Chlorination of 2,4,6-trichlorophenol

Detection of the polychlorinated gem-dichlorocyclohexadienones was performed by means of numerous tests and only one example of the chlorination of 2,4,6-trichlorophenol in the presence of A1C13 (ref. 12) is described below ... 

Chlorination of 2,4,6-trichlorophenol to tetrachlorophenol or pentaclorophenol is usually performed with an acid (refs. 12, 13). For this reason it was important to observe the reactivity of polychlorinated gem-dichlorocyclohexadienones in chlorophenols in the presence of acids. To do this we studied the behaviour of a mixture containing the following components at 70°C ... 

Fig. 13. Formation of chlorinated benzoquinones during chlorination of 2,4,6-trichlorophenol...

Chloranil (42), 2,3,5,6-tetrachloro-l,4-benzoquinone, is prepared either by the oxidative chlorination of 2,4,6-trichlorophenol or by the oxidative hydrolysis of pentachlorophenol. 

Dehalogenation of chlorinated arenes.3 Palladium (10%) on carbon catalyzes the rapid transfer of hydrogen from ammonium formate to aryl chlorides to provide the parent arene. Dehalogenation of 2,4,6-trichlorophenol proceeds through di-chloro- and chlorophenol and is complete within 10 minutes at ambient temperature and pressure. 

The synthesis of chlorarul [118-75-2] (20) has been improved. The old processes starting from phenol or 2,4,6-trichlorophenol have been replaced by new ones involving hydroquinone chlorination. These processes allow the preparation of chlorarul of higher purity, avoiding traces of pentachlorophenol. Different types of chlorination conditions have been disclosed. The reaction can be performed according to the following stoichiometry, operating with chlorine in aqueous acetic acid (86,87), biphasic medium (88), or in the presence of surfactants (89). 

Oxidation of saligenin with chromic acid or silver oxide yields saUcyladehyde as the first product. Further oxidation results in the formation of sahcyhc acid, which is also obtained when saligenin is heated with sodium hydroxide at 200—240°C. Chlorination of an aqueous solution of the alcohol gives 2,4,6-trichlorophenol, and bromination in an alkaline medium yields 2,4,6-tribromophenol and tribromosaligenin. When saligenin is heated with one mole of resorcinol in the presence of anhydrous zinc chloride, 3-hydroxyxanthene forms. 

In the chlorination of 2,4-dichlorophenol it has been found that traces of amine (23), onium salts (24), or triphenylphosphine oxide (25) are excellent catalysts to further chlorination by chlorine ia the ortho position with respect to the hydroxyl function. During chlorination (80°C, without solvent) these catalysts cause traces of 2,4,5-trichlorophenol ( 500 1000 ppm) to be transformed iato tetrachlorophenol. Thus these techniques leave no 2,4,5-trichlorophenol ia the final product, yielding a 2,4,6-trichlorophenol of outstanding quaUty. The possibiUty of chlorination usiag SO2CI2 ia the presence of Lewis catalysts has been discussed (26), but no mention is made of 2,4,5-trichlorophenol formation or content. 

The photocatalytic activity of ZnO nanomaterials for the degradation of some organic pollutants in water [173] (e.g., dyes [174]) was explored by several groups to achieve environmental benefits. Recent studies have indicated that ZnO can be used under acidic or alkaline conditions with the proper treatment [175,176]. ZnO nanomaterials were used as photocatalysts for the degradation of phenol [177] and chlorinated phenols such as 2,4,6-trichlorophenol [178]. ZnO nanomaterials were also used for the degradation of Methylene Blue [179], direct dyes [180], Acid Red [181], and Ethyl Violet [182],... 

Chlorinated phenols have been traditionally applied in the production of wood preservatives, insecticides and disinfectants. Common chlorinated phenols found in wood preservatives are 2,3,4,6-tetrachlorophenol (TeCP), 2,4,6-trichlorophenol... 

In a dilute aqueous solution at pH 6.0, 2,4,6-trichlorophenol reacted with an excess of hypochlorous acid forming 2,6-dichlorobenzoquinone (18% yield) and other chlorinated compounds (Smith et al., 1976). Based on an assumed 5% disappearance after 330 h at 85 °C, the hydrolysis half-life was estimated to be >40 yr (Ellington et al., 1988). 

