Substituted phenols, aromatic

Polymeric adsorbents have also been found to be very useful, and even highly water-loving undesired materials like p-toluene sulphonic acid from waste streams can be recovered via ad.sorption and regeneration with solvents like fv -propanol. In such instances, the regeneration of activated carbons is not satisfactory, even with aqueous sodium hydroxide. Solutes like phenols, substituted phenols, aromatic amines, heterocyclic amines (pyridine, picolines, etc.) can be recovered, in a rewarding way, from aqueous solutions. 

The low specificity of electron-donating substrates is remarkable for laccases. These enzymes have high redox potential, making them able to oxidize a broad range of aromatic compounds (e.g. phenols, polyphenols, methoxy-substituted phenols, aromatic amines, benzenethiols) through the use of oxygen as electron acceptor. Other enzymatic reactions they catalyze include decarboxylations and demethylations [66]. 

Antioxidants inhibit oxidation and are usually employed in combination with UV absorbers. Most antioxidants used for urethane coatings fall into the following classes substituted phenols, aromatic amines, condensation products of aminophenols with aldehydes, thio compounds, and phosphites. Often combinations of antioxidants from the above categories exhibit a synergistic effect. More recently Mathur et al. (125) carried out an extensive study involving the use of one to six stabilizers, selected from the above antioxidants and UV stabilizers, employing several independent test methods, to study the thermooxidation of urethane and urethane-urea films. 

Classification Substituted phenolic aromatic organic compd. 

Bromine Water. Phenols, substituted phenols, aromatic ethers, and aromatic amines, since the aromatic rings are electron rich, undergo aromatic electrophilic substitution with bromine to yield substituted aryl halides. For example. 

As mentioned in the previous section, R-, RO-, and RO2 radicals and hydroperoxides are the main products of hydrocarbon oxidation. For this reason, easily oxidized polymers (polyolefins, polyamides, polystyrene, etc.) are stabilized by compounds that can react directly with peroxide radicals or directly with hydroperoxides. They are substituted phenols, aromatic amines, mercaptans, organic sulfides, etc. they are called antioxidants. 

At present, the most widely used chain-terminating antioxidants that react with peroxide radicals are substituted phenols, aromatic amines, and additives that decompose hydroperoxides into molecular products - sulphides and others. 

Pyrolysis of biomass is carried out under inert atmosphere and forms, depending on the residence time and temperature, char, oil, and gas. Pyrolysis with long residence time at low temperamre (400°C) produces a black solid (charcoal), while fast pyrolysis at high temperarnre (500°C) favors the formation of a black liquor (bio-oil). The short contact times (<2s at ca. 500" C) thus maximize the liquid yield. Fast pyrolysis is preferred by the chemical industry because of the relative ease of handling liquids. However, bio-oil produced by pyrolysis of bulk biomass contains more than 400 different components like carboxylic acids, ketones, aldehydes, sugars, furans, (substituted) phenols, aromatics, and tar (Table 1). Separation of useful chemicals from this complex pool is very difficult. As an alternative, pyrolysis can also be used as a first step for generating heat or electricity, followed by combusting the pyrolytic products. Excellent papers and reviews that describe fast pyrolysis in more detail are available [27-32]. 

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

Make acid yields coumaUc acid when treated with fuming sulfuric acid (19). Similar treatment of malic acid in the presence of phenol and substituted phenols is a facile method of synthesi2ing coumarins that are substituted in the aromatic nucleus (20,21) (see Coumarin). Similar reactions take place with thiophenol and substituted thiophenols, yielding, among other compounds, a red dye (22) (see Dyes and dye intermediates). Oxidation of an aqueous solution of malic acid with hydrogen peroxide (qv) cataly2ed by ferrous ions yields oxalacetic acid (23). If this oxidation is performed in the presence of chromium, ferric, or titanium ions, or mixtures of these, the product is tartaric acid (24). Chlorals react with malic acid in the presence of sulfuric acid or other acidic catalysts to produce 4-ketodioxolones (25,26). 

ULLMANN GOLDBERG Aromatic substitution Cu catalyzed substitution of aromatic halides in the synthesis of disryls, diaiyl ethers, diaryl amines, phenols... 

Aromatic rings are hydrogenated with a variety of catalysts. However, aromatic alkoxy and hydroxyl substituents are susceptible to hydrogenolysis under most conditions used to saturate the ring. Hydrogenolysis does not occur to any appreciable extent with ruthenium catalysts even though high temperatures and pressures are required. Thus, substituted phenols are... 

