Na-Acetate + Na-Pyrosulfate -> Acetic Anhydride

[Rhodium]

Manufacture Of Acetic Anhydride

Patent US1430304

(Kudos to psyloxy for finding this patent!)

To all whom it may concern:

Be it known that I, Henry Dreyfus, of London, England, have invented certain new and useful Improvements Relating to the Manufacture of Acetic. Anhydride (for which I have filed applications in France, 478,951, June 30, 1914; in Switzerland Dec. 11, 1914; in Italy June 5, 1917, and in Great Britain Dec. 13, 1919), of which the follow my is a specification.

I have found that salts of pyrosulfuric acid, such for example as sodium pyrosulfate (Na₂S₂O₇) produced by the known method of heating the bisulfate to decompose it into pyrosulfate with elimination of water, can be employed for the manufacture of acetic anhydride by bringing them into reaction with salts of acetic acid. The reaction takes place in such a way that by heating, the salt of pyrosulfuric acid combines with the salt of acetic acid, forming a neutral salt of sulfuric acid. By employing for example pyrosulfate of sodium and anhydrous acetate of sodium, preferably in powder, sulfate of sodium and acetic anhydride are obtained. The reaction is effected by mixing intimately, excluding any trace of moisture. The sodium acetate is believed to react in chemically equivalent quantities according to the equation



but it is preferable to employ an excess of the sodium pyrosulfate. The reaction takes place on heating. The acetic anhydride formed may distill off in proportion as the reaction proceeds.

The reaction is preferably performed in the presence of diluents such as glacial acetic acid or acetic anhydride or mixtures thereof, in which case one has a still more intimate mixture.

As compared with previously known processes the present invention presents the advantage that it is not necessary to cool, but on the contrary it is necessary to heat, which simplifies both the apparatus and the process of manufacture. Moreover pyrosulfate of sodium is much cheaper than the materials hitherto employed for the manufacture of acetic anhydride. In particular I can employ the pyrosulfate of sodium obtained by the method of strongly heating acid sodium sulfate, NaHSO₄, which decomposes into pyrosulfate of sodium and water.

Instead of acetate of sodium other salts of acetic acid may be employed.

[hypo]

on heating to 150-200°C hydrogensulfates (eg. NaHSO4) lose half a molecule
of water and turn into pyrosulfates (bisulfates, eg. Na2S2O7).
on stronger heating, those lose a molecule of SO3 to give normal
sulfates.

2NaHSO4 --(-H2O)--> Na2S2O7 --(-SO3)--> Na2SO4

(my point: 150-200°C is easily doable in a ghetto-lab   ,
just let it run until no more water is removed. this rocks   )

[Vitus_Verdegast]

I am stunned.

OTC acetic anhydride, and cheap as dirt, using non-toxic chemicals!

Wonderful!

[moo]

This made my day. How many times does one encounter a nice reaction which is otherwise OTC except for the Ac2O?      

[Antoncho]

Yeah, this info seems quite interesting... The only thing that remains to bee found out is - WHAT KIND OF YIELD one might expect from this reaction. Oh wait... the patent also says nothing about the rxn time, as well as temperature and qtty of solvent...

As you can see, there's still some work to bee done bee4 we start applauding ourselves    

I was about to post a 'complete success' write-up on this rxn based on a work done by Physicist of HyperLab, but it turned out that his results are dubious - pyrosulfate he used was self-made and represented a 'melt' - as fallen_Angel noted, Na2S2O7 melts at 400 C, which probably means that Physicist got most fo his NaHSO4 unchanged. Consequently, the reaction went like this:

NaHSO₄ + NaAcO ^__> Na₂SO₄ + AcOH  

But anyway, dehydration of NaHSO4 is quite doable in the kitchen in an enamel-coated metal dish on a gas stove. SWIM used to melt both lead (322 C) and NaNO3 (307 C) in this fashion - however, he wasn't able to decompose NaNO3, which means that the temp didn't rise above 380 C.

NaHSO4 is said to decompose at >186 C, right above its melting point, that is. Take note that KHSO4 melts at 210 Ñ and decomposes at >300 C so it's much less suitable for this preparation.


And yet another thing i would like to comment upon. In the patent they say to use some GAA as a 'solvent'. Naturally, this means that the final product will bee a mixture of AA and GAA which needs to bee separated. Fractional distillation is possible, but hardly desirable, taking in account close bp's and nasty smell. Fortunately, there is another, much superior way.

The only thing one needs to do is to shake the mixture with some of the very same Na-Acetate and filter. In this way it is possible to separate mixtures containing as much as 50% GAA, with almost quantitative yield and purity as high as 99,5%.

When GAA:AA ration is too big (like, 1:1) a neutral diluent may bee used - such as toluene or benzene.

