A Dibromination Dibromance Part IV

We divided the procedure into three different studies. One study involved the “traditional” use of 1 mL of concentrated HBr and H2O2. The second study mixed 0.5 mL of HBr and 0.5 mL of HCl, and the third study used 1 mL of HCl. The products were recovered by neutralizing the reaction mixture and collecting the precipitate. The reaction mixtures containing HBr turn bright orange and cloudy and then eventually fade to white.  The HCl-only reaction stayed clear and colorless throughout the reflux but did form a white precipitate after neutralization and cooling. Both the HBr-only and HBr-HCl mix yielded abundant white solid. The HCl-only reaction gave a very cloudy solution but the product oiled out and/or passed through the filter paper. We performed IR spectroscopy on the recovered solids.  It was difficult to distinguish between the different products by IR. Interestingly, the dihalogenated products gave very small unsaturated C-C bond peaks. Some differences in the fingerprint region were tentatively identified but the presence of small amounts of ethanol in the products was a complication as well. Gas Chromatography was more helpful in identifying products. Commercial meso-1,2-dibromo-1,2-diphenylethane and trans-stilbene were used as known standards. The HBr-only experiments showed a major peak corresponding to meso-1,2-dibromo-1,2-diphenylethane (~36 min). The HBr-HCl mix gave two major peaks. One of the peaks was associated with meso-1,2-dibromo-1,2-diphenylethane. The area under the peak likely corresponding to 1-bromo-2-chloro-1,2-diphenylethane (~33 min) was typically greater than the dibromo peak. The HCl-only study gave two peaks at ~30 min. The area under the higher retention time peak was typically about 4x the other. This may correspond to two diastereomers of 1,2-dichloro-1,2-diphenylethane. The HCl-only reaction often had a significant peak close to the retention time of trans-stilbene (~28 minutes). All three experiments tended to give a cluster of small peaks between 25 and 30 minutes.


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