[15114-43-9] · C3HBr2N3O3 · 1,3-Dibromoisocyanuric Acid · (MW 286.87)
(electrophilic bromination of aromatic compounds, oximes)
Alternate Name: DBI.
Solubility: sol CH2Cl2, H2SO4.
Preparative Method: dibromoisocyanuric acid has been prepared by treatment of isocyanuric acid (0.1 mol) and LiOH (0.2 mol) with Br2 (0.4 mol) in water (1 L) at 20 °C.1 After vigorous stirring to effect dissolution of Br2, the mixture is cooled slowly in a refrigerator for 24 h. The product is collected by filtration, washed with ice-cold bromine water, and then dried in vacuo, first over KOH, then over P2O5 (88% yield).
Handling, Storage, and Precautions: dibromoisocyanuric acid should be stored refrigerated and protected from light and moisture to avoid decomposition. DBI is an irritating solid and precautions should be taken to avoid inhalation of the powder or contact with skin.
Dibromoisocyanuric acid is reputed to be the most powerful reagent known for the electrophilic bromination of aromatic compounds. Nitrobenzene, which is brominated using Bromine/Fe or N-Bromosuccinimide/50% H2SO4 only at elevated temperatures, is converted to the m-bromo derivative (88% yield) upon reaction with DBI in conc. H2SO4 in 5 min at 20 °C. Similarly, m-dinitrobenzene, benzoic acid, acetophenone, and trifluoroacetophenone (eq 1)2 are all smoothly converted to the expected monobromides by reaction with 0.5 equiv of DBI in conc. H2SO4 at rt.1 Due to the mild conditions of the reaction, alkyl groups attached to the aromatic ring are not affected (eq 2).3 Furthermore, perbrominations of a variety of aromatic compounds may be achieved under more forcing conditions (eq 3).4
Reaction of oximes with DBI and NaHCO3 in aqueous dioxane affords acceptable yields of the geminal
Scott C. Virgil
Massachusetts Institute of Technology, Cambridge, MA, USA