See

Patent GB372434

180 parts of acetic anhydride and 20 parts of acetic acid are shaken for 1 hour with the addition of 28 parts of sodium acetate. The product is filtered quickly and a filtrate is obtained amounting to 178 parts consisting of 99,5% acetic anhydride.



Is there anyone who cares for this synth enough to try it out?



Yours,

Antoncho

[hypo]

check the completition of the conversion to pyrosulfate by weight?
(weigh Na2SO4, dissolve in water, add exact amount of H2SO4, evaporate
water, heat until constant weight and check that product has supposed
weight)

100g Na2SO4
 69g H2SO4(100%)
----------------
156g Na2S2O7

[Mountain_Girl]

First time I saw the patent I was naturally quite interested but my reaction, like Antoncho's, is tempered with weary scepticism.
Guess both of us have spent way too much time, money & effort on patents that did not perform as promised.

So it would be dandy if more people could try this before we get too excited.

[My submission to the Hive complaint department: Not enough bees working on the OTC precursors/reagents]

Anyhow, a slight bit of extra info:

Sodium Hydrogensulfate

Sodium hydrogensulfate occurs as the monohydrate, NaHSO4· H2O, in the system sodium sulfate – sulfuric acid – water,  or exists as the solid phase NaHSO4 at a sulfuric acid concentration of 62 %. The monohydrate is converted to the anhydrous salt at 58.45 ± 0.05 °C.

The thermal decomposition represented by the equation

    2NaHSO4 <=> Na2S2O7 + H2O

takes place near the melting point, which can be determined only approximately (ca. 183 °C) with a water vapor pressure of 2500 Pa (25 mbar). Conversion to sodium disulfate is complete after heating for ca. 4 h at 240 – 260 °C. Sodium disulfate decomposes above 400 °C to form sodium sulfate with liberation of sulfur trioxide.

Production.
Sodium hydrogensulfate is formed as an intermediate in the production of hydrochloric acid by the Mannheim process and is a byproduct of the manufacture of chromium(VI) oxide. The reaction between sulfuric acid and sodium chloride may be carried out by the old process using cast iron retorts heated with gas or oil, or by the use of submerged combustion equipment in brick-lined vessels. The addition of a stoichiometric amount of sulfuric acid to sodium sulfate or Glauber's salt at 200 – 280 °C produces molten sodium hydrogensulfate. The same reaction can be utilized to produce sodium hydrogensulfate in aqueous solution at 80 °C directly.

Ullmann's Encyclopedia of Industrial Chemistry
DOI:

10.1002/14356007.a24_355

[hermanroempp]

..which goes more into detail with the method of how the acetic anhydride is produced.

From Patent US1368789:
....
For the purpose of more fully explaining my invention, I give the following specific example:
Into an apparatus provided with an agitator and capable of being heated and cooled, and containg 1600 kilos of dry sodium sulfate, there is introduced while rapidly agitating, 800 kilos of sulfuric anhydride, without paying much attention to the temperature. The sulfuric anhydride can be produced and introduced in any suitable manner.
The absorption takes place rapidly and when the sulfuric anhydride is entirely absorbed, as can be ascertained by a condenser no longer showing a reflux of boiling sulfuric anhydride, then, while agitating, the resulting addition product (he means Na₂S₂O₇, produced like Na₂SO₄ + SO₃ ^__> Na₂S₂O₇) is added progressively to a mixture of 1640 kilos of dry pulverized sodium acetate with 1600 kilos of acetic anhydride, cooling appropriately to prevent a rise of temperature.
After some time the temperature is raised to about 60° or 70° C, which temperature is maintained for some time in order to complete the reaction, and finally the acetic anhydrid is distilled off, preferably in vacuo.
The acetic anhydride is obtained in a practically quantitative yield and the product is of a purity that cannot be obtained direct by other processes.
....

1600 kg of sodium sulfate = 11264 Mol
800 kg of sulfur trioxides = 10000 Mol

=> the (cheaper) sodium sulfate is used in about 10% excess, if the reaction of pyrosulfate formation really works as Dreyfus states in his patent and if it goes to completion.
So I can see no reason why the "addition product" of sulfur trioxide and sodium sulfate can't be replaced by pyrosulfate produced by other means, i.e. by self-condensation of sodium hydrogensulfate...

[hermanroempp]

From Patent GB424573, which I really recommend for reading:

....

Example:
Anhydrous, neutral ammonium acetate is mixed with anhydrous sodium pyrosulphate in the proportions of two molecules of acetate to one molecule of sodium pyrosulphate, and sufficient glacial acetic acid is added to give the mixture the consistency of a thin paste.
The mixture is heated under reflux for one to two hours after which the acetic acid present and the acetic anhydride formed are distilled off. The temperature is then raised until ammonia is evolved from the dry residue, which consists of a mixture of ammonium and sodium sulphates, the ammonia being absorbed in acetic acid. When no more ammonia is evolved the temperature is raised still more so that the sodium bisulphate formed during the removal of the ammonia is changed into sodium pyrosulphate.

