Tetraphenylphosphonium

Tetraphenylphosphonium chloride [2001-45-8] M 314.9, m 273-275". Crystd from acetone. Dried at 70° under vacuum. Also recrystd from a mixture of 1 1 or 1 2 dichloromethane/pet ether, the solvents having been dried over anhydrous K2CO3. The purified salt was dried at room temperature under vasuum for 3 days, and at 170" for a further 3 days. Extremely hygroscopic. 

Polymer-supported tetraphenylphosphonium bromide is a recyclable catalyst for halogen-exchange reactions. The reaction of 1 equivalent of chloro-2,4-dinitrobenzene with 1 5 equivalents of spray-dned potassium fluoride and 0.1 equivalent of this catalyst in acetonitnle at 80 C for 12 h gives 2,4-dinitro-fluorobenzene m 98% yield An 11% yield is obtained without the catalyst [3 /]. 

Tetrasubstituted phosphonium halides are just as effective as their ammonium counterparts. A combination of tetraphenylphosphonium bromide and either 18-crown-6 or polyethylene glycol dimethyl ether with spray-dried potassium fluoride converts 4-chlorobenzaldehyde to 4-fluorobenzaldehyde in 74% yield [67] In addition, the halogen of a primary alkyl chloride or bromide is easily displaced by fluorine in aqueous saturated potassium fluoride and a catalytic amount of hexadecyltributylphosphonium bromide [68] (Table 7 Procedure 4, p 194)... 

The use of phthaloyl dichlonde as a scavenger for potassium nitrite and/or potassium oxide [108, 109, III] significantly increases yields of aryl fluorides, m fluoronitrobenzene is obtained in 70% yield with sulfolane as a solvent at 200 °C after 72 h Addition of tetraphenylphosphonium bromide as a phase-transfer catalyst to the phthaloyl dichlonde scavenger system further increases the yield of m-fluoronitrobenzene to 89% under less forcing conditions 150-180 C, 5 h) [if 2] This optimized technique can be applied to give m-fluorobenzonitnle from in-m-trobenzonitnle in 86% yield [/i2]... 

Tetraphenylphosphonium Hydrogen Dilluoride Preparation, 193 Trimethylsilyl Fluoride Preparation, 193... 

Reaction of Na2Se and Na2Sc2 with Se in the presence of ethanolic solutions of tetraalkyl-ammonium halides and catalytic amounts of I2 yields dark green or black crystalline polyselenides (jc = 3,5-9) depending on the conditions used and the particular cation selected. Tetraphenylphosphonium salts and crown ether complexes of alkali or alkaline earth cations in dimethylformamide solution can also be used. " )... 

Meanwhile, it was found by Asai and colleagues [48] that tetraphenylphosphonium salts having such anions as Cl, Br , and Bp4 work as photoinitiators for radical polymerization. Based on the initiation effects of changing counteranions, they proposed that a one-electron transfer mechanism is reasonable in these initiation reactions. However, in the case of tetraphenylphosphonium tetrafluoroborate, it cannot be ruled out that direct homolysis of the p-phenyl bond gives the phenyl radical as the initiating species since BF4 is not an easily pho-tooxidizable anion [49]. Therefore, it was assumed that a similar photoexcitable moiety exists in both tetraphenyl phosphonium salts and triphenylphosphonium ylide, which can be written as the following resonance hybrid [17] (Scheme 21) ... 

If direct homolysis occurs in the case of tetraphenylphosphonium tetrafloroborate, triphenylphosphonium ylide was expected to function as a photoinitiator of radical polymerization because of its similar structure. Therefore, another milestone was reached by Kondo and colleagues [50] who investigated the use of triphenylphosphonium ethoxycarbonylmethylide (TPPY) (Scheme 22) as an effective photoinitiator for the polym-... 

This species has been isolated as the tetraphenylphosphonium salt (Ph4P)8e which is produced in the following complex reaction at 20 °C [138] ... 

At present there is no more than indirect evidence for the existence of the halogeno-halothiophosphoric acids and the dibromo compound. So the unsoluble nitron dibromo-phosphate precipitates in case of the partial hydrolysis of POBr3 in acetone and in presence of nitron (5). Further the partial hydrolysis of PSCI3 and PSCI2F in presence of big cations, such as tetraphenylphosphonium or -arsonium yields stable salts (22), which suggests the primary formation of the free acid in the solution ... 

Aryl chlorides are not very reactive under normal Heck reaction conditions but reaction can be achieved by inclusion of tetraphenylphosphonium salts with Pd(OAc)2 or PdCl2 as the catalysts.138... 

