Boffis
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Naphthalic acid
As a byproduct of preparing acenaphthenequinone I have recovered a small amount of naphthalic acid. The material is rather impure and appears as a
fine, straw coloured, powder rather than the "white crystalline compound" described in Donaldson's Naphthalene Compounds.
In the above mentioned book they makes a brief mention of this compound and that it can be purified by treating with bleach to which it is inert. I
have tried this and sure enough much of the brown colour of the crude compound was rendered insoluble and filtered off. The acid then being
precipitated with aqueous HCl. It is however, still a straw coloured powder, just a little paler and repeated treatment has no further effect.
It is quite insoluble in water but dissolves in alkalis and can be re-precipitated with acid but this does not change its colour.
Has anyone else ever come across this compound or its salts? Can it be purified by recrystallising a salt, if so which one? The Na and K salts are
very soluble, don't seen to crystallise well and take the colour of the solution from my experience. Does it esterify? And what does the commercial
product look like.
It is a useful compound that ready forms an anhydride that reacts in a similar manner to phthalic anhydride. It is also the starting material for many
perylene dyes.
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Jenks
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What happens if you rinse the salts with a solvent? Maybe start with something non-polar that it surely wouldn't dissolve in and work your way up
through acetone to alcohols. If you only have a little, this might be a good candidate for a plug filtration of the acid through silica gel, as it is
non-polar enough to not bind irreversibly. Of course there is decolorizing carbon, but the naphthyl group might like to stick to that, so only use a
little carbon.
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Boffis
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Hi Jenks; naphthalic acid is sparingly soluble in most solvents so this idea is probably worth following up. I have found a reference that states that
it is soluble in hot alcohol so I may be able to recrystallise it from this solvent. I have tried charcoal on the sodium and potassium salts and it
didn't work.
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