Paraformaldehyde & formalin question

Friendlycat · Sun Sep 25, 2005 12:58 pm

If I want to make 100g 37% formalin from paraformaldehyde, is it as simple as adding 37g (100%) paraformaldehyde and adding water to make it up to 100g and then heating?

I ask because I've seen methylamine synths with paraformaldehyde and NH4CL where a lot more water is used than the corresponding synth with formalin and NH4CL. Why is that?

bio · Working Bee

If the formalin is made stronger say 50-55% yield improves in the reaction with NH4Cl.

According to Ullmans........The boiling points of pure aqueous solutions containing up to 55 wt % formaldehyde are between 99 and 100 °C at atmospheric pressure.

So distilling or refluxing the calced amount of paraform should give the aqueous concentration desired.

Friendlycat · Thu Sep 29, 2005 9:36 am

How long do you reflux the paraformaldehyde? I see that the para disolves readily in hot water, but that doesn't mean depolymerisation does it?

bio · Working Bee

This is one way, reliability unknown to me. A catalyst is needed to speed things up. Check Vogel seems there is a procedure there as well.

Excuse the cut and paste job

.................To obfain a formaldehyde solufion add 100 g of paraformaldehyde granules fo a boffle and dilufe wJ fo make 250 mL of solufion. Add a small amounf of sodium hydroxide, approximafely 120 mg, fo fhe soh boffle and shake fo dissolve some of fhe paraformaldehyde. Place fhe boffle info a hof wafer bafh healed
to 60deg for 25-30 minufes. Every 5 minufes shake fhe boffle and open if fo venf any gasses. Some of fhe parafon not have dissolved, it can be filtered off, or heat the bottle longer. The resulting formaldehyde solution 40% and will remain fresh for a few days if refrigerated. ..............

Friendlycat · Tue Oct 04, 2005 4:12 am

Well thank you,
I guess the NaOH won't interfere when synthesising Methylamine.HCL

bio · Working Bee

It's such a miniscule amount it shouln't matter but I'd add the calced amount of HCl anyway when complete if it shows over pH 8 or so.