Chlorination of phenol

Halogenation Bromination and chlorination of phenols occur readily even in the absence of a cata lyst Substitution occurs primarily at the position para to the hydroxyl group When the para position IS blocked ortho substitution is observed... 

Chlorination of Phenols. Industrially, the phenols are chlorinated without solvent. Chlorine reacts rapidly with phenol and with the chlorophenols, which makes it difficult to determine the relative reaction rates because of the superchi orin ation that sometimes results from an unsatisfactory chlorine dispersion. Studies have yielded the relative reaction rates iadicated ia Figure 1. 

Monochlorophenols. Chlorination of phenol [108-95-2] between 50 and 120°C gives a ortho ratio of 1.65. To improve the selectivity in the paia position, it is possible to use dialkyl sulfides, diaiyl sulfides (12), oi alkyl and aiyl sulfides combined. Sulfides are active only at low tempeiatuies (<50 C), because at high tempeiatuies the active species decomposes into sulfui and chlorine. 

Carr and England211 investigated the kinetics of the hydrochloric acid-catalysed chlorination of phenol by N-chloro-succinimide, -acetamide, and -morpholine, and found that the latter compound gave third-order kinetics, viz. 

The proper use of solvents is crucial for selectivity in fine ehemical processes, both homo-and heterogeneous ones. It has been claimed that phenols can be chlorinated in aprotic solvents to give the ortho product selectively in the presence of a small amount of an amine. Para chlorination of phenol is favoured by the presence of diphenylsulphide. 

Smith, J.G., Eee, S. F., and Netzer, A. Model stndies in aqneons chlorination the chlorination of phenols in dilnte aqneons... 

Sechrist, W.D. Chamberlain, N.S. Chlorination of phenol bearing mbber wastes. In Proceedings of 6th Industrial Waste Conference, Purdue University, Lafasette, IN, November 1951 396. 

Chlorination can result in unacceptable taste intensification, where potable water is concerned. This often originates in the chlorination of phenols present in trace amounts from industrial pollution. If economics permit, use of chlorine dioxide (Section 12.2) or ozone (Section 8.3) in place of chlorine will minimize taste intensification and will also avoid formation of carcinogenic chlorocarbons, notably chloroform. These carcinogens may form from chlorination of contaminants such as acetone, a commonly used solvent that finds its way into water supplies ... 

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). 

Pentachlorophenol. CAS 87-86-5f. This compound cun be produced by the chlorination of phenol in the presence of AICL. or by hydrolysis of hexachlorobenz.ene with NaOH in methanol. Pentachlorophenol is used as a wood preservative for poles, crossarms, and pilings and thus competes with creosote. 

In addition to influencing the rate of a reaction, pH may also control the products where alternate or sequential pH-dependent reactions take place. An example of this type of reaction is the chlorination of phenol. Lee and Morris (37) have shown that the chlorination of phenol proceeds by the stepwise substitution at the 2, 4, and 6 positions of the aromatic ring. The rate of each of these reactions depends on the product of phenate or chlorophenate anion and the hypochlorous acid concentrations. Since each phenolic compound has a slightly different acid dissociation constant, the species of chlorophenols that are formed depend on the pH of the solution. 

The role of polychlorinated gem-dichlorocyclohexadienones as reaction intermediates which can then produce desired me/a-chlorinated products or imdesired coupled products has been described.17 Chlorination of phenol and sometimes the ether complicates the hydrolysis of some primary alkyl phenyl ethers in concentrated aqueous perchloric acid solution.18 Unexpected chlorination has also been established in the reaction of 2-amino-5-chlorobenzophenone with HC1 in aqueous methanol (1 1 v/v), 2-amino-3,5-dichlorobenzophenone being amongst the products.19... 

Monochlorophenols represent an important class of environmental water pollutants of moderate toxicity to mammalian and aquatic life they possess relatively strong organoleptic effects, with taste thresholds of 0.1 pg/L (ppb). Their principal sources are the natural degradation of chlorinated herbicides (e.g., chlorophenoxyacetic acids), chlorination of phenolic substances in waste effluents, and chlorine treatment of drinking water. Of the three chlo-rophenols examined here, 3-chlorophenol exhibited the greatest resistance to sonolysis. 

The kinetics of the chlorination of phenol and 2-naphthol by l,3-dichloro-5,5-dimethylhydantoin (2) in aqueous acidic media have been interpreted10 in terms of an initial rate-limiting formation of a charge-transfer complex between the substrate and the chlorinating agent. A kinetic study of the chlorination of nine aryl ethers by 1-chlorobenzotriazole in acetic acid has also led to mechanistic conclusions.11... 

