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Author: Subject: Methanol -> methanal
Ramiel
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smile.gif posted on 19-8-2002 at 02:14
Methanol -> methanal


I have already asked this question at an anarchy board, and no response save from MadScientist, so he reccomended that he come here.
I have great respect for this board already!
ok, here we go... verbatim:
Since formaldehyde (Methanal) is hard to buy because of restrictions [it being carcinogenic] and the lack of a good supplier in the first place, I want to manufacture my own. Two questions:

Because methanol is found easily, and is a primary alcohol (fast reaction); oxidizing it (e.g. with Cr^2O^7 2-) would yield a high purity methanal.
(1) The Cr^2O^7 needs to be acidified, would the H+ from 2 parts of Hydrochloric work just as well as the H+ from 1 part Sulfuric?

(2) Reaction:
3.(CH^3OH => HCHO + 2H+ + 2e-)
Cr^2O^7 2- + 14H+ + 6e- => 2Cr 3+ + 7H^2O
Is that right?
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vulture
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[*] posted on 19-8-2002 at 05:29
Don't use HCl!!!!


Please do not use HCl with a strong oxidizer like K2Cr2O7, KMnO4, H2O2, etc because this will yield toxic chlorine gas! I'm working on the equation, can't get it right aaargggh:mad:



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[*] posted on 19-8-2002 at 06:09


Here's everything according to redoxtheory:

Cr2O7 +6e -> 2Cr 3+ X2
CH3OH -2e -> CH2O X6

So:

2Cr2O7 2- + 6CH3OH -> 4Cr +3 + 6CH2O

4- 12+
+16H+ +8H2O

follows:

2Cr2O7 2- + 6CH3OH + 16H+ -> 4Cr +3 +6CH2O + 8H2O

Total reaction:

2K2Cr2O7 + 6CH3OH + 8H2SO4 ->

2Cr2(SO4)3 + 6CH2O + 8H2O + 2K2SO4

We still miss 6 oxygens and 12H, but that nicely forms 6H2O so:

2K2Cr2O7 + 6CH3OH + 8H2SO4 -> 2Cr2(SO4)3 + 6CH2O + 14H2O + 2K2SO4


Done.




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[*] posted on 19-8-2002 at 11:12
Obtaining methanal


Okay, I see you are from Australia so unfortunately you maybe can't just get methanal from consumer products. But I am surprised that you would be able to get dichromates and not such a simple organic chemical! According to some resources I found, it is also possible to use KMnO4 for this oxidation. But in any case, methanal is fairly soluble in water and if you have an excess of oxidizing agent, it will be oxidized to formic (methanoic) acid. And if you have some formic acid along with your stronger acid and methanol all in solution, you may get some methyl formate (ester of methanol and formic acid) as well.

So as you can see it's not terribly simple. Why do you want methanal? Maybe there's a different way to obtain what you're after.
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[*] posted on 19-8-2002 at 17:39
Two practical options


Copper Chromite and oxygen or vacuum,

or

Depolymerize common paraformaldehyde into formaldehyde. Just dissolve it in methanol and heat it. In many cases, paraformaldehyde works just fine as it is.

PrimoPyro
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Ramiel
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[*] posted on 20-8-2002 at 01:57


Yes, I understand about the oxidation of HCl now, thanks for that. The reason I was interested in using HCl or something similar is it's ease of aquisition and the fact that sulfuric catalyses the reaction between methanol and methanoic acid (resulting in the ester methyl methanoate), wheras HCl doesn't [ to my knowledge ].

I understand that if the experiment is conducted drop by drop, in a water bath at 80 C, then the formaldehyde is driven off as it is produced. This would stop much of it being further oxidised to the formic acid.

Thanks, that reaction concurrs.

In Australia, formaldehyde is classified as a dangerous carcenogen, therefore it is far beyond my means to get hold of any isomer of CH2O. I can, however get as much KMnO4 as I need from a friendly chemistry teacher. ;)

As for why I want formaldehyde? Well to preserve my victims, of course :D (manufacturing Research Department 'X)
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[*] posted on 20-8-2002 at 05:46


I'm not sure, but IIRC KMnO4 will oxidize methanol to formic (methanoic) acid.

If your using conc. H2SO4, KMnO4 is a very dangerous option, not only because of the possible formation of Mn2O7, but also because the mixture could spontaneously ignite. I would then consider using H3PO4.




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[*] posted on 20-8-2002 at 14:26
Using KMnO4...


It may be that the dichromates are better oxidizers for this reaction. But aldehydes are so easy to oxidize that I think it will be easy to accidentally form HCOOH either way. I do know that when I did a quick web search I found a respectable looking page from an .edu site that said KMnO4 could be used as well as dichromates. Maybe it's not as effective but many people do not want to work with hexavalent chromium compounds because of their health and environmental effects.

Of course in neither case would you use concentrated acid with your oxidizing agent!
And if you do use KMnO4, save the precipitated MnO2 that you will get during the oxidation. It is much more active (at least when fresh) than the manganese dioxide that you might buy at a ceramics place or get out of old dry cells. It can be used as a mild oxidizing agent in its own right or used as the starting point for making many inorganic manganese compounds.
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Ramiel
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[*] posted on 21-8-2002 at 02:53
How to make Formaldehyde


Well, then it seems it is a bit of a challenge ;) I put it to your collective chemical genius. :)

by the way, we used fuming sulphuric in a lab at school with both Dichromate and Permanganate ions.
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[*] posted on 21-8-2002 at 08:08
FUMING SULFURIC???


I'm sorry, but I find that very hard to believe. Fuming sulfuric acid is sulfuric acid with 20-60% SO3 dissolved in it, also called oleum, and is very difficult to safely manipulate. I doubt schools would allow students to work it, nor even have the money to acquire it, since it is expensive.

