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Org. Process Res. Dev. 2015, 19, 1784. DOI:10.1021/acs.oprd.5b00274 ◆ A significant exotherm at the beginning of the reaction as the addition of bromine commenced was observed. ◆ Analysis of the reaction mixture by HPLC and 1H-NMR after a small amount of bromine was added indicated a nearly complete isomerization of 12 into dimethyl fumarate (13) , and we attributed the observed exotherm to this phenomenon. ◆ After the consumption of both 12 and 13 by HPLC, excess bromine was carefully quenched by the addition of aqueous solutions of inorganic reducingreagents, typically sodium thiosulfate, sodium sulfite or sodium bisulfite. ◆ During one of manufacturing campaigns, a significant amount of 13 (~20%) was observed after the quench. ◆ Investigation showed that if solutions of 10 are left in prolonged contact with concentrated solutions of these inorganic reducing reagents at room temperature (~20 °C), the reduction of signifi
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