4- phosphine oxide

The tertiary phosphine oxides form the most stable and least reactive class of all organophosphorus compounds. Those oxides with no P hydrogen atom are particularly stable Me3P=0 and PhjP O do not decompose below 450°C and are reported to be stable up to 700°C. Almost aU are non-toxic crystalline solids. Tertiary phosphine oxides are weaker bases than the corresponding tertiary amine oxides. 

One of the simplest methods of preparation is by direct oxidation of the corresponding phosphine, for which a variety of oxidising agents may be used. 

The ease of oxidation of phosphines varies considerably. Lower trialkyl phosphines are oxidised simply on exposure to air or oxygen - some are spontaneously inflammable. Higher alkyl phosphines are less reactive and replacement of an alkyl with aryl groups increases their stability. Triphenylphosphine, PhjP, is quite stable in air. 

Tertiary phosphine oxides may be prepared by thermal decomposition of quaternary phospho-nium hydroxides or alkoxides (6.109, 6.110). Tetraxis hydroxymethylphosphonium chloride reacts with an excess of caustic soda in an unusual way to give the corresponding oxide with hydrogen and formaldehyde (6.111). 

An important preparative method is the reaction of alkylmagnesium halides with phosphoryl, phosphonyl or phosphinyl halides (6.112-6.114). 

1 Preparation. - Supercritical nitrous oxide has been shown to oxidise phosphines to the related phosphine oxides under mild conditions, allowing a simple isolation of products. Oxidation of precursor phosphines by hydrogen peroxide is the final step in the synthesis of the chiral functionalised phosphine oxides (219) and (220). A novel resolution procedure for the preparation of P-stereogenic phosphine oxides is afforded by the reactions of racemic chiral tertiary phosphines with an optically pure camphorsulfonyl azide, followed by separation of the diastereoisomeric phosphazenes, and acid 

Photolysis of (244) in the presence of alcohols likewise results in the formation of esters of methyl(phenyl)phosphinic acid. However, O-isotopic labelling studies provide evidence of, at least, the partial involvement of a pentacovalent phosphorus intermediate in this reaction, and so the previous assumption of the intermediacy of (245) may not be the whole story. The phosphole oxide dimers (246) have been shown to undergo regioselective reduction and complexation on treatment with the dimethylsulfide-borane adduct, to form the bicyclic system (247). Treatment of the propadienylphosphine oxide 

Relatively few papers have appeared describing the reactivity of phosphine sulfides and selenides. The P-aryl phosphetan sulfide (260) undergoes photolysis at 254 nm to form a variety of products, which are assumed to arise from 

1 Preparation. - The reaction of diphenylphosphinyl chloride with dicyclopentadienylsamarium (or samarium diiodide), followed by an alkyl halide (or alkyl tosylate, epoxide, or a,P-unsaturated ketone), provides a route to a 

Walker, Organophosphonis Reagents In Organic Synthesis, Ed. J. I. G. Cadogan, Academic Press, New York (1979) 

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To a mixture of 100 ml of dry dichloromethane, 0.10 mol of propargyl alcohol and 0.11 mol of triethylamine was added a solution of 0.05 mol of Ph2PCl in 75 ml of dichloromethane in 3 min between -80 and -90°C. The cooling bath was removed, and when the temperature had reached 10°C, the reaction mixture was poured into a solution of 2.5 ml of 362 HCl in 100 ml of water. After vigorous shaking the lower layer was separated and the aqueous layer was extracted twice with 25-ml portions of dichloromethane. The combined solutions were washed twice with water, dried over magnesium sulfate and then concentrated in a water-pump vacuum, giving almost pure allenyl phosphine oxide as a white solid, m.p. 98-100 5, in almost 1002 yield. 

The phosphorus ylides of the Wittig reaction can be replaced by trimethylsilylmethyl-carbanions (Peterson reaction). These silylated carbanions add to carbonyl groups and can easily be eliminated with base to give olefins. The only by-products are volatile silanols. They are more easily removed than the phosphine oxides or phosphates of the more conventional Wittig or Homer reactions (D.J. Peterson, 1968). 

