Amines, antioxidant action

This equation seems to be a key reaction point in the antioxidant action of these amines—>N radicals in the presence of oxygen are transformed via peroxy radical intermediates into nitroxyl radicals. The nitroxyl radicals are very persistent and react efficiently with radicals produced on polyolefine degradation. Such radical interception blocks the chain in radical oxidation and therefore causes the antioxidant activity of sterically hindered amines (Brede et al. 1998). 

Schwetlick, K. Habicher, W. D. Antioxidant action mechanisms of hindered amine stabilizers. Polym. Degrad. Stab. 2002, 78, 35-40. 

Larger alkyl groups are required when the Mannich base is used as an additive to fuels, lubricants, etc. In some cases the anticorrosion power is afforded by exhaustive aminomethylation of polyfunctional substrates with aliphatic amines, thus obtaining branched basic derivatives (see, e.g., 499, Sec. A. 1) that arc able to protect the material against acid corrosion.Detergent- (sec also 513, Table 38) and antioxidant - actions can be combined with the anticorrosion ability of certain additives to oils and fuels, although the undesired formation of emulsion or foam may be favored. 

Shlyapintokh, V.Ya. Ivanov, V.B. Antioxidant action of sterically hindered amines and related compounds. In Developments in Polymer Stabilisation Scott, G., Ed. Applied Science London, 1982 Vol. 5, 41-70. 

Al-Malaika, S. Ibrahim, A.Q. Rao, J. Scott, G. Mechanisms of antioxidant action photoantioxidant activity of polymer-bound hindered amines. II. bis acrylates. J. Appl. Polym. Sci. 1992, 44, 1287-1296. 

K.B. Chakraborty and G. Scott, Mechanism of antioxidant action the behavior of hindered amine U.V. stabilizers during the processing of LDPE, Chem. Ind. 1978, 237-238. 

In addition, many of the organosulfur compounds and organometallic compounds used in rubber compounds as vulcanization accelerators are known to have antioxidant activity. Mercaptobenzimidazole and its zinc salt have been shown to have antioxidant activity. In addition, mercaptobenzimidazole, when combined with other known antioxidants, has been shown to have a synergistic effect in oxidation prevention when metal ion catalyzed oxidation is prevalent. Also, metal and amine salts of dialkyldithio-carbarnates have been shown to have antioxidant action. 

The reaction probably proceeds by means of the initial formation of a tt complex between the ROO radical and the cresol. Phenols are, however, ineffective antioxidants at higher temperatures, since they can themselves then decompose into free radicals. There is stronger evidence of complex formation in the antioxidant action of amines ... 

Al-Malaika, S., Scott, G. and Wirjosentono, B. (1993) Mechanisms of antioxidant action Polymer-bound hindered amines by reactive processing, part III - Effect of reactive antioxidant structure. Polymer Degrad. Stab, 40, 233-238 Al-Malaika, S., Ibrahim, A.Q. and Al-Malaika, S. (1988) Mechanisms of antioxidant action Photoantioxidant activity of polymer-bound hindered amines I Bis maleate esters. Polymer Degrad. Stab., 22, 233-239 Al-Malaika, S. and Scott, G. (1995) US Patent 5382633. 

Investigation of the reactions of these compounds with cumylperoxide radicals and cumyl hydroperoxide showed that the mechanism of antioxidant action of these compounds is similar to that of previously studied sulphur-containing phenol and amine derivatives, namely, they efficiently terminate oxidation chains by reacting with peroxide radicals (Fig. 9.10) and catalytically convert hydroperoxides into molecular products (Fig. 9.11). 

Following the action of extraordinary stimulants (hypoxic hypoxia, hypoxia + hyperoxia, hypodynamia + hyperthermia), animals demonstrate an accumulation of malonic dialdehyde with a simultaneous fall of antiradical activity of the liver tissue. A preliminary introduction to rats of acetylene amine 3,4,5-tris(morpho-linopropynyl)-l-methylpyrazole 103 and also of tocopherol antioxidant and gutumine antihypoxant averts activation of the lipid peroxidation processes. The inhibition of peroxidation with this agent is mediated by stabilization of ly-zosomal and mitochondrial membranes. Unsaturated amines prevent destruction of the organelle membranes provoked by UV irradiation and incubation at 37°C (pH4.7)(78MIl). 

