Antioxidants primary-radical terminating

An effective method of thermal stabilization is through the use of a radical terminating primary antioxidant. The most common class of antioxidant for radical termination is a hindered phenol (4). Phenolic antioxidants are highly effective at relatively low concentrations (i.e., <0.5 wt%) in inhibiting decomposition. The mechanism involves a chain-breaking donation of a hydrogen atom from the antioxidant to the reactive peroxy-radical (Fig. 4.3). This produces a less-reactive... 

Antioxidants act either by radical trapping, interfering in the radical propagation, or by decomposition of the hydroperoxide formed. In this way they inhibit the formation of new radicals. The former are known as chain breaking or chain terminator antioxidants (primary antioxidants). The latter, the hydroperoxide decomposing agents, are also known as preventive antioxidants (secondary antioxidants). 

Primary antioxidants terminate free radical chains and function as electron donors. They include the phenolic antioxidants, butylated hydroxyanisole (BHA), butylated hydroxy-toluene (BHT), tertiary butyl hydroquinone (TBHQ), alkylgalates, usually propylgallate (PG), and natural and synthetic tocopherols and tocotrienols. 

In terms of potential chemical interactions, the effects of NO on ROS-induced injury are multiple, and some effects can be classified as prooxidant and others may be classified as antioxidant still others can be classified as both. In terms of the metal-catalyzed Haber-Weiss reaction, there are two primary effects of -NO. The binding of NO to metal ions will prevent the Fenton reaction and thus results in an antioxidant action. Another important antioxidant action of NO (and its oxidized product N02) is its reaction with hpid radicals, thus resulting in radical chain termination. ... 

Franchi and coworkers reported on the effect of solvents on hydrogen atom abstraction from phenolic antioxidants by primary alkyl radicals , which could be useful when studying oxidations at low oxygen partial pressures because under those conditions the addition of oxygen to substrate alkyl radicals can be reversible (equation 36) and alkyl radicals could play a role in termination reactions (equation 37)" ... 

There are two major classes of antioxidants and they are differentiated based on their mechanism of inhibition of polymer oxidation chain-terminating or primary antioxidants and hydroperoxide-decomposing secondary antioxidants [5]. Primary or free-radical scavenging antioxidants inhibit oxidation via very rapid chain-terminating reactions. The majority of primary antioxidants are hindered phenols or secondary aryl amines. Generally, hindered phenols are nonstaining, nondiscoloring, and are available in a wide... 

A common type of radical scavenger is a hindered phenol, such as buty-lated hydroxy toluene (BHT). A radical can react with BHT by removing a hydrogen atom and forming a new phenoUc radical. However this radical is sterically hindered from further reactions by the two t-butyl groups and therefore the propagation steps terminate with the formation of this stable radical. Antioxidants that act as radical scavengers are sometimes referred to as primary antioxidants. 

In primary antioxidants, active H-atoms in the anti-aging molecule (-OH, -NH, and -SH-compounds are involved here) act as chain terminators in radical chain reactions and thus protect the rubber molecules from recombining and/or chain cleaving. Mono- or oligo-functional, substituted phenols, mono- or oligo-functional, secondary aromatic amines, or heterocyclic mercapto-(-SH)-compounds are exam-... 

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