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.
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.
It's funny, because the same has happened to me while recrystallizing a 6 membered lactam. I started with an off-white >95% pure powder and ended up with neat orange crystals (pentane/EtOAc). I only determined the purity with NMR though.
It's funny, because the same has happened to me while recrystallizing a 6 membered lactam. I started with an off-white >95% pure powder and ended up with neat orange crystals (pentane/EtOAc). I only determined the purity with NMR though.
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By HPLC chromatogram
By HPLC chromatogram
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What happened when you took a melting point?
What happened when you took a melting point?
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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.
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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I started with an off-white >95% pure powder and ended up with neat orange crystals (pentane/EtOAc).
I only determined the purity with NMR though.
I started with an off-white >95% pure powder and ended up with neat orange crystals (pentane/EtOAc).
I only determined the purity with NMR though.
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VOTE