Organic acids and process for preparing same

A process for preparing a mixture of polycyclic aromatic polycarboxylic acids carrying nuclear nitro groups that is soluble in acetone but insoluble in water which comprises subjecting a slurry containing coal to reaction with aqueous nitric acid having a concentration of about 5 to about 90 percent at a temperature of about 15.degree. to about 200.degree. C. for about 0.5 to about 15 hours, mechanically separating the solids in the resulting slurry, extracting the resulting solids with a polar solvent and then separating the polar solvent from the extract to recover the desired carboxylic acid mixture.