Antioxidant aromaticity

Known emissions from the production stage, which are not covered by characterisation factors and which may contribute significantly to the toxicity impact categories, include emissions of components occurring in small quantities in the raw materials (typically well below 5%) like siccatives (organic metal compounds), softeners (phthalates), antioxidants (aromatics) and wetteners (surfactants). Due to lack of readily available knowledge of their exact identity and/or lack of readily available data on their inherent environmental properties, it has not been possible to include them in the case study. 

Sometimes curing agents, antioxidants and accelerators can interact, creating new toxic chemicals e.g., when guanidine accelerators are used during the vulcanisation of rubber with sulfur with phenylene diamine-based antioxidants, aromatic amines and isothiocyanates can be produced, both of which are suspected carcinogenic agents [11]. 

Because of the involvement of phenoxyl radicals in inhibition of hydrocarbon autoxidation by phenolic antioxidants most kinetic studies of this radical have focussed on self-reactions, reaction with autoxidation products such as hydroperoxides and peroxides, and reaction with other phenolic antioxidants, aromatic amines, and transition metal complexes. 

Antioxidant and deactivation additives substituted phenols, dithiophosphates, dithiocarbamates, alkylated aromatic amines. 

The metal coordination complexes of both sahcylaldehyde phenyhiydrazone (91) and sahcylaldoxime provide antioxidant (92) protection and uv stabihty to polyolefins (see Antioxidants). In addition, the imines resulting from the reaction of sahcylaldehyde and aromatic amines, eg, p- am in oph en o1 or a-naphthylamine, can be used at very low levels as heat stabiLizers (qv) in polyolefins (93). 

Alkylation. Benzene and phenol feedstocks are readily alkylated under Friedel-Crafts conditions to prepare extensive families of alkylated aromatics. These materials generally are intermediates in the production of surfactants or detergents such as linear alkylbenzenesulfonate (LABS) and alkylphenolethoxylate (APE). Other uses include the production of antioxidants, plasticizers, and lube additives. 

Environmental Impact of Ambient Ozone. Ozone can be toxic to plants, animals, and fish. The lethal dose, LD q, for albino mice is 3.8 ppmv for a 4-h exposure (156) the 96-h LC q for striped bass, channel catfish, and rainbow trout is 80, 30, and 9.3 ppb, respectively. Small, natural, and anthropogenic atmospheric ozone concentrations can increase the weathering and aging of materials such as plastics, paint, textiles, and mbber. For example, mbber is degraded by reaction of ozone with carbon—carbon double bonds of the mbber polymer, requiring the addition of aromatic amines as ozone scavengers (see Antioxidants Antiozonants). An ozone decomposing polymer (noXon) has been developed that destroys ozone in air or water (157). 

Several stabilizers are useful in minimizing oxidative degradation during thermoplastic processing or in the bulk soHd. Phenothiazine, hindered phenohc antioxidants such as butylated hydroxytoluene, butylatedhydroxyanisole, and secondary aromatic amines in concentrations of 0.01—0.5% based on the weight of polymer, are effective. 

The tendency of aliphatic ethers toward oxidation requires the use of antioxidants such as hindered phenoHcs (eg, BHT), secondary aromatic amines, and phosphites. This is especially tme in polyether polyols used in making polyurethanes (PUR) because they may become discolored and the increase in acid number affects PUR production. The antioxidants also reduce oxidation during PUR production where the temperature could reach 230°C. A number of new antioxidant products and combinations have become available (115,120,124—139) (see Antioxidants). 

Although aminyl radicals are stable towards oxygen, they can oxidi2e other aromatic amines, phenols and thiols (10), and regenerate the diarylamine. Thus, mixtures of phenols and diarylamines frequendy show better antioxidant activity than either one alone. This is called synergism. 

Radical Scavengers Hydrogen-donating antioxidants (AH), such as hindered phenols and secondary aromatic amines, inhibit oxidation by competing with the organic substrate (RH) for peroxy radicals. This shortens the kinetic chain length of the propagation reactions. 

