Phosphonium ions substitution

Polysulfides have been prepared with many different types of cations, both monoatomic Hke alkah metal ions and polyatomic Hke ammonium or substituted ammonium or phosphonium ions. In this chapter only those salts will be discussed in detail which contain univalent main-group cations although a large number of transition metal polysulfido complexes have been prepared [7-9]. 

Another substituted derivative of BINAP was used by Lemaire et al. [109]. The ammonium salt catalysts (7 and 8, Fig. 41.10) were prepared in situ from the bro-mohydrates and [Ru( /3-2-methylallyl)2(/72-COD)], and immobilized in several ionic liquids. By comparative studies of the hydrogenation of ethyl acetoacetate, the best results were obtained with imidazolium- and pyridinium-containing ionic liquids. No significant ee was observed with the phosphonium salt. This observation was attributed to problems of solubility and to the ability of complexation for the phosphonium ion. From the anionic side, use of the [BF4] anion appeared superior compared to [PF6] and [(CF3S02)2N]A... 

The results of the pulse radiolysis in aqueous solution of substituted phosphonium ions have been investigated38 in addition to those of the electrode reduction of benzyl triphenyl-phosphonium ion39 and quaternary phosphonium salts with hydrated electrons40-42. The radiolysis of methyltriphenylphosphonium, dimethyldiphosphonium and trimethyl-phenylphosphonium ions in neutral aqueous solutions leads to phosphoranyl radicals... 

The fast reversible formation of the phosphonium salt also deserves attention since it is the first step in important reactions in organosi1 icon chemistry. As a consequence of the particularly high susceptibility of the silicon in the phosphonium ion to nucleophilic attack, phosphoryl compounds catalyze nucleophilic attack in substitution at silicon (6). 

Although asymmetrically substituted carbon atoms are by far the most common type of stereogenic center in organic compounds, several other kinds of stereogenic centers are encountered. Tetravalent nitrogen (ammonium) and phosphorus (phosphonium) ions are obvious extensions. Phosphine oxides are also tetrahedral and are chiral if all three substituents (in addition to the oxygen) are different. Not quite... 

Substitution of hydroxyl groups in perchlorinated phenols and acids through phosphonium ions 333 Darzens condensation 335 Perchloroacetylenes 336 Syntheses 336... 

Like the Arbusov reaction, this alkylation is a nucleophilic substitution by the counteranion of the intermediate phosphonium ion, although most of the driving force for the reaction is provided by the positive charge on phosphorus and its tendency to form a double bond with the alkoxy oxygen (62). 

SUBSTITUTION OF HYDROXYL GROUPS IN PERCHLORINATED PHENOLS AND ACIDS THROUGH PHOSPHONIUM IONS... 

The higher nucleophilicity of phenoxide and perchlorobenzoate counterions causes immediate nucleophilic substitution on the corresponding phosphonium ion phenoxy group, giving triphenylphosphine oxide and either perchlorodiphenyl ether or pentachlorophenyl pentachlorobenzoate respectively (p. 324) (92). Similarly, the reaction of triphenylphosphine dibromide with excess of silver pentachlorobenzoate yields pentachlorobenzoic anhydride in quantitative yield (Veciana, 1977). 

Simple coordination and ion-association, as with ( Onium ), FeCl4. Onium stands for one of the following cation types hydrated hydronium ion, (H20)3H+, a rather labile cation requiring stabilization by solvation with an oxygen-containing solvent a substituted ammonium ion, R NH(4 >, where R is an alkyl or aralkyl group and n may vary from 1 to 3 a substituted phosphonium ion R4P+ ... 

Nucleophilic substitution reactions involving initially pentacovalent P atoms have no parallel in carbon chemistry. There is evidence that they can proceed via tetrahedral phosphonium ions or octahedral transition states since either of these configurations can exist in equilibrium with trigonal bipyramidal arrangements (3.87) and (3.88). Knowledge of these reactions is, however, at present very limited. 

Compound (7.391b) can be made by reacting PCI5 with SP(NH2)3, while the isomer of linear P5N4CI13 is obtained from a reaction between liquid ammonia and PCI5 (7.392). A substituted phosphonium ion may also be obtained from this reaction, while under other conditions the amino-phosphazene (7.393) can be made. The latter compound may also be made by reaction (7.394). 

It is interesting to note that the very widely used Makosza catalyst , benzyl triethyl ammonium chloride, does not show high efficiency in this study. 4) Phosphonium ions are somewhat more effective and thermally stable than the corresponding ammonium catalysts and both are better than arsonium systems. 5) Substitution of the quaternary ion by alkyl rather than aryl groups yields more effective catalysts. 6) Reaction rates are generally greater in orf/io-dichlorobenzene (and presumably in other chlorocarbon media) than in benzene, and botli are better than heptane. In connection with this latter point, Ugelstad and coworkers have studied the reactions of quaternary ammonium phenoxide ions with alkyl halides in a variety of media and concluded that the... 

For reaction of n -decyl methanesulfonate with aqueous sodium chloride (eq 3), five percent ring substituted phosphonium ion catalysts have activities 0.6-0.7 times that of the highly active soluble benzyltributylphosphonium bromide.The activities decrease rapidly with increasing ring substitution to <0.3 times that of the soluble catalyst at 20% iring-substitution. 

Organic Cations The organic cations, whose dilute solution can be used in wellbore treatments to minimize polymer plugging, constitute a large class of compounds. They have two common characters a cationic end group and some hydrocarbon substitution on the cation. The cation can be an ammonium ion, a phosphonium ion, pyridinum ion, sulfonium ion, chromium ion or oxonium ion. The hydrocarbon substitution in the case of an ammonium ion can be primary, secondary, tertiary or quaternary. The number of carbons must be smaller than 10 for anionic polymers. When the carbon number is too large, the organic cation precipitates with an anionic polymer such as 30% hydrolyzed polyacrylamide. 

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