Lithium, alkyls analysis

However, Li2COs was not observed by Andersson and Edstrom in their XPS analysis of the graphitic anode that had been precycled and then stored at 60 °C for 7 days. They found that, during the storage, the original SEI consisting of lithium alkyl carbonate was indeed unstable and disappeared with time, as... 

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. 

Once chain initiation is complete, the monomer consumption rate is determined only by the chain propagation step. With the less efficient lithium alkyl initiators in hexane or cyclohexane, rather large amounts of monomer are needed to complete chain initiation. The appearance of a first order decay in monomer concentration, invariably obtained in these experiments, is not a very sensitive indication of the complete absence of initiator. Analysis of trial samples for hydrolysis products of lithium alkyls or spectroscopic determination that the polymer anion concentration has reached a plateau are preferable. A seeding technique is often used [32, 59] where the real initiator is a pre-formed active polymer... 

Since Evans et al. [78] has discovered that prochiral alkyl(dimefliyl) phosphine boranes can undergo the enantioselective deprotonation of one methyl group, using butyllithium and ( )-sparteine 141, these compounds have been widely used for the synthesis of P-chirogenic borane phosphines [79-105]. Lithium alkyls form chiral complexes 142 with sparteine 141 and related chiral diamines, which were investigated by single crystal X-ray analysis (Scheme 43) [82-87]. 

In the literature, both the (R,S) and the (S,S) diastereomers of lithium alkyl 2 have been proposed as the major diastereomer [4a, 5a]. Based on these predictions, both retention and inversion of the configuration at C(3) have been postulated for the reactions of (/ ,S)-2 with alkyl halides. Our X-ray structural analysis of (R,S)-2 shows that the reaction of the (/ ,iS)-configured stereoisomer and inversion of configuration [for the reaction of R,S)-2 with iodomethane in toluene] do in fact take place. 

The direct evidence of this reaction mechanism is the observation of carbonyl stretching signature at -1,650 cm" in FTIR spectrum. The decomposition products from lithium salt were also found through the XPS surface analysis, such as alkoxides or oxides, a competition reaction between solvents and salts. However, the formation of alkyl carbonate seems to be predominant when EC is the component of electrolyte because of the more reactive nature of EC toward cathodic reductions [28]. The formation of lithium alkyl carbonate was also confirmed in an independent work, where the reduction products of EC in a supporting electrolyte were hydrolyzed by DjO and then subject to NMR analysis, which identified ethylene glycol as the major products formed, as indicated by the singlet at H spectrum [29]. Therefore, Aurbach and co-workers concluded the reduction products of EC and PC, lithium ethylene dicarbonate (LEDC) and lithium propylene dicarbonate (LPDC), respectively ... 

The results (Table 7) show that nearly all types of lithium alkyls may be employed. Analysis of the diastereomeric ratio clearly shows a predominance of the syn isomo in almost all cases. Howevo-, an interesting trend is the increasing amount of anti isomer formed on going from primary to secondary and totiary butyllithium. A complete reversal of the diastereofacial selectivity does, in fact, occur. For -BuLi, the syn-anti ratio is 91 9 for r-BuLi is 12 88. ... 

In order to establish the correct absolute stereochemistry in cyclopentanoid 123 (Scheme 10.11), a chirality transfer strategy was employed with aldehyde 117, obtained from (S)-(-)-limonene (Scheme 10.11). A modified procedure for the conversion of (S)-(-)-limonene to cyclopentene 117 (58 % from limonene) was used [58], and aldehyde 117 was reduced with diisobutylaluminium hydride (DIBAL) (quant.) and alkylated to provide tributylstannane ether 118. This compound underwent a Still-Wittig rearrangement upon treatment with n-butyl lithium (n-BuLi) to yield 119 (75 %, two steps) [59]. The extent to which the chirality transfer was successful was deemed quantitative on the basis of conversion of alcohol 119 to its (+)-(9-methyI mande I ic acid ester and subsequent analysis of optical purity. The ozonolysis (70 %) of 119, protection of the free alcohol as the silyl ether (85 %), and reduction of the ketone with DIBAL (quant.) gave alcohol 120. Elimination of the alcohol in 120 with phosphorus oxychloride-pyridine... 

In the complexes of w/Ao-substituted benzyl ethers, the benzylic hydrogen atoms are diastereotopic. Alkylation of the derived lithium compounds occurs completely stereoselective-ly anti to the tricarbonylchromium face from a rotamer in which the benzylic methoxy group is anti to the or/Ao-substituent2,3. The stereochemistry of the alkylation was confirmed unambiguously by X-ray analysis of the product3. 

Radioactivation analysis has been used to measure bromine in polymers (37—39) and recently a novel technique for trace oxygen has been reported (40). Any polymer or other material (e.g. metal alkyl) which is miscible with butyl lithium solutions may be analysed since the procedure involves the intermediate production of triton particles by the nuclear reaction 6Li (n, a) t. The tritons then act as nuclear projectiles for the activation of oxygen 0 (t, n) 18F and the radioactivity due to fluorine-18 is measured. A sensitivity of 1 x 10 g in a 0.5 g sample is claimed. 

Notably, the lithium enolates have the planar methylenecyclopropane-type structure56, but give C-alkylation products49"52. X-ray structure analysis of the lithium enolate56 and bicyclobutyllithium57 TMEDA complexes revealed that both crystallize as lithium bridging dimers. 

Using the normal addition procedure (02 diffusion into a 75/25 benzene/THF solution of poly(styryl)lithium) the 37% dimer fraction analyzed for 19% alkyl radical dimer and 18% macroperoxide after LiAlH4 reduction. The yield of macroperoxide was also confirmed by thermal decomposition experiments in refluxing toluene, followed again by size exclusion chromatography analysis of the dimer fraction. The amount of hydroperoxide could be deduced from the difference between the amounts of total peroxide (determined by iodometric titration) versus the amount of macroperoxide determined by LiAlH4 reduction. 

The rates for the methylation of cyclopentanone and for the proton abstraction from 2-methylcyclopentanone were significantly increased by a factor of 7500 and 5, respectively, when six equivalents of HMPA were added to the reaction. Using 31P, 7Li and 13C NMR spectroscopy, Suzuki and Noyori found that the tetrasolvated Dy dimer was exclusively generated from the tetrameric (T0,4) and dimeric (D0,4) tetrasolvated lithium amine-free enolate of cyclopentanone (0.16 M in THF, —100 °C, ratio 2/3)275. Kinetic analysis gave a first-order reaction in dimer and HMPA for the reaction with a modulation for free HMPA33, and a first-order reaction in dimer for deprotonation, independent of HMPA. Possible transition state structures for alkylation and proton abstraction are drawn in Scheme 85. 

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