Sciencemadness Discussion Board

How to form formalin from paraformaldehyde?

chochu3 - 7-11-2005 at 03:41

I have tried making formalin from paraformaldehyde and distilled waster using a little NaOH. The product had a pink tint to it. Is this from adding to much sodium hydroxide?

My source of paraformaldehyde is from Campa-Chem. I wash the crystals with water until it gets most of the blue color off. Then I add water that has been heated to 75 degrees celsius to wash off more of the dye. In the end my crystals still have a slight light blue tint.

I also heard one could heat some deionized water to 70 degrees celsius then add the paraformaldehyde to it in which it would dissolve upon further heating.

Has anyone ever tried to make formalin from paraformaldehyde or have any suggestions?

S.C. Wack - 7-11-2005 at 04:25

This product is hardly "paraformaldehyde". It contains very large amounts of dye and perfume and is specially made not to dissolve easily, for obvious reasons.

I happen to know that a dilute solution of formaldehyde (lets just call it that regardless of what it might actually be in solution or water vapor) can be made by distilling this product repeatedly with dil. H2SO4 (water only added after the first distillation) until all of the HCHO has distilled over. This will take several times as it does not distill easily. There is still some perfume. The solution can be evaporated to yield a cleaner polymer.

Or do your own thing.

I do not suggest using this product for anything other than its labelled use.

[Edited on 7-11-2005 by S.C. Wack]

While the subject has been broached…

BromicAcid - 7-11-2005 at 19:05

This might seem like too easy the subject for some or it might seem like I didn’t do any searching at all, but considering the price of shipping though my normal suppliers of concentrated aqueous formaldehyde I was considering just buying some paraformaldehyde from them and converting to formaldehyde. I searched the web and most of my hits were in relation to older photography formulas and they all involved taking the paraformaldehyde and heating to boiling or near boiling in water and adding a few drops of concentrated NaOH. Is this solution really (for the most part, I’ve read how formaldehyde can be) a solution for formaldehyde that can be used as such in a synthesis? I found some hits for sciencemadness in the bunch but just a vague outline of the procedure.

Also S.C. Wack you mentioned a distillation with dilute sulfuric acid, is this just preformed by adding the paraformaldehyde to a solution of dilute sulfuric acid and distilling, giving a distillate of formaldehyde, does it come over as an azeotrope or do I have to lead the distillation under the surface of the liquid that condenses to bubble the formaldehyde gas through the liquid? I figure I have to make it as I cannot find it in OTC products any more, the local pet store sold solutions of formalin that either specifically stated “Formaldehyde Free!” or “Less then 3% formaldehyde.”

S.C. Wack - 7-11-2005 at 20:32

The subject of depolymerizing real paraformaldehyde came up earlier and I stand by my answer in that thread, reflux for a few hours. I find addition of anything unnecessary.

IIRC H2SO4 was chosen after reading the large body of patents bought by Thetford, although that product itself is not covered by any patents. It was also chosen as a pH <2 serves to dissolve various polymers, some HCHO polymers do not dissolve in alkali. There are also additives that modify the depolymerization, though whether they are in this product, I don't know.

This product was not heated high enough over its mp to release any monomer, there was probably a good reason (the appearance of the product on melting) why I didn't do strong heating. I did get some of the perfume oil to distill on moderate heating. I had a feeling that the formaldehyde reacts with the dye and perfume some upon dry distillation.

The bp with aq. distillation was not taken as no Claisen was used; the apparatus was flask, receiver, Liebig, 3-way adapter, and addition funnel. Water was added at the same rate that it distilled off, and three or four volumes of water were necessary to get all of the formaldehyde into the receiver.

In any case, IMHO the pure product is likely best bought if you can find it, rather than made from this crap. It is probably cheaper that way anyways. Believe me, I'm all for purifying crap OTC products, and sure, go ahead and try it, but you will get expensive formaldehyde by this route also.

S.C. Wack - 29-3-2014 at 16:32

I revisited this later without the acid, and although nothing but dye seems to be dissolving in water because a large volume of prill remains after heating in the RBF + condenser for days, decanting, repeating &so on, a large amount of formaldehyde will be found in the distillate after distilling these combined solutions.

BTW little formaldehyde comes over under aspirator vacuum distillation of this distillate. If the pot contents are poured out on a plate while hot after the excess water has come off (when the temperature rises), a wax with riot control possibilities is obtained on cooling. If this wax is set aside in a desiccator thingy for some time maybe er years with say conc. sulfuric acid drain cleaner, a much more agreeable product resembling genuine paraformaldehyde in every way will be waiting.

