Alkyllithium compounds preparation

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. 

K or Li, as well as with Zn—Me3SiCl and with certain compounds prepared from WCle and either lithium, lithium iodide, LiAlH, or an alkyllithium (see 17-17). The reaction has been used to convert dialdehydes and diketones to cycloalkenes. Rings of 3-16 and 22 members have been closed in this way, for example. 

As with organomagnesium reagents, there is usually loss of stereochemical integrity at the site of reaction during the preparation of alkyllithium compounds.25 Alkenyllithium reagents can usually be prepared with retention of configuration of the double bond.26,27... 

Alkyllithium compounds are only rarely used for the preparation or organogermanes or... 

Using alkyllithium compounds, a distannane with a very long Sn—Sn bond, 3.03A, and a syw-peripheral conformation122 was prepared. Thus, reaction of di-t-butyl(chloro)2,4,6-triisopropylphenyl)tin, 78, with f-butyllithium gives 1,1,2,2-tetra-f-butyl-l,2-(2,4,6-triisopropylphenyl)ditin, 79, which displays a restricted rotation about the Sn—C bond as well as the Sn—Sn bond, even at high temperatures. 

In contrast to the non-trivial routes for the syntheses of pure aluminum(I) or gallium(I) subhalides, indium(I) chloride or bromide can simply be prepared by melting mixtures of elemental indium and indium trihalides [39]. When these in-dium(I) halides were treated with bulky alkyllithium compounds, deep violet orga-noelement indium dusters (13-18) were obtained [Eq. (3)] [40, 41]. 

The classical preparation of alkyllithium compounds by reductive cleavage of alkyl phenyl sulfides with lithium naphthalene (stoichiometric version) was also carried out with the same electron carrier but under catalytic conditions (1-8%). When secondary alkyl phenyl sulfides 73 were allowed to react with lithium and a catalytic amount of naphthalene (8%) in THF at —40°C, secondary alkyllithium intermediates 74 were formed, which finally reacted successively with carbon dioxide and water, giving the expected carboxylic acids 75 (Scheme 30) °. 

Alkyldiazenido complexes, mechanisms of formation, 27 223-225 Alkylfluorophosphines, 13 367-378 Alkyl ftillerides, 44 38 Alkylidiboranes cyclic, 16 215, 216 electron diffiaction studies of, 16 216 NMR of, 16 216 preparation of, 16 214, 215 Alkyllithium compounds, crystal structures, 37 83-85... 

Addition of a primary alkyl group to enolizable ketones can be performed using magne-sium-ate complexes . The additional presence of 2,2 -bipyridyl (1 equiv.) in the reaction mixture improves the yields. The ate complexes are prepared in situ from the corresponding Grignard reagents and alkyllithium compounds (equations 140 and 141). 

Alkyllithium compounds as well as polymer-lithium associate not only with themselves but also with other alkalimetal alkyls and alkoxides. In a polymerization initiated with combinations of alkyllithiums and alkalimetal alkoxides, dynamic tautomeric equilibria between carbon-metal bonds and oxygen-metal bonds exist and lead to propagation centers having the characteristics of both metals, usually somewhere in between. This way, one can prepare copolymers of various randomness and various vinyl unsaturation. This reaction is quite general as one can also use sodium, rubidium or cesium compounds to get different effects. 

Anionic polymerizations initiated with alkyllithium compounds enable us to prepare homopolymers as well as copolymers from diene and vinylaromatic monomers. These polymerization systems are unique in that they have precise control over such polymer properties as composition, microstructure, molecular weight, molecular weight distribution, choice of functional end groups and even copolymer monomer sequence distribution. Attempts have been made in this paper to survey these salient features with respect to their chemistry and commercial applications. 

Anionic polymerization of vinyl monomers can be effected with a variety of organomciallic compounds alkyllithium compounds are the most useful class. A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds ate soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. 

Alkyllithium compounds LiR can be prepared by the reaction between lithium metal and an alkyl halide in an inert solvent such as benzene ... 

In 1950, Letsinger reported that carbonation of 2-lithiooctane, 15, prepared by exchange of (—)-2-iodooctane with s-butyllithium in petroleum ether at —70 °C, gave (—)-2-methyl-heptanoic acid21. However, after first warming the 2-lithiooctane solution to 0°C over 20 minutes the resulting carboxylic acid was racemic. This was the first observation that a secondary alkyllithium compound inverts much more slowly than does a primary RLi compound. 

In the preparation of large batches of alkyllithium compounds (10-1,000 gallons) it is desirable to increase the quantity of sodium by about 25% and to activate the diethyl ether by prolonged refluxing with lithium in order to avoid long induction periods (15-24 hrs.) and dangerous surges of reaction. 

Simple, unfunctionalized organolithium compounds are usually prepared by reductive lithiation of alkyl halides with lithium metal at ambient temperature or above [26]. Reductive lithiation is fastest for alkyllithium compounds (the more substituted the better) and slowest for aryllithium compounds. The order of reactivity follows logically from the relative stabilities of the intermediate radicals, whose formation is the rate-determining step of the sequence. 

Some success has been reported with Reaction 4 using low temperatures (22). We have obtained up to 61% with the procedure cited in Ref. 22 with some difficulty. A number of other routes have been found for preparing allyllithium, including the cleavage of allyl ethers with lithium metal, exchange of alkyllithium compounds with allyltin compounds, and... 

Most alkyllithium compounds are prepared by the direct synthesis method shown in equation (1). For example, lithium metal reacts with bromomethane in ether to form methyl lithium and lithium bromide (equation 16). ... 

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