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5. During the distillation, if your product was darkening you were asked to stop the process. What is the major cause of the discoloration as it relates to the experiment performed in lab last week? Be specific.

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braza909

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The reaction procedure you provided, is a kind of Baeyer-Villliger oxidation of ketone to ester. You are using Trifluoroacetic acid (TFA) there, which is a strong acid, so in work up, if you didn't wash it properly by NaHCO3 (Base), it may remain in the mixture. Boiling point of TFA is 72.40C, and when you heat your crude product to 1000C for distillation, TFA starts changing its color (darkening). Other thing is, you are using Sodium percarbonate in the reaction, during the reaction they get converted to peroxides which is the major cause of darkening. If you use sufficient amount of Na2S2O5 during work up, remained residual peroxides would be removed, and the darkening would not be occur.

Whenever peroxides are heated to more temperature, they get darkened.

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