lab production of oleum ?

[psyloxy]

With my recent interest in sulfur chemistry I, of course, cannot leave out the almighty SO₃, or oleum for that matter.

I want to personally thank Vitus_Verdegast for posting this most informative piece of chemistry:

Post 463311

(Vitus_Verdegast: "More suggestions...", Chemistry Discourse).

Na₂S₂O₇ + 2 H₂SO4 ^__> H₂S₂O7 + 2 NaHSO₄

H₂S₂O₇ <^___> H₂SO₄ + SO₃

Apparently the only thing you need to get a good strength oleum, and thus SO₃, is Na₂S₂O₇. Many hive members have expressed 'difficulties' in preparing it by the traditional way of heating sodium bisulfate.

To my knowledge thermal decomposition of persulfates has only been briefly mentioned here :

Post 480352

(Chewbacca: "decomp products", Chemicals & Equipment). However, it seems to be the preferred method to get highly pure disulfates in a controllable way and high yield. I think the first report of that method can be found in Chem. - Ztg., 45.1921;1113-1114, which was a pain in the ass to get from the library and finally the wrong publisher and volume (always fun to get stuff from pre-WWII).

On the other hand the few sentences from Inorg.Chem., 21.1982;744 and Ber.d.D.Chem.Ges.B, 71.1938;2596 (in that order) seem to be enough to explain how it is done :

"Pure K₂S₂O₇ was made by the thermal dissociation of analytical grade K₂S₂O₈ from Merck at 290°C for ¹/₂ h in a stream on N₂ to avoid contamination with H₂O. Sulfur trioxide was not given off. "

"K₂S₂O₈, when heated to 290°C for half an hour gives off exactly 1 atom of oxygen"

I think the process for preparing anhydrides from pyrosulfates (

Post 462958

(Rhodium: "Na-Acetate + Na-Pyrosulfate -> Acetic Anhydride", Novel Discourse)) should be retried with pyrosulfates prepared this way.

According to

Post 246368

(Antoncho: "Re: Nitroalkane Preparation FAQ", Methods Discourse) oleum can be produced by bubbling sulfur trioxide into sulfuric acid.


Now for the questions that won't let me sleep:

Does sulfuric acid / low % oleum readily take up SO₃ ?? How does temperature influence the uptake ?
Who around here makes their own oleum / SO₃ - and how ?


prior art overview

A must read :

Post 418829 (missing)

(lugh: "Industry", Chemicals & Equipment)

1) SO₃

Post 58152 (missing)

(terbium: "SO3 from P2O5", Chemistry Discourse)  - a bit counter productive

Post 259376

(lugh: "Re: Methylene Sulfate", Novel Discourse)  - decomposition of ferrous sulphate

decomposition of various disulfates
CA, 1960;20435 : Li₂S₂O₇ decomposes at 60 - 70°C (!)
Bull.Soc.Chim.Fr., 1972;4106-4110 K₂S₂O₇ at 440°C
Rev.Chim.Miner., 4.1967;589-620 : BaS₂O₇ at 160 - 300°C
Anal.Chim.Acta, 20.1959;20-25 Na₂S₂O₇  at 197 - 800°C
Acta Chem.Scand.,  1.1947;781-789


2) pyrosulfates from bisulfates

CA, 1954;5009.
J.Prakt.Chem., 5.1872;367

Patent BP904971

3) pyrosulfates from sulfates

Patent DE40696

Liebigs Ann.Chem., 172.1874;106
J.Chem.Soc., 27.1874;212

--psyloxy--

[psyloxy]

Anal.Chim.Acta, 20.1959;20-25

La décomposition thermique a été étudiée par LEVI ET MIGLIORINI⁹. Le persulfate de potassium anhydre ne change pas de poids jusqu´à 230°C. Il se décompose alors brusquement avec perte d'oxygène en fournissant du pyrosulfate de potassium.

babelfish translation:
The thermal decomposition was studied by LEVI AND MIGLIORINI. The anhydrous potassium persulphate does not change a weight until 230°C. It breaks up then abruptly with loss of oxygene by providing potassium pyrosulphate.

[9]: Gazz.chim.ital., 36.1906;599 and  Gazz.chim.ital., 38.1908;10-20 EDIT: as far as I'm able to comprehend Italiano these articles are concerned with the decomposition in solutions!

--psyloxy--

[lugh]

Perhaps the most bee friendly approach besides the contact process, illustrated in

Post 418829 (missing)

(lugh: "Industry", Chemicals & Equipment), or the chamber process, described in

Post 428197

(lugh: "Sulfuric Acid by the Chamber Process", Chemicals & Equipment) is to oxidize sulfur dioxide with ozone, producing sulfur trioxide    An alternative to burning sulfur for the preparation of sulfur dioxide is to heat sulfur with sulfuric acid, as mentioned in

Post 507414

(lugh: "Alternative Route to Sulfur Dioxide", Chemicals & Equipment)

[psyloxy]

Don't you think that's a rather involved process as compared to

1) decomposing sodium persulfate - mild conditions, quick process, ~quantitative yield
2) dissolving the pyrosulfate in sulfuric acid, thereby generating oleum - without ever having to deal with any not-so-basic apparatus, noxious gas (SO₂, SO₃, O₃) or catalyst



I mean, I'm not talking about tons of the stuff, merely kilos, if at all !