Stilbenequiaones such as (5) absorb visible light and cause some discoloration. However, upon oxidation phenolic antioxidants impart much less color than aromatic amine antioxidants and ate considered to be nondiscoloring and nonstaining. 

Aromatic Amines. Antioxidants derived from -phenylenediarnine and diphenylamine are highly effective peroxy radical scavengers. They are more effective than phenoHc antioxidants for the stabilization of easily oxidized organic materials, such as unsaturated elastomers. Because of their intense staining effect, derivatives of -phenylenediamine are used primarily for elastomers containing carbon black (qv). 

Radical Trapping. Figure 2 shows some of the reactions of aromatic amines that contribute to their activity as antioxidants and to their tendency to form highly colored polyconjugated systems. 

These compounds are used most frequentiy in combination with hindered phenols for a broad range of apphcations in mbber and plastics. They are also able to suppress color development caused by oxidation of the substrate and the phenoHc antioxidant. Unlike phenols and secondary aromatic amines, phosphoms-based stabilizers generally do not develop colored oxidation products. 

Antioxidants resistant to extraction by lubricants and gasoline are preferred for the stabili2ation of elastomers used in automotive appfications such as gaskets and tubing. Aromatic amine antioxidants, such as A/-phenyl-Ar-(p-toluenesulfonyl)-A-phenylenediamine [100-93-6] (37), with low solubifity in hydrocarbons, are extracted slowly from elastomers and are used for these appfications. 

Raw NBR containing 1.5% of the built-in antioxidant retained 92% of its original resistance to oxidation after exhaustive extraction with methanol. NBR containing a conventional aromatic amine antioxidant (octylated diphenyl amine) retained only 4% of its original oxidative stabiUty after similar extraction. 

It is also possible to graft an aromatic amine antioxidant bearing a sulfhydryl group on to the backbone of an elastomer. 

AGE-Gontaining Elastomers. The manufacturing process for ECH—AGE, ECH—EO—AGE, ECH—PO—AGE, and PO—AGE is similar to that described for the ECH and ECH—EO elastomers. Solution polymerization is carried out in aromatic solvents. Slurry systems have been reported for PO—AGE (39,40). When monomer reactivity ratios are compared, AGE (and PO) are approximately 1.5 times more reactive than ECH. Since ECH is slightly less reactive than PO and AGE and considerably less reactive than EO, background monomer concentration must be controlled in ECH—AGE, ECH—EO—AGE, and ECH—PO—AGE synthesis in order to obtain a uniform product of the desired monomer composition. This is not necessary for the PO—AGE elastomer, as a copolymer of the same composition as the monomer charge is produced. AGE content of all these polymers is fairly low, less than 10%. Methods of molecular weight control, antioxidant addition, and product work-up are similar to those used for the ECH polymers described. 

Aromatic amines are the most effective primary antioxidants (Fig. 34) but they are discolouring and can only be used where the darker colours are acceptable (for instance in rubber adhesive formulations containing carbon blacks as fillers). The... 

Process 4, conversion of peroxy radicals to hydroperoxides can be interrupted by traditional primary antioxidants (see Fig. 16). The fastest reacting primary antioxidants are the aromatic amines (e.g. Naugard 445). However, these materials yellow upon exposure to UV light which restricts their applieations. More common in adhesives are the hindered phenol types of which numerous types are available, with Irganox 1010 the most common choice for adhesives. 

Without antioxidants virtually all rubber products, including those made from modem synthetic rubbers, undergo unacceptable performance degradation upon aging [195]. Various aromatic materials and particularly phenols have proven to... 

In the case of carbohydrates blue chromatogram zones are produced on a yellow background that slowly fades [2]. Steroids, vitamins, antioxidants, phenols and aromatic amines yield, sometimes even at room temperature, variously colored chromatogram zones [5]. -Blockers and laxatives also acquire various colors [7, 10]. The detection hmits are in the nanogram to microgram range [5]. 

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