Studies on Arylhydrazones, Part-XII: Action of Bromine on Ethylhydrogen Mesoxalate Phenylhydrazones

Abstract

The nature of brominated product is dependent on the amount of
bromine and time of reaction in the bromination of ethylhydrogen mesoxalate
phenylhydrazones (IV). The products are identified as (Z-) form.
Bromination of (IV) further revealed that nuclear bromination first takes
place, followed by displacement of COOH group and then again nuclear
bromination. It seems that electron withdrawing groups in aromatic nucleus
deactivates the ring to such an extent that bromination in the nucleus does
not take place even with excess of bromine in the presence of sunlight and
on increasing the  temperature. On the other hand, electron releasing groups
in the aromatic nucleus activate the ring and nuclear bromination occurs
with excess of bromine in sunlight.