Application Antioxidants

This allylic radical continues the chain. Steps [2] and [3] can be repeated again and again. 

Oxidation is shown at one allylic carbon only. Reaction at the other labeled allylic carbon is also possible. 

Unsaturated lipids are more easily oxidized than saturated ones because they contain weak allylic C-H bonds that are readily cleaved in Step [1] of this reaction, forming resonance-stabilized allylic radicals. Because saturated fats have no double bonds and thus no weak allylic C-H bonds, they are much less susceptible to air oxidation, resulting in increased shelf life of products containing them. 

Problem 15.26 which C - H bond is most readily cleaved in linoleic acid Draw all possible resonance structures for the resulting radical. Draw all the hydroperoxides formed by reaction of this resonance-stabilized radical with O2. 

An antioxidant is a compound that stops an oxidation reaction from occurring. 

The purported health benefits of antioxidants have made them a popuiar component in anti-aging formuiations. 

Naturally occurring antioxidants such as vitamin E prevent radical reactions that can cause cell damage. 

Synthetic antioxidants such as BHT— butylated hydroxy toluene—are added to packaged and prepared foods to prevent oxidation and spoilage. 

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Yoshikawa T, Naito Y, Kondo M. Ginkgo biloba leaf extract review of biological actions and clinical applications. Antioxid Redox Signal 1999 1 469-480. 

In specialized applications, antioxidant selection becomes constrained by other requirements. In sensitive electrical applications, for example, the electrical conductivity characteristics of antioxidants must be considered. Battery seals are an example, where the antioxidant must have low electrical losses to ensure maximum shelf life of the products. In some applications, long-term exposure to high temperature places stringent requirements on an antioxidant. Appliances are an example, where exposure to high temperature and surfactants can be expected. Antioxidants may be blended in a polymer to provide a range of protection unavailable with a single antioxidant. Antioxidants must be selected on the basis that they will not adversely react with other ingredients in a polymer compound. 

PrabhuUcar S, Tian H, Wang X, Zhu J-J, Li C-Z (2012) Engineered proteins redox properties and their applications. Antioxid Redox Signal 17 1796-1822... 

Applications. These materials are stiU in developmental infancy. Current production is limited to one commercial process in Europe and a demonstration-scale process in North America. The lignins produced in these processes have potential appHcation in wood adhesives, as flame retardants (qv), as slow-release agents for agricultural and pharmaceutical products, as surfactants (qv), as antioxidants (qv), as asphalt extenders, and as a raw material source for lignin-derived chemicals. 

Diarylamiaes fuactioa as mbber antioxidants by breaking the peroxidative chain reactions leading to mbber deterioration. Nearly all commercial synthetic mbbers (see Elastomers, synthetic), including neoprene, butyl, styrene—butadiene, and the acrylonitrile—butadiene mbbers, can be protected with about 1—2% of an alkylated diphenylamine. DPA itself is not used as a mbber antioxidant. An objectionable feature of these antioxidants is that they cause discoloration and staining which limits their use to applications where this is not important. 

There is also a large number of synthetic heterocyclic compounds with other important practical applications, as dyestuffs, copolymers, solvents, photographic sensitizers and developers, as antioxidants and vulcanization accelerators in the rubber industry, and many are valuable intermediates in synthesis. 

Supercritical fluid extraction (SFE) has been widely used to the extraction processes in pharmaceutical industries. Besides application of SFE in phannaceuticals, it has been applied on a wide spectmm of natural products and food industries such as natural pesticides, antioxidants, vegetable oil, flavors, perfumes and etc [1-2]. 

The present method is applicable with slight modifications to the preparation of both the ortho and para aminonaphthols and to many homologues, benzologues, and heterocyclic isologues of these substances. The chief feature of novelty is in the use of stannous chloride as an antioxidant in preparing and crystallizing the amine hydrochlorides. 

Oxidation of polyethylene with the formation of carbonyl groups can lead to a serious increase in power factor. Antioxidants are incorporated into compounds for electrical applications in order to reduce the effect. 

When polyethylene is to be used in long-term applications where a low power factor is to be maintained and/or where it is desired to provide thermal protection during processing, antioxidants are incorporated into the polymers. These were discussed extensively in Chapter 7 but a few particular points with regard to their use in polyethylene should be made. Although amines have been used widely in the past phenols are now used almost exclusively. 

One key consideration in developing radiation curable adhesive systems is the thermal stability and volatility of any photoinitiators used. These chemicals are designed for liquid systems where these issues do not arise. Few of the commercial photoinitiators have adequate thermal stability at the highest hot melt temperatures (180-200°C) and many are too volatile. Reduced application temperatures and special antioxidant packages are often required. 

Certain fillers are commonly added to protect the urethane backbone from oxidative degradation. Carbon black and titanium dioxide are commonly used in conjunction with antioxidants to protect polyether polyurethanes in exterior adhesive applications that may be exposed to oxygen and light (Fig. 12). 

Purification of poloxamers has been extensively investigated due to their use in medical applications, the intention often being to remove potentially toxic components. Supercritical fluid fractionation and liquid fractionation have been used successfully to remove low-molecular weight impurities and antioxidants from poloxamers. Gel filtration, high-performance liquid chromatography (HPLC), and ultrafiltration through membranes are among the other techniques examined [5]. 

Phenol can be alkylated to alkylphenols. These compounds are widely used as nonionic surfactants, antioxidants, and monomers in resin polymer applications ... 

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