CHLOROPHENOL (Identity, Physical and Chemical Properties, Analytical Methods)

Chlorophenols (CPs) are organic chemicals formed from phenol (1-hydroxybenzene) by substitution in the phenol ring with one or more atoms of chlorine.  Nineteen congeners are posible, ranging from monochlorophenols to the fully chlorinated pentachlorophenol (PCB).  Chlorophenols, particularly trichlorophenols (T₃CP), tetrachlorophenols (T₄CP), and PCP, are also available as sodium or potassium salts.

Chlorophenols are solids at room temperature, except for 2-MCP, which is a liquid.  The aqueous solubility of chlorophenols are up to four orders of magnitude more soluble in water than the parent compounds.  The acidity of chlorophenols increases as the number of chlorine substitutions increases.  The n-octanol/water partition coefficients of chlorophenols increases with chlorination, indicating a propensity for the higher chlorophenols to bioaccumulate.  Taste and odour thresholds are quite low.

Technical grade chlorophenol products are heterogeneous mixtures of chlorophenols, unreacted precursors, and a variety of dimeric microcontaminants.  As a result of the semiquantitative nature of the reaction of chlorine with molten phenol, commercial formulations of chlorophenols contain substantial quantities of other chlorophenols.  When the alkaline hydrolysis of chlorobenzenes is used to manufacture chlorophenols, the technical product can contain unreacted chloro-benzene.

A number of other compounds are present as microcontaminants in technical tri- and tetrachlorophenol preparations, as a result of the elevated reaction temperatures used.  These include the polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated phenoxyphenols (“predioxins”), polychlorinated diphenil ethers, polychlorinated benzenes, and polychlorinated biphenils.  Lower chlorophenol preparations do not contain detectable levels of dioxins, presumably because their manufacture does not occur at sufficiently high temperatures.  Tri- and tetrachloro-dibenzo-p-dioxins predominate int T₃CP formulations, while the hexa, hepta, and octa congeners are the major PCDD contaminants in technical T₄CP and PCP.  2,3,7,8-tetra-chlorodibenzo-p-dioxin (2,3,7,8-TCDD) occurs primarily as a contaminant of 2,4,5-T₃CP, though it is present at low µg/litre concentrations in T₄CP, PCP, and Na-PCP.  Chlorophenol formulations contain a similar array of PCDFs.  Phenoxyphenols may comprise as much 1-5% of the formulation.

A large number of sampling and analytical methods have been developed for the determination of chlorophenols in different media.  Sensitive methods, such as gas chromatography, high-performance liquid chromatography, and mass spectrometry are increasingly used.

For further information :

Chlorophenols Other Than Pentachlorophenol; WHO; Geneva; 1989