It would probably be more sensible to add some water to the more expensive methanolic product, and try to vacuum off the methanol.

Refinery - 30-3-2014 at 14:16

Paraformaldehyde should decompose to formaldehyde by pyrolytic heating, and formaline can be obtained by leading the formaldehyde gas into water.

notCRAZYatALL - 18-7-2015 at 17:26

The paraformaldehyde will decompose to formaldehyde at what temp? Does it need to be heated in the absence of oxygen?

[Edited on 19-7-2015 by notCRAZYatALL]

kykeon - 19-7-2015 at 00:43

If a methanolic solution will work for you, its very easy. Just reflux paraformaldehyde in methanol for about 45 minutes.
You can make it fairly concentrated, If I recall correctly Ive made a 40% solution this way, but you can probably go higher if you want to.


[Edited on 19-7-2015 by kykeon]

beerwiz - 12-11-2015 at 10:38

I do this all the time. To get a 37% formaldehyde solution, weigh out 37g of paraformaldehyde and put it into 100ml of distilled water.

Setup your mag stirrer and heater, preset the temp to 60 degrees on your water bath, it may take a while until it reaches that temp and stays put without major fluctuations depending on your model.

I use a 250ml beaker for this, put the beaker with the paraform and water on the water bath and cover it with cling wrap to limit the smell/evaporation.

For 100ml 37% formaldehyde I add a total of 1ml 1N NaOH slowly drop by drop over the course of an hour. About 45min to 2 hours later (from the start of heating at 60 C) you'lll see that you now have a clear solution with a few tiny pieces of paraformaldehyde on the bottom that you can filter out. Your 37% formaldehyde solution is now ready to be used. If you want to store it long term, you can add 5% methanol to it by volume or in this case 5ml.

If you keep it in the freezer you don't even need to add methanol and it will hold for at least a month or more.

JJay - 12-11-2015 at 14:41

Quote: Originally posted by beerwiz  
I do this all the time. To get a 37% formaldehyde solution, weigh out 37g of paraformaldehyde and put it into 100ml of distilled water.

Setup your mag stirrer and heater, preset the temp to 60 degrees on your water bath, it may take a while until it reaches that temp and stays put without major fluctuations depending on your model.

I use a 250ml beaker for this, put the beaker with the paraform and water on the water bath and cover it with cling wrap to limit the smell/evaporation.

For 100ml 37% formaldehyde I add a total of 1ml 1N NaOH slowly drop by drop over the course of an hour. About 45min to 2 hours later (from the start of heating at 60 C) you'lll see that you now have a clear solution with a few tiny pieces of paraformaldehyde on the bottom that you can filter out. Your 37% formaldehyde solution is now ready to be used. If you want to store it long term, you can add 5% methanol to it by volume or in this case 5ml.

If you keep it in the freezer you don't even need to add methanol and it will hold for at least a month or more.


That wouldn't make a 37% solution... it would make a 27% solution. To make a 37% solution, you would want to use 63 mL H2O, correct?

beerwiz - 12-11-2015 at 16:54

Quote: Originally posted by JJay  
Quote: Originally posted by beerwiz  
I do this all the time. To get a 37% formaldehyde solution, weigh out 37g of paraformaldehyde and put it into 100ml of distilled water.

Setup your mag stirrer and heater, preset the temp to 60 degrees on your water bath, it may take a while until it reaches that temp and stays put without major fluctuations depending on your model.

I use a 250ml beaker for this, put the beaker with the paraform and water on the water bath and cover it with cling wrap to limit the smell/evaporation.

For 100ml 37% formaldehyde I add a total of 1ml 1N NaOH slowly drop by drop over the course of an hour. About 45min to 2 hours later (from the start of heating at 60 C) you'lll see that you now have a clear solution with a few tiny pieces of paraformaldehyde on the bottom that you can filter out. Your 37% formaldehyde solution is now ready to be used. If you want to store it long term, you can add 5% methanol to it by volume or in this case 5ml.

If you keep it in the freezer you don't even need to add methanol and it will hold for at least a month or more.


That wouldn't make a 37% solution... it would make a 27% solution. To make a 37% solution, you would want to use 63 mL H2O, correct?


Now I'm not sure, can someone confirm?

JJay - 13-11-2015 at 03:43

I'm pretty darn sure.

