1,2-Dichlorobenzene (o-Dichlorobenzene)

o-Dichlorobenzene was first synthesized by Laurent in 1836 through chlorination of benzene and has been manufactured on an industrial scale since the early 20th century. [1] Commercial production yields a mixture of ortho (1,2-), meta (1,3-), and para (1,4-) dichlorobenzene isomers in proportions controlled by reaction conditions; the ortho isomer is typically the second-most produced after the para isomer. Major uses include as a solvent for metal degreasing, dye carriers in textile dyeing, and as a chemical intermediate in the synthesis of the herbicide 3,4-dichloroaniline (a precursor to diuron, propanil, and other phenylurea herbicides). It is also used as a grain fumigant and as a component of moth control products (though paradichlorobenzene is more commonly used for this). [2] The EPA lists o-dichlorobenzene as a HAP under the Clean Air Act and as an RCRA hazardous waste constituent. It is moderately persistent in soil (half-life weeks to months) and has been detected in groundwater near chemical plants and hazardous waste sites. Long-term animal studies found liver and kidney tumors in rodents, and the EPA classifies it as a Group C possible human carcinogen (insufficient human data, limited animal evidence). [3] Its acute toxicity profile focuses on central nervous system depression, liver toxicity, and kidney damage — effects shared with many chlorinated aromatic solvents.

Chemical manufacturing workers producing o-dichlorobenzene and its derivatives (dichloroaniline, dyes) face occupational inhalation and dermal exposures. Textile workers using it as a dye carrier have significant exposures. Laboratory chemists use it as a specialty high-boiling solvent. General population exposures come from contaminated drinking water near industrial sites, and from consumer moth repellent products containing dichlorobenzene mixtures.

Liver and kidney toxicity are the primary concerns for significant exposures: hepatocellular damage (elevated liver enzymes, histopathological changes) and nephrotoxicity are documented in both animal studies and some occupationally exposed workers. [3] CNS effects (headache, dizziness, narcosis) occur at high vapor concentrations. o-Dichlorobenzene is a skin and mucous membrane irritant. The Group C possible carcinogen designation is based on limited animal tumor data (lower confidence than the Group B2 probable carcinogen compounds).

Chemical synthesis workers, textile dye workers, and laboratory chemists using o-dichlorobenzene as a solvent face occupational risk. Residents near chemical plants or hazardous waste sites with contaminated groundwater have environmental exposures.

1. Industrial workers should use local exhaust ventilation and monitor air concentrations; the OSHA PEL is 50 ppm and NIOSH REL is 50 ppm. 2. Wear chemical-resistant gloves and eye protection for liquid handling. 3. Test private wells in areas near former chemical plants. 4. Use activated carbon filtration for drinking water if contamination is detected. 5. In textile dyeing, explore water-based and supercritical CO₂ dyeing alternatives to solvent carriers.