This morning I decided to purify some of the commercial 1-naphthol that I have. 1-naphthol is supposed to be a pure white solid, but the commercial stuff that I have is light brown, despite being an unopened bottle from Acros Organics and claiming 99+% purity. I suppose it’s either old or whatever the brown impurity is is less than 1% by mass. I would like to use some 1-naphthol to make the dye Martius yellow, and the procedure specifies that if the naphthol is discolored, it should be distilled before using it.
Commercial 1-naphthol prior to purification.
I added 20 grams of the commercial stuff to a 500 mL round bottom flask, and set up the apparatus shown here:The 1-naphthol melted, and then began to boil, but I needed to insulate the apparatus with foil to allow it to make it to the receiving flask before condensing. I also shouldn’t have used Keck clips. The one on the right quickly melted after the gaseous naphthol heated up the glassware.Melted Keck clip.
My hotplate did not get quite hot enough to get the naphthol to distill, and it kept refluxing in the boiling flask and still head instead. Because of this, I got out my bunsen burner and carefully heated the boiling flask by moving the flame back and forth across it until nearly everything distilled.
After removing the distilled naphthol from the receiving flask and grinding it into a powder, I found that I had about 17.3 grams, for an 87% recovery. The distilled naphthol is still not completely pure, as it is a slightly off-white color, but it is obviously more pure than the material that I started with, and should be acceptable for making Martius yellow.