An alternative mechanism by which additives may protect polymers from photo-oxidation is radical trapping. Additives which operate by this mechanism are strictly light stabilizers rather than antioxidants. The most common materials in this class are the hindered amines, which are the usual additives for the protection of poly (ethylene) and poly (propylene). The action of these stabilisers is outlined in Reactions 8.3-8.5. 

The retarding action of antioxidants (InH), such as phenols and aromatic amines, was proved to be the result of chain termination by accepting the peroxyl radicals. 

The rare example of synergistic action of a binary mixture of 1-naphthyl-A-phcnylaminc and phenol (1-naphthol, 2-(l,l-dimethylethyl)hydroquinone) on the initiated oxidation of cholesterol esters was evidenced by Vardanyan [34]. The mixture of two antioxidants was proved to terminate more chains than both inhibitors can do separately ( > /[xj). For example, 1-naphtol in a concentration of 5 x 10 5 mol L-1 creates the induction period t=170s, 1 -naphthyl-A-phenylamine in a concentration of 1.0 x 10-4 mol L 1 creates the induction period t = 400s, and together both antioxidants create the induction period r = 770 s (oxidation of ester of pelargonic acid cholesterol at 7= 348 K with AIBN as initiator). Hence, the ratio fs/ZfjXi was found equal to 2.78. The formation of an efficient intermediate inhibitor as a result of interaction of intermediate free radicals formed from phenol and amine was postulated. This inhibitor was proved to be produced by the interaction of oxidation products of phenol and amine. 

Nitroxyl radicals as alkyl radical acceptors are known to be very weak antioxidants due to the extremely fast addition of dioxygen to alkyl radicals (see Chapter 2). They retard the oxidation of solid polymers due to specific features of free radical reactions in the solid polymer matrix (see Chapter 19). However, the combination of two inhibitors, one is the peroxyl radical acceptor (phenol, aromatic amine) and another is the alkyl radical acceptor (nitroxyl radical) showed the synergistic action [44-46]. The results of testing the combination of nitroxyl radical (>NO ) (2,2,6,6-tetramethyl-4-benzoylpiperidine-l-oxyl) + amine (phenol) in the autoxidation of nonene-1 at 393 K are given here ([>NO ]o + [InH]o = 1.5 x 10 4mol L 1 p02 98 kPa) [44]. 

We observed a more complicated behavior in the study of retarding action of amines (IV-benzyl-IV -phenyl-l,4-benzenediamine and 4-hydroxyphenyl-2-naphtalenamine) on fuel T-6 oxidation catalyzed by the copper powder [13]. Both antioxidants appeared to retard the autoxidation of T-6 very effectively. They stop chain oxidation during the induction period in concentrations equal to 5 x 10 5mol L 1 and higher. The induction period was found to be the longer, the higher the concentration of the antioxidant and lower the amount of the copper powder introduced in T-6. 

The stabilizers chosen for evaluation include different types of heat and light stabilizers selected to represent different mechanisms of action as well as chemical compositions (ArJi). Types of stabilizers evaluated include benzotriazole and benzophenone light stabilizers [ultraviolet (UV) light absorbers], hindered amine light stabilizers (HALS, catalytic radical scavengers), hindered phenol heat stabilizers (antioxidant radical scavengers), and thioester heat stabilizers (antioxidant hydroperoxide decomposers). 

Unsaturated and Vulcanized Rubbers. Oxidation occurs most readily at polymers with structural double bonds, such as natural rubber, polybutadiene, or polyisoprene. Aromatic amines and sterically hindered phenols are effective antioxidants. From the rubber antioxidants, 96.8 million pounds were amines, and 20 million pounds were phenols. Amines act also as antiozonants whereas phenols are not effective. Furukawa shows that amines have a lower oxidation potential which is a prerequisite for antiozonant action. 

The effectiveness of antioxidants depends substantially on whether raw or cured rubbers are used and how many free impurities and ingredients are present. For example, sulfur reduces the stabilizing power of aromatic amines, whereas dithiocarbamates enhance the stabilizing action. 

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