Photodebromination of dibromobutane: Possibility and evidence

The reduction of organic dibromides, such as 2,3-dibromobutane (2,3-DBB), 1,2-dibromobutane (1,2-DBB) and 1,2-dibromocyclohexane, appears to exist with cathodic barrier. For instance, 2,3-DBB can only be reduced at a potential more negative than −1.5 V vs. SCE in DMSO with bare carbon electrodes. To reduce the cathodic overvoltage for 2,3-DBB, we found that cobalt tris(5-aminophenanthroline) (Co(5-NH2-phen)32+) is a useful catalyst. Incorporating Co(5-NH2-phen)32+ could shift the onset potential for the reduction of 2,3-DBB to −1 V. As Co(5-NH2-phen)32+ was further modified with 1-aminopyrene (1-NH2-Py), the resulting derivative, Py-Co(5-NH2-phen)32+, could shift the onset potential to a more positive value, −0.45 V, as the system was irradiated with white light. Using Py-Co(5-NH2-phen)32+ and diethylamine (DEA) as the photocatalyst and sacrificial donor, 2,3-DBB could then be photochemically degraded into butene and bromide ions. IR spectral analysis and bromide-ion analysis confirmed these results. Besides 2,3-DBB, 1,2-DBB and 1,2-dibromocyclohexane could also be degraded under the photosensitization of Py-Co(5-NH2-phen)32+. Accordingly, the proposed photodebromination is considered as an effective alternative for the degradation of organic dibromides, and Py-Co(5-NH2-phen)32+ is a potential photocatalyst in this aspect.