Chlorination and chloramination of a widely used antibacterial additive, triclo-san, which is used in many household personal care products, results in the formation of chloroform, 5,6-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5-dichloro-2-(2,4-dichlorophenoxy)phenol, 4,5,6-trichloro-2-(2,4-dichlorophenoxy)phenol, 2, 4-dichlorophenol, and 2,4,6-trichlorophenol [119]. The reaction of triclosan with monochloramine is slow, however, compared to chlorine [120]. The chlorophenox-yphenols are formed via bimolecular electrophilic substitution of triclosan. 

Exon JH, Roller LD Toxicity of 2-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol. In Proceedings of 5th Conference Water Chlorination Chem Environ Impact Health, pp 307-350, 1985... 

Exon JH, Koller ED Toxicity of 2-chlorophe-nol, 2,4-dichlorophenol and 2,4,6-trichlorophenol. In Jolley RL et al. (eds) Water Chlorination, Vol. 5, Chemistry, environmental impact and health effects. Chelsea, MI, Lewis Publishers, 1985... 

Reactions. -Hydroxybenzoic acid undergoes the typical reactions of the carboxyl and hydroxyl moieties. When heated above its melting point, it decomposes almost completely into phenol and carbon dioxide. It reacts with electrophilic reagents in the predicted manner and does not undergo the Friedel-Crafts reaction. Nitration, halogenation, and sulfonation afford the 3-substituted products. Heating -hydroxybenzoic acid with 8 IV-nitric acid results in a 95% yield of picric acid. In a similar fashion, treatment with chlorine water yields 2,4,6-trichlorophenol (50). 

Trichlorophenol may enter the environment as emissions from combustion of fossil fuels and incineration of municipal wastes, as well as emissions from its manufacture and use as a pesticide, and in the use of 2,4-D, in which it is an impurity. Significant amounts may result from the chlorination of phenol-containing waters (United States National Library of Medicine, 1997). 

Chlorinated phenols are among the most important contaminants in the environment (aqueous systems and soils) due to their widespread use in industry and agriculture and for domestic purposes for over 50 years. It is well-known that chlorophenols are toxic at low levels. The more highly chlorinated phenols such as trichlorophenols and pentachlorophenol are also persistent. Five of the chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, 2,4,6-trichlorophenol and pentachlorophenol) have been classified as priority pollutants by the US Environmental Protection Agency (EPA). 

Sulfonated Fe and Mn phthalocyanines are catalysts for the oxidative degradation of chlorinated phenols such as 2,4,6-trichlorophenol, a contaminant from paper mills that use chlorine for bleaching. Fe-tetrasulfophthalo-cyanine supported on poly(vinyl-4-methylpyridinium) converts 2,4,6-trichlorophenol with the K+ salt of Caro s acid, KHSO5, or H2O2 as the oxidant (112) ... 

A phenol derivative, phenolphthalein is prepared by the reaction of phenol with phthalic anhydride in the presence of sulphuric acid and used as an indicator for acidity or alkalinity. Chlorinated phenol is much safer than phenol. Chlorine gas reacts with phenol to add one, two or three chlorine atoms and to form, respectively, chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol . The chlorination of phenol proceeds by electrophilic aromatic substitution. The latter two molecules are less soluble in water than phenol and appear to be a stronger antiseptic than phenol. Interestingly, in the first half of the past century, a bottle of antiseptic chlorophenols was a common attribute as a medicine in many homes. Its solution was used for bathing cuts, cleaning grazes, rinsing the mouth and gargling to cure sore throats. Nevertheless, it was revealed that its solution likely contains dioxins. 

Chlorinated aromatic compounds such as 2,4,6-trichlorophenol (278) are well known recalcitrant pollutants because of their slow biodegradation by microorganisms. Hydrogen peroxide oxidation of (U- C)-278 catalyzed by FePcS (iron tetrasulfophthalocyanine) was... 

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