Alkylphosphonium

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

Similarly, N-allcylammonium [28] and alkylphosphonium [29] salts form lamellar phases with smectic bilayer structures. In both cases. X-ray scattering also showed the isotropic liquid not to be completely disordered and still displaying similar features to the mesophase. Buscio et al. [28] showed that in N-allcylammonium chlorides the feature was not only much broader than that observed in the mesophase but increased in width with decreasing chain length. 

Room temperature ionic liquids arc currently receiving considerable attention as environmentally friendly alternatives to conventional organic solvents in a variety of contexts.144 The ionic liquids have this reputation because of their high stability, inertness and, most importantly, extremely low vapor pressures. Because they are ionic and non-conducting they also possess other unique properties that can influence the yield and outcome of organic transformations. Polymerization in ionic liquids has been reviewed by Kubisa.145 Commonly used ionic liquids are tetra-alkylammonium, tetra-alkylphosphonium, 3-alkyl-l-methylimidazolium (16) or alkyl pyridinium salts (17). Counter-ions are typically PF6 and BF4 though many others are known. 

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... 

The cations in ionic liquids are generally bulky monovalent organics. The typical cations of ionic liquids, not including the familiar alkylammonium and alkylphosphonium ions, are shown in Fig. 2. It is primarily the cations, which account for the low melting points of ionic liquids. The dialkylimidazolium ions, such as 1-butyl-3-methyl imidazolium [BMIM], have been widely investigated because low-melting ionic liquids can be made readily from such cations and because of their thermal and chemical stability. 

Fig. 2. Typical cations used in ionic liquids, excluding alkylammonium and alkylphosphonium ions.

Q Yang, X-Y Liu, K Umetani, N Kamo, J Miyake. Partitioning of triphenyl-alkylphosphonium homologues in gel bead-immobilized liposomes chromatographic measurement of their membrane partition coefficients. Biochim Biophys Acta 1417 122-130, 1999. 

The cations of the ionic liquid include organic and inorganic cations. Examples of cations include dialkylimidazolium ion, tetra-alkylphosphonium ion, etc. and these cations can be associated with a number of different anions (Fig. 1). The anion includes organic and inorganic anions such as PFg, CF3S03, CF3C00, etc. and Lewis acids such as AlCU", GaC, etc. 

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). 

Long-chain alkylphosphonium azides and thiocyanates have been used as a source of anionic nucleophiles in the reaction of n-octyl halides and esters (n-octX X = Cl, Br, I, OTs, OMs) a substitution process is able to occur even in non-polar solvents909. 

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... 

Vinylmagnesium bromide reacts as a Michael acceptor with a zincated hydrazone, yielding a 1,1-bimetallic species, which in some cases can be sequentially trapped with two different electrophiles.246 2463 The reaction proceeds via metalla-aza-Claisen rearrangement. The dimethyl hydrazone anion behaves as an azaallylic system (Scheme 81).247 Vinylphosphonium salts add Grignard reagents, forming alkylphosphonium ylides. These ylides... 

Phosphonium ions exchange with acidic deuterium sources to form P—D bond-containing products. Alkylphosphoniums react with D O as ... 

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

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