Ah, the old "predict the solubility of my unknown compound" question. In general, I'd say an increase in color is due to oxidation. Since you are starting with a mixture, we don't know if this is oxidation of your product or an impurity.
I cannot answer your question about the color and whether it may have occurred on the solid during storage or during crystallization (more likely as contact has increased), but I can make a suggestion on how you might purify your compound. I used to start with TLC. Faster moving impurities are generally less polar and less likely to precipitate in non-polar solvents. Slower are generally more polar and more likely to precipitate from a non-polar solvent and less likely from a polar solvent. One can add the strategy of chromatography/filtration to recrystallization. A non-polar impurity may adhere more to charcoal in a polar solvent and a polar impurity may adhere to silica gel in a non-polar solvent.
A qualitative opinion of the solids is that neither look like the kind of crystalline solid characteristic of a pure compound. A slower crystallization favoring precipitation of like-to-like crystals may be all that is necessary.
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Topic: Change of colour after recrystallization (Read 4053 times)