The second model of a biological membrane is the liposome (lipid vesicle), formed by dispersing a lipid in an aqueous solution by sonication. In this way, small liposomes with a single BLM are formed (Fig. 6.11), with a diameter of about 50 nm. Electrochemical measurements cannot be carried out directly on liposomes because of their small dimensions. After addition of a lipid-soluble ion (such as the tetraphenylphosphonium ion) to the bathing solution, however, its distribution between this solution and the liposome is measured, yielding the membrane potential according to Eq. 

The complex bis(tetraphenylphosphonium)[bis(l,2-diselenosquarato)palladate(II)], (Ph4P)2 [Pd(dssq)2], is the first coordination compound of the new ligand 1,2-diselenosquarate.343... 

Flewelling, R. F., Hubbell, W. L., Hydrophobic ion interactions with membranes. Thermodynamic analysis of tetraphenylphosphonium binding to vesicles, Biophys. J. 1986, 49, 531— 540. 

TTF salts containing similar ferrocenium anions have been prepared through metathesis reactions between (TTF)3(BF4)2 and the tetraphenylphosphonium salts of the desired anions [71]. The crystal structure of (TTF)(CpFeCp-CONHCH2 S03)-1/3H20 contains isolated TTF dimers. Hydrogen bonds of the —NH—OS- and NH—0=C- type are present between anions. Two phases of the TTF salts with the... 

An oxoiron(V) species such as 6 derived from 1 and peroxides is accessible in nonaqueous media (51). The reaction of the tetraphenylphosphonium salt of la with 2 to 5 equivalents of m-chloroperbenzoic acid (mCPBA) at — 60°C in n-butyronitrile produces within about 10 s a bis-iron(IV)- i-oxo dimer followed by an as - yet uncharacterized EPR - silent iron(IV) intermediate. After 15 min, the deep green oxoiron(V) species 6 forms with distinct absorption maxima at 445 nm (e — 5400 Mr1 cm-1) and 630 nm (s — 4200 M-1 cm-1). At —60°C, 6 decays by 10% in 90 min, but it is stable for at least one month at 77 K. Selected spectral data for the oxoiron(V) species are shown in Fig. 13. DFT calculations favor the low-spin (S = 1/2) configuration of the ground state. The calculated Fe-0 bond length of 1.60 A is in excellent agreement with the EXAFS results. The Fe atom is displaced out of the 4-N plane by 0.5 A. 

Finally, quatemization of aromatic phosphines (example 21, Table XI) is exemplified for tetraphenylphosphonium bromide. 

A suspension of tetraphenylphosphonium iodide (2.0 g, 0.0043 mol) in anhydrous ether (5 ml) was combined with a 1 N solution of phenyl lithium (5 ml, 0.005 mol). The reaction mixture was allowed to stand for 8 days, after which the dark red supernatant solution was decanted. (In addition to the lithium salts, it still contained 10% phenyl lithium.) The residue was washed with anhydrous ether under nitrogen. Thereby was precipitated the pentaphe-nylphosphorane as crude crystals. The supernatant turbid suspension was discarded. This purification procedure was repeated until the supernatant ether remained clear. The thus isolated product was recrystallized from cyclohexane under nitrogen to yield the pure pentaphenylphosphorane (1.79 g, 60%) of melting point (mp) 124°C. 

Alkanes and short alcohols actually partition into the interior of the membrane [171]. The well-shielded tetraphenylphosphonium (TPP+) and tetraphe-nylborate (TPB-) ions are also deeply intercalated into the lipid bilayer [6,169]. The binding site of TPB- is located somewhere below the head-group region in the vicinity of the ester groups, while the cation TPP+ binds a few tenths of a nanometre further outwards [6],... 

A full report has now appeared of solvent effects on the rates of hydrolysis of benzyltriphenylphosphonium bromide. The remarkable increase in rate in media of low polarity is largely attributable to a shift of the pre-equilibrium between phos-phonium and hydroxide ions in favour of the intermediate hydroxyphosphorane.129 In a similar vein, a study of medium and deuterium isotope effects on the rate of hydrolysis of tetraphenylphosphonium chloride in acetone-water mixtures has been reported.130... 

The membrane potentials of cells and organelles such as mitochondria can be measured using the distribution of hydrophobic cations (dibenzyldimethyl-ammonium [43, 44, 158,195], tetraphenylphosphonium [96,157], butyltri-phenylphosphonium [132]). The ion concentration in the supernatant is measured the ion-exchanger ion is XV. 

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