Reactivity phosphorus compounds

To take advantage of both modified layered silicate and the substantial presence of phosphorus, the combined use of phosphorus-modified silicates and phosphorus compounds may represent an innovative solution to achieve high levels of flame retardancy. Phosphonium-modified layered silicates in epoxy resins were associated with organo-phosphorus FRs by Schartel et al.59 Ion exchange of Na-montmorillonite was carried out using tetraphenyl phosphonium bromide. Triphenyl phosphate and a reactive phosphorus compound were used as FR incorporated in the epoxy resin. 

The use of phosphorus in fire-retardant polyurethane foams leads to a high char formation, combined with easy processing, because of the relatively low density of most phosphorus compounds. This combination of desirable properties has made phosphorus compounds, with or without halogen, the most widely used fire retardants for polyurethanes. Reactive phosphorus compounds such as FYROL 6 , are used extensively. TYROL 6 , supplied by Stauffer Chemical Co., is widely used for polyurethane foams (38). 

Some of this effort has been directed to replacement of tetrabromobisphenol A, a major reactive component of circuit boards (wiring boards). Extensive development of flame-retarded halogen-free circuit boards has taken place especially in Europe and the Far East to find alternatives to tetrabromobisphenol A-based epoxy circuit boards. The use of phosphate ester additives usually depresses the thermomechanical properties excessively, and so the use of reactive phosphorus compounds has been the preferred approach. 

Additive flame retardants continue to dominate the flexible foam market despite extensive work on reactive phosphorus compounds (200,201). A phosphonate-phosphate diol (6) has been used as a component of a blended flame retardant for flexible polyurethanes. A reactive phosphate diol (135) has recently been introduced by Clariant for use in flexible polyurethanes. 

See also phosphorous acid.) [PHOSPHORUS COMPOUNDS] (Vol 18) Phosphomc acid reactive dyes... 

Phosphorus compounds exhibit an enormous variety of chemical and physical properties as a result of the wide range ia the oxidation states and coordination numbers for the phosphoms atom. The most commonly encountered phosphoms compounds are the oxide, haUde, sulfide, hydride, nitrogen, metal, and organic derivatives, all of which are of iadustrial importance. The hahde, hydride, and metal derivatives, and to a lesser extent the oxides and sulfides, are reactive iatermediates for forming phosphoms bonds with other elements. Phosphoms-containing compounds represented about 6—7% of the compound hstiugs ia Chemical Abstracts as of 1993 (1). 

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g. Phosphorus in Waters, Effluents and Sludges by Spectrophotometry-phosphomolybdenum blue method. Phosphorus in Waters and Acidic Digests by Spectrophotometry-phosphovanadomolybdate method. Ion Chromatographic Methods for the Determination of Phosphorus Compound, Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination of Molybdate Reactive Silicon-1 -amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acid reduction method. Pretreatment Methods to Convert Other Eorms of Silicon to Soluble Molybdate Reactive Silicon, Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992... 

The electrochemical generation and reactivity of phosphoniumyl and related charged radicals have been recently reviewed by Kargin and Bunikova [8]. In 1995, Yasui reviewed the reactivity of trivalent phosphorus compounds in single electron transfer (SET) processes [41] and, in 1990, the EPR features and reactivity of phosphoniumyl radicals were reviewed by Tordo [42]. 

In the course of the tempestuous development of organophosphorus chemistry, interest has only recently been focused on compounds of formally quinquevalent phosphorus having coordination number 3, such as 1, 2, or 3, although one of the other species of this kind has long been postulated as reactive intermediate of solvolysis of phosphorylation reactions. Definite evidence of even proof of the existence of such coordinatively unsaturated phosphorus compounds, however, has been obtained only recently in mechanistic studies, by trapping reactions with suitable cycloaddends, or actually by direct isolation. 

The RNA world hypothesis then rekindled interest in the still open question of the origin of the phosphorus. How could acceptable synthetic routes to the nucleic acids be developed, if it was not even clear which phosphate derivatives were available on the primeval Earth An RNA world is not possible without reactive phosphates or similarly efficient phosphorus compounds Thus, the search for effective phosphorus or phosphate sources continued unabated. 

