MELLITIC

ACID (

See also:

• BENZENE, C6H6

benzene hexacarboxylic acid), C6(000H)6  , was first discovered in 1799 by M . H . Klaproth in the mineral honeystone, which is the aluminium salt of the acid . The acid may be prepared by warming honeystone with ammonium carbonate, boiling off the excess of the ammonium salt and adding ammonia to the solution . The precipitated alumina is filtered off, the filtrate evaporated and the ammonium salt of the acid purified by recrystallization . The ammonium salt is then converted into the lead salt by precipitation with lead acetate and the lead salt decomposed by sulphuretted hydrogen . The acid may also be prepared by the oxidation of pure carbon, or of hexamethyl benzene, in the cold, by alkaline potassium permanganate (F . Schulze, Ber., 1871, 4, p . 802 ; C . Friedel and J . M . Crafts, Ann. chim. ph s., 1884 [6], t, p .

470) . It crystallizes in

fine silky needles and is soluble in water and alcohol . It is a very stable compound, chlorine, concentrated nitric acid and hydriodic acid having no action upon it . It is decomposed, on dry distillation, into carbon dioxide and pyromellitic acid, C10H6O3; when distilled with lime it gives carbon dioxide and benzene . Long digestion of the acid with excess of phosphorus pentachloride results in the formation of the acid chloride, C6(000I)6, which crystallizes in needles, melting at 19o° C . By heating the ammonium salt of the acid to 150-16o° C. as long as ammonia is evolved, a mixture of Paramide (mellimide), C6 (co > NH) 3, and ammonium euchroate is obtained . The mixture may be separated by dissolving out the ammonium euchroate with water . Paramide is a white amorphous powder, insoluble in water and alcohol .