Phenols from aromatic amines

In an acetone extract from a neoprene/SBR hose compound, Lattimer et al. [92] distinguished dioctylph-thalate (m/z 390), di(r-octyl)diphenylamine (m/z 393), 1,3,5-tris(3,5-di-f-butyl-4-hydroxybenzyl)-isocyanurate m/z 783), hydrocarbon oil and a paraffin wax (numerous molecular ions in the m/z range of 200-500) by means of FD-MS. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out (Chapter 2). The method of Dinsmore and Smith [257], or a modification thereof, is normally used. Mass spectrometry (and other analytical techniques) is then used to characterise the various rubber fractions. The mass-spectral identification of numerous antioxidants (hindered phenols and aromatic amines, e.g. phenyl-/ -naphthyl-amine, 6-dodecyl-2,2,4-trimethyl-l,2-dihydroquinoline, butylated bisphenol-A, HPPD, poly-TMDQ, di-(t-octyl)diphenylamine) in rubber extracts by means of direct probe EI-MS with programmed heating, has been reported [252]. The main problem reported consisted of the numerous ions arising from hydrocarbon oil in the recipe. In older work, mass spectrometry has been used to qualitatively identify volatile AOs in sheet samples of SBR and rubber-type vulcanisates after extraction of the polymer with acetone [51,246]. 

There are several chemical compounds found in the waste waters of a wide variety of industries that must be removed because of the danger they represent to human health. Among the major classes of contaminants, several aromatic molecules, including phenols and aromatic amines, have been reported. Enzymatic treatment has been proposed by many researchers as an alternative to conventional methods. In this respect, PX has the ability to coprecipitate certain difficult-to-remove contaminants by inducing the formation of mixed polymers that behave similarly to the polymeric products of easily removable contaminants. Thus, several types of PX, including HRP C, LiP, and a number of other PXs from different sources, have been used for treatment of aqueous aromatic contaminants and decolorization of dyes. Thus, LiP was shown to mineralize a variety of recalcitrant aromatic compounds and to oxidize a number of polycyclic aromatic and phenolic compounds. Furthermore, MnP and a microbial PX from Coprinus macrorhizus have also been observed to catalyze the oxidation of several monoaromatic phenols and aromatic dyes (Hamid and Khalil-ur-Rehman 2009). 

Of these reactions, the reaction of the peroxyl radical with phosphite is the slowest. The rate constant of this reaction ranges from 102 to 103 L mol 1 s 1 which is two to three orders of magnitude lower than the rate constant of similar reactions with phenols and aromatic amines. Namely, this reaction limits chain propagation in the oxidation of phosphites. Therefore, the chain oxidation of trialkyl phosphites involves chain propagation reactions with the participation of both peroxyl and phosphoranylperoxyl radicals ... 

In its simplest form this reaction, by means of which the extremely numerous technical azo-dyes are manufactured, consists in condensation of aromatic diazo-compounds with phenols or aromatic amines to form azo-compounds. From the labile diazo-system the very stable azo-complex is produced. The azo-dyes, therefore, are, without exception, derivatives of azobenzene or else of azonaphthalene, etc. 

In recent years, numerous applications of such peroxidase-catalyzed oxidative coupling of phenols and aromatic amines have been reported (Table 7). These peroxidase-catalyzed biotransformations lead to modified natural products with high biological activities [110-118]. Several examples have also been described for the oxidative coupling of phenols with peroxidases and other oxidative enzymes from a variety of fungal and plant sources as whole cell systems... 

The polymerization of phenols or aromatic amines is applied in resin manufacture and the removal of phenols from waste water. Polymers produced by HRP-catalyzed coupling of phenols in non-aqueous media are potential substitutes for phenol-formaldehyde resins [123,124], and the polymerized aromatic amines find applications as conductive polymers [112]. Phenols and their resins are pollutants in aqueous effluents derived from coal conversion, paper-making, production of semiconductor chips, and the manufacture of resins and plastics. Their transformation by peroxidase and hydrogen peroxide constitutes a convenient, mild and environmentally acceptable detoxification process [125-127]. 

The halogenation of phenols and aromatic amines in aqueous solution also provides evidence for diffusion control, but the interpretation is complicated by the fact that either the formation of the o-complex or the proton loss from the (7-complex can be rate-determining. The reaction path for the halogenation of aromatic amines in aqueous acids is believed to be that shown for N,N-dialkyl anilines in Scheme 9. Where the formation of the o-complex is rate-determining, the kinetic form for attack by the molecular halogen is given by (39). In this equation, the observed rate coefficient (k ) is related to the rate coefficient for the reaction of the amine molecule (k) by (40), where KSH+ is the... 

