Lithium /-butoxide

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). 

Solutions of butyllithium in hexanes and sec-butyllithium in cyclohexane were purchased from the Aldrich Chemical Company, Inc. It Is recommended that only freshly opened bottles or extremely well protected solutions be used as the presence of lithium butoxide in partially decomposed bottles results in formation of the corresponding butyl ester as an undesired by-product. 

Formation of the lithium /-butoxide in this manner is very exothermic and causes the hexane to boil during addition. 

The polymerization of styrene with less anionic butyllithium has been studied by several workers (31, 32, 33). The results of Tobolsky and Boudreau (34) showed that the butyllithium polymerization of styrene follows the electronic behavior of an anionic reaction. Electron releasing groups on the aromatic ring decreased the reactivity of the monomer. Braun and co-workers and Worsfold and Bywater (35) have studied the production of isotactic polystyrene by butyllithium catalysis. Worsfold and Bywater found that water plays an important role in the isotactic polymerization and concluded that the production of lithium hydroxide in situ is important for the isotactic steric control. Added lithium butoxide, lithium methoxide or lithium carbonate were not effective. They concluded the associated forms of butyllithium do not produce isotactic steric control but require association with lithium hydroxide. 

Cleavage and resolution of epoxides.1 The aluminum reagent obtained by reaction of (R)-l with diethyl- or dimethylaluminum chloride shows slight reactivity in reactions with epoxides, but the ate complex (2), prepared from 1, (C2H5)2A1C1, and lithium butoxide, converts cyclohexene oxide into the chlorohydrin (3) in 40% ee. 

The TPD of a BuOH(20 L)/Li(17 ML)/Au(poly) surface, prepared by condensing ultrapurified BuOH on a Li/Au(poly) surface kept at 120 K, revealed, in addition to the features characteristic of bulk BuOH at 200 K, peaks for mle = 57 (curve a), 44 (curve b), 43 (curve c) and 2 (curve d), centered at 580 K (see Figure 27). Also noteworthy is the presence of a second mle = 2 peak at 435 K. A reaction pathway consistent with these data involves the dehydrogenation of BuOH to form the corresponding lithium butoxide (BuOLi) and lithium hydride, which at a sufficiently high temperature undergoes thermal decomposition to yield elemental Li and dihydrogen ... 

C, C4H9OK. The calculation of / assumes that the isotope exchange catalyzed potassium <-butoxide proceeds 2600 times faster than that catalyzed by lithium <-butoxide and that the reaction becomes tenfold faster on increasing the temperature by 25°C. 

Lithium butoxides increase the rate of reaction of lithium alkyls with olefins in cyclohexane or hexane but decrease it in benzene. The propagation rate is, however, decreased in both types of solvent [77, 78] according to information presently available. In fact, as far as is known, butoxides reduce rates where the mechanism has been suggested to be dissociative and increase them in the other cases. More data are still required to confirm that this always happens. The experiments with polystyryllithium [77] show that the polymer dimers in solution are not dissociated by lithium fert.-butoxide as would be expected if mixed aggregates of the type (PstLi. BuOLi ) were formed. In this case, at least, the rate effect appears to be caused by addition of butoxide to the polystyryllithium dimers. The reaction still shows half order characteristics, and the rate depression is almost complete at a 1 1 ratio of butoxide to polymer chains. The major species present in solution would seem to be (PstLi. BuOLi)2 at this point. Similar results have been obtained with polyisoprenyllithium in cyclohexane [78]. The nature of... 

Lithium -butoxide 5.8 6.2 Sodium -butoxide 8.2 8.3 Potassium t-butoxide... 

Chloral, CChCHO, can be anionically or cationically polymerized. The polymerization is initiated above the ceiling temperature of 58° C and then allowed to proceed well below the ceiling temperature. Phosphines and lithium /-butoxide are especially suitable as anionic polymerization initiators, whereas tertiary amines only produce poly (chlorals) of low thermal stability. Anionic copolymerization of chloral with excess isocyanates produces alternating polymers, as is also the case for the cationic copolymerization of chloral with trioxan. 

Following a procedure similar to Dileone s, we have reacted diepoxides, including BADGE, with MDI. The catalysts used were lithium butoxide and tetraethylammonium bromide. Products were isolated by additions to the DMF solution of first water and then, in some reactions, methanol. 

Ring chain equilibria in the polymerization of < -valerolactone by lithium butoxide in THF have been found to be in accord with Jacobson-Stockmayer theory. The relative reactivities in the propagation of /ff-propiolactone are markedly temperature sensitive k /k+ varies from 5.6 at —20 C to 150 at 35 °C, the counterion being potassium complexed with dibenzo-18-crown-6 in dichloromethane. Roda and co-workers have continued their study of 2-pyrrolidone. The reactions of di-isopropenylbenzene (DIB) continue to be of interest. A paper by Beinert et al. in 1978 described the synthesis of a reagent, claimed to be an efficient difunctional initiator, by the reaction of one mole of /m-DIB with two of s-butyl-lithium. Protonation of the reagent solution with methanol generated butane and the hydrocarbon (5) was recovered. This species... 

When (Me5C5)2Lu( i-Me)2Li(THF)2 is treated with tert-butanol the bridging structure of the complex is destroyed and (Me5C5)2LuOBu-t is formed along with lithium butoxide and methanol [102]. 

X 10 exp(—13407/T) s for n-BuLi can be evaluated. As with all rate coefficients of ionic polymerization, this elimination also depends on the reaction system. The lithium hydride (LiH) elimination from butyllithium in the presence of polar additives such as lithium butoxide is reported to be several times faster than from pure lithium alkyl [90, 91], and in ethereal solvents proton abstraction or ether cleavage may occur [92]. 

HF calculations of the structures and vibrational frequencies of monomers and dimers of lithium alkyl carbonates (methyl, ethyl, and propyl carbonate lithium) and lithium alkoxides (lithium methoxide, lithium ethoxide, lithium propoxide, and lithium butoxide) indicate that they adopt dimeric structures. Dimerisation energies of 214 kJ mol for lithium alkyl carbonates and 266 kJ mol for lithium alkoxides are calculated and are found to be approximately independent of the chain length. 

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