Sciencemadness Discussion Board - On making paraformaldehyde from formalin

On making paraformaldehyde from formalin

NaK - 24-6-2020 at 11:14

This experiment is inspired by a few comments on this board and the industrial method.

Let's preface this with saying that if you can buy paraformaldehyde (like it is the case in a lot of countries) this is not worth it.
Also formalin on its own is sufficient for a lot of reactions. There are some though that require water-free conditions and are only practical with paraformaldehyde.

Because I did multiple trial and error runs with reusing formaldehyde solutions with unknown concentrations I can't confidently comment on the yields but they should be at least around 70%, probably a lot higher.

So here is how I did it:
(1) add 40% formaldehyde solution to a (preferably round bottom) flask
(2) assemble a vacuum distillation setup (or if you are really lazy attach a gas adapter and call it a day.)
(3) distill the solution under strong vacuum. The better the vacuum the better the separation. A run with a boiling point of 80C (500mbar) was a complete disaster as the distillate was almost as concentrated as the original solution. Aim for a boiling point between 20 - 40C (20-80mbar)
(4) Distill off at least half the volume of the solution. A sudden color change from colorless to milky-white is an indicator for rapid polymerization.
(5) Stop distilling when you have a syrup-like thick liquid
(6) Poor from flask into a beaker or preferablly a crystalizing dish. Let it dry on the open air and stir from time to time. It will transform to a slurry, then a kind of wax and finally become completely opaque and brittle. For me it took two days on a dish to become completely solid. To speed up the process you can crush the hard parts in a morter to expose more undried surface area.
(7) If you need it completely water free the last step is to dry it in a vacuum desicator over P4O10 (preferred) or a plastic bag with freshly ground NaOH.

Additional notes:
1. Aspirator vacuum is recommended as formaldehyde in the pump oil might be slightly unpleasent.

2. Air drying of the paraformaldehyde releases formaldehyde gas. Best drying conditions I found were outside on a warm day with a small breeze. Removes all formaldehyde vapors and is very quick as well.

Refinery - 24-6-2020 at 12:00

Regarding on the topic, are there any reasonable otc sources of (para)formaldehyde, since I haven't found any consumer use for this substance?

NaK - 24-6-2020 at 12:35

Formalin is sometimes sold as a fish treatment. It's insanely expensive though, mine was like 20€/l

draculic acid69 - 24-6-2020 at 17:43

How could you treat fish with formaldehyde?

mackolol - 25-6-2020 at 01:37

When I was making paraformaldehyde, I didn't want to bother with any vacuum distillations and etc.
I just have read somewhere that treatment of 40% formalin with sulfuric acid should yield paraformaldehyde too.

I fillled flask with my freshly bought formalin and poured some amount H2SO4. I put the flask in freezer but nothing happened overnight.
So I just left the flask as it was not willing to clean it up. After 1 day some white precipitate covered flask walls and after yet few days I was left with decent amount of white cake that covered the flask. After some scratching I got my paraformaldehyde out and filtered it. I don't know how big the yield is, but taking in mind that formalin is very cheap it looks like good way to go.

Then I tried to thermally crack the paraformaldehyde by refluxing it in methanol, because I wanted to make anhydrous formaldehyde/methanol solution, but after almost a day of reflux and no effects I gave up. I thought that methanol should crack the polymer bonds somehow even if the temperature wasn't too high.

DavidJR - 25-6-2020 at 22:14

Quote: Originally posted by mackolol

I fillled flask with my freshly bought formalin and poured some amount H2SO4. I put the flask in freezer but nothing happened overnight.
So I just left the flask as it was not willing to clean it up. After 1 day some white precipitate covered flask walls and after yet few days I was left with decent amount of white cake that covered the flask. After some scratching I got my paraformaldehyde out and filtered it.

How much acid did you add?

[Edited on 26-6-2020 by DavidJR]

Dihydrogenmonoxide - 26-6-2020 at 05:54

Quote: Originally posted by draculic acid69

How could you treat fish with formaldehyde?

I'm not 100% sure but there is some kind of parasite that is sitting on the outside of the fish. When you add formaldehyde to the water it doesn't hurt the fish but the parasite dies off. It's said to be quite effective

Dihydrogenmonoxide - 26-6-2020 at 05:58

Quote: Originally posted by mackolol

When I was making paraformaldehyde, I didn't want to bother with any vacuum distillations and etc.
I just have read somewhere that treatment of 40% formalin with sulfuric acid should yield paraformaldehyde too.

I fillled flask with my freshly bought formalin and poured some amount H2SO4. I put the flask in freezer but nothing happened overnight.
So I just left the flask as it was not willing to clean it up. After 1 day some white precipitate covered flask walls and after yet few days I was left with decent amount of white cake that covered the flask. After some scratching I got my paraformaldehyde out and filtered it. I don't know how big the yield is, but taking in mind that formalin is very cheap it looks like good way to go.

Then I tried to thermally crack the paraformaldehyde by refluxing it in methanol, because I wanted to make anhydrous formaldehyde/methanol solution, but after almost a day of reflux and no effects I gave up. I thought that methanol should crack the polymer bonds somehow even if the temperature wasn't too high.

One of the biggest problems with homemade paraformaldehyde: It tends to form really long chains that are very hard to dissolve again. Industrially there are some methods to reduce this but I didn't bother to look into them right now. Higher temperatures in a different solvent could have worked better

[Edited on 26-6-2020 by Dihydrogenmonoxide]

Fyndium - 15-3-2021 at 11:07

About paraformaldehyde smell.

I have a very old, +14 years small bottle of para, and just got some new. Now, the new has slight odor, but the old one smells like death. Does it have shelf life or is it still useable? It's still free flowing white powder.

Triflic Acid - 14-7-2021 at 05:03

Odd, you say that yours has a slight odor. Mines is nauseating to be around when open. It has a kind of burning sensation. Is it just the heat in my garage lab, or is there something wrong with one of our paraformaldehydes?

karlos³ - 14-7-2021 at 06:46

I have a bottle that must be around ~5 years old and its a free flowing white powder too with just a very faint smell.

Triflic Acid - 14-7-2021 at 07:22

What is the temp there?

karlos³ - 14-7-2021 at 08:46

Maybe around ~25°C?

Triflic Acid - 14-7-2021 at 09:24

My lab is reaching 40 on some days, maybe that's why?

karlos³ - 14-7-2021 at 12:32

But is it just plain formalin smell?

Triflic Acid - 14-7-2021 at 13:13

Yeah, but very strong

karlos³ - 15-7-2021 at 08:48

Just got home, one of the first things I made was a formaldehyde solution from PFA...
I opened said bottle, and I am not sure if it was just fine dust or actual vapor, but a little cloud exited the bottle

It looked more like dust and not vapor though.
The smell was just very faint as I had in mind from memory.

Catslovechemistytoo - 11-9-2024 at 22:29

Quote: Originally posted by Dihydrogenmonoxide

So can anyone please explain how to prepare paraformaldehyde with shorter chains?
Because it seems like homemade paraformaldehyde made by vacuum distillation can impair reactions in which it's used.

chemship1978 - 12-9-2024 at 02:45

In case anyone is interested, I have large quantities of paraformaldehyde to sell cheaply. It's a very useful formaldehyde storage form, as it doesn't degrade at all with time. It can be easily depolymerized in solution with a small amount of base.