Zinc dust distillation of 2-naphthol
glass beads or coarse sand
2-naphthol Xn N R 20/22-50 S (2)-24/25-61
zinc (dust) F R 10-15 S 7/8-12-43
If 1-naphthol could have also been used as an alternative was not investigated.
Dangerous substance information
naphthalin Xn N R 22-50/53 S 36/37-60-61
burner (gas or alcohol)
- One adds to a test tube a heaping spatula-tipful of 2-naphthol and of zinc dust and mixes these by carefully shaking. Afterwards one fills the test tube with glass beads about 3.5 cm high or with sand about 2.5 cm high.
- One warms the test, which is held at an angle, with the burner flame (in the case of an alcohol burner as powerfully as possible) such that if possible only the bottommost part is directly heated, but not the glass beads or sand (see Elucidation). At the bottom a dark, possibly green mixture develops, vapors circulate in the test tube and one sees a transparent liquid flowing down the glass beads (with sand difficult to see), while at the top of the test tube a brilliant white, very fine crystallized power is deposited.
- After one has produced some sublimate, one ends the heating, otherwise decomposition products are produced which cause impurities.
- In order to examine the product one can scratch off some of the material with a spatula. It can be recognized as napthalin not only through its very pure color but above all through its highly typical smell, which reminds one of mothballs. Another possibility to differentiate the product from the reactant is the insolubility of naphthalin in strongly basic solutions (safety goggles!).
- One can obviously save the naphthalin, but the amount is quite small. If one has used glass beads, then one can, of course, use these again. Inasmuch as it is very difficult to get them fully clean, it would be a possibility to specifically save them for similiar purposes.
- All remaining waste can be disposed of as halogene-free organic waste.
Zinc dust acts even under drastic conditions without acid or base catalysis as a strong reducing agent, and is even capable of reducing a (activated) aromatic hydroxyl compound to a hydrocarbon, a synthetic transformation which is otherwise, in contrast to aliphatic alcohols, only possible with very special methods. Since the yield is usually very poor and in addition substantial rearrangements and eliminations within the molecules can occur, this reaction has never had a important preparative significance. It was however previously important in analysis, so for example morphine yielded as a major product phenanthrene, which was of great importance for the structural investigation (which lasted for a good century) of this molecule, and which at the same time shows how dramatic the above mentioned side reactions turn out. The sand or glass beads by the way do act as a cooler in order that the reaction partners have enough time to react with one another.
If someone should find that the product does not smell at all like mothballs, then this could be because the naphthalin for this purpose has been replaced over the last decades by p-dichlorobenzene, which occurs as a cheap by-product in the industrial production of chlorobenzene or o-dichlorobenzene.