Lithium salts, aggregation

Lithium hydroxide can be used for preparation of numerous lithium salts. The dominant use is the preparation of lithium stearate [4485-12-5], which is added to lubricating greases in amounts up to about 10% by weight. This salt has very low water solubiHty and extends the acceptable viscosity for the grease to both low and high temperatures (see Lubrication and lubricants). Lithium hydroxide is also used in production of dyes (62) and has been proposed as a source of lithium ion for inhibition of alkaH-aggregate expansive reactivity in concrete (63). 

The kinetics of polymerization and conductometric studies of barium polystyrene with one active end-group per chain were reported by De Groof et al. 79,80). Formation of an unconventional anionic species, Ba2 +, (CH(Ph)CH2—)j, had to be postulated to account for the results. The existence of such a species is supported by the recent study of the kinetics of polymerization of lithium polystyrene performed in the presence of barium polystyrene endowed with two active endgroups 78). The polymerization of the lithium salt is retarded by the presence of the barium salt, and the retardation is accounted for by the formation of the inert aggregated anions,... 

A completely different tactic is the use of microwave energy absorption of this energy by a peptide results in decreased aggregation. Lithium salts facilitate the solution of peptides in these polar solvents, increase the rate of swelling of polar resins, and improve coupling yields. Sometimes the order of addition of two solvents to a peptide makes a difference. The inclusion of pyridine can also have a beneficial... 

The work carried out to date indicates that not all lithium salts are effective in diminishing the alkali-aggregate expansion reaction [10]. Optimum dosage requirements and long-term effects have to be evaluated. Before the relative effects of various lithium compounds such as hydroxide, carbonate, nitrate, fluoride, perchlorate, chloride, etc., can be substantiated much more work employing reliable predictive tests has to be carried out. 

Nuclear magnetic resonance (NMR) has proven to be a very powerful technique for probing the structures of carbanions in the condensed phase. In particular, much work has been completed on the ion-pairing behavior of carbanions with lithium cations as well as the formation of aggregates of these lithium salts. A full discussion of this topic, particularly the methodology, is beyond the scope of this chapter, but a brief overview is appropriate. 

The situation becomes even more complex when other lithium salts are present in the solution. For example, when a lithium halide such as LiBr is added to solutions of alkyllithiums, mixed aggregates are formed where a bromide anion takes the... 

Some ion conductive properties of lithium salt/ IL solutions are summarized in Table 3.17. Generally, the ionic conductivity of ILs containing lithium salts are lower than those of pure ILs, even though the addition of lithium salt increases the net number of ions in the system, due to smaller formula weight of lithium. According to the literature, the major reason for these phenomena may be the increase in viscosity and Tg (some specific values are shown in Table 3.17). The aggregation oflithium ions in ILs, which causes the decrease in the effective carrier ion number, might be another reason for the decrease in ionic conductivity. 

Amidolithiums have the same ionic bonds and tendencies to aggregation as other lithium salts. The primary unit is normally the planar ring dimer (LiNRR )2- Groups R and... 

Lithium salts of dianions of unsaturated carboxylic acids can adopt the structure of lithium dienolates, 3 or 4 (equation 3), or lithium salts of oxycarbonyl substituted allyl anions, 5 or 6 (equation 4). In any case these formulations provide an oversimplified view of the structures, as these dianions are expected to form ion pairs and aggregates in weakly polar solvents such as diethyl ether or thf. ... 

This seemingly simple result may have far reaching consequences. For example, it may help to explain the effect of added lithium salts in nucleophilic additions to cyclohexanones as discussed earlier in this chapter. Thus, model (63) shown in Figure 472.135-137 explain the enhancement of rate and may also be relevant to the origins of stereoselectivity in this reaction. Of course, the exact location of the lithium atom and the aggregation state of the adding nucleophile are subject to speculation, since for lithium these parameters seem to be highly variable. 

The aggregation of fluorinated surfactants in nonaqueous solvents has also been studied. These surfactants form aggregates at lower concentrations than ordinary hydrogenated surfactants in water. Chrisment et al. have studied nonionic fluoro-alkyllipopeptides in DMSO and found progressive and very limited aggregation in this solvent as expected from the low polarity of the solvent [65], In addition, the lithium salt of nonadecafluorodecanoic acid has been studied with 19F NMR in formamide, A-methylformamide, and ethylene glycol [66],... 

The aggregation of lithium salts of living polymers in hydrocarbons is disrupted by their coordination with added solvating agents like ethers or amines. As a result the propagation is accelerated and its stereochemistry is greatly modified. The complexity... 

The lithium salt of 2,3-dimethylindole reacts in THF with primary iodides to give 3-substituted 3Ff-indoles. Interestingly, the reaction is dependent on the concentration of the salt, implying that an aggregated species may be involved (Equation (71)) <91H(32)685>. 

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