If both ortho positions bear substituents other than hydrogen, the allyl group will further migrate to the para position. This reaction is called the para-Claisen rearrangement. The formation of the para-substituted phenol can be explained by an initial Claisen rearrangement to an ortho-2l y intermediate which cannot tautomerize to an aromatic o-allylphenol, followed by a Cope rearrangement to the p-allyl intermediate which can tautomerize to the p-allylphenol e.g. 6 ... 

With respect to aromatic substrates, the Vilsmeier formylation reaction works well with electron-rich derivatives like phenols, aromatic amines and aromatic heterocycles like furans, pyrroles and indoles. However various alkenes are also formylated under Vilsmeier conditions. For example the substituted hexatriene 6 is converted to the terminal hexatrienyl aldehyde 7 in 70% yield ... 

Substitutions Rotating Pt Some phenols, aromatic amines... 

Recently, a kinetic study has been made of the substitution of diazotised sulphanilic acid in the 2 position of 4-substituted phenols under first-order conditions (phenol in excess) in aqueous buffer solutions at 0 °C131a. A rough Hammett correlation existed between reaction rates and am values, with p about -3.8 however, the point for the methoxy substituent deviated by two orders of magnitude and no explanation was available for this. The unexpectedly low p-factor was attributed to the high reactivities of the aromatic substrates, so that the transition state would be nearer to the ground state than for reaction of monosubstituted benzene derivatives. 

Resole syntheses entail substitution of formaldehyde (or formaldehyde derivatives) on phenolic ortho and para positions followed by methylol condensation reactions which form dimers and oligomers. Under basic conditions, pheno-late rings are the reactive species for electrophilic aromatic substitution reactions. A simplified mechanism is generally used to depict the formaldehyde substitution on the phenol rings (Fig. 7.21). It should be noted that this mechanism does not account for pH effects, the type of catalyst, or the formation of hemiformals. Mixtures of mono-, di-, and trihydroxymethyl-substituted phenols are produced. 

In a phenol, a hydroxyl group is attached directly to an aromatic ring. The parent compound, phenol itself, Cr,HsOH (4), is a white, crystalline, molecular solid. It was once obtained from the distillation of coal tar, but now it is mainly synthesized from benzene. Many substituted phenols occur naturally, some being responsible for the fragrances of plants. They are often components of essential oils, the oils that can be distilled from flowers and leaves. Thymol (5), for instance, is the active ingredient of oil of thyme, and eugenol (6) provides most of the scent and flavor of oil of cloves. 

The rate constant of Reaction 8.1 is much greater than the rate constant of Reaction 8.2, which means that antioxidants of this type can be used in very low concentrations with good effect. A typical thermoplastic would contain only 0.01-0.5% by mass of such an antioxidant. Typical compounds which work by this mechanism include substituted phenols and secondary aromatic amines. 

It can also be mentioned that polyphosphazenes substituted with aromatic groups, such as phenols or naphthols, can form inter- and intra- molecular excimers by coupling reaction of the planar aromatic rings of the substituents under illumination [467-471,473,725]. These species disappear as soon as the light is switched off. 

The steric bulk of the perfluoroalkyl group can be demonstrated by examining crystal structures of suitable compounds. For example, the crystal structure of the para-substituted phenol clearly shows the size of the C6F13 group with respect to the aromatic ring (Figure 3.5). 

It might be expected that the activating effect of p-NO2 on nucleophilic aromatic substitution would be related to the a value of the substituent. From various studies of nucleophilic aromatic substitution, Miller and Parker213 obtained a <7 value for /2-NO2 of 1.27, very close to the values based on the ionization of substituted phenols or anilinium ions (Section ELD). 

It has already been seen (see Section II,B and V,E) that vinylketene complexes of cobalt6,95 and chromium22 react with alkynes to produce cyclo-pentadienones, indanones, and substituted phenols. It has been shown108,109,144,145 that similar products may be derived from the alkyne adducts 247. Indeed, when alkyl or aryl substituted alkynes were reacted with vinylketene complex 221.e, a mixture of organic and organometallic products was isolated. In the cases where the alkyne is attached to an aromatic substituent, the expected alkyne adduct (247.h and 247.i) is isolated in low yield. However, when the vinylketene complex was treated... 

Clear evidence that covalent binding of substituted phenols and aromatic amines occurs to SPHS was provided by the presence of various phenoloxi-dases. 

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