124 Chlorinated Hydrocarbons ers, and road or rail tankers. Steel is a suitable duction of 3,4-dichlorobenzyl chlo- material for construction of containers. ride, 3,4-dichlorobenzaldehyde, 3,4-di- For information on storage and handling, see chlorobenzotrichloride, and 3,4-dichloroben- Section 8.1.5. zoic acid, from which disinfectants, crop pro- Freight classifications are given in Table 49. tection products, and dyes are produced. 2,3,6-Trichlorotoluene. 2,3,6-Trichloro- toluene is used on a small scale, together 8.2.6. Uses with 2,4,5-trichlorotoluene, to produce 2,3,6- trichlorobenzoic acid, a herbicide precursor. Isomeric mixtures of the monochlorotoluenes Producers of chlorinated toluenes are: Bayer are hydrolyzed to cresol on a considerable scale. AG (FRG); Enichem (Italy); Hodogaya Chemi- Chlorotoluenes are also used as solvents in reac- cals Co. Ltd. (Japan); Hoechst AG (FRG); Ihara tions and to dissolve special products, e.g., dyes. Chemical Ind., Ltd. (Japan); Occidental Chem- 2-Chlorotoluene. 2-Chlorotoluene is a start- ical Co., Ltd. (USA). ing material in the production of 2-chloro- benzyl chloride, 2-chlorobenzaldehyde, 2- chlorobenzotrichloride, 2-chlorobenzoyl chlo- 8.3. Chlorinated Biphenyls ride and 2-chlorobenzoic acid, which are NewsomeNote: PCBs precursors for dyes, pharmaceuticals, opti- Industrial use of the polychlorinated biphenyls cal brighteners, fungicides, and products of first began in 1929 in the USA [880, 881]. The other types. 2-Chlorotoluene is also used in outstanding properties of these compounds, such the production of dichlorotoluenes (chlorina- as their high chemical and thermal stability, high tion), 3-chlorotoluene (isomerization), and o- dielectric constant, and the fact that they form chlorobenzonitrile (ammonoxidation). only incombustible gases in an electric arc, made 4-Chlorotoluene. 4-Chlorotoluene is used them appear ideally suited for use as insulating mainly to produce p-chlorobenzotrichloride, and cooling fluids for transformers and as di- from which is obtained p-chlorobenzotrifluoride, electric impregnants for capacitors. an important precursor of herbicides (e.g., In subsequent years many other applications trifluralin:α,α,α,-trifluoro-2,6-dinitro-N,N- were found as well (see Section 8.3.5), particu- dipropyl-p-toluidine). Other side-chain-chlo- larly for isomeric mixtures containing two to six rinated products or their derivatives are 4- atoms of chlorine per mole of biphenyl. chlorobenzyl chloride (for pharmaceuticals, In the mid-1960s, improved analytical meth- rice herbicides, and pyrethrin insecticides), 4- ods revealed that polychlorinated biphenyls chlorobenzaldehyde (for dyes and pharmaceuti- were accumulating in nature as a consequence of cals), 4-chlorobenzoyl chloride (for pharmaceu- their extremely low rates of biological degrada- ticals and peroxides), and 4-chlorobenzoic acid tion (rates which decrease as the chlorine content (for dyes). 4-Chlorotoluene is also a starting rises). The compounds were detected in fresh material in the synthesis of 2,4- and 3,4-di- water in all parts of the world, but also in many chlorotoluene and of 4-chlorobenzonitrile. animals (e.g., birds, fish, and plankton). In the late 1970s, it was further discovered that at tem- 2,4-Dichlorotoluene. 2,4-Dichlorotoluene peratures of 500 to 800 ◦C in the presence of is used via its side-chain-chlorinated intermedi- oxygen, polychlorinated biphenyls can give rise ates to produce fungicides, dyes, pharmaceuti- to polychlorinated dibenzofurans and dibenzo- cals, preservatives, and peroxides (curing agents dioxins, including (although to a much smaller for silicones and polyesters). extent) the particularly toxic compound 2,3,7,8- 2,6-Dichlorotoluene. 2,6-Dichlorotoluene tetrachlorodibenzodioxin [882 – 887]. is used to produce 2,6-dichlorobenzaldehyde, a In the meantime, all but a few of the well- dye precursor, and 2,6-dichlorobenzonitrile, a known producers (see Section 8.3.5) discon- herbicide. tinued the production of chlorinated biphenyls. 3,4-Dichlorotoluene. 3,4-Dichlorotoluene Moreover, in many countries the production, is used in small amounts in the pro- sale, and use of polychlorinated biphenyls have Chlorinated Hydrocarbons 125 Table 49. Freight classification GGVE/GGVS and IMDG Code and IATA-DGR US-DOT RID/ADR class number class UN No. pack. group 2- and 4-Chlorotoluene3 3 3.3 2238 III UN 1993 Flammable liquid 2,3-Dichlorotoluene 3 4 not restricted 2,4-Dichlorotoluene 3 4 not restricted 2,6-Dichlorotoluene 3 4 not restricted 3,4-Dichlorotoluene 3 4 not restricted been restricted or entirely prohibited by legisla- hexachlorobiphenyl [26601-64-9]. Such mix- tion. tures are liquid to viscous (pour points increase For many years, o-, m- and p-terphenyl mix- with chlorine content