Phosphites and Phosphonites

Organic phosphorous(III) compounds are very effective hydroperoxide decomposers. They react stoichiometrically with hydroperoxides, oxidizing the phosphite to phosphate. Sterically hindered aromatic phosphites can also react as chain scission antioxidants. Since phosphites and phosphonites are sensitive to hydrolysis, hydrolysis resistant derivates have to be used. Their contribution to long-term stabilization is small, because they do not react directly with oxygen. In addition to the reaction of phosphites with peroxides and oxygen radicals, positive effects are also described due to complexing with catalytic metal residues. 

Ta ble 3.2 Degree of yellowing (Yl) according to ASTM D 1925-70 [550] in polypropylene and polyethylene with various processing stabilizers multiple extrusion processing at 280 °C (PP) or 260 °C (PE) [525] 

Because phosphites and phosphonites are sensitive to hydrolysis, they must be stored in dry conditions. Aromatic phosphites with a high degree of purity are less sensitive to hydrolysis than aliphatic phosphites [186]. 

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A kinetic study of the previously reported substitution of aromatic nitro groups by tervalent phosphorus has established an aromatic 5n2 mechanism. Similarities in values of activation energies, and in relative reactivities of phosphite and phosphonite esters, between this displacement and the Arbusov reaction suggest a related mechanism (31), while the lack of reactivity of p-dinitrobenzene is attributed to the need for intramolecular solvation (32). The exclusive formation of ethyl nitrite, rather than other isomers, is confirmed from the decomposition of triethoxy-(ethyl)phosphonium fluoroborate (33) in the presence of silver nitrite. A mechanism involving quinquevalent phosphorus (34) still seems applicable, particularly in view of the recent mechanistic work on the Arbusov reaction. ... 

D. Cyclic Esters of Phosphorous Acid.—There has been some controversy about the stable stereochemistry at phosphorus in cyclic phosphites and phosphonites this now appears to be resolved by agreement in a series of papers. The stereochemistry of 2-alkoxy-4-methyl-l,3,2-dioxaphosphorins... 

As to Irgafos 168 the reader is advised to notice the results of a round-robin involving PP/(Irganox 1076, Irgafos 168) [209a], Ultrasonication at room temperature with anhydrous n-hexane or acetone is a suitable soft extraction mode for the determination of aromatic phosphites and phosphonites, such as Ultranox 626 and Sandostab P-EPQ, which easily degrade in heating extraction procedures [210]. 

Table 6 Phosphites and Phosphonites. (It should be noted that the phosphite and phosphonite classes of stabiliser are particularly reactive and can be prone to decomposition in extraction solvents and food simulants)... 

Among the nucleophilic monomers studied are 5,6-dihydro-4T/-l,3-oxazines, cyclic phosphites and phosphonites, iminodioxolanes, and imines electrophilic monomers include... 

Unwanted degradation and oxidation processes can be avoided or at least suppressed for some time either by structural modiflcation of the polymer or by special additives. In practice, the addition of so-called antioxidants is particularly effective. Chemical substances that slow down oxidations and the following aging phenomena serve for this purpose. Antioxidants are sufficiently effective even in concentrations below 1 wt% and are added as early as possible to the polymer to be protected, e.g., already during the drying of powdery polymeric materials or during the preparation of granulates. Some of the most important so-called primary antioxidants are sterically hindered phenols and secondary aromatic amines secondary antioxidants are thioethers as well as phosphites and phosphonites. 

A number of ortho hindered alkyl-substituted phenyl phosphites and phosphonites were found to be effective process stabilizers for polypropylene and high density polyethylene combining more effective stabilization activity at high temperatures with good storage stability at relatively elevated humidity and ambient temperature, as well as resistance to discoloration. 

These published data prompted the authors [82] to undertake a more detailed study of the phosphorylation of isatin by the esters of P(III) acids and hydrophosphoryl compounds. At room temperature in the absence of traces of moisture isatin 49a, 1-acetylisatin 49b, and 5-bromoisatin 49c react with trialkyl phosphites and phosphonites with the formation of the unstable 1,3,2-dioxaphospholanes 87 with a pentacoordinated phosphorus atom, which isomerize in alcohol solution to the stable phosphoryl compounds 88 ... 

Whereas bidentate phosphites and phosphonites are excellent ligands for rhodium-catalyzed asymmetric hydrogenation, bidentate phosphoramidites (not shown) gave very poor results with low reaction rates and enantioselectivities. Results of a number of other monodentate phosphoramidites in the asymmetric hydrogenation of. V-acetyl dehydrophenylalanine derivatives are shown in Table 14.7.31-35-36-39-40... 

Schwetlick K and Habicher W D (1996) Action mechanism of phosphite and phosphonite stabilizers, In Polymer durability degradation, stabilization and lifetime prediction, Clough R L, Billingham N C and Gillen K T (Eds), Adv Chem Ser 249 349-358. 

Schwetlick, K. Mechanisms of antioxidant action of phosphite and phosphonite esters. In Mechanisms of Polymer Degradation and Stabilisation Scott, G., Ed. Elsevier Science New York, 1990 23-60. 

In a previous paper, the effectiveness of certain hindered mono phosphites and phosphonites as processing stabilizers for polyolefinsC1) was discussed. 

Table 1. Direkt synthesis of polyamides by using phosphites and phosphonites in NMR-Py solution3...

Table 13. Direct polycondensation of amino acids and dipeptides using phosphites and phosphonites in pyridine8...

Hydroperoxide decomposers phosphites and phosphonites, organo-sulfiir compounds. React with peroxides React with peroxides... 

Simple aliphatic aldehydes are also said to yield products which contain the equivalent of 2-3 mol of RCHO per phosphorus atom, some of which have been shown to have an oxyphosphorane structure. (For an introductory account of this fascinating area of phosphorus chemistry, the reader should consult early reviews by Ramirez . ) The phosphite ester obtained from 2-hydroxybenzaldehyde and diethyl chlorophosphite cyclizes with rearrangement to the l,2-benzoxaphosph(V)ole derivative 205 (R = H, R = EtO), and a similar process was observed in the case of phosphites and phosphonites derived from 2-hydroxyacetophenone to give 205 (R = Me) . 

Examples of widely used secondary antioxidants are phosphites, phosphonites, and sultides (Fig. 11.7). Usually, secondary antioxidants are used in combination with primary antioxidants to benetit from a synergistic effect. The main action of phosphites and phosphonites is the oxidation to the corresponding phosphates by reacting with hydroperoxides. These P compounds are mainly used as melt stabilizers during processing. Sulfur compounds act as well as hydroperoxide decomposers via sulfur oxide and sulfenic acid formation. Sulfur compounds are preferably used in combination with phenolic antioxidants to improve the long-term thermal stability of polymers at temperature ranges between 100 and 150 °C. 

Stabilization. The chemical industry, in cooperation with the PP manufacturers, succeeded in developing effective organic systems for process, long-term and special stabilization. These mainly involve sterically hindered phenols and, for the first two purposes, thioethers, phosphites and phosphonites. The concentration of the stabilizers will range from a few parts per million (ppm) to several percent, highly depending on the end-use requirements. 

Figure 5.6 Phosphites and phosphonites suitable for isomerization-hydroformylation.

Substances capable of reacting with hydroperoxides without creating radical decomposition products are called secondary antioxidants. These are in particular phosphites and phosphonites as well as sulfur costabilizers. Sulfur compounds are already very active at room temperature, while phosphites are active only at increased temperatures. The active application range of phosphites/phosphonites is therefore essentially limited to common processing temperatures. 

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