Phenolic compounds/units

At present, chlorine dioxide is primarily used as a bleaching chemical in the pulp and paper industry. It is also used in large amounts by the textile industry, as well as for the aching of flour, fats, oils, and waxes. In treating drinking water, chlorine dioxide is used in this country for taste and odor control, decolorization, disinfection, provision of residual disinfectant in water distribution systems, and oxidation of iron, manganese, and organics. The principal use of chlorine dioxide in the United States is for the removal of taste and odor caused by phenolic compounds in raw water supplies. 

Phenol, the simplest and industrially more important phenolic compound, is a multifunctional monomer when considered as a substrate for oxidative polymerizations, and hence conventional polymerization catalysts afford insoluble macromolecular products with non-controlled structure. Phenol was subjected to oxidative polymerization using HRP or soybean peroxidase (SBP) as catalyst in an aqueous-dioxane mixture, yielding a polymer consisting of phenylene and oxyphenylene units (Scheme 19). The polymer showed low solubility it was partly soluble in DMF and dimethyl sulfoxide (DMSO) and insoluble in other common organic solvents. 

Since lignins are polymers of phenolics and are major plant constituents with resistance to microbial decomposition, they are the primary source of phenolic units for humic acid synthesis (178, 179). Once transformed, these humic acids become further resistant to microbial attack and can become bound to soils (180) form interactions with other high molecular weight phenolic compounds (ex. lignins, fulvic acids) and with clays (181) and influence the biodegradation of other organic substrates in soils (182, 183). 

Most of the odours coming from livestock production units are associated with the biological degradation of the animal wastes (35), the feed and the body odour of the animals (1). Volatile fatty acids and phenolic compounds were found to contribute mostly to the strong, typical odour of animal houses by the help of sensory evaluations parallel to the chemical analysis (29), (30). 

At the Sikes Disposal Pits Superfund site in Crosby, Texas, an HTTS unit was used to treat hazardous organic compounds including phenolic compounds, xylene, benzene, polynuclear aromatic hydrocarbons (PAHs), toluene, creosote, dichloroethane (DCA), vinyl chloride, and naphthalene (D184581, p. 216). The estimated treatment cost was 115 million including approximately 20 million in capital costs and 95 million in operation and maintenance costs. The estimated total cost for thermal treatment was 81 million. A total of 496,000 tons of soil and debris were incinerated. This corresponds to a total unit cost for incineration of 230 per ton and a unit cost of 160 per ton for thermal treatment (D184581, p. 227). 

Reactions of anthocyanins and flavanols take place much faster in the presence of acetaldehyde that is present in wine as a result of yeast metabolism and can also be produced through ethanol oxidation, especially in the presence of phenolic compounds, or introduced by addition of spirit in Port wine technology. The third mechanism proposed involves nucleophilic addition of the flavanol onto protonated acetaldehyde, followed by protonation and dehydration of the resulting adduct and nucleophilic addition of a second flavonoid onto the carbocation thus formed. The resulting products are anthocyanin flavanol adducts in which the flavonoid units are linked in C6 or C8 position through a methyl-methine bond, often incorrectly called ethyl-link in the literature. 

Figure 6.5 shows the structures of tra 5-cinnamic acid and four cinnamic acid derivatives (phenolic compounds) reported to be present in potatoes. Because potatoes are one of our major food plants, we validated with the aid of HPLC and LC/MS the content and distribution of antioxidative phenolic compounds in parts of the potato plant, in potato tubers, in the peel and flesh of tubers, in potatoes sold commercially in Korea and the United States, and in home-processed potatoes. The following discussion, based on our own studies, is followed by a brief overview of analytical methods for potato phenolic compounds by other investigators. 

Table 6.6 Content of phenolic compounds of freeze-dried powders prepared from fresh potatoes sold in the United States... 

Berhow MTB, Kanes K, Vandercook C. Survey of Phenolic Compounds Produced in Citrus. Technical Bulletin Number 1856. United States Department of Agriculture, 1998. 

Early results with enzymes in organic solvents demonstrated that enzymes work best in organic solvents if there are lyophilized from aqueous solution at or near the optimum pH value in water (seeSection 12.4, below). Any specific pH effect of organic solvents, however, can be dismissed it was found that the pKa of amino, carboxylic, and phenolic compounds does not differ by more than 0.3 units in the aqueous and lyophilized states (Costantino, 1997). 

Figure 2.20. Transformation of catechol by laccase (0.4 units mT1), tyrosinase (0.4 units ml-1) and birnessite (600ugml 1) after repeated addition of substrate. Reprinted from Pal, S., Bollag, J.-M., and Huang, P. M. (1994). Role of abiotic and biotic catalysts in the transformation of phenolic compounds through oxidative coupling reactions. Soil Biol. Biochem. 26, 813-820, with permission from Elsevier.

A holistic view regarding the mode of action of phenolic allelochemicals recognizes the effects of these compounds as one of several stresses on plants. Complexes of the individual phenolic compounds become the effective unit causing allelopathy. In summary, explanations of the mode of action of phenolic allelochemicals must take into account that these compounds act in concert, the different compounds vary in toxicity but they have similarities in their mechanisms of action, and they all appear to disrupt cellular functions at multiple target sites. 

The solvent often exerts a profound influence on the quality and shape of the spectrum. For example, many aromatic chromophores display vibrational fine structure in non-polar solvents, whereas in more polar solvents this fine structure is absent due to solute-solvent interaction effects. A classic case is phenol and related compounds which have different spectra in cyclohexane and in neutral aqueous solution. In aqueous solutions, the pH exerts a profound effect on ionisable chromophores due to the differing extent of conjugation in the ionised and the non-ionised chromophore. In phenolic compounds, for example, addition of alkali to two pH units above the pKa leads to the classical red or bathochromic shift to longer wavelength, a loss of any fine structure, and an increase in molar absorptivity (hyper chromic... 

The vinylphenol unit was similaily introduced to imidazole-containing copolymers cf. Section 4-4), but the incorporation resulted only in the increase of hydro-phobicity of the polymer catalyst On the other hand, some rate enhancements were observed due to phenolic compounds bound onto Bl-VP copolymers, and cooperative catalysis for die intraoanplex reactirxi was implied (71). 

Total wine polyphenols are oxidised by the Folin-Ciocalteu reagent - composed of a mixture of phosphotungstic and phosphomolybdic acids which are reduced by the oxidation of the phenols, forming a mixture of blue oxides of tungsten and molybdenum. The blue coloration has an absorption maximum at approximately 750 nm, the intensity of which is proportional to the level of phenolic compounds present in the wine. The sequential analyser method is a direct automation of the manual method and results are expressed as a unit-less index. 

There is a common feature of the polymer composition in PC, PPO, epoxy and phenol-formaldehyde resin, all contain phenoxy moieties in their repeating unit. Hence, it is not unexpected that the major pyrolysis products of these plastics are phenols. The reason of the production of phenolic compounds is the higher bonding energy of the C-0 linkage in the phenoxy moiety related to that of other bonds along the polymer chain. 

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