For about 100 years, chemicals obtained as by-products in the primary processing of coal to metallurgical coke were the main source of aromatic compounds used as intermediates in the synthesis of dyes, drugs, antiseptics, and solvents. However, over 97% of the aromatic hydrocarbons, such as benzene, toluene, and xylenes, are now obtained largely from petroleum. Naphthalene, phenanthrene, heterocyclic hydrocarbons such as pyridines and quinolines, and some phenols are still obtained from coal tar.