Acetyl-anhydride production

[zeocrash]

ok i was looking at the production for this compound, on meg's site it says mix axetic chloride with sodium ethanoate, destiling and repeating.
Today i had a thought. would it be possible to get acetic anhydride by esterifying ethanoic acid (CH₃COOH) and ethanol (CH₃CH₂OH), to form ethyl ethanoate (CH₃COOCH₂CH₃)
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Ethyl-ethanoate

the etyle ethanoate could then be oxidised using an oxidising agent to form acetic anhydride
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acetic anhydride

Any thoughts

[Einsteinium]

I think that most direct oxidation will rather hydrolyse ethyl acetate (ethyl ethanoate) into acetic acid and ethanol (if done in watery conditions), or oxidize it into acetic acid and aldehydes and/or into acetic acid and other carboxylic acids (I'm almost certain NaOCl, KMnO4, direct electrolytic oxidations, Na2CrO7, CrO3 will all gives similar results). I never heard of this synthetic route thus either it dosen't work or requires exotic ($$$)oxidants/solvents, else the industry would have certainly tried it. You can deshydrate acetic acid with sulfuric acid in catalytic amount, with some way to remove the water produced but it requires very high temperatures (600-800C, this is an industrial process). There is a lot of patents for this process but this isn't really suited for lab scale in my opinion (if you ever try this home burning reaction <img border="0" title="" alt="[Eek!]" src="eek.gif" /> with say, a furnace tube, be sure to tell me how it went :D .

[Arthis]

I have found that at Rhodium

Acetic Anhydride

The apparatus for this process is similar to that used for the preparation of acetyl chloride. The same precautions for exclusion of moisture must be observed but it is unnecessary to provide the inverted funnel arrangement, since hydrogen chloride is not evolved.

In a 250ml. rb flask fitted as for making acetyl chloride, place 60 g. of finely pulverized anhydrous sodium acetate (*) Arrange in place the condenser, dry receiving flask and drying tube; the receiver need not be cooled. Check to insure that all connections are tight. Cool the reaction flask in a bath of cold water and add dropwise, through the addition funnel, 40 g. (36 ml.) of acetyl chloride.

After the addition has been completed, remove the water bath and shake the flask to obtain good mixing of the reactants. Recheck the connections for tightness.

Dry the outside of the flask with a towel and heat it with a mantle or oil bath. Continue the heating until no more distillate comes over but do not overheat the solid residue.

To the distillate add 4-6 g. of finely powdered anhydrous sodium acetate, to react with a small amount of acetyl chloride that may be present. Add a boiling chip and redistill the crude acetic anhydride. Collect the product distilling at 132-138? in a dry flask. The yield is 30-40 g.

* Note: Commercial anhydrous sodium acetate usually contains some moisture. To remove moisture fuse 70-80 g. in a casserole (either in an ordinary oven, or a microwave) and stir until no more water is evolved. Do not overheat! Cool and quickly pulverize. Store in a tightly sealed container before use.



Another method given which can be easier since you don't have to make acetyl chloride first; (method for it at rhodium too)

"...(1) Acetic anhydride. To 50 g. acetic anhydride in a round-bottomed flask of 1500 cc. capacity, placed in cold water, 440 g. of powdered sodium acetate (dried by fusion at 320 C) and at the same time a solution of 22. g of sulfur in 320 g. bromine is added while stirring. The operation takes about 30 minutes.

"The mixture is then stirred for a further 5 minutes, after which period the initially dark brownish-red colour has changed into pale yellow, and the anhydride is distilled off from a water bath under reduced pressure. The crude anhydrie (310 g) is redistilled under normal pressure, and the fraction boiling between 134-138 C is collected. Yield, 295 g. of 98% purity = 87.5%. The so purified anhydride contains neither bromine nor sulphur compounds and leaves no residue on evaporation..."


Maybe the link: link (http://www.rhodium.ws/chemistry/anhydrides.html) would be better that numerous quotes.