I have some phenol (liquid) but it has a reddish brown/orange color. Has anyone encountered this problem? What is the reason? Is it oxidized? I'm not sure if I can use it in my reactions anymore.
Fa,
Phenol discolors quickly when in contact with iron or copper. Higher storage temperature also lead to more rapid discoloration. To minimize discoloration store phenol at temperatures below 60°C (140°F) in dark glass containers. The dark color is formed when polymerization of phenols occur, such reactions produce high molecular weight colored poly-residues and are likely catalyzed by trace metals eg. Cu and Fe. Minimization of color in high purity phenol can therefore be best achieved by using inert containers constructed of stainless steel or lined carbon steel. If during the time of bulk industrial storage the tanks and transfer piping are not constructed of stainless steel or lined carbon steel, some impurities will be incorporated into the phenol leading to discoloration.
Phenol also darkens when exposed to light, so whenever possible reagent containers should be kept in the dark and nitrogen-blanketed to minimize color development.
Redistilling the discolored phenol under reduced pressure in a N2 atmosphere.
Regards
Redistilling your discolored phenol under reduced pressure under a N2 atmosphere can remove the color.
First re distilled with careful precautions and then keep it in a dark bottle at 4 degree. No polymerization will occur.
That is normal in extraction/hydrolysis. If you have a freeze-dried sample mixed with aqueous methanol and HCl started with a pale colour at the end after complete refluxing for 2h the colour turns red. I found some good explanation such mentioned above plus effect of PH.
Good luck
Aly R Abdel-Moemin
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