Phosphites sterically hindered

Besides the commercially available stabilizers, a number of highly effective stabilizers can be found in the patent literature. Several combinations of stabilizers exhibit synergetic effects in particular the combinations thio ether/sterically hindered phenols and phosphite/sterically hindered phenols, respectively. The combination trimethyl hexyl borate/triphenyl phosphite is another known synergetic stabilizer. 

Phenolic aryl phosphite/sterically hindered phenols with two different functional groups... 

PD—S) to yield phosphates and alcohols, see Scheme 5 reaction a. Sterically hindered aryl phosphites (e.g., AO 14) have an additional chain breaking activity, i.e. they react with peroxyl and alkoxyl radicals during their function as antioxidants (reactions 5b and 5c) [18]. 

Sterically hindered phenols and other additives containing thioesters, phosphites, phosphonites and hindered amine moieties were analysed by FAB-MS and LD-FTMS. The laser desorption technique was preferred for analysis of polymer additives because of undesirable fragmentation from FAB experiments [93]. 

Synergism based on the mixture of a chain-breaking antioxidant (sterically hindered phenol) and a hydroperoxide decomposer (organic sulfides or phosphites). 

The effect of different phosphite moieties was studied with ligands 2d-o. In general, sterically hindered phosphite moieties are necessary if enantio-... 

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. 

Phosphites are known to act by a preventive mechanism, i.e. preventing the formation of initiating radicals from hydroperoxides by reducing the latter to alcohols, see reaction 4 [20]. In addition to their peroxidolytic activity (PD), sterically hindered aromatic phosphites, e.g. Ultranox U626, act also by chain breaking (CB) mechanism. These phosphites react with the propagating alkylperoxyl (ROO ), reactions 5, and alkoxyl (RO) radicals, reactions... 

To obtain more information on the nature of the quasiphosphonium intermediates involved in these systems we have studied the reactions gf sterically hindered neopentyl esters by means of 1P nmr spectroscopy. Trineopentyl phosphite and a-bromoacetophenone gave rise to a peak at +41 ppm due to the ketophosphonium intermediate 3 (R = Me.CCH, R = Ph X = Br ) within half an hour of mixingJthe reactants in acetone-dfi at 27 °C ( p nmr shifts are relative to 85% H-PO. down-field positive). Peaks due to the ketophospnonate 4 +19 ppm and the vinyl phosphate 7 (-7 ppm) were also observed (compound 4 and 7 have satisfactory elemental analysis and spectroscopic data ). The concentration of the intermediate reached a maximum after about two hours when it was precipitated from acetone solution by the addition of anhydrous ether to give white crystals of trineopentyloxy (phenacyl)phosphonium bromide, identified by elemental analysis and nmr spectroscopy ( XP 6+41, in CDCl ). When redissolved in acetone-dg, deuterochloroform, acetic acid, or acetic acid-acetone mixtures, the intermediate decomposed to yield keto-phosphonate 4 but none of the vinyl phosphate 6 (Perkow product). Nor was the course of reaction affected by the addition of chloride ion or of a-chloro-acetophenone in acetonitrile. 

Very bulky phosphite ligands (see Fig. 6.3) also yield unstable rhodium complexes (sterically hindered phosphites are commercially available as antioxidants for polyalkenes). The cone angle of the ligand shown is as high as 175° and the complex formed with rhodium has the formula HRh(CO)sL apparently there is not enough space for the coordination of a second phosphite. (In a trigonal bipyramidal complex there is room for two bulky ligands at the two axial positions but this would leave an equatorial position for a a-bonded hydride... 

The first step in the synthesis of nonvolatile plasticizers - which are of increasing importance - is hydroformylation of a long-chain olefin, for which rhodium phosphite catalysts have very useful properties. The current use of sterically hindered phosphites as antioxidants for polyalkenes together with their much simpler... 

Very bulky phosphite ligands (see Fig. 6.3) [12,13,30,36] also yield unstable rhodium complexes (sterically hindered phosphites are commercially available as antioxidants for polyalkenes). The cone angle of the ligand shown is as high as... 

Miscellaneous. - Several new optically active tervalent phosphorus acid derivatives have been prepared for use as ligands in asymmetric metal catalysed reactions. These include the cyclic diaminophosphines 57, the cyclic bisamino-phosphine 58, and the compounds 59, 60, 61, and 62 containing a 1,1 -binaphthalene group as the chiral inducer. A new diphosphoramidite (63) has been used for improved regioselectivity of rhodium-catalysed hydroformylations of alkenes. A new sterically hindered chiral phosphite (64) derived from glucose and a Cu(I) complex of 64 have been prepared. ... 

Alkyl and aryl phosphite esters are also effective melt stabilizers. They are often used in combination with hindered phenols to give highly efficient melt stabilizing systems and to reduce discoloration of the polymer because of the oxidation products of the phenols present. Phosphites (particularly those derived from aliphatic alcohols and unhindered phenols) are, however, generally susceptible to hydrolysis. Consequently, moisture-sensitive phosphites affect adversely the handling characteristics (i.e., flow properties) of the additive package and are a source of other problems corrosion of metal surfaces, formation of dark colored spots, and gel formation. In practice, hydrolysis-resistant phosphites based on sterically hindered phenols are used, e.g., AOs 17 and 18, Table 1. 

