Antioxidants classifying

Table 1 Some commercial antioxidants classified according to the two different antioxidant mechanisms...

Alkylated diphenyl amines (11) and derivatives of both dihydro quiaoline (12) and polymerized 2,2,4-trimethyl-l,2-dihydroquiQoline [26780-96-1] (13) develop less color than the -phenylenediamiaes and are classified as semistaining antioxidants. Derivatives of dihydro quiaoline are used for the stabilization of animal feed and spices. 

Hindered Amines. Hiadered amines are extremely effective ia protecting polyolefins and other polymeric materials against photodegradation. They usually are classified as light stabilizers rather than antioxidants. 

Hindered amines are generally classified as light stabili2ers. The three selected products are derivatives of 1,6-hexanedianiine and are effective antioxidants for polyolefins. 

Commercial use of many chlorinated derivatives imposes stress on the stabHity of the solvent. Inhibitors classified as antioxidants (qv), acid acceptors, and metal stabilizers are added to minimize these stresses. AH the chloriaated derivatives hydrolyze at a slow but finite rate when dissolved ia water. Hydrolysis of chloriaated solvents typicaHy Hberates hydrogen chloride that can corrode storage containers and commercial metal-cleaning equipment. The Hberated hydrogen chloride can be neutralized by an appropriate epoxide to form noncorrosive chlorohydrins (qv). 

Another type of chemical change is initiated by light, which may trigger autolytic, that is, free radical (Type I) or singlet oxygen (Type II) reactions. These changes are routinely classified as oxidation. Rancidity in cosmetics, especially those containing unsaturated Hpids, is commonly prevented by use of antioxidants (qv). 

Optimising the use of phenolic compounds in foods 317 16.1.2 Classifying natural antioxidants... 

Natural antioxidants may be classified according to their nutritive value or according to their solubility. The hydrophobic vitamin E and the hydrophilic vitamin C are thus important both as nutrients and as antioxidants. The nonnutritive antioxidants may similarly be divided into lipid-soluble and water-soluble antioxidants, as shown in Fig. 16.3, which will also form the basis for a discussion of exploitation of combinations of anhoxidants in order to improve protective effects. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Antioxidative protection mechanisms can be classified into at least four categories [2], i.e., compartmentation, detoxification, repair, and utilization the first two have a direct relationship to antioxidizability. 

The structures of four of the synthetic carotenoids (beta-carotene, canthaxanthin, beta-apo-8 -carotenol, beta-apo-8 -carotenoic acid) are shown in Fig. 8.2. By virtue of their conjugated double bond structure, they are susceptible to oxidation but formulations with antioxidants were developed to minimize oxidation. Carotenoids are classified as oil soluble but most foods require water soluble colorants thus three approaches were used to provide water dispersible preparations. These included formulation of colloidal suspensions, emulsification of oily solutions, and dispersion in suitable colloids. The Hoffman-LaRoche firm pioneered the development of synthetic carotenoid colorants and they obviously chose candidates with better technological properties. For example, the red canthaxanthin is similar in color to lycopene but much more stable. Carotenoid colorants are appropriate for a wide variety of foods.10 Regulations differ in other countries but the only synthetic carotenoids allowed in foods in the US are beta-carotene, canthaxanthin, and beta-8-carotenol. 

Different types of aquatic DHS were shown to exhibit comparable rate constants for trapping hydroxyl radicals. Peroxy radical photooxidants (i. e., a mixture of different HS-derived species) were shown to be important for the elimination of alkylphenols, which are typical compounds classified as antioxidants. 

Inhibition of Oxidation. Several antioxidants were tested in chloroprene at 45°C. Those which can be classified as mainly suppressors of initiation (I), because of their ability to destroy hydroperoxides—namely, zinc dialkyldithiophosphates, zince dialkyldithiocarbamates, triphenyl-phosphine, and the like—had no inhibiting effect at the 100-p.p.m. level. 

The mechanisms of inhibition by peroxide decomposers, metal deactivators, and ultraviolet absorbers are fairly well understood in general terms, although many details of the individual reactions remain to be elucidated. Classifying a preventive antioxidant into one of the three categories above will only rarely describe its entire function. The dual behavior of dialkyl dithiophosphates in the liquid phase has been mentioned. Many other phosphorus- and sulfur-containing antioxidants commonly classified as peroxide decomposers can also act as chain breakers. Similarly, the structure of many metal deactivators and ultraviolet absorbers indicates that they must also have some chain-breaking activity. 

Additives are all formulation constituents other than the active ingredient. Although additives could be classified into excipients and vehicles (excipients for solid preparations and vehicles for liquid ones), there are several other agents used in pharmaceutical formulations with specific functions such as preservatives, sweeteners, coatings, colorants, antioxidants, surfactants, emulsifying agents, and flavors. Since they comprise a vast amount of products, this section will deal with additives for compounding pharmaceutical products for internal use only [17,18]. 

Biocides and antioxidants used as direct food additives are classified as preservatives (B-81MI11507, B-72MI11500). Their function is to enhance the keeping ability, or stability, of food products. The use of such additives is carefully controlled in most countries, and the majority of substances employed have a long history of safe use (b-81MH1509). 

From a technical and practical point of view, the components of plant extracts can be classified as essential oils, fatty oils, pungent constituents, colours (pigments) and natural antioxidants. 

Reactions can be classified on the basis of their order, which is the sum of the powers to which the concentrations of the participating species are raised in the rate law. If a = p = 1 in equation 14, the reaction is first-order in A, first-order in B, and is globally of second order. Reactions 4 and 5 respond to this kind of second-order reaction rate law, and the k values have been established for the reactions between several oxidant species and antioxidants. 

In other applications the pattern of evolution of styrene, butadiene and acrylonitrile as a function of temperature has provided a unique way for classifying different types of ABS. The loss of the antioxidant butylated hydroxytoluene (BHT) was also detected by MS preceding EVA copolymer degradation [165] BHT was identified at a concentration level of 20 ppm. Lehrle and co-workers [52] have described a successful controlled release system for the stabilisation of rubber by encapsulating efficient but rather mobile antioxidants to prevent loss from the host polymer. The performance of the controlled-release of the antioxidant BHT from alginate matrix particles was studied by means of DSC, TG and TG-MS. Polyisoprene rubber is more resistant to oxidation when protected in this way than by the equivalent concentration of unencapsulated antioxidant. 

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