Keywords: Formaldehyde, Acetaldehyde, Acetic Anhydride, Tube Furnace,
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FORMALDEHYDE
[J. Russ. Phys. Chem. Soc, 1913, 53, 286.]
Methylalcohol (100 c.c.) is placed in a flask which is kept at a temperature of 40°, and connected to a horizontal combustion tube in which a roll of copper foil (5 cm. long) is placed.
The other end of the combustion tube is connected to a condenser and a well cooled receiver.
A stream of air is driven through the alcohol causing a mixture of air and alcohol vapour to pass through the copper coil, which should be heated until it just glows.
The reaction will proceed without further heating and a solution of formaldehyde in methyl alcohol will collect in the receiver.
Small explosions on the copper do no harm, but the temperature should not exceed a dull red heat or some of the aldehyde will be decomposed.
A much improved yield (about 80 per cent.) may be obtained by substituting pumice, coated with a mixture of silver and copper, for the roll of copper foil.
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REMARKS:
The silver/copper on pumice is not worth the effort except someone plans to build an pilot plant for processing amounts of methanol in the range of hundreds of liters or more.
A plain coppertube filled on about 8 cm length with copper scrubbpads will do fine, it stands and conducts the heat much better as glass and is unbreakable. The methanol used shoud contain some water for better yields.
This coppertube can be used without further modifications to pyrolize acetone to ketene which is bubbled into GAA to yield acetic anhydride which is to be discarded immediately as it is a scheduled substance. (acetone is boiled, the vapours are passed through the tube which is heated to red dull heat (650° to 750°) - no air here!
Also without air proceeds the dehydrogenation of ethylalcohol to yield acetaldehyde at temperatures between 270° to 330°, with yields of about 50% per pass and a selectivity of more than 95% to acetaldehyde.
So a piece of coppertube, one or two copper-scrubbpads and a propane batwing-torch will produce:
- Formaldehyde
- Acetaldehyde
- Acetic Anhydride
In unlimited amounts.
Slightly tweaking the protocol/catalyst used, gives:
- benzaldehyde from benzoic acid
- benzaldehyde from toluene
- benzene from benzoic acid
- benzene from acetylene
- ........
- ........
endless possibilities
!ATTENTION!
Doing this without any clue using "common sense" instead will produce severe burns and problems in the respiratory tract. The dangers regarding explosions and fires are actually less than in usual batch-style reactions as the reaction chamber - the tube - is solid metal and is VERY small on the volume.
This post is dedicated to Randolph Carter whose old posts inspired me to walk the "divine way of the tube" and who never answers my PMs.