Numerous reactions of carbonyl compounds, alcohols, olefins, etc., with compounds bearing E14=X bonds in which the latter act as direct analogs of phosphorus and arsenic ylides have already been accomplished.17 Recently, an interest in reactivity of compounds with multiple E14-X bonds is increasing due to challenges of important practical applications (see,... 

In 1969, Fiaud and Kagan[U1 tested ephedrine boranes but achieved only 3.6-5% enantiomeric excess in the reduction of acetophenone. Itsuno et a/.[121 reported in 1981 an interesting enantioselective reduction of a ketone using an amino alcohol-borane complex as a catalyst. Buono[131 investigated and developed the reactivity of phosphorus compounds as ligands in borane complexes for asymmetric hydrogenation. 

Phosphorus compounds, 19 19-73 bond properties of, 19 26 chemical properties of, 19 20-31 chiral-centered, 19 25-26 economic aspects of, 19 67-69 as flame retardants, 19 51 inorganic, 11 487-488 oxidation states, coordination numbers, and geometries of, 19 20-26 as oxyacid derivatives, 19 20 reactive organic, 11 496 497 titanium in, 25 56-57 triply connected, 19 25 U.S. prices of, 19 68t U.S. production of, 19 67t... 

Reactive liquid-phase sintering, 5 661 Reactive molecules, oliigonucleotides conjugated to, 17 636-637 Reactive organic phosphorus compounds, 11 496-497... 

The aromaticity of the phosphorus compounds with the A—D bonding type (shown in Scheme 1) will be discussed below, using structural, energetic, and magnetic criteria. The chemical reactivity—in relation to the aromatic stabilization—will be mentioned as well. 

Transport of contaminants by surface runoff is illustrated in the experimental results of Turner et al. (2004), which deal with the colloid-mediated transfer of phosphorus (P) from a calcareous agricultural land to watercourses. Colloidal molybdate-reactive phosphorus (MRP) was identified by ultrafiltration associated with particles between l am and Inm in diameter. Colloidal P compounds can constitute a substantial component of the filterable MRP in soil solution and include primary and secondary P minerals, P occluded or adsorbed on or within mineral or organic particles, and biocolloids (Kretzschmar et al. 1999). 

Trivalent phosphorus compounds are more readily oxidized than the corresponding nitrogen derivatives on account of their higher nucleophilicity however, the oxidation of such highly reactive substrates by dioxiranes has been sparsely studied. Only about a handful of examples are available in the literature, such that little may be said about the general trends in reactivity and selectivity. 

The chemistry of phosphorus compounds with a delocalized P-C double bond proves to be very versatile. Whereas the physical properties of phosphamethin-cyanines are similar to the corresponding methin- or azamethin-cyanines, their chemical properties are distinguished by the higher reactivity of the phosphorus atom and the phosphorus-carbon double bond. 

The most direct synthesis is performed by reaction of a dihalo compound with a tricoordinated phosphorus compound including a reactive P—Y bond (reaction 101). This synthesis, first used with secondary phosphines, the corresponding phosphides or diphosphines (Y = H, Na, K, PPh2)2b,38°, has subsequently been developed also with silylphosphines (Y = SiMe3),132,381-383 which are easier to handle (reaction 102). The same kind of cyclization by intramolecular alkylation can be achieved using a functional phosphine prepared in a multi-step synthesis380,384,385 (reaction 103). 

This enhanced reactivity of compounds of silicon and phosphorus is typical of all of the heavier nonmetals in contrast to the elements of the second row. 

The most reliable method for generating nitrenes is the thermal or photochemical elimination of nitrogen from azides. An alternative method which is useful for indole and carbazole synthesis is the deoxygenation of aromatic nitro compounds with trivalent phosphorus compounds. Triethyl phosphite is the most commonly used reagent, though more reactive compounds may be useful in special cases (B-79MI30600). 

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