Nitration of benzenoid compounds by palladium salts and by nitrogen dioxide
The nitration of benzenoid compounds by palladium nitrate and by a mixture of palladium acetate and sodium nitrite has been studied under a variety of conditions. The latter system yields nitrobenzene semi-catalytically in chloroacetic acid at 100°(ca. 1200% in an oxygen atmosphere), with relatively little by-product (ester) formation. The use of nitrogen dioxide in place of sodium nitrite results in a fully catalytic system. Observations which bear on the mechanisms are discussed. Aromatic nitration has also been effected in good yield by passing nitrogen dioxide into a solution of the aromatic compound in trifluoroacetic acid. In contrast to the reactions involving palladium(II), this is almost certainly an SE2 process involving the nitronium ion.