....

Very nice, this one. First, a new method of producing sodium pyrosulfate is described here, by simply melting ammonium and sodium sulfate together. Second, the escaping ammonia is absorbed into acetic acid, forming ammonia acetate, which can be used again in the process of procuring the acetic anhydride. The only drawback is that a mixture of acetic acid and acetic anhydride is obtained, which compounds can not so easily be separated by fractional distillation, but can be separated with the use of sodium acetate as already mentioned by Antoncho  

[hypo]

> The only drawback is that a mixture of acetic acid and acetic anhydride are
> obtained, which are not so easily separated by fractional distillation

where's the problem? been there, done that. you get a nice 139-140°C fraction
even without column. with column yields are much better of course.

[hermanroempp]

..is not mentioned in these patents, hopefully it is done under normal pressure, otherwise the pressure should have been mentioned in one of these three Dreyfus patents.
I think the key to success may be the use of very finely powdered, ultradry pyrosulfate/acetate mixture and, of course, the use of an inert diluent (acetic acid or acetic anhydride).
Dreyfus doesn't state it explicitly, but it seems to be better to work with a slurry instead of a dry mixture.

[hypo]

ok, two warnings:  

1) NaHSO4 was heated on gas flame. take care with that. nasty white fumes
evolved before conversion was complete (there were still mass amounts of
H2O given off). experiment was aborted when those fumes started to
appear. so try to use temperature control!

2) the above mixture was heated with NaOAc on oilbath at 220°. only
a bit of AcOH distilled off. it was then heated on gas flame. first this
gave white somewhat acetic smelling fumes which were piped through water.
then the still head started to become sulfur yellow (!!), then some
liquid started to condense (thermometer shows 142°C which sounds
perfect), then the wash water started to smell _foul_. not exactly H2S
like, but not too far from H2S either. experiment aborted at this moment.
sorry guys, this bee has lots of work to do right now and is not willing to
perform this kind of adventure   . another time. anyway, a few ml of
liquid with sulfur-yellow precipitate were obtained. it does not smell
like pure Ac2O, but not like AcOH either. possibly a mix of those two though.

hope this helps   .

[hermanroempp]

The problems you have encountered may have resulted from:

- incomplete conversion of the hydrogensulfate
- sulfuric acid present in your impure (hydrogensulfate still present) pyrosulfate, which may lead to oxidation of the acetate on high temperatures
- not using an inert diluent, e.g. glacial acetic acid

Btw., heating of a hydrogensulfate with an acetate is a well
known, very old procedure for obtaining glacial acetic acid  
Anyway, the problem seems to be to obtain the pyrosulfate dry and uncontaminated with sulfuric acid. After digging in the patent literature, I found the following:

Translated from Patent DE40696, entitled "Process for the synthesis of pyrosulfates of alkali metals as well as of ammonium":


....
The first method of production (the method of making pyrosulfates from the corresponding hydrogensulfates by strong heating) has the big disadvantage, that at the high temperature of brown glowing heat, some part of the already formed pyrosulfate is decomposed, producing sulfur trioxide.
....
The inventor now has found out that hydrosulfates, especially these of the alkalis and ammonium, or equimolar mixtures of neutral sulfates with sulfuric acid (very interesting) can be transformed under elimination of water into pyrosulfates at relatively low temperatures (260°-320°C) without even forming a trace of sulfur trioxide when the heating is done under vacuum.
....
The preparation goes as follows:
For the synthesis of sodium pyrosulfate, 240kg of sodium hydrogensulfate or a mixture of 142kg sodium sulfate with 98kg of sulfuric acid monohydrate in the form of 66°B sulfuric acid  (this corresponds to sulfuric acid of 96%), are brought into a retort made from cast iron, equipped with an agitator. The retort is fixed to a pump and is heated to 260°C while the apparatus is being evacuated. The mixture is finally heated to 300°-320°C within 5 to 8 hours, while the mass is agitated. From 260°-280°C (at a vacuum of 500-600mm Hg) the main part of the reaction formed water distills off, and the mixture is only heated to 320°C to make sure that the reaction has been completed. The remaining melt is cast into plates, it consists of pure sodium pyrosulfate.
In the same manner the pyrosulfates of other alkali metals as well as the pyrosulfate of ammonium can be produced. It is hereby suitable to install a condenser with receiver between retort and vacuum pump. Between condenser and receiver a glass tube should be installed. This enables the operator to see when the reaction has finished, because no more water will be observed in the glass tube then.

....

(italics mine)