proves that incorporation of styrene is due to a different initiation and not propagation. 

To a solution of trimethylsilylmethyl lithium (from chloromethyltrimethyl-silane (15.8mmoI) and lithium dispersion (196mmol)) in ether (30ml) was added cyclohexane carboxaldehyde (14.2 mmol) at ambient temperature, with stirring. After a further 10min at ambient temperature, the solution... 

A. (E)-l-Propenyllithium. A dry (Note 2), 500-ml., three-necked, round-bottomed flask equipped with a Teflon -covered magnetic stirring bar, a 200-ml. pressure-equalizing dropping funnel, an efficient reflux condenser, and an immersion thermometer is capped with serum stoppers (Note 3) and flushed with argon (Note 4). Lithium dispersion (Note 5), [22.4 g. of a 50% wjw suspension in Amseo,... 

Lithium dispersion can be safely destroyed by carefully adding it in small portions to a large excess of technical tert-butyl alcohol in a metal pan. If too much lithium is added at one time, the reaction with the ferf-butyl alcohol can become very vigorous. Under these circumstances, a fire can be avoided by covering the pan with a second, larger metal pan or with an asbestos sheet. 

Purification of 1,2-dibromoethane was accomplished by passing a small quantity rapidly through a 5-cm. column of alumina. Addition of 1,2-dibromoethane to the lithium dispersion is accompanied by visible evolution of ethylene (ethene). 

Our entry into sonochemistry was spurred by our need for high yield preparations of symmetrical organics and bimetal lies. Our first efforts(16t17) with lithium wire were satisfactory but have since been greatly improved by using of lithium dispersion(18) ... 

Caution. Tetrahydrofuran is extremely flammable and forms explosive peroxides only freshly distilled, peroxide-free material should be used. Lithium-dispersion is a hazardous material and must be handled in dry conditions and under an inert gas atmosphere. Trimethylchlorosilane and trichloromethylsilane can cause severe skin and eye burns. All manipulations should be carried out in a well-ventilated fume hood protective gloves and safety glasses should be worn. 

Although the results obtained with this monomer pair with lithium dispersion by Overberger and Yamamoto (40) should be strictly comparable to those obtained by electropolymerization, factors specific to the latter process may be dominant rather than surface effects which predominate in the former case. 

Metallic lithium in the form of a suspension has been used to polymerize isoprene (97) but the system is not too suitable for an exact analysis of the mechanism. The conversion-time curves are sigmoidal in shape. Minoux (66) has shown that the overall rate is not very dependent on the amount of lithium dispersion used as expected if the organo-lithium intermediates are highly associated. The molecular weight of the polymer is more dependent on quantity of lithium used. The observed kinetic behaviour is very similar to that shown in lithium alkyl initiation. This suggests that apart from differences in the initiation step, the mechanisms are quite similar. 

Lithium dispersion (0.5% sodium in mineral oil, Aldrich) is washed with hexane to remove the oil before use and dried by passing a stream of nitrogen over it. Di-tert-butyldichlorosilane is commercially available (Huls, bp 191°C) or can be prepared by chlorination of di-tert-butylchlorosilane (benzoyl peroxide in refluxing carbon tetrachloride for 8 h, yield > 90%). trans-Butene is commercially available (Aldrich) in lecture bottles and is used as is. Tetrahydrofuran is freshly distilled under nitrogen from sodium ketyl benzophenone immediately prior to use. 

Caution. Lithium dispersion is a flammable, moisture-sensitive material. Manipulations should be carried out in a dry box or inert-atmosphere glove bag. 

Miller and Rauhut (43) have observed that a lithium dispersion at 50° will initiate the formation of crystalline polymer from /-butyl acrylate in bulk or in non-polar solvents. 

I), a highly reactive lithium dispersion is required for preparation of the last two species. 

The nature of the lithium surface is important. Varying the particle size of the lithium dispersion from 25 pm with a surface area of 2782 cm to 150 pm with a surface area of 464 cm reduced the optical purity of the resulting acid by nearly 50%. It was also demonstrated that the amount of sodium impurity in the lithium dispersion had a significant effect not only on the stereochemical results of the metallation reaction but also on the reactivity of the metal surface itself. For example, reaction of chiral l-iodo-2,2-diphenylcyclopropane with 25 pm lithium dispersions containing 0.002 %, 0.02 % and 1 % sodium yielded after carbonation l-methyl-2-cyclopropanecarboxylic acid (99) with optical purities of 13 %, 16% and 36%, respectively. The increase in optical purity with increase in sodium content may be a consequence of lowering the ionization potential of the metallic surface . ... 

The stereochemistry of the reaction is also dependent on the halogen. The reaction of chiral l-halo-2,2-diphenylcyclopropane with 25 xm lithium dispersions containing 1% sodium produced the results shown in Table 16. It should be noted that the optical purity of the acid varies in the same order as the carbon-halogen bond strength Cl > Br > I. 

West and Glaze found that vinyllithium can be prepared directly from vinyl chloride and a lithium dispersion containing about 2% of sodium (preferred temperature 0-10°). 

The surface area of the J-in. wire is 1,660 sq. in./lb. The Lithium Corp. lithium shot has a particle size of approximately 4 to 16 mesh. Lithium dispersions available in mineral oil, petrolatum, or paraffin wax have a mean diameter of 15 microns and a surface area of 5.3 x 10 sq. in./lb. The compositions are as follows ... 

Peterson and coworkers were the first who showed that 1-alkenes can react with lithium dispersion under relatively mild conditions to give the corresponding 1 -alkynyllithium compounds and lithium hydride as the major products. Thus 1 -hexene 113 was converted into 1-hexynyllithium 116 in 65% yield within 1 h at the reflux temperature of the olefin (64 °C). It is reasonable to assume that 1,2-dilithio-hexane 114 is formed first loosing lithium hydride to give 1-hexenyllithium 115, which was detected as a side-product in 4% yield. 

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