Solubility lithium alkoxide

Other, even milder bases than LDA and LHS, such as lithium methoxide and lithium /-butoxide, may be used in organic syntheses (143,144). Lithium methoxide is available commercially as a 10% solution in methanol and lithium /-butoxide as an 18% solution in tetrahydrofuran (145). Lithium /-butoxide is also soluble in hydrocarbon solvents (146). Both lithium alkoxides are also available as soHds (147) (see Alkoxides, metal). 

The solubility of normal lithium alkoxides in hydrocarbon solvents is much lower than that of the branched ones. This can be attributed to formation of insoluble associated species in the case of the normal alkoxides. The solubility of lithium diaUcylamides is lower than that of the analogous alkoxides . 

Metathesis reactions between Group 2 metal alkoxides and lithium amides in hexane yield the metal amide and lithium alkoxide according to Eq. (7).60 The lithium alkoxide is insoluble in hexane and is easily separated from the hexane-soluble amide. 

Although metal alkoxides were successfully used as a synthon for the synthesis (see Scheme 9) of more interesting homo- and heteroleptic metal alkyls, they have not attained the same importance as their sterically hindered aryloxide analogues. This finding might be due to the general solubility of both the products [i.e., desired metal alkyls and alkali metal (generally lithium) alkoxides] in hydrocarbon solvents. This limitation has made a cleaner separation of the products more difficult. 

The addition reaction of 2 mol of i ec-butyllithium with l,3-bis(l-phenylethenyl)benzene. Equation 7.12, proceeds rapidly and efficiently to produce the corresponding dilithium species that is soluble in toluene or in cyclohexane [46, 73]. Although this dilithium initiator is useful for the preparation of homopolymers and triblock copolymers with relatively narrow molecular weight distributions, it is necessary to add a small amount of Lewis base or 2 or more equivalents of lithium alkoxide (e.g., lithium iec-butoxide) to produce narrow, monomodal molecular weight distributions. 

Aldehydes can be converted to peroxy acids via ozonation in methyl or ethyl acetate, or to methyl esters via ozonation in 10% methanolic KOH (eq 36). Ethyl esters can be produced analogously, but the use of higher alcohols results in low KOH solubility and poor conversion. This problem can be overcome by adding the aldehyde to a solution of lithium alkoxide in THE at —78 °C and treating this mixture with ozone (eq 37). Additionally, the direct preparation of methyl esters can be accomplished via alkene ozonolysis in methanolic NaOH or by addition of NaOMe to a MeOH-CH2Cl2 ozonolysis solvent system. ... 

The most direct method of preparing telechelic polydienes utilizes a dilithium initiator which is soluble in hydrocarbon solution [220, 221]. The most expedient method of preparing such a dilithium initiator is to react two moles of an alkyllithium compound with a divinyl compound which will not homopolymerize. Unfortunately, because of the association behavior of organolithium compounds in hydrocarbon media [176-178], many potential systems fail because they associate to form an insoluble network-like structure [221]. Expediencies such as addition of Lewis bases can overcome solubility problems of dilithium initiators, however, such additives tend to produce high amounds of 1,2- and 3,4-microstructures (see Table IV). One exception is the adduct formed from the addition of two equivalents of sec-butyllithium to l,3- i5 (l-phenylethenyl)benzene as shown in Eq. (79) [222,223]. Although this is a hydrocarbon-soluble, dilithium initiator, it was found that biomodal molecular weight distributions are obtained monomodal distributions can be obtained in the presence of lithium alkoxides or by addition of Lewis base additives [224,225].This initiator has also been used to prepare telechelic polymers in high yields [226]. 

Crystallization in the presence of tmeda affords a tetrameric aggregate of composition [(tmeda)NaCH2C6H2Me2(OLi)]4, 205 [178]. A distorted U4O4 cube forms the central part of the molecule. Both the lithium and sodium atoms act as bridges between the methylene units and the oxygen atoms. The compound can be regarded as a model intermolecular superbase and overcomes the problem of differing solubilities of lithium alkoxides and the heavier alkali metal hydrocarbyls. 

It is important to consider the possible reasons for the association effects which lead to bimodal molecular weight distributions for polymers formed using 90 as initiator in the absence of added Lewis base or lithium alkoxide. Leitz and Hocker [199] proposed that double diphenylethylene-based dilithium initiators form dimeric dianion aggregates (93) and that is why they are soluble in hydrocarbon solutions compared to other dilithium species. This type of dimeric structure is consistent also with the dimeric association... 

