Fast Colorimetric Titration of Boron Tribromide Using N,N-Dimethylaniline
Dr. Jason G. Gillmore
A large number of organic transformations are either initiated or catalyzed by boron tribromide (BBr3), and correct stoichiometric addition to these reactions is often crucial to their success. Few procedures for the quantification of BBr3 concentration currently exist, so there is a need to develop additional reliable methodologies. Here we report that N,N-dimethylaniline (DMA) has been identified as a colorimetric titrant for accurately determining the concentration of BBr3 in solution. Our protocol is fast, direct, and works for a range of BBr3 concentrations. An initial Lewis acid-base reaction between the nitrogen and boron centers forms a blue complex. At the equivalence point, additional catalytic BBr3 initiates an electrophilic aromatic substitution reaction which results in a loss of the B-N coordination and causes an instantaneous color change from blue to yellow, giving an easy-to-identify endpoint.
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