<unk>  is a brown or black liquid of high viscosity, which smells of naphthalene and aromatic hydrocarbons.<unk>  is among the by-products when<unk>  is carbonized to make coke or gasified to make<unk>  gas.<unk> s are complex and variable mixtures of phenols, polycyclic aromatic hydrocarbons (PAHs), and heterocyclic compounds.
Coal tar
Toluene
Nitrazine
Dimethylphthalate
Methylene diphenyl diisocyanate
Naphtha
Trichloroethylene
Dinitrobenzene