Thus, multifunctional 1,1-diphenylethylenes, such as 73 and 94, are precursors for useful, hydrocarbon-soluble, multifunctional organolithium initiators such as 90 and 95, respectively. Their hydrocarbon solubility appears to be a consequence of a specific type of intermolecular association (e.g., 93) which is favored over the more usual type of 3-dimensional association which leads to insolubility for most dilithium initiators [89, 220]. However, perhaps because of their unique association, these initiators require the addition of either a Lewis base, such as tetrahydrofuran, or a lithium alkoxide salt to initiate rapidly (relative to propagation) and quantitatively. 

There is evidence also that oxygen in lithium alkoxides can complex with lithium alkyls. Both the strong donor strength of alkoxy oxygen and the fact that lithium n-butoxide is soluble in hydrocarbon solutions of n-butyl-lithium have been mentioned earlier. 

In electrolytes based on solvent mixtures both solvent compounds may react to form films of scarcely soluble materials. PC/THF mixtures yield alkoxides and alkylcarbonates [188] EC/ether blends mainly yield alkylcarbonates, which are thought to be the reason for smaller lithium loss during cycling [188]. PC based electrolytes with LiAsF6and LiC104 form films containing alkylcarbonates which allow the access of other molecules, such... 

The unique feature of the alkyllithium compounds that makes them useful as diene initiators is their character as exceedingly powerful bases yet they are soluble in organic solvents and quite thermally stable. Alkyllithium compounds are sufficiently basic to add to hydrocarbon monomers. However, lithium salts of stabilized anions, such as acetylide and fluorenyl anions, are too weakly basic to add to such double bonds. Similarly, alkoxides and mercaptides fail to react with hydrocarbon monomers, but lithium alkyl amides react analogously to alkyllithium compounds. 

Alkali and alkaline-earth derivatives of phenol and the lower alcohols (methoxides, ethoxides) have been known for more than a century. Traditional applications for them include use as lubricants (e.g., lithium greases), polymerization catalysts, and surfactant stabilizers. Based on their solubility and volatility (both generally low), alkaline-earth alkoxides were presumed to be... 

It is of practical use for metals whose alkyl derivatives are commercially easily available, namely, lithium and magnesium. Metal hydrides can be used as starting material mainly for alkali and alkaline-earth metals. Although Zn(OR)2 alkoxides derived from classic OR groups are insoluble soluble tetranuclear zinc alkyl or hydridoalkoxides [ZnX(OR )]4 (X = R or H) can be obtained starting from zinc alkyls or hydride [30,31]. 

Most metal chlorides undergo only partial metathetical halide/alkoxide exchange upon reaction with alcohols or no reaction at all even at elevated temperatures. The metal alkoxide chlorides thus obtained, MClx(OR), have not been used in sol-gel processing (see, however. Section 7.10.3.3.2). In order to achieve the preparation of homoleptic metal alkoxides from metal chlorides basic conditions are essential in order to trap the liberated HCl. This can be achieved by reaction of metal chlorides with alcohols in the presence of a base such as ammonia or, less often, trialkylamines or pyridine (Equation (11a)). The base also increases the equilibrium concentration of alkoxide ions, which are a more powerful nucleophile for reaction with the metal chloride than the parent alcohol. For this reason the use of alkali alkoxides (M OR), mostly lithium, sodium, or potassium alkoxides, proves to be more successful (Equation (11b)). The use of LiOR has advantages for the preparation of insoluble metal methoxides because LiCl is soluble in methanol and is thus easily separated from insoluble metal alkoxides. 

Development of xanthate and dithiocarhamate derivatives overcomes several drawbacks of the sulfonium monomer (Scheme 7.2b and c). Xanthates and dithiocarbamates are easily prepared by the reaction of bis(halomethyl)benzene with alkylxanthate and dialkyldithiocarbamate salts respectively. Both precursors are stable at room temperature and soluble in organic solvents. This means the polymerization of these monomers can be performed in organic solvents e.g. THE) with the addition of alkoxide base e.g. potassium tert-butoxide). For the dithiocarhamate precursor, lithium bis(trimethylsilyl)amide can be used as the base and the polymerization proceeds at 35 The elimination temperature of these precursor polymers is typically lower than that of the sulfonium polymers with xanthate elimination at 160-250 °C and dithio-carbamate at 180 °C. It has been found that elimination of dithiocarbamate gave materials with reduced structural defects. Both xanthate and dithiocarbamate routes avoid the corrosive acid byproducts (HCl) present in the sulfonium elimination. This is particularly advantageous in device fabrication as adds have a negative impact on indium tin oxide electrodes and interfaces. ... 

Amongst the alkali metals, the lithium derivatives would be expected to be the least ionic as is shown by their solubility in organic solvents and volatility of lithium tert-butoxide (110°/0.1 mm) alkoxides of other alkali metals tend to be nonvolatile and decompose on being heated to higher temperatures even under reduced pressure. 

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