Hydroxyl phenolic compounds

We 11 Start by discussing m more detail a class of compounds already familiar to us alcohols Alcohols were introduced m Chapter 4 and have appeared regularly since then With this chapter we extend our knowledge of alcohols particularly with respect to their relationship to carbonyl containing compounds In the course of studying alco hols we shall also look at some relatives Diols are alcohols m which two hydroxyl groups (—OH) are present thiols are compounds that contain an —SH group Phenols, compounds of the type ArOH share many properties m common with alcohols but are sufficiently different from them to warrant separate discussion m Chapter 24... 

Phenolic compounds are commonplace natural products Figure 24 2 presents a sampling of some naturally occurring phenols Phenolic natural products can arise by a number of different biosynthetic pathways In animals aromatic rings are hydroxylated by way of arene oxide intermediates formed by the enzyme catalyzed reaction between an aromatic ring and molecular oxygen... 

Campbell LM, DCG Muir, DM Whittle, S Backus, RJ Nostrum, AT Fisk (2003) Hydroxylated PCBs and other chlorinated phenolic compounds in lake trout (Salvelinus namaycush) blood plasma from the Great Lakes region. Environ Sci Technol 37 1720-1725. 

Most phenolic compounds are readily oxidized at carbon electrodes. The oxidation potentials vary widely depending upon the number of ring hydroxyl groups and their positions on the ring. Many compounds of biomedical and industrial interest are phenolic and LCEC based trace determinations are quite popular. 

How the aliphatic monomers are incorporated into the suberin polymer is not known. Presumably, activated co-hydroxy acids and dicarboxylic acids are ester-ified to the hydroxyl groups as found in cutin biosynthesis. The long chain fatty alcohols might be incorporated into suberin via esterification with phenylpro-panoic acids such as ferulic acid, followed by peroxidase-catalyzed polymerization of the phenolic derivative. This suggestion is based on the finding that ferulic acid esters of very long chain fatty alcohols are frequently found in sub-erin-associated waxes. The recently cloned hydroxycinnamoyl-CoA tyramine N-(hydroxycinnamoyl) transferase [77] may produce a tyramide derivative of the phenolic compound that may then be incorporated into the polymer by a peroxidase. The glycerol triester composed of a fatty acid, caffeic acid and a>-hydroxy acid found in the suberin associated wax [40] may also be incorporated into the polymer by a peroxidase. 

The result obtained by GC-MS, with the same SPME conditions, from the black thick balm of a crocodile mummy (sample 1400, Musee Guimet, Lyon, France) is presented in Figure 10.11. The composition of the extract is close to that of sample 1998 but phenolic compounds were not detected. The GC-MS chromatogram obtained with the same substance after acid methanolysis and silylation is presented in Figure 10.12. Except for the sesquiterpenoids eluted between 10 min and 22 min, the observed compounds originate from a beeswax. The biomarkers of this substance are hexadecanoic acids hydroxylated in position 14 or 15 and long chain hydrocarbons, acids and alcohols eluted between 50 min and 90 min. Diterpenoid or triterpenoid resin components are not observed. 

In Table 15 are recorded the dissociation constants of certain phenolic compounds. From these data it becomes obvious that the introduction of aldehyde groups, or other substituents, changes the dissociation constant of phenolic hydroxyls by over one-hundred fold. Moreover, oxidation studies carried out in this laboratory have shown that the native lignins from bagasse, white Scots pine and birch contain... 

Addition of a hydroxyl group to a six-carbon benzene ring yields 1-hydroxybenzene or phenol, which forms the basis of all subsequent phenolic compounds (Fig. 3.2). Resorcinol or 1,4-dihydroxybenzene is formed when a second hydroxyl group is added at the 4-position on the benzene ring. 

The addition of hydroxyl radicals to benzene ring of alkylaromatic hydrocarbon gives phenolic compounds. Phenols retard oxidation, terminating the chains (see Part II). 