from − 22 to + 18 ◦C), and tures were chlorinated and then used as plasticiz- they are fire-resistant. Further chlorination gives ers, flame retardants, and fillers in thermoplastic soft to brittle thermoplastic waxes. pattern and holding waxes. This application like- Chlorinated biphenyls are soluble in many wise has been substantially discontinued [888], organic solvents, particularly when heated, but particularly in view of the persistent nature of are soluble in water only in the ppm range. Al- the compounds in question and their accumula- though they are chemically very stable, includ- tion in the environment. Possible toxicological ing to oxygen of the air, they can be hydrolyzed hazards are either unknown or have not been ad- to oxybiphenyls under extreme conditions, e.g., equately investigated (Table 50). with sodium hydroxide solution at 300 – 400 ◦C and under high pressure. Toxic polychlorodiben- Table 50. MAK and TLV values of chlorinated biphenyls zofurans may be formed under these conditions. The fact that the compounds may eliminate MAK TLV hydrogen chloride to a small extent at a high tem- NewsomeNote: These are (FRG) (USA) 3 3 maximum daily exposure levels. mg/m mg/m perature explains why hydrogen chloride accep- tors are often added to transformer fluids based Chlorinated biphenyls (42 % Cl) 1 III B 1 Chlorinated biphenyls (54 % Cl) 0.5 III B 0.5 on polychlorinated biphenyls. The excellent electrical property data of polychlorinated biphenyls, such as high dielec- In view of the above, this article is devoted tric constant, low power factor, high resistivity, primarily to a review of recent patents covering favorable dielectric loss factor, and high dielec- methods for the disposal of polychlorinated bi- tric strength, have already been mentioned. phenyls. For information regarding the produc- tion of these compounds and their specific physi- cal and chemical properties, attention is directed 8.3.2. Disposal to earlier surveys [882, 889, 890]. Many products containing chlorinated biphenyls are still in use throughout the world, particu- 8.3.1. Physical and Chemical Properties larly in transformers, rectifiers, and capacitors There are 209 possible chlorinated biphenyls. with long service lives. Industry and national The mono- and dichlorobiphenyls [27323-18- governments are now faced with the need to 8], [25512-42-9] are colorless crystalline com- dispose of these products without causing addi- pounds (the melting points of the pure isomers tional pollution of the environment. Appropriate lie between 18 and 149 ◦C). When burned in air, official regulations exist in many countries [888, they give rise to soot and hydrogen chloride. 891 – 902]. The most important products are mixtures Attention is drawn in the following survey to whose principal components are trichlorobiphe- patents concerned with the removal of polychlo- nyl [25323-68-6], tetrachlorobiphenyl [26914- rinated biphenyls from electrical devices and 33-0], pentachlorobiphenyl [25429-29-2], or 126 Chlorinated Hydrocarbons with the disposal of these compounds. It is im- 8.3.3. Analysis possible to say which of the processes have ac- tually reached maturity and which are already The analytical methods most frequently used being used. for detecting chlorinated biphenyls are capil- According to the present state of knowl- lary column gas chromatography coupled with edge, polychlorinated biphenyls can be de- mass spectrometry in the MID (Multiple Ion De- stroyed harmlessly by combustion at tempera- tection) mode and capillary column gas chro- tures above 1000 ◦C and a residence time of 2 s, matography with ECD (Electron Capture Detec- e.g., in a rotary burner equipped with a scrubbing tor). These methods are suitable for solution of tower for hydrogen chloride [888, 902 – 904]. even the most difficult problems. Clean-up steps Regulations in the Federal Republic of Germany are necessary when complex matrices are con- specify a temperature of 1200 ◦C, a residence cerned, such as preliminary separation by col- time of 0.2 s, and a residual oxygen content in umn chromatography. the combustion gas of 6 % [897]. HPLC (High Pressure Liquid Chromatogra- Removal of polychlorinated biphenyls from phy) and infrared spectroscopy are applicable to silicone- and hydrocarbon-based transformer a limited extent. fluids and heat transfer media is accomplished Summary polychlorinated biphenyl determi- through the formation of a separable fraction nations are also possible, though not usual. rich in polychlorinated biphenyls [905], treat- These require either exhaustive chlorination and ment with polyalkylene glycol and alkali metal measurement of the decachlorobiphenyl content hydroxide [906, 907], treatment with sodium or else dechlorination and subsequent measure-