Tetraalkylphosphonium

Another catalytic system which has been successfully applied to the autoxidation of substituted toluenes involves the combination of Co/Br" with a quaternary ammonium salt as a phase transfer catalyst (ref. 20). For example, cobalt(II) chloride in combination with certain tetraalkylammonium bromides or tetraalkylphosphonium bromides afforded benzoic acid in 92 % yield from toluene at 135-160 °C and 15 bar (Fig. 19). It should be noted that this system does not require the use of acetic acid as solvent. The function of the phase transfer catalyst is presumably to solubilize the cobalt in the ArCH3 solvent via the formation of Q + [CoBr]. ... 

Besides the advantage of recyclability, reactions in ionic liquids are generally faster and are run under milder conditions than reactions with conventional solvents. Further activation may come from ultrasonic agitation.520 Since the majority of ionic liquids used are imidazolium salts, the effect of these solvents can be at least partly attributed to the in situ formation of carbene complexes (Section 9.6.3.4.10).521 Cross-coupling of ArB(OH)2 can also be efficiently performed in ionic liquids based on long-chain tetraalkylphosphonium salts, in which case aryl bromides and some aryl chlorides can be processed in the presence of the trivial ligand PPh3.522... 

The use of ionic liquids as reaction media for the palladium-catalyzed Heck reaction was first described by Kaufmann et al, in 1996 [85]. Treatment of bromoben-zene with butyl acrylate to provide butyl trans-cinnamate succeeded in high yield in molten tetraalkylammonium and tetraalkylphosphonium bromide salts, without addition of phosphine ligands (Scheme 5.2-16). 

More than 600 ionic liquid systems can, in principle, be generated from around 10 simple anions such as (BF4)" and (PFg) and the l-alkyl-3-methylimidazolium cation substimted with various alkyl groups in the 2-, 4-, or 5-position, or N-alkylpridinium substimted in the 3- or 4-position. When heteropolyanions and tetrafkylammonium and tetraalkylphosphonium cations are added to the hst, a grand total of more than a quarter of a million ionic liquid systems is possible. 

ESR data obtained on y-irradiation of tetraalkylphosphonium salts in solution (96% sulphuric acid) at 77 K differ markedly from those for the trialkylphosphonium ions44. The latter irradiation produces the expected phosphabetaine radical cation and, for example, tetrabutylphosphonium iodide has features assigned previously to I2 45. On the other hand, PH was not detected44,46. Trialkylphosphonium salts, such as trimethyl and triethyl compounds, produce radicals whose ESR spectra are characteristic of the radical cations of R3P +. The central region of the ESR spectra is dominated by features from... 

The catalysts must supply the system with lipophilic cations in order to form, with required anions, ion pairs able to enter nonpolar media. The most typical catalysts are tetraalkyl ammonium (TAA) salts R4N+X, particularly those having at least 16 carbon atoms in the four R groups. Similar lipophilic catalysts are tetraalkylphosphonium and -arsonium or trialkylsulfonium salts, which are less available and usually less stable. They are therefore of negligible practical use. There are a few reports on the use of trialkylamines as catalysts in some two-phase reactions. Usually these amines are qua-ternized by a reactant actually these reactions are catalyzed by TAA salts. More complicated is the generation of dihalocarbenes with trialkylamines. The amines form, with the carbene, an ammonium ylide, which acts as a base in the organic phase. 

The synthesis of pentasil zeolites is supported by organic cations. Argauer et al. (1) first described syntheses with tetraalkylammonium and tetraalkylphosphonium compounds. The organic cations may not only initiate and sustain a certain crystallization process but also may lead to products of a new structure. This "templating" behaviour is explained by the structure-directing effect of the organic cations in the process of crystallization (2,3). 

Ionic liquids are quite simply liquids that are composed entirely of ions [96, 97]. They are generally salts of organic cations, e.g. tetraalkylammonium, alkylpyridi-nium, 1,3-dialkylimidazolium, tetraalkylphosphonium (Fig. 7.28). Room temperature ionic liquids exhibit certain properties which make them attractive media for performing green catalytic reactions. They have essentially no vapor pressure and are thermally robust with liquid ranges of e.g. 300 °C, compared to 100 °C for water. Polarity and hydrophilicity/hydrophobicity can be tuned by a suitable combination of cation and anion, which has earned them the accolade, designer solvents . 

