Alkylphosphonium salt

Commonly used ionic liquids are N-alkylpyridinium, N,N -dialkylimidazolium, alkylammonium and alkylphosphonium salts. 

The use of tetra-alkylphosphonium salts to catalyse heterogeneous reactions involving anion transfer has been described. ... 

Ketophosphonium salts are considerably more acidic than alkylphosphonium salts and can be converted to ylides by relatively weak bases. The resulting ylides, which are stabilized by the carbonyl group, are substantially less reactive than unfunctionalized ylides. More vigorous conditions are required to bring about reactions with ketones. Stabilized ylides such as (carboethoxymethylidene)triphenylphosphorane (Entries 8 and 9) react with aldehydes to give exclusively trans double bonds. 

K. Okamoto and M. Okamoto also investigated the biodegradability of neat PBS before and after nanocomposite preparation with three different types of OMLF. They used alkylammonium or alkylphosphonium salts for the modification of pristine layered silicates, and these surfactants are toxic for microorganisms [56]. 

Part of the discrepancies can be removed by considering a reaction which becomes important only in water. It was found that in acidic aqueous solutions water soluble phosphines react with activated olefins yielding alkylphosphonium salts [83-85] (Scheme 3.5). The drive for this reaction is in the fast and practically irreversible protonation of the intermediate carbanion formed in the addition of TPPMS across the olefinic bond. Under... 

Two standard routes to y-functional phosphonium salts with electron-withdrawing groups consist in using the corresponding Michael alkenes to achieve either halide substitution in the -position to the functional group, in order to obtain y-functional vinylphosphonium salts, or Michael addition in the presence of acid to produce the y-functional alkylphosphonium salt (reaction 85). 

TPPMS serves as ligand in a variety of catalysts for hydrogenation,6 hydroformylation, and C-C bond formation.7 In aqueous solutions, it reacts with activated olefins,8 alkynes,9 and aliphatic as well as aromatic aldehydes,10 giving the corresponding substituted alkylphosphonium salts. 

Polystyrene-bound benzaldehydes can be smoothly olefinated with benzyl- or cin-namylphosphonium salts in DMF or THF using sodium methoxide as a base (Entry 1, Table 5.5 [64-67]). Alkylphosphonium salts, however, only react with resin-bound aldehydes upon deprotonation with stronger bases, such as butyllithium [30,68-70]. The more acidic acceptor-substituted phosphonium salts, on the other hand, even react with resin-bound aldehydes and ketones upon treatment with tertiary amines, DBU, sodium ethoxide, or lithium hydroxide [71-75], but stronger bases are also used occasionally [76]. 

Wittig reactions can also be performed with support-bound phosphorus ylides. Polystyrene-bound alkylphosphonium salts have been prepared from the corresponding alkyl mesylates or halides and trialkyl- or triarylphosphines (Figure 5.8 [60,80]). Because polystyrene is a hydrophobic support, salt formation does not proceed smoothly and quaternization of phosphines generally requires forcing conditions. The... 

Figure 5.8. Wittig olefination with polystyrene-bound alkylphosphonium salts [68,83,84],...

Although the reaction conditions have been greatly modified, no evidence whatsoever has been found for the generation of pentaalkylphosphorane according to Eq. (13b). This is also true for other reactions of noncyclic alkylphosphonium salts with lithium alkyls. 

Thus, in alkylphosphonium salts too the C—H functions adjacent to the positively charged key atom were too acidic to let the attacking nucleophile proceed on its way towards the phosphorus center. A way out of this dilemma should consist in the application of a phosphonium salt with less acidic neighboring C—H functions. Such a salt was tetraphenylphosphonium iodide which in the reaction with phenyllithium did indeed lead to the first compound containing five covalent carbon-element bonds, pentaphenylphosphorane, (C6H5)5P (12)23). Its covalent nature was... 

Quantitative yields of alkylphosphonium salts are obtained in the reactions of primary alcohols with triphenylphosphine in 48%... 

Wittig reagents. Magnesium (activated by iodine) can serve as a base for ylide generation from alkylphosphonium salts. 

A large variety of ILs of high purity with water content below lOOppm and halide content below lOppm are now available commercially. These include numerous iV-alkylpyridinium, 7V,7V -dialkylimidazolium, alkylammonium and alkylphosphonium salts, covalent hydrophobic ILs (e.g. l,2-dimethyl-3-propyliniidazolium bis(trifluoromethylsulfonyl)imide, task-specific ILs, Bronsted acidic ILs (e.g. 3-[triphenylphosphonio]propane-l-sulfonic acid tosylate), nitrile-fiinction sed ILs, perfluorinated ILs (e.g. tetrabutylammonium nonafluorobutane sulfonate, BASF Basionics (e.g. 1,2,3-trimethylimidazolium methyl sulfate), and TOMATS for heavy metal extraction (e.g. methyltrioctylammonium thiosalicylate)... 

The Wittig olefination involves non-stabilized ylides, which are generated upon treatment of the corresponding resin-bound alkylphosphonium salts with strong bases (NaHMDS, LiHMDS, KO Bu, nBuLi). Supported phospo-nium salts can be prepared from the corresponding bromoalkene by refluxing with a resin-bound phosphine. 

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