[John In WI]

I was hoping for some sage formic acid advice.

I have a 500ml 98% bottle that is at least 2 years old.  I pulled it out of the freezer today (set to 0C), and noticed a block of ice on the bottom, and clear liquid on top.

I know about the procedure for purifying acetic acid using fractional crystallization, but had never heard of it with formic. 

After this length of time, certainly a large amount of the acid would have decomposed to water and CO, but I'm wondering if I can decant off the water/formic acid solution, and get a fairly dry formic acid ice? (then go ahead and dry it with boric anhydride).

My intent is to dry it, then distill it directly into my reaction--a formylation of an amine with acetic anhydride.

Any thoughts?

[discodermolide]

I was hoping for some sage formic acid advice.

I have a 500ml 98% bottle that is at least 2 years old.  I pulled it out of the freezer today (set to 0C), and noticed a block of ice on the bottom, and clear liquid on top.

I know about the procedure for purifying acetic acid using fractional crystallization, but had never heard of it with formic. 

After this length of time, certainly a large amount of the acid would have decomposed to water and CO, but I'm wondering if I can decant off the water/formic acid solution, and get a fairly dry formic acid ice? (then go ahead and dry it with boric anhydride).

My intent is to dry it, then distill it directly into my reaction--a formylation of an amine with acetic anhydride.

Any thoughts?

It seems to me that formic acid is cheap so why not just buy a new bottle. The effort you will have to "dry "it will be more costly that a new bottle and you still cannot be sure what you will get is formic acid in the desired purity required, especially after distillation!
If I remember correctly heating formic acid causes its decomposition, so distillation is out, especially as it produces carbon monoxide. So you may end up with a sudden release if gas in your apparatus, so don't distill it.
Buy a new bottle.

[Nosterius]

From the book "purification of laboratory chemicals, fifth edition", there are many ways to dry formic acid.

Phtalic anhydride, anhydrous CuSO4, boric anhydride are suitable drying reagents but may need different heating/time of contact. It also needs to be distilled at reduced pressure (b.p. 25°C at 40 mm Hg) and the receiver flask is cooled in ice-water.

It can also be purified by fractionnal cristallisation (which is probably what you did by putting the bottle in the freezer).

You should definitely try to get a hand on this book. And you should definitely buy a new bottle of formic acid as pointed out by Disco; it's a cheap reagent not worth the time to purify it.