Phosphine oxides are prepared similarly[644]. Selective monophosphiny-lation of 2,2 -bis[(lrifluoromethanesulfonyl)oxy]-l,1 -binaphthyl (784) with diphenylphosphine oxide using dppb or dppp as a ligand takes place to give optically active 2-(diarylphosphino)-1,1 -binaphthyl (785). No bis-substitution is observed[645,646]. 

Patents on the catbonylation of methyl chlotide [74-87-3] using carbon monoxide [630-08-0] in the presence of rhodium, palladium, and tidium complexes, iodo compounds, and phosphonium iodides or phosphine oxides have been obtained (26). In one example the reaction was conducted for 35... 

The reaction with sodium sulfite or bisulfite (5,11) to yield sodium-P-sulfopropionamide [19298-89-6] (C3H7N04S-Na) is very useful since it can be used as a scavenger for acrylamide monomer. The reaction proceeds very rapidly even at room temperature, and the product has low toxicity. Reactions with phosphines and phosphine oxides have been studied (12), and the products are potentially useful because of thek fire retardant properties. Reactions with sulfide and dithiocarbamates proceed readily but have no appHcations (5). However, the reaction with mercaptide ions has been used for analytical purposes (13)). Water reacts with the amide group (5) to form hydrolysis products, and other hydroxy compounds, such as alcohols and phenols, react readily to form ether compounds. Primary aUphatic alcohols are the most reactive and the reactions are compHcated by partial hydrolysis of the amide groups by any water present. 

Another very important reaction initially involving nucleophilic attack on an aldehyde carbonyl is the Wittig reaction. An yUd adds to the carbonyl forming a betaine intermediate which then decomposes to produce an olefin and a tertiary phosphine oxide. 

Phosphine Oxides. Development of cyanoethylphosphine oxide flame retardants has been discontinued. Triphenylphosphine oxide [791 -28-6] C gH OP, is disclosed in many patents as a flame retardant, and may find some limited usage as such, in the role of a vapor-phase flame inhibitor. 

These are water-soluble crystalline compounds sold as concentrated aqueous solutions. The methylol groups are highly reactive (118—122) and capable of being cured on the fabric by reaction with ammonia or amino compounds to form durable cross-linked finishes, probably having phosphine oxide stmctures after post-oxidizing. This finishing process, as developed by Albright Wilson, is known as the Proban process. 

APO. Research on ethylenimine [151 -56-4] led to the development of tris(azitidinyl) phosphine oxide [545-55-1] (APO) as a flame retardant for... 

Numerous diamines and aromatic dianhydrides have been investigated. WhoUy aromatic Pis have been stmctiirally modified by incorporating various functional groups, such as ether, carbonyl, sulfide, sulfone, methylene, isopropjlidene, perfluoroisopropyUdene, bipyridyls, sdoxane, methyl phosphine oxide, or various combinations of these, into the polymer backbone to achieve improved properties. The chemistry and apphcations of Pis have been described in several review articles (4). 

Carbodiimide formation is markedly accelerated when phosphine oxides (R PO) or phosphates are used as catalysts. Intermediates with P—NR bonds have been postulated as iatermediates ia these reactioas (59,60). 

Garbodiimide Formation. Carbodiimide formation has commercial significance in the manufacture of Hquid MDI. Heating of MDI in the presence of catalytic amounts of phosphine oxides or alkyl phosphates leads to partial conversion of isocyanate into carbodiimide (95). The carbodiimide (39) species reacts with excess isocyanate to form a 2 + 2cycloaddition product. The presence of this product in MDI leads to a melting point depression and thus a mixture which is Hquid at room temperature. 

Neutral Extractants. Many neutral organophosphoms extractants are available phosphate esters, phosphonate esters, phosphinate esters, and phosphine oxides. The most popular neutral extractant is tributylphosphate (TBP), which reacts with RE elements according to a solvation mechanism ... 

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

After apphcation to the fabric, the compounds are polymerized by reaction with gaseous ammonia (11,12), then oxidized to phosphine oxides by reaction with hydrogen peroxide. The stmcture of the polymer is shown (13). 

However, Ciba-Geigy has introduced (31,32) a type of phosphine-based photoinitiator. In general, the compound can be described as a bis(acyl)phosphine oxide and is prepared by the reaction of a monoaLkylphosphine with a substituted ben2oyl chloride (33). The composition of the first commercial product is proprietary. 

