Chlorophenols

6 Other halogenated organic compounds of environmental concern 3.3.6.1 Chlorophenols 

Initially, the main concern with commercial PCP products was the contamination with PCDDs (albeit not TCDD) as by-products from the manufacturing process, and many of the envirotoxic effects originally attributed to PCP have been shown to be effects of the dioxins. Toxic actions directly related to PCP are uncoupling of oxidative phosphorylation resulting in increased metabolism and the breakdown of energy reserves, immunological effects, liver and kidney damage and reproductive disturbances (National Research Council, 1986 Eisler, 1989). Today the use of PCP is rather restricted, but in areas where the preparations are still in extensive use, PCP poses a threat to aquatic environments in particular. 

A range of selective procedures has been introduced for the formation of monochloro and dichlorophenols from phenolic intermediates in the great majority of which free chlorine has not been used. For the monochlorination of phenol and acylphenols these methods have been summarised in Table 8.1 (refs.7-13). 

For the synthesis of dichloro and polychlorophenols the chlorination of a less chlorinated precursor has been the method of choice, doubtless because the presence of one or two chlorine atoms partially deactivates the ring. The preparations of some compounds in this class are listed in Table 8.2 (refs.14-17). 

A number of other strategies have been devised for the synthesis of polychlorophenols containing other functional groups. 

5-dichlorothiophene has been ring-expanded to a dichlorophenolic derivative by way of a bicyclic intermediate. Ethyl 2-diazoacetoacetate was introduced dropwise into a solutton of 2,5-dichlorothiophene in toluene containing rhodium(ll) acetate and the mixture stirred for 20 hours at ambient temperature toproduce 1,3-dichloro-6-acetyl-6-ethoxycarbonyl-2-thiabicyclo-[3,10]hex-3-ene in 67% yield, which upon refluxing in toluene for 38 hours was transformed into ethyl 2,4-dichloro-5-hydroxy-6-methylbenzoate with a yield of 86% (ref. 18). 

Phenol Phenylselenyl Phenol in dichloromethane was treated with 

The best method for determining pentachlorophenol is conversion into the methyl ether followed by analysis using gas chromatography with an electron-capture detector, or gas chromatography coupled v/ith mass spectrometry [2]. Both of these methods require an extensive amount of pretreatment and highly-trained personnel for the operation of the equipment. 

Ervin and McGinnis [3] attempted to overcome this problem by developing a high performance liquid chromatographic method for determining in water low concentrations of pentachlorophenol and 

Source Reproduced by permission from Elsevier Science, UK [3] 

The method involves chloroform extraction of acidified waste water samples and rotary evaporation without heat After redissolving in chloroform the samples were analysed directly by high performance liquid chromatography on a microparticulate silica gel colunm. A number of solvent combinations are possible and 98 2 cyclohexane-acetic acid is preferred. The minimum detectable concentration is Ippm (without sample concentration) and the coefficient of variation is 1-2%. The t)q)e of separation achieved with a microparticulate silica gel column is shown in Fig. 4.1. The first peak as determined by gas chromatographic-mass spectrometric analysis, consisted of a complex mixture of polychlorinated compounds, including octa-, hepta- and hexachlorodibenzo-p-dioxins as well as a mixture of products including 2,4,6-trichlorophenol. The third peak was mainly 2,3,4,6-tetrachlorophenol and the fourth peak was pentachlorophenol. 

De Ruiter et al. [4] observed that photochemical decomposition by ultraviolet irradiation of dansyl derivatives of chlorinated phenolic 

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Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

Halogen, Chloral hydrate, sodium chloroacetate, chlorobenzene, />-chlorophenol, dichlorhydrin, bromobenzene, iodobenzene. 

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