4-Chlorophenol and its intermediates

Table II. Mass Spectral Data for Acetylated 4-Chlorophenol and Its Intermediates...

Figure 6. Concentration changes of 4-chlorophenol and its intermediates. Experimental conditions 4-chlorophenol = 10 3 M, TiO2 = 1 g/L, pH = 4.0, 1 =...

Dynamics of the Reaction Network. Information on the concentration changes of 4-chlorophenol and its intermediates (4-chlorocatechol, 4-chlororesorcinol, hydroquinone, and hydroxyhydroquinone) allows us to perform some dynamic analysis of the photocatalytic oxidation of 4-chlorophenol. Scheme IV shows a reaction network that can be established to describe the overall mineralization of 4-chlorophenol. According to this reaction network, 4-chlorophenol (4-CP) first decomposes to 4-chlororesorcinol (4-CRE), 4-chlorocatechol (4-CCA), or hydroquinone (HQ) 4-chlorocatechol is the major primary product. Further oxidation of the primary intermediates yields hydroxyhydroquinone (HHQ), as the secondary intermediate, which is readily mineralized to carbon dioxide. For simplicity, a pseudo-first-order expression was used to model the dynamics of the reaction network (eqs 9-14). 

Seven reaction constants (k -k-j) are used to describe the formation and degradation of 4-chlorophenol and its intermediates. Equations 15-19 list the analytical solutions of equations 9-14, respectively. 

A complete pathway for the mineralization of 4-chlorophenol can be described by the hydroxylation reaction through dechlorination, ring cleavage, and mineralization. Reaction kinetics of the 4-chlorophenol and its intermediates can be reasonably well approximated by using a complex parallel and consecutive first-order reaction mechanism. 

Chemical Analysis. Gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) techniques were used to analyze 4-chlorophenol and its oxidation intermediates. For GC-MS analysis, the samples were acetylated in pyridine. The samples were first evaporated to dryness. Then 200 xL of pyridine and 200 (xL of acetic anhydride were added to the dry residue. The samples were heated at 65 °C for 2-3 h to ensure the complete acetylation reaction, and then gently evaporated to dryness in a nitrogen stream. Finally, the residue was redissolved in 0.1 mL of hexane for GC analysis. A GC (HP model 5890) equipped with mass selective detector (HP model 5971) and SPB-5 capillary column (Supelco Co., PA., 25- X 0.2-mm i.d. X 0.33-p.m film thickness) was used. To separate different intermediate products, various oven-temperature programs were performed. The GC-MS interface line was maintained at 300 °C. The mass-... 

Salicylate is an intermediate in the metabolism of PAHs including naphthalene and phen-anthrene, and its degradation involves oxidation to catechol. The hydroxylase (monooxygenase) has been extensively studied (references in White-Stevens and Kamin 1972) and in the presence of an analog that does not serve as a substrate, NADH is oxidized with the production of H2O2 (White-Stevens and Kamin 1972). This uncoupling is characteristic of flavoenzymes and is exemplified also by the chlorophenol hydroxylase from an Azotobacter sp. that is noted later. 

An alternative method to make PAEs is the acyclic diyne metathesis (ADIMET) shown in Scheme 2. It is the reaction of a dipropynylarene with Mo(CO)6 and 4-chlorophenol or a similarly acidic phenol. The reaction is performed at elevated temperatures (130-150 °C) and works well for almost any hydrocarbon monomer. The reaction mixture probably forms a Schrock-type molybdenum carbyne intermediate as the active catalyst. Table 5 shows PAEs that have been prepared utilizing ADIMET with these in situ catalysts . Functional groups (with the exception of double bonds) are not well tolerated, but dialkyl PPEs are obtained with a high degree of polymerization. The progress in this field has been documented in several reviews (Table 1, entries 2-4). Recently, a second generation of ADIMET catalyst has been developed that allows... 

