3,3′-DICHLOROBENZIDINE

Note: Normally found as the salt, 3,3′-dichlorobenzidine dihydrochloride (C12H10Cl2N2⋅2HCl). CASRN: 91-94-1; molecular formula: C12H10Cl2N2; FW: 253.13; RTECS: DD0525000; Merck Index: 12, 3109 Physical state, color, and odor: Colorless to grayish-purple needles or crystals with a mild or pungent odor Melting point (°C): 132-133 (Shriner et al., 1978) Boiling point (°C): 402 (Callahan et al., 1979) 420 (NIOSH, 1997) Diffusivity in water (x 10-5 cm2/sec): 0.51 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant, pKa: 5.4, 3.3 (Korenman and Nikolaev, 1974) Flash point (°C): No flammable vapors were evolved at 200 °C (Shriner et al., 1976) Henry’s law constant (x 10-8 atm⋅m3/mol): 4.5 at 25 °C (estimated, Howard, 1989) Bioconcentration factor, log BCF: 3.49 (activated sludge), 2.97 (algae), 2.79 (golden orfe) (Freitag et al., 1985) 2.70 (bluegill sunfish, Appleton and Sikka, 1980) Soil organic carbon/water partition coefficient, log Koc: 2.86 (silty clay: pH 6.3, CEC 47.9 cmolc/kg); 2.92 (silty clay: pH 6.8, CEC 39.4 cmolc/kg); 3.08

(sand: pH 6.8, CEC 23.1 cmolc/kg); 1.86 (sand pH: 7.2, CEC 8.1 cmolc/kg); 3.21 (sand: pH 7.2, CEC 10.1 cmolc/kg) (Nyman et al., 1997)

Octanol/water partition coefficient, log Kow: 3.51 at 23 °C and pH 8.7 (shake flask-UV/LSC, Banerjee et al., 1980) Solubility in organics: Soluble in ethanol, benzene, and glacial acetic acid (Windholz et al., 1983)

3.11 mg/L at 25 °C (shake flask-LSC, Banerjee et al., 1980) 4.0 mg/L at 22 °C (dihydrochloride, U.S. EPA, 1980a) 3.99 ppm at pH 6.9 (Appleton and Sikka, 1980) Vapor pressure (mmHg): 10-5 at 22 °C (assigned by analogy, Mabey et al., 1982) 4.2 x 10-7 at 25 °C (estimated, Howard, 1989) Environmental fate: Biological. In activated sludge, 2.7% mineralized to carbon dioxide after 5 d (Freitag et al., 1985). Sikka et al. (1978) reported 3,3′-dichlorobenzidine is resistant to degradation by indigenous aquatic microbial communities in a 4-wk period. Under aerobic and anaerobic conditions, 3,3′-dichlorobenzidine is mineralized very slowly (Boyd et al., 1984; Chung and Boyd, 1987). Nyman et al. (1997a) studied the transformation of 3,3′-dichlorobenzidine under laboratory controlled conditions at 20 °C. Wet sediment (50 g) and water (150 mL) from Lake Macatawa, Holland, MI were placed in glass serum bottles and purged with nitrogen to ensure anaerobic conditions to which 3,3′-dichlorobenzidine was added. The bottles were incubated in the dark at 20 °C for 12 months. Soil and water samples were retrieved periodically for transformation product identification using HPLC. The investigators identified 3-chlorobenzidine as a transient metabolite from the biological transformation of 3,3′-dichlorobenzidine. 3-Chlorobenzidine rapidly dechlorinated forming the end product benzidine. Photolytic. An aqueous solution subjected to UV radiation caused a rapid degradation (half-life <10 min) to monochlorobenzidine, benzidine, and several unidentified, brightly-colored, waterinsoluble chromophores (Banerjee et al., 1978). In a similar experiment, 3,3′-dichlorobenzidine in an aqueous solution was subjected to radiation at λ=310 nm for approximately 15 min. During the period of irradiation, concentrations of 3,3′-dichlorobenzidine decreased rapidly. 3-Chlorobenzidine formed as a transient intermediate which underwent dechlorination forming a benzidine, a stable photoproduct. Depending upon the wavelength used, the benzidine yields ranged from 8 to 12% of the total 3-chlorobenzidine transformed (Nyman et al., 1997). A carbon dioxide yield of 41.2% was achieved when 3,3′-dichlorobenzidine adsorbed on silica gel was irradiated with light (λ >290 nm) for 17 h (Freitag et al., 1985). Chemical/Physical. 3,3′-Dichlorobenzidine will not hydrolyze to any reasonable extent (Kollig, 1993). At influent concentrations of 1.0, 0.1, 0.01, and 0.001 mg/L, the GAC adsorption capacities at were 300, 190, 120, and 73 mg/g, respectively (Dobbs and Cohen, 1980). Exposure limits: Potential occupational carcinogen. Given that no standards have been established, NIOSH (1997) recommends the most reliable and protective respirators be used, i.e., a self-contained breathing apparatus that has a full facepiece and is operated under positive-pressure or a supplied-air respirator that has a full facepiece and is operated under pressure-demand or under positive-pressure in combination with a self-contained breathing apparatus operated under pressure-demand or positive-pressure. OSHA recommends that worker exposure to this chemical is to be controlled by use of engineering control, proper work practices, and proper selection of personal protective equipment. Specific details of these requirements can be found in CFR 1910.1003-1910.1016. Symptoms of exposure: May cause irritation of eyes, nose, throat, and skin (Patnaik, 1992) Toxicity: LC50 (48-h) for bluegill sunfish 2 mg/L (Sikka et al., 1978).