Fuming sulfuric acid with permanganate is asking for explosions, sponteanous ignition of anything just a bit flammable in the vicinity and production of ozone.




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[*] posted on 22-8-2002 at 00:14


Fuming sulfuric, yep that's the stuff. There was only a v. small bottle of it, and we used a couple of drops.
Besides, we were working with alkenes, so there were no flames.
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[*] posted on 28-8-2002 at 09:10


Besides, we were working with alkenes, so there were no flames.

Err, adding highly concentrated sulfuric acid to permanganate will cause Mn2O7 to form, a highly unstable and very strong oxidizer which decomposes explosively into ozone which then would auto-ignite anything flammable. Certainly if you're working with highly reactive alkenes!!!




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[*] posted on 28-8-2002 at 18:08
Vulture is right


Also, very reactive ozonides will form upon treatment of alkenes with ozone gas. This is a very simple procedure known as ozonolysis. Ozonides of small alkenes are explosive and heat intolerant.

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[*] posted on 29-8-2002 at 00:40


The stuff was a syrupy viscosity. Of course the oxidizers were in solution, and pretty dilute, but we added this conc. sulphuric (which was indeed fuming copiously) strait away. So, in Australia you're allowed to make ketones, play with ozone and learn how to make TNT, but not allowed within 100m of formaldehyde... lol.
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[*] posted on 16-9-2002 at 06:21


I had thought of using a weak oxidizer such as H2O2 such that the reaction of methanol was not driven to the carboxylic acid product, and then I had a brain wave! how about using an inhibitor with a strong oxidizer or a catalyst with an even weaker oxidizer?

Here is a snippet of information I got from anguil.com which caught my eye;

In the formaldehyde production process, methanol reacts with air in the presence of catalyst to produce formaldehyde. Process yields are normally quite high, with over 95% - 98% of methanol ending up as formaldehyde.
[snip]
There is an exothermic/heat release of 300° F/149° C was expected during oxidation
[snip]
A precious metal catalyst was selected as the core of the catalytic system due to its ability to provide 98% DRE of the formaldehyde, methanol, dimethyl ether, and carbon monoxide at a catalyst bed inlet temperature as low as 500° F/260° C. The catalyst is deposited on a monolithic, honeycomb, stainless steel substrate. - I assume that simply a fine amount of this catalyst would be sufficient for lab manufacture.
[snip]
the required oxidation temperature is 500° F/260° C. The outlet temperature of the catalyst bed is approximately 800° F/427° C.
[snip]
The system operating provides well over the 98+% destruction efficiency required.

Any thoughts on adopting this method in the manufacture of methanal from methanol (wood alcohol)?
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[*] posted on 16-9-2002 at 06:51
Electrolysis


The steinberg-patent i`ve posted on the electrochemistry may be also interesting to you.
Although the production of methanol is the main purpose of the patent, it has to be noticed that formaldehyde, oxalic acid and glycollates also form as byproducts.
And the process is quite a simple one: no exotic electrodes(charcoal-electrodes with a big surface would do well..), K2CO3 as starting material(recycled in the process), air.
The most importent thing to keep in mind is the current density.
I dont know the limit of current density for this process, but it has to be kept so low, that no hydrogen develops.

Other methanol patents, just for knowing: US 4326041; US 4598061; US 5254520

HLR

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[*] posted on 18-10-2002 at 11:29


To obtain methanol is you can perform the destrutive distillation of wood. Or methanol can be extracted from solvents through distillation. I know here in the U.S some solvent called Denatured Alcohol have 90% *ethnol and about 10% methanol. Which can be isolated through distillation. But if you are doing that be careful Methanol is highly toxic.



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[*] posted on 27-10-2002 at 12:51


I believe he's trying to synth Methanal not aquire Methanol:P
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[*] posted on 27-10-2002 at 12:53


Also seperating EtOH and MeOH by disstillation is quite impractical.
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[*] posted on 27-10-2002 at 18:11
Doesn't the reaction


between acetone and bleach ..... if it is let to become hot .... produces methanal instead of chloroform.




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[*] posted on 27-10-2002 at 18:45
catalytic dehydrogenation


speaking of conversion of methanol to methanal, is something i've researched a bit myself and am interested in too. probably the most useful but of information i found on the topic is in the pdf that i've attached. it shows experimental data on various catalyists for the conversions and reaction conditions. if one could construct an apparatus that passed methanol vapor + air over a catalyist one could have a LARGE amount of methanal if they wanted.

Attachment: methanol-CHOH.pdf (149kB)
This file has been downloaded 1530 times

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Ramiel
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[*] posted on 28-10-2002 at 00:38


That seems to be an interesting doccument after looking at it breifly, thanks.

by the way, boob raider, which bleach do you mean, sodium hypochlorite (household bleach), or chlorines, or what?
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[*] posted on 1-8-2009 at 16:49


PREPARATION OF FORMALDEHYDE

In the usual way.

Attachment: jacs_42_867_1920.pdf (973kB)
This file has been downloaded 1807 times

Saw the name H. Adkins in Blazter's document and figured that this is a non-bullshit patent.

US19330613

[Edited on 2-8-2009 by S.C. Wack]
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[*] posted on 14-8-2009 at 19:35


Is starting from hexamine a viable preparatory method? I know the reaction with HCl has been used to make methylamine, but that's after a series of reactions, the first would be to form ammonium chloride and formaldehyde. One could probably filter off the ammonium chloride and then distill?
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[*] posted on 14-8-2009 at 20:59


Trioxane is in fuel starter tablets and will produce anhydrous formaldehyde upon heating.
paraformalfdehyde and formaldehyde solutions are sold as champa-chem or something like that, they are dirty and need to be purified however.




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