Ethyllithium, formation

It will be immediately clear from the boiling point of trimethylsilylpropyne (96 C at atmospheric pressure) that the use of a hexane solution of BuLi for the lithiation of propyne is not advisable. The best way is to metallate propyne with a solution of ethyllithium in Et20, prepared from C2HjBr and lithium. iJwy/lithium in Et70 would be less suitable, because of the formation of small amounts of octane (b.p. 128 C) during its preparation (Wiirtz-coupling). 

Conductivity studies show that organoalkali compounds, such as ethyllithium, C2H5—Li, are good conductors when dissolved in diethyl-zinc. Ionization apparently occurs, and, since the formation of ethide ions, C2H7, is unlikely, the reaction may be best represented as a sbl-volysis by the acidic zinc compound ... 

Treatment of cyclopropyl phenyl ketone and cyclopropyl methyl ketone with ethyllithium and phenyllithium, respectively, afforded the corresponding (alkyl)(cyclopropyl)(phenyl)methox-ides which underwent deoxygenation on exposure to lithium in ammonia before hydrolysis to give the corresponding hydrocarbons in excellent yields.For example, formation of 1-phenylethylcyclopropane (1). ... 

Alberts and Wynberg studied the addition of ethyllithium to PhCHO, mediated by the lithiated product (k)-l-phenyl-l-propanol-dj [40]. The (i )-l-phenyl- 1 -propanol enantiomer was formed in 17% enantiomeric excess in the reaction. For this asymmetric induction rendered by the product, the authors coined the expression enantioselective autoinduction . It was suggested that the formation of mixed aggregates consisting of the labeled chiral mediator and the or-ganoHthium reagent influences the stereochemistry of subsequent C-C bond formation [41]. 

When organolithium compounds are dissolved in nonpolar solvents, there is a strong tendency of the solute molecules to associate into aggregates. For instance, butyllithium is hexameric in hexane solution. This is true of ethyllithium as well. Addition of Lewis bases to these solutions causes formation of strong complexes between the bases and the organometallic compounds. This causes the clusters to break up through a succession of equilibria with tetrameric and dimeric intermediates, all becoming complexed with the Lewis bases. Particularly effective bases are those... 

When the polymerizations of cyclic sulfides are carried out with anionic initiators, many side reactions can occur. On the other hand, common anionic initiators, like KOH yield optically active polymers from optically active propylene sulfide [194]. An example of a side reaction is formation [192] of propylene and sodium sulfide in sodium naphthalene initiated polymerizations. Such reactions are very rapid even at —78°C. A similar reaction was shown to take place with ethyllithium [195] ... 

Alkylated diboranes are produced by exchange of diborane with a few metal alkyls, e.g., ethyllithium (113) and trimethylgallium (114). Similarly, alkyl exchange has been observed between aluminum borohydride and both tin and lead tetramethyl with formation of, among other products, methylated diboranes (115). 

Reaction scheme (f) has been most widely subscribed to by polymer chemists. In this writer s opinion it is not a likely pathway for reaction. The enthalpy change for dissociation of hexamer into monomer molecules, Eq. (7), is not known, but is probably on the order of 100 kcal/mole of hexamer, at a minimum. This, coupled with an unfavorable entropy effect, should make the free energy change for Eq. (7) so large (positive) that no reasonable assumption about the kinetic behavior of the various candidate species will suffice to make the concentration of monomer rate-determining. It must be recalled that the mass spectral data for ethyllithium vapor at 87° C failed to show the presence of any monomer. Intermolecular exchange of alkyl groups, observed in NMR studies of ethyllithium (47), almost certainly proceeds by dissociation of hexamer into tetramer and dimer. The enthalpy of dissociation of polyisoprenyllithium dimer has been estimated to be about 37 kcal/mole 31b). If a similar value obtains for short chain n-alkyllithium compounds (and there is reason to believe it does), the rate of formation of monomer could not possibly be as fast as the observed rates of initiation. Finally, it is difficult to see how a monomeric alkyl-lithium species could confer the required stereospecificity in reaction with an olefin 73). 

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