You're dead on.  Purge the flask with an inert gas beforehand.  Even propane will work.  If the coil is completely submerged, it shouldn't catch fire, but why present the risk? Methanol does have a good range of explosive limits.  A good idea nonetheless, prepuce. 

What sort of power supply are you running? I know for sure a computer power supply will not do it, they have surge/short protection that will cause them to turn off instantly if there is a short.  Unless the resistance is high enough of course, such as nichrome or a perfectly balanced gauge of copper wire (like you suggested)

The reaction itself is an exothermic one and I am not really sure if it will work submerged in the MeOH. The old text book procedures to demonstrate this effects always told to heat the wire and suspend it above the MeOH so as it reacted with the Methanol vapors it would convert them to formaldahyde and heat the wire keeping it red hot for a long period of time. The wire will stay heated after the reaction has kicked in due to the exothermic nature of the reaction.

Would NiCr wire work for this? or does it need to be copper?

I know hot Cu will turn CH3OH into CH2O + H2, and no oxygen is needed...

However, I am pretty sure that reaction is endothermic, while the oxidation of the H2 present is exothermic enough to make up, and continue the endothermic reaction.

Pt wire automatically does it with out any needed heat, IIRC, this to me seems like Ni would do it if Pt, Pd, and Cu all do it as well.. and so possibly NiCr wire could work.

Best to blow some propane through it anyways I think.

Considering the surface area of the wire, this probably isn't the best method unless you can have it reflux for several hours, while collecting the gas that comes off of it.

I'm sure you'd be much better passing MeOH through some Cu powder, or something like that which has a ton of surface area.

Before I acquired paraformaldehyde, I was in the process of making a heavily copper laced per-lite pebbles. Well, it was similiar to perlite at least?
I'm sure better things exist, that is just what I choose to use at the time. Calcium sulfate, activated carbon, etc all laced heavily in Cu powder would probably be very useful.

The Cu powder being produced by dissolving a copper hydroxide/oxide in ammonia, and evaporating on the substrate, and then reduce the Cu hydroxide left with the methanol at a high heat. Perhaps by the pyrolysis or reduction of the nitrate might be useful as well...

Can most all primary alcohols be dehydrogenated to the aldehyde this way?

I.e ethanol, propanol, Benzyl alcohol, etc? I've never heard any success other then with MeOH, and even then.. never any yields or if it were even satisfactory given the time and apparatus needed.

According to my textbook, the reaction is: CH3OH + O2 -> (copper) -> HCHO + H2O

If it's not obvious from the way I stuck it in the equation, the copper is a catalyst. That's why I used a copper wire and not nichrome.

The reason I don't think the reaction is exothermic to the point of being self sustaining is that during my first experiment I immediatly turned off the power supply when it caught fire, and the reaction stopped instantly, even though the copper was still partially in the MeOH.

I tried this again by keeping the wire submerged, filling the reaction flask with CO2 and another problem immediately presented itself. When under the liquid, the wire wouldn't get hot enough to cause the reaction. I traded my voltage source for a computer power supply that could provide 26A at 5V, but that didn't work because the voltage was too low. So I switched to 12V. It made the liquid boil like crazy but the wire wouldn't get red hot. I suspect it can't be done without vaporizing the whole pot.

I was surprised that all this made no formaldehyde, since my little experiment that caught fire did, but then I realized there was no available oxygen. An inert atmosphere won't work for the same reason.

So I thought maybe the wire could be moved above the surface of the MeOH and the liquid refluxed while the temperature of the copper was carefully controlled. To be safe (for once) I looked up the temperature of formaldehyde formation using this procedure, and found it was done industrially at 550 - 600C. Then I looked up the autoignition temperature for MeOH and found it was 470C. It seems there's something wrong here.

I kept poking around and found reference to the fact that diluting MeOH with 3-4 times the volume of water will make it inflammable. I don't that's the answer, though, because it doesn't form an azeotrope, so the MeOH would boil off first and explode or burn furiously before the water came over.

The only way I can think of that this could be done would be to set up a matrix of copper wire closely spaced and criss crossing itself, putting enough current through it to make it red hot, then spraying a mixture of 4 parts water and one part MeOH over it at a fairly slow rate. That must be how they're doing it industrially.

PP

Sedit ,  yours all sound like good ideas, except for one thing. Supposedly the reaction that turns MeOH into HCHO takes place between 550 and 600C. At the high point this is over 100 degrees above the autoignition temperature. I would think that having MeOH fumes would make it more likely that you'd have an explosion than a fire.

Maybe the reaction temps don't have to be that high, though. Have you seen references to the required temps?

The other textbook I was reading definintly explained the procedure like this. Take a piece of heavy copper wire and heat it in a bunsen flame until it glows red hot. At that point plunge it into a beaker of MeOH, then note the odor produced.

Do you think that copper sulfate would work as the copper catalyst in the tube? I'll bet that diatomaceious earth would make a great carrier. It's said to have a very high internal surface area and it's cheap and available.

I'd like to try your idea if we knew that the catalyst didn't have to go beyond the autoignition temp of MeOH. I like that much better than fabricating a copper sieve.

PP

Thanks for the link, Vesp. I'll definitely look at it.

I tried one more time with the heated copper. This time I diluted the MeOH with four times it's own volume, and suspended the hot wire about the surface of the liquid. I checked a sample of the MeOH to make sure that it had been made non-flammable, and it had.

My idea was to use a mag. stirrer and turn it up high enough that it would contiuously splash MeOH/Water on the hot wire. It worked, kind of. It's just that when the solution hit the wire it apparently split and the MeOH still burned. It wasn't much of a flame and it was pretty to watch. Nevertheless I had to use the wet towel to put it out. I added more water and tried again.

Sedit said,
"PP if you want to test if to see if its formaline now you could add an acid which will turn it to its insoluble trimer paraformaldahyde."

When I wrapped up the experiment I noticed that the MeOH had become cloudy. Does formaldehyde cause that? It looks like very diluted milk. I tried the test with acid but it was inconclusive. It looks like something may be falling out of the suspension but I won't know that for a while.

I started this thread because I had heard several people talking about needing formaldehyde, then I got the idea of doing the way I've been talking about. I assume it can be used to do interesting things so I wouldn't mind having some. 

PP

Its not so great, and I only got qualitative yields.
Though, I think solvent extraction with something like IpOH or another solvent that salts out would do the trick for aldehydes, as well as some other things...

sulfuric acid - might be impure though from the dye that would be trapped. Paraformaldehyde can be purchased for the same thing as well though, however.