Phenol and Other Aromatics

Phenol is mainly derived from benzene, but can also be obtained from propylene. It serves as the basis for several important monomers, in addition to its direct use as a reactive monomer via condensation with formaldehyde. This first man-made polymer, phenol-formaldehyde, appeared in 1901 and bears the trademark Bakelite , after its inventor Bakeland. By reacting phenol with acetone, bis-phenol A is obtained. This serves as the basis for the manufacture of epoxy and polycarbonate. 

Urea is obtained by the reaction between ammonia (NH3) and carbon dioxide 

As stated previously, condensation between urea and formaldehyde leads to the formation of the polymer urea-formaldehyde. A third member in this series is the melamine, which will also react with formaldehyde leading to the polymer melamine-formaldehyde. Melamine may also be derived by thermal decomposition of urea. 

Both monomers for the production of Nylon 6-6 (one of the earliest polyamides) may be synthesized from benzene adipic acid and hexamethylene diamine. 

Phthalic acids (iso, tera and ortho) are manufactured in the petrochemical industry from the three isomers of xylene. These acids and the corresponding anhydrides are the major basis for polyesters and alkyds. 

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Fig. 8.1 Number of publications on electrochemical treatment of the major classes of organics at BDD (a) phenol, (b) aliphatics, (c) substituted phenols and other aromatics, (d) Drugs and pesticides, (e) Surfactants, (f) Dyes, (g) Real wastewaters...

Regarding fhe kinefic modeling, few contributions propose kinetic models for fhe PC oxidation of phenol and other aromatics (Chen and Ray, 1998, 1999 Li et al., 1999b Wei and Wan 1992 ), with kinetic models being based mainly on the initial rates of reacfion only. Such models fail to account for fhe formafion of fhe differenf reaction intermediates, which may play an important role in the overall mineralization rate. More recently, Salaices et al. (2004) developed a series-parallel kinetic model based on observable aromatic intermediates. This model was applied to a wide range of pH, phenol concenfrafion, and cafalysf t)q)e. In this model, however, some steps... 

Once the kinetic reaction scheme for the impromoted FC reaction of phenol and other aromatic species was determined, the next step was to... 

The usual method of acetylation by means of acetic anhydride or a mixture of acetic acid and anhydride is to reflux the hydroxy compound and the anhydride for 10-15 minutes. In the present instance, the temperature is kept low by the presence of ice and the hydrolysis of the anhydride is inhibited, permitting it to react with the hydroxy compound. Phenol and other aromatic hydroxy compounds can be acetylated by this method. 

Later, Tressl et al. (1976) also proceeded to the thermic degradation (2 h, 200 JC) of ferulic acid (H.87) and identified the same phenols as Fiddler et al., plus 4-isopropylguaiacol and vanillin alcohol (4-hydroxy-3-methoxybenzenemethanol) which have not been found in coffee. For isoeugenol (H.38), the formula is written as the (E)-( trans -) isomer, but nothing was specified in the text. Tressl et al. (1976) also published the results of thermal decomposition of cinnamic, p-coumaric (H.84) and sinapic (H.90) acids. Many of the simple phenols (and other aromatic compounds) formed have also been identified in roasted coffee volatiles. A thermic fragmentation of quinic acid (E.62) has shown that simple acids, phenols and polyphenols originate from this precursor (Tressl et al., 1978a). 

There are several reports on the destruction of phenols and other aromatics in wastewaters by ultraviolet (UV) light-catalyzed oxidation. Hydrogen peroxide and ozone have been used as oxidizing agents. McShea and co-workers... 

Ozone also reacts with low concentrations of NO2 to form (Equation 4.24) an oxidant that is important in nighttime atmospheric chemistry, the nitrate radical, NO3. This species, which is unstable in the presence of light, reacts fairly rapidly with many compounds such as alkenes (including terpenes), phenols and other aromatic compounds,... 

Besides that, electrochemical methods can be used to activate aromatic substrates by means of redox-umpolung procedure, which makes possible to cOTivert imreactive arenes, azoles, phenols, and other aromatic compounds, bearing electron-donating groups, into the intermediate radical cation species, which are able to react with nucleophiles (Scheme 61) [47, 187]. 

The first step of the cycle [Sch. 7, (1)] involves the removal of two electrons from the protein, one coming from the metal ion and the other usually coming from the porphyrin moiety, which contains the iron [257]. The intermediate thus generated is known as Compound I. This species that contains two oxidizing equivalents of the protein can oxidize two substrate molecules. The first step, which is described in Eq. (2) of Sch. 7, involves formation of Compound II via reduction of the porphyrin jr-cation radical, while the second step leads to the resting state of the protein via a reaction between Compound II and a second substrate molecule [Sch. 7, (3)]. Both Compounds I and II are sufficiently stable so that several spectral methods have been used to determine the electronic structure of these species [258-262]. Kinetic studies for formation of these compounds have also been carried out [263-269]. The rate-limiting step under steady state conditions is most often the reduction of Compound II [266-271], a result that is accounted for by an easier reduction of the porphyrin radical as compared with the Fe(IV) center in Compound II. Traditional substrates for peroxidases are phenols and other aromatic dyes, although in cytochrome c peroxidase the substrate is ferro-cytochrome c [272, 273]. 

Alkylphenol ethoxylate (APE) surfactants make up approximately 10% of overall consumption. While effective in many industrial applications, they face a number of environmental challenges that could greatly reduce their use in the future. Of major importance are questions concerning their relatively slow rate of biodegradation and the possible toxicity of degradation intermediates, especially phenols and other aromatic species. In the United States and western Europe, many detergent manufacturers have voluntarily discontinued their use in household products. 

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