In a similar appHcation, Cape Industries has announced its intention to commission a solvent extraction plant to recover acetic acid from an effluent generated at its dimethyl terephthalate [120-61-6] faciHty (Wilmington, North Carolina) (44,45). The plant was commissioned in Eebmary 1995. In this case, the solvent will be CYANEX 923 extractant [100786-00-3], CYANEX 923 is also a phosphine oxide, but unlike TOPO is a Hquid and can be used without a diluent (46,47). This has the benefit of reducing plant size, capital, and operating costs. 

Stmcture is isomeric with secondary phosphine oxides. 

Pure tetrahedral coordination probably occurs only ia species where there are four identical groups and no steric distortions. Both PCU and PBr" 4, present ia soHd phosphoms haUdes, appear to have poiat symmetry. Other species, eg, H PO and POCl, have only slightly distorted tetrahedra. Similar geometries occur ia salts, esters, and other derivatives of phosphoric, phosphonic, and phosphinic acids as well as phosphine oxides and phosphonium salts. 

Much effort has been placed in the synthesis of compounds possessing a chiral center at the phosphoms atom, particularly three- and four-coordinate compounds such as tertiary phosphines, phosphine oxides, phosphonates, phosphinates, and phosphate esters (11). Some enantiomers are known to exhibit a variety of biological activities and are therefore of interest Oas agricultural chemicals, pharmaceuticals (qv), etc. Homochiral bisphosphines are commonly used in catalytic asymmetric syntheses providing good enantioselectivities (see also Nucleic acids). Excellent reviews of low coordinate (coordination numbers 1 and 2) phosphoms compounds are available (12). 

Preparation and Properties of Organophosphines. AUphatic phosphines can be gases, volatile Hquids, or oils. Aromatic phosphines frequentiy are crystalline, although many are oils. Some physical properties are Hsted in Table 14. The most characteristic chemical properties of phosphines include their susceptabiUty to oxidation and their nucleophilicity. The most common derivatives of the phosphines include halophosphines, phosphine oxides, metal complexes of phosphines, and phosphonium salts. Phosphines are also raw materials in the preparation of derivatives, ie, derivatives of the isomers phosphinic acid, HP(OH)2, and phosphonous acid, H2P(=0)0H. 

In general, if the desired carbon—phosphoms skeleton is available in an oxidi2ed form, reduction with lithium aluminum hydride is a powerful technique for the production of primary and secondary phosphines. The method is appHcable to halophosphines, phosphonic and phosphinic acids as well as thein esters, and acid chlorides. Tertiary and secondary phosphine oxides can be reduced to the phosphines. 

If aromatic aldehydes or ketones are used, the tertiary phosphine product sometimes rearranges to a mixed phosphine oxide. 

The secondary phosphine oxides oi sulfides can be oxidized to phosphinic acids oi thiophosphinic acids. 

Pentavalent phosphorus derivatives can be converted to phosphonyl halides or phosphine oxides by partial hydrolysis or by other oxygen donors. 

Phosphine Oxides. Controlled oxidation of secondary or tertiary phosphines using H2O2 yields the corresponding phosphine oxides. Control... 

Phosphine oxides having higher alkyl substituents are also prepared industrially using Grignard reagents. 

Phosphine oxides may be prepared by the acid-cataly2ed reaction of phosphine with carbonyl compounds such as ketones (94). 

Because of their relative instabiUty, primary phosphine oxides caimot be isolated and must be converted direcdy to derivatives. Primary and secondary phosphine oxides undergo reactions characteristic of the presence of P—H bonds, eg, the base-cataly2ed nucleophilic addition to unsaturated compounds such as olefins, ketones, and isocyanates (95). 

Tertiary phosphine oxides are stable. The temperatures required for thermal decomposition are approximately 300°C higher than the corresponding amine oxides (96). Trimethyl phosphine oxide is stable to 700°C. 

Phosphonium salts are typically stable crystalline soHds that have high water solubiUty. Uses include biocides, flame retardants, the phase-transfer catalysts (98). Although their thermal stabiUty is quite high, tertiary phosphines can be obtained from pyrolysis of quaternary phosphonium haUdes. The hydroxides undergo thermal degradation to phosphine oxides as follows ... 

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