Antioxidants commercial

P. R. Dean II, Index of Commercial Antioxidants oN Antio pnants, 4th ed., Goodyear Chemicals, Akron, Ohio, 1983. 

The effect substitution on the phenolic ring has on activity has been the subject of several studies (11—13). Hindering the phenolic hydroxyl group with at least one bulky alkyl group ia the ortho position appears necessary for high antioxidant activity. Neatly all commercial antioxidants are hindered ia this manner. Steric hindrance decreases the ability of a phenoxyl radical to abstract a hydrogen atom from the substrate and thus produces an alkyl radical (14) capable of initiating oxidation (eq. 18). 

Commercial Antioxidants Table 4 includes the main classes of antioxidants sold in the United States and the suppHer s suggested apphcations. Some of these are mixtures rather than single substrates. This is especially tme of alkylated amines and alkylated phenols. The extent of alkylation and the olefins used for alkylation can vary among manufacturers. Table 4 is not a complete listing of available antioxidants in the United States. 

Isopropyl Ether. Isopropyl ether is manufactured by the dehydration of isopropyl alcohol with sulfuric acid. It is obtained in large quantities as a by-product in the manufacture of isopropyl alcohol from propylene by the sulfuric acid process, very similar to the production of ethyl ether from ethylene. Isopropyl ether is of moderate importance as an industrial solvent, since its boiling point Hes between that of ethyl ether and acetone. Isopropyl ether very readily forms hazardous peroxides and hydroperoxides, much more so than other ethers. However, this tendency can be controlled with commercial antioxidant additives. Therefore, it is also being promoted as another possible ether to be used in gasoline (33). 

A cooperative interaction between two or more antioxidants (or antioxidant function) that leads to an overall antioxidant effect greater than the sum of the individual effects of each antioxidant is referred to as synergism. Synergism can be achieved in different ways. It may arise from the combined action of two chemically similar antioxidants, e.g., two hindered phenols (homosynergism), or when two different antioxidant functions are present in the same molecule (autosynergism) the latter is exemplified by many commercial antioxidants (e.g., Irgastab 2002, AO 29 Table lb), which have CB and UVA activity. 

Ionol is a commercial antioxidant, 2,6-di-/cr/-butyl- -cresol, manufactured by Shell Chemical Corp. Inhibitors appear to minimize formation of polymeric side products, although with isoprene the effect is often small. 

The antirads, including numerous commercial antioxidants, having labile hydrogens in their stmc-mre intermpt the radical chain reactions, through transfer of the labile hydrogen and yield a highly stabilized radical from them, e.g., with a hindered phenol. 

Antioxidant. Substances that retard or inhibit autoxidation at moderate temperatures and pressures. Commonly Icnown, commercial antioxidants are aromatic amines, alkylated phenols, cresols, and hydroquinones. 

Pressure Reactions The Parr pressure reaction apparatus (Parr Instrument Co., Moline, Illinois) was used for all pressure and gas studies. A specially designed Teflon stopper was used in place of the original rubber stopper so that the commercial antioxidants in the rubber would not contaminate the reaction mixture. Standard 99.9% oxygen, lamp-grade nitrogen, and Type-1 grade-E breathing air were obtained from Sooner Supplies (Shawnee, Oklahoma). 

Phenols readily undergo aromatic substitution since the hydroxyl group is ringactivating and ortho,para-directing. Phenols are easily oxidized to quinones. Phenols with bulky ortho substituents are commercial antioxidants. 

Commercial antioxidants of monocyclic phenols have only one hydroxy group in the molecule. Pospisil, Taimr, and Kotulak determined the activity of monocyclic dihydrobenzenes. They prepared numerous... 

The polycyclic phenols, being somewhat more effective and relatively nonvolatile, afford good protection at both ambient and elevated temperatures. This improvement in activity, however, is generally accompanied by a sacrifice in color. For methylenebisphenols the discoloration may be caused by oxidation products of the antioxidant in which a highly conjugated system is developed. For example, Kharasch and Joshi (7) found that a purple color developed when oxygen was bubbled through an alkaline alcoholic solution of 4,4 -methylenebis(2,6-di-fert-butylphe-nol), III, a commercial antioxidant. They showed that this color was caused by the anion, V, of a quinonemethide type oxidation product, IV, of the phenol. 

Following protein hydrolysis, an additional reaction can be carried out to obtain plastein, a water-soluble, heat stable antioxidant. Plastein is a mixture of higher molecular weight protein-like substances formed by the condensation of lower-molecular weight peptides, such as protein hydrolysates, during the plastein reaction (Yamashita et al, 1971). A study conducted by Ono et al. (2004) assessed the production of plastein from squid hepatopancreas and indicated its high potential as a commercial antioxidant due to its thermostability, tastelessness, and high solubility in water. 

Butylated Hydroxytoluene (BHT) BHT is also a monohydroxyphenol (Figure 4) and is widely used in foods. This fat-soluble antioxidant is available as a white crystalline compound. BHA is less stable than BHT at high temperatures and has lower carry-through properties. BHA and BHT act synergistically, and several commercial antioxidant formulations contain both of these antioxidants. BHT is effectively used in oxidation retardation of animal fats. It is postulated that BHA... 

Table 1 Some examples of commercial antioxidants representing the major antioxidant mechanisms...

Generally, the compatibility of antioxidants in polymers is improved when the antioxidant and the host polymer have similar characteristics. Compatibility of antioxidants in nonpolar hydrocarbon polymers, therefore, decreases with increasing antioxidant polarity and increases with the number, length, and branching of the inert alkyl substituents attached to the antioxidant function.Many commercial antioxidants with higher molecular masses (e.g.. Table 1, compare AO 5 with AO 1) have been developed and many have inert long (8 to 18 C-atoms) alkyl chains (e.g.. Table 1, AO 4). 

In polypropylene in an air oven test at 140°C (PP ), on the other hand, the lower members of the series are completely ineffective, as is BHT. The highest member of the series, the commercial antioxidant IRGANOX 1076 (III, R = ClgH37) is highly effective under these conditions. 

Substitued phenols are commonly applied as commercial antioxidants and the above presented reaction can play a role in the mechanism of polymer stabilization against oxidation. 

Poly(ethylene-co-1,4-cyclohexane dimethylene terephthalate) The thermal and photochemical oxidation processes of a polyester based on poly(ethylene-co-l,4-cyclohexanedimethylene terephthalate) (PECT) with approximately 30% of 1,4-cyclohexanedimethanol have been studied by means of chemiluminescence [88], Also, the stabilization activity of some commercial antioxidants has been evaluated, and it has been related to hydroperoxide levels in the polymer. 

To prevent oxidation of reduced organosulfur in the wood cell walls, conservators are currently investigating antioxidants. Commercial antioxidants (ascorbic acid, anthocyanidins, proanthocyanins, flavon-3-ols, flavonones and flavonols) are being used to prevent oxidation of reduced species by mopping up free radicals. 

VI. Registered Trade Names and Formulae of Commercial Antioxidants... 

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