Selective Bromination For Polynitro Stilbenes

Brominated aromatic compounds are widely used as pharmaceuticals, pesticides, dyestuff and fire retardants. An efficient methodology for bromination of polynitro stilbenes using molecular bromine as brominating agent over ZnO/H-beta-25 has been developed, which is conducted under mild condition, in good to high yield with less pollution, excellent region-and chemo-selectivities. These results indicate that trans polynitro bistilbenes involving the conjugated olefinic bond of distyryl structures suffer ortho bromination in 90% selective yield, and polynitro stilbenes involving polynitro monostyryl structure lead to a adduct to vinyl site in 95% yield. The regenerability of zeolite is good and they are reused. Then, based on these results of experiments and thermodynamic calculations, the mechanism for catalytic bromination of polynitro stilbenes is electrophilic reaction. Namely, The Brφnsted acid site in zeolite framework promoted the polarization of molecular bromine, which further interacts with ZnO to form positive-charged bromine. Moreover, ZnBr2 appeared to be a co-catalytic species. This reaction most likely occurs via a noncovalent binding of Br+ to benzene ring involving styryl structure.All objective structures of brominated aromatic compounds are verified through analysis methods existed. The architecture of unknown product is further confirmed by single crystal X-ray diffraction analysis.