Another variation of the classic Darzens reaction is a one-pot synthesis of dietliyl 1-perfluoro-alkyl-1,2-epoxyalkylphosphonates using the nucleophilic attack of lithium diethyl phosphite on the carbonyl carbon of perfluorinated P-oxophosphonium salts (Scheme 4.8). The resulting intermediate can eliminate in two directions. When the oxygen anion in the least sterically hindered position (R = R = Me) attacks the neighboring carbon atom, diethyl 1-perfluoroalkyl-1,2-epoxyalkylphosphonates aie obtained in moderate yields (42-51%) after elimination of PhjP (anti fashion). The formation of a-(perfluoroalkyl)vinylphosphonates by attack at phosphorus (syn fashion) can be a competing reaction. The results indicate that the selectivity can be controlled to produce exclusively either epoxyphosphonates or vinylphosphonates. ... 

The patent describing this development discloses that a mixture of a thermally stable phenolic antioxidant and a sterically hindered phosphite was used in a hydrotreated base stock. However, the heterosynergism between the radical scavenger (phenolic antioxidant) and the hydroperoxide decomposer (phosphite) was not shown in solvent-refined base stocks. An additional benefit of this technology is energy saving, due to extremely good control of viscosity. 

This reaction is. a welcome expansion of the base-catalysed addition of dialkyl phosphites which fails with sterically hindered olefins and with unsaturated aldehydes occurs at the carbonyl group. An example of the efficiency of the method with sterically hindered alkenes is afforded by the reaction of mesityl oxide which leads to diethyl (1, l-dimethyl-3-oxobutyl)phosphonate 7 0... 

The reaction of alkoxy radicals with triethyl phosphite apparently is sufficiently rapid to swamp out their known rapid conversion to alcohols or ketones, since such products were not detected. It would be interesting to know whether unsymmetrical or less sterically hindered dialkyl peroxides could be induced to interact via a polar mechanism. 

Chemical re-stabilization of recycled material against the thermal and light-induced degradation is essential. Addition of 0.1-0.5 wt% of a sterically hindered phenol and a phosphite at a ratio varying from 10 1 to 1 10 is recommended [Pauquet et al., 1994]. For outdoor applications, hindered amine light stabilizers with UV-absorbers of the benzotriazole type are to be used [Herbst et al., 1995,1998]. Examples of blends used for polymer recycling are listed in Table 1.81. For more details see Chapter 16 in this book. 

It is important to recognize that additives suitable for one type of resin may have detrimental effects on another and/or on their additives. Furthermore, the stabilizing systems of one polymer type may neutralize the system of another polymer. For example, to stabilize blends comprising 55-75 wt% PO, 5-25 wt% PS, 5-15 wt% PVC, and 0-10 wt% of other thermoplastics, 0.1-0.5 wt% of a stabilizer mixture was added. The mixmre comprised a sterically hindered phenol [e.g., pentaerythritol ester], and a phosphite [e.g., tris(2,4-di-tert-butyl phenyl)phosphite] at a ratio of 5 1 to 1 5. For other compositions of PCW, different stabilizers, viz., thio-propionic acid, benzophenones, oxahdes, benzotriazoles, HALS, and/or CaO may have to be used [Pauquet et al., 1994]. 

Commingled polyolefins are re-stabilized using about 0.06 wt% of a hindered phenol antioxidant, and about 0.09 wt% phosphite. Acids present in the mixture should be neutralized by addition of a sufficient amount of CalOH). For other compositions of PCW, other stabilizers, viz., thio-propionic acid, benzophenones, oxalides, benzo-triazoles, or sterically hindered amines may have to be used [Pauquet et al., 1993]. 

Typical processing stabilizers for polypropylene and butylated hydroxy-toluene (BHT) as the primary antioxidant and phosphates and phosphonates as secondary antioxidants. Examples of the latter that are commonly used are tetrakis-(2,4-di-terr-butyl-phenyl)-4-4 -bisphenylylenediphosphonite, distearyl-pentaerythrityl-diphosphonite, tris-(nonylphenyl)-phosphite, tris-(2,4-di-teft-butyl-phenyl)-phosphite and bis(2,4-di-ferr-butyl-phenyl)- pentaerythrityl-diphosphite. In commercial polypropylenes, phosphorous compounds are always used together with a sterically hindered phenol. The compounds are commonly added in concentrations between 0.05 and 0.25%. 

Mechanistically, hydrophosphonylation and hydrothiophosphonylation takes place via pentacoordinate state that could be achieved only toward fluoride ion activation F in ionic liquid medium. Other anions, e.g. Cl , Br , I or HP04 did not work because they are not strong enough to lead to hypervalency. If other sterically hindered and less reactive cyclic phosphites (47a) and (47b) were treated with equimolar quantity of TBAF, the P-F bonded intermediate (48a) or (48b) was formed as confirmed by NMR analysis. These intermediates were then reacted with allyl bromide H2C = C(C02Me)CH2Br, to give phosphonate (49) as a sole product (Figure 4). 

CAS 68610-51-5 EINECS/ELINCS 271-867-2 Synonyms p-Cresol dicyclopentadiene butylated polymer 4-Methyl phenol reaction product with dicyclopentadiene and isobutylene Classification Sterically hindered phenol Definition Butylated reaction prod, of p-cresol and dicyclopentadiene Properties Off-wh. to tan powd. sol. in acetone, ethyl acetate, ethanol, methylene chloride, llq. phosphites insol. in water m.w. 600-700 dens. 1.10 flash pt. (COC) 215 C... 

Sterically hindered tris[(hydroxyphenylthio)phenyl]phosphites, e.g., P[OPh( butyl)(methyl)SPh( butyl)(methyl)OH]3 (Hostanox OSP-1 Clariant), said to be especially useful in antimony oxide catalysed polyesters as they prevent formation of antimony metal and its associated grey discoloration [44] ... 

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