Why does the evaporation residue turn black over time when acetic anhydride is stored for a long period?
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After several jars of acetic anhydride product and some bottle-packed samples were left for over a month, the evaporated residues turned black. It wasn’t like this at first; the color of the evaporation residue was very light. I don’t know what’s causing it right now. Has anyone else encountered this situation?
:(That’s the case with most organic substances; darkening occurs only when a small amount of them oxidize, and it depends greatly on the storage time and environment.)
Under normal circumstances, it is oxidation, resulting in blackening