N-Hexyl lithium

The effect of penultimate units on the rate constants of anionic propagation is observed also in other systems. For example, the addition of styrene to the lithium salt of 1-phenyl-n-hexyl anion is 4 times faster than to polystyryl lithium 51). Similarly, the addition of monomer to the lithium salt of 1,1-diphenyl-n-hexyl lithium is faster than the addition to 1,1,3-triphenyl-n-octyl lithium or 2-poly-sty ry 1-1,1-diphenyl ethyl lithium, the latter two salts having comparable reactivities52 . See also Ref.53)... 

In a similar fashion one prepares 1,2-diphenyl-hexyl lithium by reacting n-butyl lithium with 1,1-diphenyl ethylene. It is a relatively slow initiator for hydrocarbon monomers but convenient for acrylates and methacrylates. Its use precludes side reactions that occur with other initiators. Preparation of cumyl potassium was described by Ziegler124 and the same method yields the respective cesium salt. This initiator is stable and shows no change on storage at ambient temperature. After completion of the preparation, it is advantageous to chill the solution to - 70 °C and after a few hours to filter or decant it from the precipitated methoxide. 

The reaction of lithium naphthalide with 4-n-hexyl-1,3,2-dioxathiolane... 

At — 65 °C in THF allylic ethers may be metalated with methyl-lithium in high yield without any Wittig rearrangement With n-hexyl iodide the metalated species (227 M = Li) underwent alkylation preferential y to oxygen. However, with cyclohexanone (227 M = Li) gave ratios the inverse of those predicted from alkylation studies. Thus when (227 R = Bu M = Li) reacted widt cyclohexanone, the product... 

The adducts of either butyllithium with DPE (1,1-diphenylhexyllithium) or polymeric organolithiums with DPE are the preferred initiators for polymerization of a wide variety of alkyl methacrylates and (ert-butyl acrylate [3]. For example, Stiihn and coworkers [77] recently reported the synthesis of well-defined, narrow molecular weight distribution polymers from methyl, ethyl, n-propyl, -butyl, n-pentyl, and n-hexyl methacrylates using the adduct of scc-butyllithium and DPE as initiator in THF at -78 °C in the presence of lithium chloride. This initiator was also used recently to copolymerize 2-tri-methylsiloxyethyl methacrylate and butyl methacrylate using analogous reaction procedures [78]. 

Currently, these molecular systems are studies as SAMs on a metal surface. An additional method of preparing ordered monolayers of molecular devices is the use of Langmuir-Blodgett (LB) films. Therefore, a compound with hydrophilic and hydrophobic subunits with the central nitroaniline core similar to 70 was synthesized as in Scheme 3.40. n-Hexylbenzene was easily brominated on neutral alumina and coupled to TMSA followed by silyl removal and coupling to the nitroacetanilide core intermediate, 68, to afford 88. The methyl ester, intermediate 90, was synthesized by the coupling of methyl 4-ethynylbenzoate (89) to 88. The amine was unmasked and the methyl ester was saponified with lithium hydroxide to afford molecular scale device 91. Compound 91 is suitable for the formation of a LB film due to its hydrophilic carboxylic acid end-group and the hydrophobic n-hexyl end-group. 

For a specific polymer, critical concentrations and temperatures depend on the solvent. In Fig. 15.42b the concentration condition has already been illustrated on the basis of solution viscosity. Much work has been reported on PpPTA in sulphuric acid and of PpPBA in dimethylacetamide/lithium chloride. Besides, Boerstoel (1998), Boerstoel et al. (2001) and Northolt et al. (2001) studied liquid crystalline solutions of cellulose in phosphoric acid. In Fig. 16.27 a simple example of the phase behaviour of PpPTA in sulphuric acid (see also Chap. 19) is shown (Dobb, 1985). In this figure it is indicated that a direct transition from mesophase to isotropic liquid may exist. This is not necessarily true, however, as it has been found that in some solutions the nematic mesophase and isotropic phase coexist in equilibrium (Collyer, 1996). Such behaviour was found by Aharoni (1980) for a 50/50 copolymer of //-hexyl and n-propylisocyanate in toluene and shown in Fig. 16.28. Clearing temperatures for PpPTA (Twaron or Kevlar , PIPD (or M5), PABI and cellulose in their respective solvents are illustrated in Fig. 16.29. The rigidity of the polymer chains increases in the order of cellulose, PpPTA, PIPD. The very rigid PIPD has a LC phase already at very low concentrations. Even cellulose, which, in principle, is able to freely rotate around the ether bond, forms a LC phase at relatively low concentrations. 

Depending upon the structural environment, lithium compounds with the system LiC—C=N— show strong differences in reactivity towards alkyl halides. For example, a solution of LiCH2CH—N—f-Bu (or c-hexyl) in THF and hexane reacts very slowly with ethyl bromide and higher homologues at temperatures below — 10°C. Smooth conversions are observed with lithiated 2-methyl-, 3-methyl-, and 4-methylpyridine and lithiated 2-methyloxazines and 2-methylthiazoles, even at temperatures in the range of — 70 °C. 

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