A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 4C6
Pammiilo. Kuchroic Arid.
O
oo\NH
CO/^ 11 (OO.OH
Hydromcllitic Add CJEI^COjH).—This additive compound is readily
formed by the action ot sodium-amalgam on an ammoniacal solution
of mellitic acid. To isolate the acid, the solution is neutralized with
acetic acid, and precipitated with lead acetate, the precipitate washed
and decomposed with hydrogen sulphide. On evaporating the filtrate,
the acid is obtained as a syrupy liquid, which gradually becomes
crystalline.
Isohydrom-dlitic Add C0H8(CO2H)6 is obtained by heating hydromellitic
acid with concentrated hydrochloric acid to 180°. It crystallizes
in thick, large, four-sided prisms, possessing a slightly acid
taste.
Isolvydromellitie acid is a very stable Ijody, which is not changed
by treating it with a mixture of strong sulphuric and nitric acids.
The cause of the isomerism of hydromellitic acid and isohjdromellitic
acid is not known.
Fyromellitic Add C6H8(CO2H}4.—When rnellitic acid ia heated it
first melts, and then is resolved into water, carbon dioxide, and pyromellitic
anhydride:—
C,
CO.OH
CO.OH
CO.OH r
CO.OH ~ u °
CO.OH
CO.OH