Pentachlorophenols

Constituents. Complex halogenated organic compounds have been widely used in commerce in the last fifty years. A few representative examples are shown in Eigure 9 pentachlorophenol has been widely used as a wood preservative, and also for termite control. 

A major concern when remediating wood-treatment sites is that pentachlorophenol was often used in combination with metal salts, and these compounds, such as chromated copper—arsenate, are potent inhibitors of at least some pentachlorophenol degrading organisms (49). Sites with significant levels of such inorganics may not be suitable candidates for bioremediation. 

Pentachlorophenol is readily degraded in biofHm reactors (53), so bioremediation is a promising option for the treatment of contaminated groundwater brought to the surface as part of a pump-and-treat operation. 

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 The old processes starting from phenol or 2,4,6-trichlorophenol have been replaced by new ones involving hydroquinone chlorination.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). 

Phenolics. Phenol (qv) and the chlotinated phenoHcs formerly comprised the largest class of iadustrial antimicrobials (see Chlorophenols). Table 5 shows the remaining phenoHcs of importance. Use of pentachlorophenol has been severely restricted only one manufacturer suppHes product for the wood preservation market. 

Common examples of compounds that are amenable to carbon adsorption are aromatics (benzene, toluene) and chlorinated organics (trichloroethylene, trichloroethane [71-55-6, 75 -(9(9-j5y, tetrachloroethylene, polychlorinated biphenyls (PCBs), DDT /T(9-77-77, pentachlorophenol [87-86-5J. Compounds that are not adsorbed effectively by carbon include ethanol [64-17-5], diethylene glycol [111-46-6], and numerous amines (butylamine [109-73-9, 13952-84-6, 75-64-9], triethanolamine [102-71-6], cyclohexylamine [108-91-8], hexamethylenediamine [108-91-8] (1). Wastewater concentrations that are suitable for carbon adsorption are generally less than 5000 mg/L. 

Wood preservatives ate appHed either from an oil system, such as creosote, petroleum solutions of pentachlorophenol, or copper naphthanate, or a water system. Oil treatments ate relatively inert with wood material, and thus, have Htde effect on mechanical properties. However, most oil treatments require simultaneous thermal treatments, which ate specifically limited in treating standards to preclude strength losses (24). 

The best protection for wood against the attack of decay fungi, insects, or marine borers is obtained by applying preservatives under pressure before installation (61,62). Both oil-type preservatives, such as creosote or petroleum solutions of pentachlorophenol, and waterborne preservatives, such as copper-chrome arsenate and ammoniacal-copper arsenate, are used when wood is to be in direct contact with the ground or in the marine environments. 

Pentachlorophenol. Because of the high melting temperature of pentachlorophenol, C HCl O, its preparation makes it necessary to raise the temperature progressively throughout chlorination. The presence of Lewis acid catalysts is essential. The most commonly used of these are AlCl and FeCL. 

Polychlorophenoxyphenols are the principal impurity in mixtures of tetrachlorophenols and pentachlorophenols. Traces of polychlorodibenzoparadioxins and polychlorodibenzofurans can also be present if the chlorination is not conducted correctiy. 2,3,7,8-Tetrachlorodibenzoparadioxia [1746-01 -6] which is highly toxic, has never been detected in any products derived by chlorination. 

Rhc ne-Poulenc, with a capacity of around 20,000 t/yr, is the world s leading producer of light chlorophenols. Excluding the unknown factors for which no statistics are available (China, Russia), the market for pentachlorophenol can be estimated at - 25, 000 t/yr. The principal producers of pentachlorophenol are given ia Table 4. 

The main applications of mono-, di-, or ttichlorophenols are in agrochemicals and for pentachlorophenol in wood protection. 2-Chlorophenol is used chiefly in the manufacture of an insecticide [41198-08-7] (55,56)... 

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