IP H NMR Chemical shifts of tetraalkylphosphonium ions formed by traping of model cations or macrocations135... 

A fundamental route for the preparation of simple tetraalkylphosphonium salts is the reaction of a tertiary phosphine with a haloalkane or other substrate upon which a simple nucleophilic substitution reaction can occur. (In comparing phosphorus nucleophiles with the corresponding nitrogen-centered nucleophiles, it must be remembered that the phosphorus is significantly more nucleophilic than is the nitrogen. For example, while triphenylamine is devoid of nucleophilic character in reaction with ordinary haloalkanes, triphenylphosphine exhibits high reactivity.) Reactivity of the phosphorus in such nucleophilic substitution reactions, as with other types of nucleophiles, decreases with increasing substitution about the electrophilic site of the substrate. 

While tetraalkylphosphonium salts may be generated by the reaction of elemental phosphorus (white or red see Section 3.2) with haloalkanes, the reaction is complicated by the concomitant formation of trialkylphosphine dihalides. The resultant mixtme is generally converted to the corresponding trialkylphosphine oxide by treatment with ethanol under... 

Substitution of the tetraalkylphosphonium for the tetraphenylphosphonium counterion was detrimental to the control of the MMA polymerization. Indeed, although the molecular weight distribution was narrow, the initiator efficiency was very low (<0.18). Phosphazenes were also investigated as counter-ions, but the initiator efficiency remained quite low Baskaran and Muller reported that the polymerization of MMA initiated by 45 was very fast (0.05 s < half life < 0.15 s —20°C < T < 20 °C) and termination was negligible. ... 

While triphenylalkylphosphonium salts as ylide precursors unambiguously lead to alkylidenetriphe-nylphosphoranes, in the case of tetraalkylphosphonium salts ylide formation may take place principally at different a-positions relative to the phosphorus. " Furthermore an intramolecular transylidation process causes the ligands at the phosphorus in methylenetrialkylphosphoranes to exist alternately as alkyl or as alkylidene substituents, thus giving rise to the formation of isomeric ylides. 

Sesto RED, Corley C, Robertson A, et al. Tetraalkylphosphonium-based ionic hquids. J. Organomet. Chem. 2005. 690, 2536-2542. 

The third force field parameter set developed within the spirit of the OPLS-AA model and thus oriented toward the calculation of equilibrium thermodynamic and structural properties was presented [73], The parameter sets concerned the cations alkylimidazolium, tetraalkylphosphonium, and /V-alkylpyridinium, and the anions [Cl]-, [Br], and the [DCA] . Validation of the force field consisted of comparison with experimental crystal structure and liquid density data [73], The fourth parameterization of a force field was published only recently. The ions modeled were the 1,2,3-trialkylimidazolium and alkoxycarbonyl imidazolium cations and alkylsul-fate and alkylsulfonate anions [74],... 

Electroactive, functionalized ionic liquid, tetraalkylphosphonium polyoxometalates were synthesized by the substitution of sodium tungstate with tetaralkylphosphoni-umbromide [(C6H13)3P(C14H29)]2W6019 [99],... 

If an alkyl halide is added to the reaction mixture after reduction but without isolating the trialkylphosphine, tetraalkylphosphonium halides are formed in 65 to 76% yield ... 

A series of asymmetrical tetraalkylphosphonium ILs were synthesized and evaluated as a new kind of lubricant for steel/steel contacts under ambient conditions [24]. Tetraalkylphosphonium ILs showed better anti wear performance and... 

The tribological properties of tetraalkylphosphonium ILs were evaluated on the basis of the chemical structure of their salts [32]. The results showed that the structure of the alkyl group in the phosphonium ILs also had a slight effect on the tribological properties of the salts. Tetraalkylphosphonium ILs have better tribological properties than 1,3-aIkylimidazolium ILs. The interaction of phosphate or thiophosphate anions and substrate surfaces yielded a phosphate boundary film that... 

Weng LJ, Liu XQ, Liang YM et al (2007) Effect of tetraalkylphosphonium based ionic liquids as lubricants on the tribological performance of a steel-on-steel system. Tribol Lett 26 11-17... 

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