Butyllithium 1,1-diphenylethylene addition

This has been studied much less frequently and appears to be a rather more complex reaction. The first results obtained, for the butyl-lithium, styrene reaction in benzene have already been described. In a similar way the addition of butyllithium to 1,1-diphenylethylene shows identical kinetic behaviour in benzene (26). Even the proton extraction reaction with fluorene shows the typical one-sixth order in butyllithium (27). It appears therefore that in benzene solution at least, lithium alkyls react via a small equilibrium concentration of unassociated alkyl. This will of course not be true for reactions with polar molecules for reasons which will be apparent later. No definite information can be obtained on the dissociation process. It is possible that the hexamer dissociates completely on removal of one molecule or that a whole series of penta-mers, tetramers etc. exist in equilibrium. As long as equilibrium is maintained, the hexamer is the major species present and only monomeric butyllithium is reactive, the reaction order will be one-sixth. A plausible... 

With diphenylhexyllithium 121) (the product of addition of butyl-lithium to 1,1-diphenylethylene) kinetic results are the same as found for fluorenyllithium initiation in the presence of moderate amounts of ether. Even in pure toluene, the rates are first order with respect to initiator concentration and monomer concentration. This simple behaviour is caused by a constant fraction of the initiator forming low molecular weight polymer. If butyllithium is used as initiator, the kinetic behaviour is too complex for analysis. 

Diphenylmethyllithium [881-42-5] can be prepared by the metalation reaction of butyllithium with diphenylmethane in addition, the adduct of butyllithium and 1,1-diphenylethylene is conveniendy prepared in either hydrocarbon or polar solvents such as THF as shown in equation 18. 

Diphenylmethylcarbanions. The carbanions based on diphenyl-methane (pZ a = 32) (see Table 1) are useful initiators for vinyl and heterocyclic monomers, especially alkyl methacrylates at low temperatures (46). 1,1-Diphenylalkyllithiums can also efficiently initiate the polymerization of styrene and diene monomers that form less stable carbanions. Diphenylmethyl-lithium can be prepared by the metalation reaction of diphenylmethane with butyllithium or by the addition of butyffithium to 1,1-diphenylethylene, as shown in equation 17. This reaction can also be utihzed to prepare ftinctionalized initiators by reacting butyffithium with a substituted 1,1-diphenylethylene derivative. Addition of lithium salts such as hthium chloride, lithium f-butoxide, or lithium 2-(2-methoxyethoxy)ethoxide with 1,1-diphenylmethylcarbanions and other organolithium initiators has been shown to narrow the molecular weight distribution and to improve the stabffity of active centers for anionic polymerization of both alkyl methacrylates and t-butyl acrylate (47,48). 

Methyl Methacrylate. The most generally usefiil initiator for anionic polymerization of MMA and related compounds is 1,1-diphenylhexyllithium which is formed by the quantitative and facile addition of butyllithium with 1,1-diphenylethylene (DPE) (eq. 17) (46). Using this initiator in THF at -78°C, it is possible to polymerize MMA to obtain polymers and block copolymers with predictable molecular weights and narrow molecular weight distributions. Controlled polymerizations are not effected in nonpolar solvents such as toluene, even at low temperatures. Other usefiil initiators for polymerization of MMA are oligomers of (a-methylstyryl)lithium whose steric requirements minimize attack at the ester carbonyl group in the monomer. These initiators are also useful for the polymerization of 2-vinylpyridine (see Methacrylic Ester POLYMERS). 

The structure of the carboxylated derivative of the addition product tvas proven from a mixed melting point determination with an authentic sample. K6-brich and Stober [21] reinvestigated this reaction in tetrahydrofuran (THF) at -80 to 20 °C and isolated a,a-diphenylheptanoic acid in 98% yield protonation and alkylation of the intermediate 1,1-diphenylhexyllithium with water and n-butyl bromide formed 1,1-diphenylhexane and 5,5-diphenyldecane in 99% and 97% yields, respectively. However, Evans and George [22] have reported that further reversible addition can occur when a large molar excess (6.4-fold) of 1,1-diphenylethylene is reacted with -butyllithium in benzene at 30 °C as shown in Scheme 1. The amount of 1,1,3,3-tetraphenyloctane isolated after hydrolysis was much less than the amount of 1,1-diphenylhexane therefore it was concluded that the second equilibrium step in Scheme 1 strongly favors the monoadduct. No 1,1,3,3-tetraphenyloctane was detected when only a 1.8-fold excess of DPE was used [22, 23]. From the kinetics of the reaction it was concluded that the addition of n-butyllithium to DPE is irreversible [23]. 

Further evidence for the quantitative addition of poly(styryl)lithium with a stoichiometric amount of 1,1-diphenylethylene can be deduced by HNMR analysis of the adduct formed after methanol termination. A characteristic peak (multiplet) at 5 3.5 ppm is observed by HNMR for the terminal methine hydrogen at the chain end in the PS-DPE and no corresponding peak is observed in the base polystyrene. Integration of the area of this peak relative to the area of the resonances corresponding to the methyl protons of the sec-butyllithium initiator fragment at 5 0.5-0.78 ppm gave a value of 1 5.9, in close... 

This lack of copolymerization reactivity of DPE was also observed for the copolymerization of 1,1-diphenylethylene and isoprene [125, 134]. As shown in Table 7, when isoprene was copolymerized with DPE in benzene using n-butyllithium as initiator, the monomer reactivity ratio was 37, which indicates that the addition of isoprene to the isoprenyllithium chain end is 37 times faster than the addition of 1,1-diphenylethylene. The unreactivity of isoprenyl carbanions toward DPE is unique to lithium the monomer reactivity ratios for isoprene in benzene were 0.38 and 0.05 with sodium and potassium as the counterions [125, 134]. When THE was used as the solvent at 0°C, ri decreased to 0.11 with lithium as counterion. 

It was anticipated that the copolymerization of substituted 1,1-dipheny-lethylenes with dienes such as butadiene and isoprene would be complicated by the very unfavorable monomer reactivity ratio for the addition of poly(-dienyl)lithium compounds to 1,1-diphenylethylene [133, 134]. Yuki and Oka-moto [133, 134] calculated values of ri=54 and ri=29 in hydrocarbon solutions for the copolymerization of 1,1-diphenylethylene (M2) with butadiene (Mi) and isoprene (Mi), respectively. Although the corresponding values in THE are ri(butadiene)=0.13 and ri(isoprene)=0.12, this would not be an acceptable solution since THE is known to form polymers with high 1,2-microstructures [3]. Anionic copolymerizations of butadiene (Mi) with excess l-(4-dimethyla-mino-phenyl)-l-phenylethylene (M2) were conducted in benzene at room temperature for 24-48 h using scc-butyllithium as initiator [189]. Anisole, triethy-lamine and ferf-butyl methyl ether were added in ratios of [B]/[RLi]=60, 20, 30, respectively, to promote copolymerization and minimize 1,2-enchainment in the polybutadiene units. Narrow molecular weight distribution copolymers with Mn=14xl0 to 32x10 (Mw/Mn=1.02-1.03) and 8, 12, and 30 amine... 

By analogy with the structure of the mcfa-substituted double diphenylethy-lene, 73, which forms a useful dilithium initiator upon addition of 2 moles of sec-butyllithium, the trifunctional diphenylethylene, 94, has been investigated as a precursor for a hydrocarbon-soluble, trilithium initiator, 95, as shown in Eq.(49) [239] ... 

Scheme 1-108. Addition of n-butyllithium onto styrene and 1,1-diphenylethylene followed or not by polymerization.

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