Wada S, Ichikawa H, Tatsumi K. Removal of phenols and aromatic amines from wastewater by a combination treatment with tyrosinase and a coagulant. Biotechnol Bioeng 1995 45 304—309. 

Husain Q, Jan U (2000) Detoxification of phenols and aromatic amines from polluted wastewater by using phenol oxidases. J Sci Ind Res 59 286—293... 

Determined by Hammond et al. (1955) from a common Hammett equation for phenols and aromatic amines. c Authors did not give the p value. d Calculated by Howard and Ingold (1963a). 

Various oligomeric condensates are formed from phenolic and aromatic amine AO and AOZ as a consequence of interactions of these reactive stabilizers with oxidizing species formed in stabilized polymers, e.g. with alkylperoxyls, alkyl hydroperoxides or ozonides [15-17]. Stabilizing efficiency is preserved in some of these compounds the latter have been discussed however mostly in connection with mechanism of action of AO or AOZ [6]. 

It was reported [231] that phenolic and aromatic aminic AO are able to form bound-in species in EPM cured with peroxides. This principle was exploited in NR doped with 2,6-di-terr-butyl-4-methylphenol and tert-butyl peroxide. Other phenolic AO bearing methyl groups may take place in a similar process too [232]. The extent of the coupling of radicals derived from phenolic antioxidants with macroalkyls is influenced by the concentration of phenols. A competitive process, autocoupling of phenol derived radicals, increases with increasing concentration of the phenolic antioxidant [17]. 

Phthalein type dyes have been prepared from 2,3-dicarboxypyrazine by heating with phenols or aromatic amines and zinc chloride. For example, compound (25) was obtained with resorcinol (1353). Efforts to prepare 2,6-diaminopyrazine through a Curtius-Schmidt reaction on 2-acetamido-6-carboxypyrazine (with sodium azide, sulfuric acid, and trichloroacetic acid) proved unsuccessful (434). The preparation of bicyclic heterocyles from 2-amino-3-carboxypyrazines has been described in Section VIII. 1D(6). 

For the measurement a moderate reduction potential between — 100 and + 100 mV vs. Ag/AgCl is appUed (Fig. 2.12). In this region the potential for electrochemical interferences is very low. However, the biggest problems arise from the high reactivity of compormds I and II with reducing substrates (electron donors), which compete with the electrode for the reduction of peroxidase. Ascorbic acid, naturally occurring phenolics and aromatic amines are among those compounds. The competitive reaction of reductants should be... 

There are many substances which would appear to be good candidates for LC-EC from a thermodynamic point of view but which do not behave well due to kinetic limitations. Johnson and co-workers at Iowa State University used some fundamental ideas about electrocatalysis to revolutionize the determination of carbohydrates, nearly intractable substances which do not readily lend themselves to ultraviolet absorption (LC-UV), fluorescence (LC-F), or traditional DC amperometry (LC-EC) [2], At the time that this work began, the EC of carbohydrates was more or less relegated to refractive index detection (LC-RI) of microgram amounts. The importance of polysaccharides and glycoproteins, as well as traditional sugars, has focused a lot of attention on pulsed electrochemical detection (FED) methodology. The detection limits are not competitive with DC amperometry of more easily oxidized substances such as phenols and aromatic amines however, they are far superior to optical detection approaches. 

In the laboratory, simple phenols can be prepared from aromatic sulforae acids by melting with NaOH at high temperature (Section 16-2), Few functional groups can survive such harsh conditions, though, and the reaction is therefore limited to the preparation of alkyl-substituted phenols. Well see a better method of phenol preparation from aromatic amines in Section 24.8. 

Utilizing a voltammetric measurement technique, the RULER quantitatively analyses the relative concentrations of antioxidants (hindered phenolic and aromatic amine) in new and used oils. This data can be trended to determine the depletion rates of the antioxidant protection package in the oil provided the instrument has been calibrated for that oil type. From pre-established limits, proper oil change cycles, potential interval extension or timely antioxidant replenishments can be determined. 

Alkylperoxy radicals participate in the chain propagation step of oxidation. In photo-oxidized PP, most ROO terminate after a few propagation steps [190]. The few ROO that escape from this recombination propagate with a great rate. At the same time, they are easily scavenged by chain-breaking phenolic and aromatic aminic AO or HAS derived NOH. Secondary and tertiary HAS associate in... 

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