[limpet chicken]

I had an idea for the synthesis of the commonly used, but hard to obtain reagent acetic anhydride.

KMnO4 oxidises primary alcohols to their respective carboxylic acids, I had the idea of using KMnO4 to oxidise anhydrous, dried ethanol with permanganate, maybe in a solvent forming an easily breakable tertiary azeotrope with AA that could be salted out.

And perhaps just use ethanol or acetic acid as the solvent for the KMnO4, and distill off the acetic anhydride.

Would this work do you think?

This might prove a good replacement for the somewhat tedious and dangerous sandwhich-toaster ketene lamp.

I believe excess permanganate would over oxidise to acetaldehyde though, maybe production of acetaldehyde then mild reduction to the acid anhydride would be better, or use of an alternative oxidant, sodium chlorate, or ammonium nitrate perhaps?

Ideas you smart people out there?

[Demotivator]

Heating acetic acid to 800C dehydrates it to the anhydride. Could be dangerous as it's very flammable.
or
Convert acetic acid to acetyl chloride. Then rxn with sodium acetate yields acetic anhydride + NaCl.

I don't think using KMnO4 to oxidise anhydrous, dried ethanol  will yield the anhydride, just acetic acid.

[limpet chicken]

I don't think the anhydride is formed by simple heating of acetic acid, it forms an azeotrope with water.

[movies]

If you did make any acetic anhydride by that method it would more than likely reaction with the ethanol before distilling.  You'd end up with ethyl acetate and acetic acid.

[Demotivator]

I don't think the anhydride is formed by simple heating of acetic acid, it forms an azeotrope with water.

Right, it wouldn't be simple. It would have to be engineered with a special column.

[limpet chicken]

A fractional distillation column? I am sure I could make one, a long fluorescent striplight tube might just be calling me I hear....

[cbee]

Azeotropes cannot be seperateed using frac. distill.  Usually some nasty semi-permeable membrane solution is required.

However, Pyrolysis of acetone (pass acetone vapor over a 700 C microfilament) gives keten.  Keten and a carb acid gives the mixed anhydride unless you use acetic acid in which case it gives acetic anhydride.  Check Vogel for the apparatus for making keten and the prep for the anhydride.


cbee

[limpet chicken]

I was aware of the ketene process, I was more looking at an alternative process, just because I was curious if it would work, but thank you

[Dorn]

Wouldn't thermal decomposition (maybe the correct term is destructive distillation) of copper acetate yield acetic anhydride?

You could get the copper acetate via
1) electrolysis of copper plates in vinegar  
2) or from copper nitrate plus acetic acid and then distill off the nitric acid (I'm not sure that would work but it might)
3) or copper nitrate + lime --> copper hydroxide
    copper hydroxide + acetic --> copper acetate
or ...

[budullewraagh]

i just had a thought.

permanganic anhydride would work

[limpet chicken]

Permanganic anhydride would work quite well at detonating into a cloud of ozone in your face, that stuff is damned unstable, most of the times I have experimented with it, it expoded on contact with stirring rods and such, not stuff I really want to reflux with anything