I was thinking about washing some RV septic tank deodorizer and then heating it in an iron pipe nipple retort with a torch to produce formaldehyde gas and bubbling the gas into water to create a formaldehyde solution... this is likely to be smelly and toxic, correct..?

[Edited on 13-11-2015 by JJay]

brew - 20-11-2015 at 16:15

Quote: Originally posted by beerwiz  
Quote: Originally posted by JJay  
Quote: Originally posted by beerwiz  
I do this all the time. To get a 37% formaldehyde solution, weigh out 37g of paraformaldehyde and put it into 100ml of distilled water.

Setup your mag stirrer and heater, preset the temp to 60 degrees on your water bath, it may take a while until it reaches that temp and stays put without major fluctuations depending on your model.

I use a 250ml beaker for this, put the beaker with the paraform and water on the water bath and cover it with cling wrap to limit the smell/evaporation.

For 100ml 37% formaldehyde I add a total of 1ml 1N NaOH slowly drop by drop over the course of an hour. About 45min to 2 hours later (from the start of heating at 60 C) you'lll see that you now have a clear solution with a few tiny pieces of paraformaldehyde on the bottom that you can filter out. Your 37% formaldehyde solution is now ready to be used. If you want to store it long term, you can add 5% methanol to it by volume or in this case 5ml.

If you keep it in the freezer you don't even need to add methanol and it will hold for at least a month or more.


That wouldn't make a 37% solution... it would make a 27% solution. To make a 37% solution, you would want to use 63 mL H2O, correct?


Now I'm not sure, can someone confirm?


Density is 1.42g, hence 37g/1.42 = 26g, hence added to 100ml of H20 is aprox 27% 26/69ml = 0.37 therefor 37% aprox, but close. So imo, its adding 37g of actual PF to 69mls of water, but maybe someone should confirm this also. :cool:

careysub - 20-11-2015 at 18:13

Whether or not it "really" makes a 37% w/v solution, many formalin preparation protocols, of which there are many on-line, call for adding 37 g of formaldehyde gas (or paraformaldehyde) to 100 mL of water. So this is apparently what many people using "37% formaldehyde solution" are actually using.

http://cshprotocols.cshlp.org/content/2008/6/pdb.rec11372.fu...
http://www.flinnsci.com/teacher-resources/biology/frequently...
http://stainsfile.info/StainsFile/prepare/fix/agents/termino...
https://books.google.com/books?id=9DzS5ueDQBkC&pg=PA57&a...

brew - 20-11-2015 at 21:49

Quote: Originally posted by careysub  
Whether or not it "really" makes a 37% w/v solution, many formalin preparation protocols, of which there are many on-line, call for adding 37 g of formaldehyde gas (or paraformaldehyde) to 100 mL of water. So this is apparently what many people using "37% formaldehyde solution" are actually using.

http://cshprotocols.cshlp.org/content/2008/6/pdb.rec11372.fu...
http://www.flinnsci.com/teacher-resources/biology/frequently...
http://stainsfile.info/StainsFile/prepare/fix/agents/termino...
https://books.google.com/books?id=9DzS5ueDQBkC&pg=PA57&a...


My bad if Ive added confusion. I do know that the polymer is apparently containing many different lengths of monomers joined, hence the idea to look up the density and use that in the math. I hadn't done the reaction, and had heard that the process requires the gas generated from PF, piped into water etc, as well as MeOH inclusion.
On a side note, agricultural and animal feed supply places are often good sources for the formalin, but that's somewhat of topic. Cheers.

ave369 - 21-11-2015 at 01:38

If you want to make formaldehyde, better make it by calcining calcium formate. This you make from formic acid and chalk, and formic acid can be distilled from glycerol and oxalic acid.

JJay - 21-11-2015 at 09:51

37% is 37%... it was a rhetorical question.

clearly_not_atara - 21-11-2015 at 14:39

I suggest using dimethoxymethane as an intermediate. It can be distilled and cracks to give formalin.

Paraformaldehyde + dry MeOH + conc H2SO4 >> (MeO)2Me (evaporates)

(MeO)2Me + 1% aq. H2SO4 >> 2 MeOH + CH2O
Quote: Originally posted by ave369  
If you want to make formaldehyde, better make it by calcining calcium formate. This you make from formic acid and chalk, and formic acid can be distilled from glycerol and oxalic acid.


It's a good way to get pure formaldehyde but that's way too much work compared to using paraformaldehyde if all you need is a solution in methanol.

FormicAcidAnimal - 24-11-2015 at 02:06

Quote: Originally posted by JJay  
37% is 37%... it was a rhetorical question.

