Peroxide decomposers light-stable

Act to decompose hydroperoxides into stable molecules such as alcohols and ethers, before they can react with light to form free radicals. Main chemical classes are trivalent phosphorous compounds and thio-synergists (esters of thiodipropionic acid). Sulfur-based organic antioxidants decompose hydroperoxides by non-radical reactions. Typical peroxide decomposers are Irgafos 168, Ultranox 626, Irganox PS 800 and others. 

Both the initiation and continuation of the oxidation are materially affected by temperature (oxidation rates are doubled for each 10°C rise in temperature), but may also be catalyzed by the presence of various metals or by light. The termination of the oxidation reaction may result from the exhaustion of the oxygen supply in lubrication systems or from the formation of stable products R + R - R-R) in the oxidation chain reaction. Antioxidant or oxidation inhibitors may function as chain terminating agents by reacting with free radicals to form stable products, by acting as peroxide decomposers, or they may act as metal passivators to prevent catalytic effects. 

Although in the absence of hyaluronic acid, dilute solutions of hydrogen peroxide remain relatively stable in the presence of cupric and chloride ions, when hyaluronic acid is also present, the hydrogen peroxide decomposes accompanied by the degradation of hyaluronic acid [91]. Fig. 4 shows the depolymerisation data as measured by low-angle laser-light scattering experiments. 

As with thermal stabilizers, photostabilizers must satisfy basic chemical and physical requirements (see the section titled ""Antioxidant permanence effects of chemical and physical factors ). In addition, they must be photo-stable, i.e., stable to UV-light, to withstand continuous periods of UV-exposure, without being prematurely destroyed or effectively transformed into sensitizing products. There are essentially three classes of compounds that are categorized as photostabilizers/ photoantioxidants UV-absorbers and pigments, peroxide decomposers including nickel complexes, and sterically hindered amine light stabilizers. 

In order for a stabilizer to function well it must also be sufficiently stable to UV light to survive the irradiation process. Photolysis studies were performed with a number of representative antioxidants of the hydrogen donor and peroxide decomposer type (Table III). When the stabilizers are photolyzed alone in n-hexane, conversions range from 10-22% with the hindered phenol, HD-1, the least stable and the aryl phosphite, PD-4, the most stable. When solutions containing both the antioxidant and the photoinitiator are photolyzed, the photoinitiator accelerates the decomposition of the antioxidants by a factor of about five. This results in the total decomposition of the HD-1 which can no longer be detected. The other antioxidants are not completely decomposed. 

Aliphatic diacyl peroxides are generally less stable than their aromatic counterparts. Acetyl peroxide decomposes at 25°C, so that careful handling is required to avoid dangerous explosion. These compounds are sensitive to shock, light, heat and metals. 

When impure, the material is unstable towards heat or light and decomposes to give an explosive residue. The pine material is more stable to light, but detonates on heating or in contact with solid alkalies [1], Preparation by action of oxygen on diallylzinc gives improved yields, but there is a risk of explosion. The peroxide is also impact-sensitive if sand is admixed [2],... 

The preparation of acyclic allylic hydroperoxides has been described before (3, 7, 9), but it is not clear how the reactivities differ from the better known saturated hydroperoxides and cyclic allylic hydroperoxides. Dykstra and Mosher prepared allyl hydroperoxide by the reaction of allyl methanesulfonate with hydrogen peroxide and alcpholic potassium hydroxide and purified the hydroperoxide by gas chromatography. It detonated on heating and decomposed on exposure to light but was relatively stable in the cold and dark. The isomeric allylic hydroperoxides formed from the autoxidation of the branched olefin, 4-methyl-2-pentene, have also been isolated and were not abnormally reactive (3). In the present study, cis- and trans-2-butene were photooxidized in the presence of methylene blue as a sensitizer (14), and the product, l-butene-3-hydro-peroxide, was isolated by preparative chromatography. 1-Butene proved unreactive and 2-butene-l-hydroperoxide could be formed only by isomerization of the secondary hydroperoxide. 

The cross-linking polymerization ceases when the two ends of the growing diradical combine with one another. Polyperoxides are exceptionally stable peroxides, but are decomposed by heat and light to alkoxy radicals (RC-0 ), which will in turn react with double bonds to form ether linkages (RC-O-CR). 

Ethers tend to be very reactive, and the less stable ones (ethyl ether and THF) decompose readily to form peroxides and more highly oxidized compounds. The decomposition process is accelerated by the solvent being exposed to light, heat, and/or air. 

The stabilizing action of sulfur-containing compoimds is related to their ability to decompose peroxide and hydroperoxide groups without the formation of free radicals, as well as to their property of terminating the reaction chains in the decomposition of polymers. Sulfur-containing compounds are used in practice as thermal stabilizers, since many of them prove to be insufficiently stable to the action of ultraviolet light and can cause sensitized decomposition of the poljmaer when the composition is irradiated. There is information that the activity of mercapto derivatives, in particular, dodecyl mercaptan, in the process of thermal decomposition of pol5Tvinyl chloride, does not decrease when the temperature is raised to 190-200°C [278]. 

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