Aryl phosphites

Other notable examples are the orthometallation (orthophenylatioti) reactions of many complexes of aryl phosphines (PAr3) and aryl phosphites P(OAr)3 with platinum metals in pailiculai, e,g, ... 

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]. 

This method involves the direct polycondensation of aromatic diamines with aromatic diacids in the presence of an aryl phosphite (triphenyl phosphite) and an organic base like pyridine.7,9 70 71 The addition of salts improves die solubility of the polymer and, with this, the maximum attainable molecular weight.71 The concentrations are, however, lower than by the dichloride method. 

A phosphite degradation reaction that occurs during hydroformylation using an aryl-phosphite-modified rhodium catalyst involves replacement of one of the aryl groups with an alkyl group corresponding to the alkyl group of the hydroformylation prod-uct[.[27] This is illustrated in Equation 2.7... 

Aryl phosphites are widely used as inhibitors of oxidation. Phosphites react with hydroperoxides and are oxidized into phosphates by the following stoichiometric reaction [1-10] ... 

Trialkyl phosphites were found to be more reactive to hydroperoxide than aryl phosphites the activation energy depends on a particular phosphite and ranges from 25 to 77 kJ mol-1. At the same time, the reaction depends weakly on the type of hydroperoxide, which can be seen from the comparison of rate constants for the reactions of two hydroperoxides (solvent was PhCl, T=303K [12]). 

Once aryl phosphite has oxidized into phosphate followed by the catalytic decomposition of hydroperoxide [6,10,19,20], The catalyst is obviously stable, since additional hydroperoxide introduced into the system immediately breaks down [10]. Repeatedly, ROOH decomposes via the acid-catalyzed reaction with the products of phosphate hydrolysis acting as catalysts [6,10],... 

The situation is different for aryl phosphites, which give rise to shorter chains than alkyl phosphites do (about 100 elementary reactions). The rate of aryl phosphite oxidation, v v suggests that chains are terminated in a linear manner [4,14,27]. Linear chain termination was interpreted in terms of the following mechanism of chain oxidation of aryl phosphites ... 

Aryl phosphites inhibit the initiated oxidation of hydrocarbons and polymers by breaking chains on the reaction with peroxyl radicals (see Table 17.3). The low values of the inhibition coefficient / for aryl phosphites are explained by their capacity for chain autoxidation [14]. Quantitative investigations of the inhibited oxidation of tetralin and cumene at 338 K showed that with increasing concentration of phosphite /rises tending to 1 [27]. 

The mechanism of inhibitory action of aryl phosphites seems to be relatively complex. Phosphites reduce hydroperoxide and thus decrease chain autoinitiation. The formed peroxyl and alkoxyl radicals react with phosphites to form aroxyl radicals. The latter terminates the chains by reaction with peroxyl radicals. On the other hand, phosphites are hydrolyzed with... 

Attack on Halogen. Predictably, the 3-bromo-3-cyano-imides (56) and (57) form quasiphosphonium salts (58) with aryl phosphites, phosphonites, and phosphinites.47 In the case of (56) these salts cyclize to the oxazaphosphorane (59), which is in equilibrium with the iminophosphorane (60), depending on the phosphorus ester used. 

Aryl phosphites were among the first ligands that were extensively studied. The results obtained with triphenylphosphine and triphenyl phosphite are strikingly similar at low ligand concentrations. At higher ligand metal ratios phosphites may retard the reaction. The electronic and steric properties of the phosphite have a large effect on the rate and selectivity of the reaction. 

Arylidene-,6-ionones, triplet oxygen cycloaddition, 199, 201 Aryl phosphites, ozone adducts, 732 Aryl-substituted olefins, selenide-catalyzed epoxidation, 384-5 Ascaridole... 

Complexes with alkyl and aryl phosphites as ligands 114... 

Low oxidation states are generally stabilized by ligands which have both a donor (lone pairs) and n acceptor (either empty d orbitals or empty antibonding Jt orbitals) capability. Examples of common ligands with these characteristics are carbon monoxide, cyanide ion, alkyl and aryl isocyanides, tertiary phosphines and arsines, and alkyl or aryl phosphites. 

Aryl phosphite 5 was studied as a possible ligand in the palladium-catalyzed allylic alkylation and allylic sulfonation reactions. This P,N-ligand was easily accessed by condensation of ferro-cenealdehyde followed by reaction with bis(2,6-dimethylphenyl)chlorophosphite.28... 

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

The aryl phosphites also are secondary antioxidants and protect against process shearing. These chemicals have little value against high... 

Peroxide Decomposers. Aryl phosphites and certain sulfur compounds such as sulfides, disulfides, and thiodipropionate esters decompose peroxides into inactive compounds which do not promote polypropylene oxidation. These chemicals function by extracting an oxygen atom from the peroxide group and reducing it to an ether or hydroxy group (9). 

Representative compounds of importance in polypropylene stabilization are tris( mixed nonyl phenyl) phosphite and dilauryl thiodipropionate-(DLTDP). The aryl phosphite is used in film grade resins and in other... 

Table II. Effect of DLTDP—Phenolic Combination with Aryl Phosphite on Heat Aging of Polypropylene...

Table III shows that the two hydroquinones had low activity. In addition, the aryl phosphites did not improve the results significantly when they were added to the formulations. The two polymeric phenolic phosphites based on the hydroquinones, however, had considerably better activity, going 62 and 81 days, respectively, compared with only 20-28 days for the other formulations. Therefore, the polymeric phenolic phosphites are more effective probably because of their low volatility.

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