The inwitro metabolites of chlorobenzene are o-chlorophenol, m- chlorophenol, and p-chlorophenol the proportions differ according to the source of the mono-oxygenase system and its state of purity (Selander et al. 1975). The o- and p-chlorophenols result from isomerization of the intermediate 3-and 4-chlorobenzene oxides, respectively. The formation of m-chlorophenol appears to occur via a direct oxidative pathway (Oesch et al. 1973). In vitro conjugation of the arene oxide with glutathione or hydration is not a significant pathway (Selander et al. 1975). 

To this purpose, in a study on the photocatalytic degradation of 4-chlorophenol, Camera-Roda and Santarelli [89] proposed an integrated system in which photocatalysis is coupled with pervaporation as process intensification for water detoxification. Pervaporation represents a useful separation process in the case of the removal of VOCs and in this study it is used to remove continuously and at higher rate the organic intermediates that are formed in the first steps of the photocatalytic degradation of the weakly permeable 4-CP. 

A hr dm 3. Recently, the electrochemical incineration of p-benzoquinone in acetate buffer has been reported by Houk et al. [54]. The cell was similar to that above cited for 4-chlorophenol oxidation (see Sec. III.B), with a Ti or Pt anode coated with a film of the oxides of Ti, Ru, Sn, and Sb. These anodes are stable but somewhat less efficient than an Fe(III)-doped Pb02 film coated on Ti employed in a previous work [55], The COD of 50 mL of 100 ppm / -benzoquinone decreased from an initial value of 190 to 2 ppm during 64 hr of electrolysis at 1 A. The major intermediate products identified were hydroquinone and aliphatic acids including maleic, succinic, malonic, and acetic acids. The suggested reaction sequence is given in Fig. 13, where succinic acid is obtained from a cathodic reduction of maleic acid, which is formed from the breakdown of the dihydroxylated derivative generated by an attack of adsorbed hydroxyl radicals onto p-benzoquinone. Further mineralization of succinic acid occurs via its consecutive oxidation to malonic and acetic acids. 

It is known that the metabolism of chlorobenzene in vivo leads to a variety of products including 4-chlorophenol, 4-chlorocatechol, 4-chloro-phenylmercapturic acid, and 4-chloro-l,2-fmn.s-dihydrodihydroxybenzene (26). When the metabolism of 4-deuterochlorobenzene was studied in this laboratory, 3-chlorophenol and an O-methylated chlorocatechol were isolated in addition to the products reported above (19). The products isolated, the proposed intermediates, and their deuterium contents are summarized in Figure 7. An intermediate, X, is postulated for this scheme... 

Some studies reported enhancements in photoactivity in the presence of a small amount of rutile phase [122-124]. Even a mechanical mixture of anatase and rutile showed much higher photoactivity for naphthalene oxidation than either pnre anatase or rutile powders [123,124]. The P25 powder is produced from TiCl4 in a flow reactor [122]. Based on a detailed investigation by x-ray diffraction (XRD) and micro-Raman spectroscopy, the rutile (formed directly in the flame) was fonnd to be covered by anatase [122,124]. However, another study based on transmission electron microscopy (TEM) with selected-area electron diffraction reported the presence of separate particles of anatase and rutile in P25 [125,126]. Diffuse reflectance spectra of P25 could be reproduced by a mechanical mixture of anatase and rutile powders, and particles of pure rutile phase were isolated from P25 upon HF treatment. Photoactivity for the decomposition of 4-chlorophenol in water was compared on four commercial photocatalysts, applying criteria of (a) initial rate of pollutant disappearance, (b) amount of intermediate products formed, and (c) time necessary to achieve total mineralization [127]. Based on criterion (c), P25 was concluded to be the most efficient photocatalyst even though it contains 20% rutile and has a moderate BET surface area (ca. 50 m /g). It was also reported to have a higher photoactivity than catalyst All in the degradation of reactive black 5 (an azo-dye) [128]. 

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