Now, we will consider the major reactions of peroxynitrite with biomolecules. It was found that peroxynitrite reacts with many biomolecules belonging to various chemical classes, with the bimolecular rate constants from 10-3 to 10s 1 mol 1 s 1 (Table 21.2). Reactions of peroxynitrite with phenols were studied most thoroughly due to the important role of peroxynitrite in the in vivo nitration and oxidation of free tyrosine and tyrosine residues in proteins. In 1992, Beckman et al. [112] have showed that peroxynitrite efficiently nitrates 4-hydroxyphenylacetate at pH 7.5. van der Vliet et al. [113] found that the reactions of peroxynitrite with tyrosine and phenylalanine resulted in the formation of both hydroxylated and nitrated products. In authors opinion the formation of these products was mediated by N02 and HO radicals. Studying peroxynitrite reactions with phenol, tyrosine, and salicylate, Ramezanian et al. [114] showed that these reactions are of first-order in peroxynitrite and zero-order in phenolic compounds. These authors supposed that there should be two different intermediates responsible for the nitration and hydroxylation of phenols but rejected the most probable proposal that these intermediates should be NO2 and HO. ... 

The study of photolysis of PBBs in the aqueous phase is more relevant to natural environmental situations than photolysis in proton-donating organic solvents. It was suggested that the photolysis of PBBs in aqueous solution would proceed by oxidative process of photohydroxylation, leading to the formation of phenolic compounds (Norris et al. 1973). However, photolysis of 2,4-dibromo-and 2,3, 4, 5-tetrahromobiphenyl in acetonitrile-water solution showed that debromination was the major reaction (Ruzo et al. 1976). No evidence of the formation of hydroxylated species (phenolic products) was found (Ruzo et al. 1976). 

It is well known 113,14 20 25> that the addition of hydroxyl-containing compounds (water, alcohols, phenols, acids) considerably promotes the interaction of epoxy compounds with amines and other nucleophilic reagents. In this case, the epoxy ring carbon atom becomes more sensitive to nucleophilic attack. The reaction proceeds through a trimolecular transition state initially suggested by Smith26 27) for the reactions of epoxy compounds with amines2... 

In some instances, combinations of Cig and silica columns are also used for better purification of the crude extracts (431, 445). A combination of Cg, silica, and amino solid-phase extraction columns has been successfully employed to fractionate anabolic and catabolic steroid hormone residues from meat in polar and nonpolar neutral and phenolic compounds, and to purify further each fraction effectively (452). Another combination of two solid-phase extraction columns, one using a graphitized carbon black sorbent and the other Amberlite resin in the hydroxyl form, allowed neutral anabolics to be isolated and separated from acidic anabolics and their metabolites (453). A combination of basic alumina column placed in tandem with an ion-exchange column has also been applied for the purification of the crude extracts in the determination of diethylstilbestrol and zeranol (427), and estradiol and zeranol in tissues (450). 

Experiments were also carried out at 80 and lOO C. According to our observations at these high temperatures, solid- phase chemical transformations may take place between certain flavor constituents and cyclodextrin hydroxyls/monoterpene alcohols and phenolic compounds appear as a result of a solid-phase transacetylation of terpeneaoetates and phenyl-acetates with the simultaneous formation of cyclodextrin-acetates/. Long term heat treatments of cyclpdextrin-flavor complexes should not be run above 6o°C in order to avoid such phenomena. 

Oxidations. This peracid has been known since 1910 but a report of its use in oxidation of organic compounds has appeared only recently. It hydroxylates phenol. 

Phenols. Phenolic compounds are used in very large quantities for a variety of industrial purposes. They may also be formed in the environment by abiotic (e.g., hydroxylation in the atmosphere see Chapter 16) or biological processes (Chapter 17). A prominent example for the latter case is the formation of 4-nonylphenol from the microbial... 

The pseudo-first order rate constants (resp. coefficients) for the direct reaction of some compounds may almost be in the order of typical hydroxyl rate constants (kR > 10 M s ), due to high concentrations of the pollutants as well as mass transfer enhancement. For example, Sotelo et al. (1991) measured values of 6.35 106 and 2.88 106 M l s"1 for the dissociating hydroxylated phenols, resorchinol (1,3-dihydroxybenzene) and phlorogluci-nol (1,3,5-tn hydroxybenzene) respectively (pH = 8.5 and T= 20 °C). 

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