Gallard, H., and von Gunter, U. (2002a). Chlorination of Phenols Kinetics and Formation of Chloroform. Environ. Sci. Technol. 36, 884-890. 

In addition to mcd, V-BrPO catalyzes the chlorination of phenol red to tetrachlorophenol blue [64], Chlorination of amines (e.g., taurine, ammonia, valine, serine, leucine) is also catalyzed by V-BrPO forming the stable chloramine derivative, even in the presence of dihydrogen peroxide. Unlike bromamines, the chloramine is not reduced by dihydrogen peroxide, or is reduced only very slowly [53],... 

Phenol is the starting material for 2,4-dichlorophenoxyacetic acid via electrophilic aromatic substitution. Chlorination of phenol gives 2,4-dichlorophenol and the sodium salt of this compound is reacted with sodium chloroacetate and acidification gives 2,4-dichlorophenoxyacetic acid. 

Sherrington and coworkers161 have examined the chlorination of phenol by J-butyl hypochlorite in the presence of cross-linked polystyrenes substituted by pendant polymethylene chains terminated with anionic or cationic head groups, as well as some hydrophilic acrylic polymers, in four solvents water, methanol, 1,2-dichloroethane and xylene. The polymers exerted a significant influence on the chlorination, particularly in polar solvents. However, no changes in the regioselectivity of the chlorination, in comparison to homogeneous systems, was observed. 

While the process at the cathode always ends finally in withdrawal of oxygen or in taking up of hydrogen, the number of possible reactions at the anode—aside from solution-phenomena, which are without interest here—is a much greater one. For, each ion which is capable of substituting can pass into the reactive state at the anode and produce reactions which cannot be numbered with the real oxidations. In the first place numerous substitutions can occur in difficultly oxidizable bodies, especially aromatic compounds, for instance the chlorination of phenols and phthale ins, nitration of acids, diazotizing of amines, etc. Substitution and oxidation processes often occur simultaneously, as in the electrolytic formation of iodoform from alcohol. 

Organic materials are generally removed by addition of powdered activated carbon. The carbon may be added at any point in the plant, although it is advantageous to have as much contact as possible. The adsorption reaction is slow at room temperature, since it is diffusion-controlled. Oxidation with chlorine, potassium permanganate, or ozone may destroy tastes and odors or it may intensify them, depending upon the particular compounds involved. For example, chlorination of phenolic compounds leads to gready increased tastes and odors. For this reason, the system must be studied in the laboratory prior to water treatment. 

Oxidants Used in Water and Waste Technology A Few Case Studies 701 Chlorination of Phenols... 

Figure 11.14. Variation in versus pH for chlorination of phenol and various chlo-rophenol intermediates. (From Lee, 1967.)...

The formation of chlorophenols in water supplies can create severe odor and taste problems. The chlorination of phenols has already been described in Section 11.5. As has been shown in Figure 11.14, the reactants are HOCl (more electrophile than OCl ) and phenolate (PhO ) (a better nucleophile than phenol (PhOH)). 

J. G. Smith, S. Lee, and A. Netzer, Model Studies of Aqueous Chlorination The Chlorination of Phenols in Dilute Aqueous Solution , Water Research, v. 10, 1976, p. 98S-90. 

Dichlorophenol has been prepared by the chlorination of phenol with chlorine gas in the presence of nitrobenzene and fuming sulfuric acid, by the decomposition of the diazotate of 2,6 dichloro-4-aminophenol, eind by the decarboxylation of 3,5-dichloro-4-hydroxybenzoic acid in quinoline or dimethyl-aniline. ... 

Properties Colorless to yellow-brown liquid unpleasant, penetrating odor. Bp 175C, fp 9.3C, d 1.265 (15.5C), flash p 225F (107C). Very soluble in water soluble in alcohol, ether, and aqueous sodium hydroxide volatile with steam. Combustible. Derivation Chlorination of phenol. 

Properties White crystals (yellow or pink when impure) unpleasant penetrating odor. Bp 217C, mp 42-43C, d 1.306, refr index 1.5579 (40C), flash p 250C (121C). Slightly soluble in water soluble in benzene, alcohol, and ether. Volatile with steam. A 1% solution is acid to litmus. Combustible. Derivation Chlorination of phenol, from chlorani-line through the diazonium salt. 

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