Phosphonium halides

Towards a simple Lewis base, for example the proton, phosphine is a poorer electron donor than ammonia, the larger phosphorus atom being less able to form a stable covalent bond with the acceptor atom or molecule. Phosphine is, therefore, a much weaker base than ammonia and there is no series of phosphonium salts corresponding to the ammonium salts but phosphonium halides. PH4X (X = Cl, Br, I) can be prepared by the direct combination of phosphine with the appropriate hydrogen halide. These compounds are much more easily dissociated than ammonium halides, the most stable being the iodide, but even this dissociates at 333 K PH4I = PH3 -t- HI... 

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 ylide Ph3P=CH2 can readily be made by deprotonating a quaternary phosphonium halide with n-butyllithium and many such ylides are now known ... 

The investigations included donor adducts with PO [93], 34,PS [+) [94], 35, and P(NMes ) +) [95], 36. While 34 was only formulated as an intermediate species, the other donor-acceptor complexes, 35 and 36, were characterized by X-ray investigations. To complete this series it may also be compared with bis(ylide)-substituted phosphonium halides [96], 37. For these cases the donors refer to... 

Partial substitution of halides on bismuth predictably gives alkoxy-bismuth halides, and salts of bismuth anions are obtained by reaction of the alkoxide with an ammonium or phosphonium halide (28). Two isostructural derivatives [Bi2Cl4(thf)2(ju,-OAr)2] (Ar = C6H3Me2-2,6 and C6H2Me3-2,4,6) are composed of dimeric units residing on a C2 axis 8. The bismuth is in a five-coordinate distorted square pyramidal geometry in each case. The apical sites are occupied by terminal... 

The reaction of phosphines and alkyl halides presents an alternative way to generate phosphonium electrophiles (Scheme 3.8). In particular, the combination of a phosphine and carbon tetrabromide (the Appel reaction) allows for in situ formation of a phosphonium dibromide salt (48, X = Br). Treatment of a hemiacetal donor 1 with the phosphonium halide 48 initially provides the oxophosphonium intermediate 38 (X = Br). However, the oxophosphonium intermediate 38 can react with bromide ion to form the anomeric bromide intermediate 49 (X = Br) with concomitant generation of phosphine oxide. With the aid of bromide ion catalysis (i.e. reversible, catalytic formation of the more reactive P-anomeric bromide 50) [98], the nucleophile displaces the anomeric bromide to form the desired glycoside product 3. The hydrobromic add by-product is typically buffered by the presence of tetramethyl urea (TMU). 

The similarity of the PC coupling constants (50—65 Hz) of certain methyl-phosphonium halides and the reagents produced by the action of organolithium... 

Quaternary ammonium and phosphonium halides were used as the phase transfer catalysts. For effective coupling, high-shear mixing and high concentrations of polymer and base were used. 

Uses. Insecticide used for fumigation preparation of phosphonium halides doping agent in semiconductor manufacture... 

Proton or deuteron relaxation is also useful in this respect as shown for NH4PO4H2(19e7 195 ana i96) an(j for e determination of rotational barriers in solid phosphonium halides.<1967-197 1968- 179andl8° iseo,210)... 

Both phosphonium halides are almost completely dissociated at room temperature and normal pressure. 

Ruthenium, cobalt and halogen are the key elements of this catalysis (2), although ruthenium in combination with halogen-containing zirconium and titanium derivatives is also effective (3). In the case of the Ru-Oo couple, the highest yields of acetic acid may generally be achieved with ruthenium oxide, carbonyls and complex derivatives in combination with various cobalt halides dispersed in low-melting quaternary phosphonium halide salts (2). 

Scheme 5.1-21 The benzylation of sodium 2-naphthoxide with benzyl bromide in ammonium or phosphonium halide salts (X = Cl, Br).

Shono et al. reduced phosphonium halides using carbonyl compounds as solvent ylids were not only formed but reacted in situ to give high yields of the... 

All the above complexes, 9-12, are isolated from reactions involving gallium or indium metal and [Mn2(CO)10] or [Re2(CO)10] in an autoclave, although 11 has also been obtained by thermolysis of 6. Some details on the reactivity of 11 toward phosphonium halides (23) have been reported and indicate formation of the halo-indium complexes [PPh4]2[Mn2(CO)8 /j-lnX2 2]. A higher nuclearity cluster has also been obtained in the reaction of [Re2(CO)10] with indium metal, viz. [Re4(CO)12 /i3-InRe(CO)5 4], 13 (24,24a). This consists of a central tetrahedral Re4(CO)12 core with each face capped by an InRe(CO)s fragment as shown in Fig. 4. 

Ethylene oxide reacts with phosphonium halides to give ylides, which are used to synthesize olefins from carbonyl compounds, such as aldehydes... 

Quaternisation of triphenylphosphine with an alkyl halide gives a quaternary phosphonium halide (4) which under the influence of a strong base eliminates hydrogen halide to give an alkylidenephosphorane [(5), an ylide]. The latter reacts with an aldehyde or ketone to give first an intermediate betaine (6), which rearranges to the oxaphosphetane (7), which then under the reaction conditions eliminates triphenylphosphine oxide to form an alkene. 

Monocyclic Phosphoranide Anion. The intramolecular oxidative addition of hydroxyalkyl phosphites, which gives P-H phosphoranes, is well known (10). Some P-H phosphoranes are so stable that the open-chain P(III) tautomers cannot be detected spectroscopically or even by attempted H2O2 oxidation (8). Thus, it is surprising to find no evidence for an equilibrium between phosphine alcohol 1 and its closed-ring tautomer phosphorane 2. Phosphine 1 is quaternized by alkyl halides giving phosphonium halides such as 3. These in turn are converted to alkoxyphosphor-anes, such as 4 by NaH (Scheme I). 

Tian J-S, Miao C-X, Wang J-Q et al (2007) Efficient synthesis of dimethyl carbonate from methanol, propylene oxide and C02 catalyzed by recyclable inorganic base/phosphonium halide-functionalized polyethylene glycol. Green Chem 9(6) 566—571... 

With phosphonium halides such as PH4I, the phosphide Si6P2 is obtained ... 

In contrast to stabilizers, fire retardants must be added in much higher concentrations, which affect thermal and mechanical properties as well as cost. Sherr and co-workers report that novel derivatives of phosphine oxides, phosphonic acids, phosphinic acid, and phosphonium halides may be used generally in concentrations as low as 2.5-5 p.p.h. to be effective fire retardants in polyethylene and poly (methyl methacrylate). 

Mono- and diphosphonium halides have been found to be flame retardants for plastic materials. Their effectiveness can be related to the formation of various active phosphorus compounds, as well as to many of the postulated mechanisms for flame retardant action. The compounds are postulated to be effective because they decompose on ignition to thermally stable phosphine oxides or phosphonic acids which, in turn, are decomposed to continuous films of phosphate glass. In addition, the phosphonium halides form alkyl halides which cool the flame and/or form halogen acids which are fame retardants. 

Tn the preceding chapter (19) we described the use of phosphine A oxides, phosphonic acids, and phosphinic acids as flame retardants for thermoplastic materials. We also have found phosphonium halides to be effective flame retardants for plastics (5, 6). These compounds were either the monophosphonium halides,... 

The monophosphonium halides can be formed readily by the reaction of a phosphine with an alkyl halide. Usually the phosphine and the halide are heated in a solvent such as butyl alcohol or acetonitrile. The phosphonium halide is isolated by filtration (if insoluble), by precipitation with ethyl ether, or by evaporation of the solvent (10, 11, 12, 13, 14, 16,18). Yields are from 50 to 100%. 

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