Phosphonium salts application

K. Manabe, Synthesis of Nobel Chiral Quaternary Phosphonium Salts with a Multiple Hydrogen-Bonding Site, and Their Application to Asymmetric Phase-Transfer Alkylation , Tetrahedron 1998, 54, 14465-14476. 

Several sol-gel entrapped catalysts are likely to soon find commercial applications. A variety of transition metal catalysts physically entrapped in silica matrices as ion pairs generated from the metal halides and quaternary ammonium or phosphonium salts developed in the mid-1990s by Avnir and Blum resulted in truly heterogeneous, stable and... 

The preparation of novel phase transfer catalysts and their application in solving synthetic problems are well documented(l). Compounds such as quaternary ammonium and phosphonium salts, phosphoramides, crown ethers, cryptands, and open-chain polyethers promote a variety of anionic reactions. These include alkylations(2), carbene reactions (3), ylide reactions(4), epoxidations(S), polymerizations(6), reductions(7), oxidations(8), eliminations(9), and displacement reactions(10) to name only a few. The unique activity of a particular catalyst rests in its ability to transport the ion across a phase boundary. This boundary is normally one which separates two immiscible liquids in a biphasic liquid-liquid reaction system. 

The formation of the heterocycle 1 from the xylylene-bis-phosphonium salt 2 and PCI3 proceeds via a detectable intermediate 3 in a cascade of condensation reactions that is terminated by spontaneous heterolysis of the last remaining P-Cl bond in a cyclic bis-ylide-substituted chlorophosphine formed (Scheme 1) [15]. The reaction scheme is applicable to an arsenic analogue of 1 [15] and to bis-phosphonio-benzophospholides with different triaryl-, aryl-alkyl- and aryl-vinyl-phosphonio groups [16, 18, 19], but failed for trialkylphosphonio-substituted cations here, insufficient acidity prohibited obviously quantitative deprotonation of the phosphonium salts, and only mixtures of products with unreacted starting materials were obtained [19]. The cations were isolated as chloride or bromide salts, but conversion of the anions by complexation with Lewis-acids or metathesis was easily feasible [16, 18, 19] and even salts with organometallic anions ([Co(CO)4] , [CpM(CO)3] (M=Mo, W) were accessible [20]. 

The salts were prepared from hydroxy phosphine oxides or phosphinates as depicted in Scheme 42 after 1 h. The reactions were carried out with trifluorometh-anesulfonic anhydride in the presence of 4A molecular sieves, and it was shown by P-NMR due to downfield shifts that the phosphonium salts were formed. However, the salts could not be isolated and were prepared in situ for NMR studies and for the application in catalysis. 

The compound has very little commercial application. It is used to prepare phosphonium salts, which also can be made by other processes. 

In this chapter, specific paragraphs are not devoted to the zwitterionic structures, such as betaines, or to the applications of phosphonium salts in organic synthesis, but both topics are mentioned incidentally. 

R3PCH=CHCH=CH2 Clin the same way, in the case of the propargylphosphonium salt, two successive isomerizations of the unsaturation from the / ,y to the opposition, combined with a Michael-type addition of nucleophiles on the intermediate allenyl phosphonium, afford various /Mieterosubstituted oc,/ -unsaturated phosphonium salts, which have found interesting applications in organic synthesis (reaction 44). 

The alkaline hydrolysis of phosphonium salts has been particularly studied from a theoretical point of view as a model for nucleophilic substitution reactions on tetracoor-dinated phosphorus. However, it also has interesting applications, since it corresponds... 

Phosphonium salts can be dealkylated by treatment with alkoxides to yield alkanes. Although the hydrolytic cleavage of phosphonium salts in solution has been well investigated, the solid-phase variant of this reaction has not yet found broad application. One example, in which traceless linking was based on the alkoxide-induced dealkylation of a resin-bound phosphonium salt, is given in Table 3.48 (Entry 1). 

The method of greatest applicability is the reaction of alkali metal phosphides with dihalo-alkanes, -alkenes, etc. (equation 4). Generally this reaction proceeds well and in high yield excess dihaloalkane should be avoided as this leads to the production of phosphonium salts which can contaminate the product. 

Apart from these well-known catalysts, much effort has been expended in the synthesis and applications of chiral phase-transfer catalysts that include various quaternary ammonium salts, metal-salen complexes, phosphonium salts, and chiral amines. However, few of these catalysts have shown promising levels of asymmetric induction in asymmetric reactions. 

By applying alternative alkylation and cathodic cleavage Horner etal S07 synthesized optically active phosphines and phosphonium salts. In reversal of their usual application as reageqts in nucleophilic substitution halides, if converted to... 

Hughes I, Application of polymer-bound phosphonium salts as traceless supports for solid phase synthesis, Tetrahedron Lett., 37 7595-7598, 1996. 

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... 

When generating the ylide from the corresponding phosphonium salt, the choice of the method of formation is important for the stereochemistry of the reaction. With the original application of lithium alkyls as bases one equivalent of lithium halogenide is always formed this lowers the stereoselectivity. Not before the development of methods for the preparation of salt-free ylide solutions, such as the sodium amide... 

The synthesis of vitamin A was certainly a pioneering work in the industrial application of the Wittig reaction 6). The decisive step in this synthesis performed by the BASF, which had already established a plant for the production of vitamin A in 1971 2S4), is the Wittig olefination of vinyl-P-ionol 503 with y-formylcrotyl acetate 507 to vitamin A acetate 508. The phosphonium salt 505 is obtained by reaction of the alcohol 503 with triphenylphosphine hydrobromide 504 2S5) (Scheme 85). 

One of the major developments in organic chemistry during the past 15 years has been the application of phase-transfer catalysis to synthesis. These reactions are often effected in an aqueous base-organic two-phase system with an ammonium or phosphonium salt or crown ether as the catalyst. Crown ethers have also been of great utility as catalysts for solid-liquid phase-transfer processes. Some of the more attractive fea-... 

The nucleophilic curing system is most common and is used in about 80% of all applications. It is based on the cross-linker (bisphenol AF) and accelerator (phase transfer catalyst, such as phosphonium or amino-phosphonium salt). Both diaminic and bisphenol type cure systems are permitted by U.S. Food and Drug Administration (FDA) regulations governing rubber articles in contact with food. The diaminic curing system is also used in some coating and extrusion applications [42]. 

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