JJay and beerwiz, you're both wrong. JJay would theoretically end up with an around 41% solution.
There are 37% v/w, w/w, v/v and w/v - all different
Usually 37% means w/v for solutions of chemicals and w/w for solid chemicals, if there's nothing else noted the container.

And to do this exactly you should heat your 37g paraformaldehyde first in ~60mL water and after(!) it fully dissolved fill it up to a volume of 100mL in a volumetric flask.

(As the density of the solution increases to about 1.1g/mL when dissoling the solid) ^^

And I wonder if paraformaldehyde decomposes to CH2O in refluxing toluence - than it could be used directly for making methylimines using a dean stark trap. Should be much more high yielding than using aqueous CH2O

PS: I my country drinking alcohol % like in vodka is very often in v/v btw., I guess as the same alcohol-content is looking higher than when measured in w/v
So % are not always %!


[Edited on 24-11-2015 by FormicAcidAnimal]

FormicAcidAnimal - 24-11-2015 at 02:55

Quote: Originally posted by clearly_not_atara  
I suggest using dimethoxymethane as an intermediate. It can be distilled and cracks to give formalin.

Paraformaldehyde + dry MeOH + conc H2SO4 >> (MeO)2Me (evaporates)

(MeO)2Me + 1% aq. H2SO4 >> 2 MeOH + CH2O

Quote: Originally posted by ave369  
If you want to make formaldehyde, better make it by calcining calcium formate. This you make from formic acid and chalk, and formic acid can be distilled from glycerol and oxalic acid.


It's a good way to get pure formaldehyde but that's way too much work compared to using paraformaldehyde if all you need is a solution in methanol.

Well you and up with a solution which is very acidic which can suck for many reactions. So it's far from beeing "pure"

[Edited on 24-11-2015 by FormicAcidAnimal]

JJay - 24-11-2015 at 09:26

Quote: Originally posted by FormicAcidAnimal  
Quote: Originally posted by JJay  
37% is 37%... it was a rhetorical question.

JJay and beerwiz, you're both wrong. JJay would theoretically end up with an around 41% solution.
There are 37% v/w, w/w, v/v and w/v - all different
Usually 37% means w/v for solutions of chemicals and w/w for solid chemicals, if there's nothing else noted the container.

And to do this exactly you should heat your 37g paraformaldehyde first in ~60mL water and after(!) it fully dissolved fill it up to a volume of 100mL in a volumetric flask.

(As the density of the solution increases to about 1.1g/mL when dissoling the solid) ^^

And I wonder if paraformaldehyde decomposes to CH2O in refluxing toluence - than it could be used directly for making methylimines using a dean stark trap. Should be much more high yielding than using aqueous CH2O

PS: I my country drinking alcohol % like in vodka is very often in v/v btw., I guess as the same alcohol-content is looking higher than when measured in w/v
So % are not always %!


[Edited on 24-11-2015 by FormicAcidAnimal]


You're confused here - a % formalin solution is not quite the same thing as a % formaldehyde solution. A % formaldehyde solution (for example, this one) is specified as w/w. When mixing two liquids, percentage is sometimes specified as v/v, but obviously that would be nonsensical for a % formaldehyde solution since formaldehyde is a gas. w/v doesn't give percentage units.

chemrox - 10-3-2016 at 18:30

Question: I have a procedure involving methylamine HCl, formaldehyde aq. sol. and a styrene (a-methyl) if it matters.. the question is can I sub in Meam 40% aq for the salt and use paraformaldehyde in place of 37% aq formaldehyde? i.e. does the paraformaldehyde depolymerize in water?

clearly_not_atara - 11-3-2016 at 11:56

Not spontaneously -- it would require the presence of acid. HCl can depolymerize formaldehyde but the reaction produces considerable amounts of bis-chloromethyl ether, as I recall, which is not a nice friendly compound.

chemrox - 11-3-2016 at 17:28

Yes and one problem with the synthesis is the acidity produced which was compensated with 25% NaOH! So I won't try it thanks. Don't need more NaOH than already required.

laserlisa - 15-3-2016 at 06:09

Quote: Originally posted by kykeon  
If a methanolic solution will work for you, its very easy. Just reflux paraformaldehyde in methanol for about 45 minutes.
You can make it fairly concentrated, If I recall correctly Ive made a 40% solution this way, but you can probably go higher if you want to.


[Edited on 19-7-2015 by kykeon]

I can confirm that this works, its really that simple.