--psyloxy--

[lugh]

Sublimed sulfur is easily and cheaply available in SWIL's neck of the woods; at the local dollar store    Persulfates are another matter, in terms of price and safety as mentioned in

Post 441606

(lugh: "Industrial Method", Chemistry Discourse)    The article on sulfur trioxide/sulfuric acid from Thorpe's Dictionary of Applied Chemistry:

[Organikum]

The process which beats all others in simplicity is still the "Nordhausen" one from the 18th century, equiring only FeSO4, heat and time. It is more suited for the outdoor lab though. The dehydarting of the FeSO4 at 350°C+ is the timeconsuming part provided that larger quantities are wanted. But also for 10 or 20 grams of SO3 it can take some days I guess.
Dehydrating the sulfate separately or buying it dry so possible might be favorable as packing the reaction-flask in clay. A clay retort would the better so available. YOu might consider a course on pottery at your local "Volkshochschule" psyloxy...  

ORG

[Vitus_Verdegast]

Patent US3885024

A pyrosulfate of ammonium or an alkali metal is prepared by reacting the hydroxide of ammonium or the alkali metal with sulfurous oxide in an alcohol, such as isopropyl alcohol, which is liquid under the reaction conditions and has more than three carbon atoms, in the presence of oxygen, at atmospheric pressure and room temperature, through the use, as catalyst, of a compound of a transition metal (e.g., CuCl₂).

[descent]

The alchemists' method is starting from FeSO4 hydrate which in our days is very cheap and is sold in every agricultural chemicals shop. In my country it is called "green stone". Green FeSO4.xH2O is allowed to stay for several days/weeks on air when it is oxydized to the pale-yellow Fe(OH)SO4. Scatter it on a newspaper, place in a not very dry place and wait. The so obtained Fe(OH)SO4 is pyrolized at 700 deg.C and it decomposes in Fe2O3 and oleum H2S2O7. The problem is that you'll need a ceramic, or better porcelaine, alambic.

[psyloxy]

Here's what Mellor's Modern Inorganic Chemistry, rev. ed. 1951 has to say on pyrosulphuric acid / pyrosulphates (p 476):

Mention has already been made of the fact that sulfur trioxide will dissolve in concentrated sulphuric acid, forming what is often called oleum or Nordhausen or fuming sulphuric acid. A similar acid is obtained by distilling partially dehydrated ferrous sulphate crystals, FeSO₄^.H₂O (preferably with a little sulphuric acid in the receiver). The recation appears to be represented:

6 FeSO₄^.H₂O ^__> Fe₂(SO₄)₃ + 2 Fe₂O₃ + 3 SO₂ + 6 H₂O

followd by:

Fe₂(SO₄)₃ ^__> + Fe₂O₃ + 3 SO₃.

The same acid is obtained by heating sodium pyrosulphate with concentrated sulphuric acid:

Na₂S₂O₇ + 2 H₂SO₄ ^__> 2 NaHSO₄ + H₂S₂O₇

Fuming sulfuric acid is a viscous, oily-looking  liquid which ich considerd to be a solution of variable proportions of sulphur trioxide in concentrated sulphuric acid. The 'fuming' of the acid is due to the escape of the sulfur trioxide. If the fuming acid be warmed, sulfur trioxide volatilizes and leaves sulfuric acid, H₂SO₄, behind. When cooled below 0°, the fuming acid furnishes crystals of pyrosulphuric acid, H₂S₂O₇ or H₂SO₄^.SO₃or H₂SO₄^.2SO₃, melting at 35°.

Another tidbit from 1960's Gmelin : H₂S₂O₇ froms when SO₃ reacts with H₂SO₄.

That tells me oleum is to be seen as a mixture of sulphuric acid and pyrosulphuric acid, rather then sulfur trioxide dissolved in sulfuric acid. AHA ! Pyrosulfuric acid is therefore relatively easy to decompose by heat with liberation of sulfur trioxide whereby  sulfuric acid is formed.



I think the patent, Vitus_Verdegast found is very intresting, so here's the 'experimental part' :

Example 1

At 25°c, 8 mmoles of KOH dissolved in isopropyl alcohol were added to a solution containing 15 mM of SO₂ and 0.1 mmole of CuCl₂ in 20 mL of wet isopropyl alcohol (0.3% H₂O), the solution being kept under an oxygen atmosphere at 760 Torr.
The reactin consumed 4 mmoles of O₂ and, after filtration, 3,75  mmoles of K₂S₂O₇ were isolated. The SO₂ conversion was 50%, while the yield in pyrosulphate was 95%.

Example 2

94 mmoles of NH₃ dissolved in 40 mL of alcohol were slowly added to 100 mL of isopropyl alcohol conataining 115 mmoles of SO₂, 31 mmols of H₂O and 0.1 mmoles of CuCl₂Pu₂ ^? under an oxygen atmosphere. The reaction totally consumed 31 mmoles of oxygen and, after filtration, 5.8g of a white solid were isolated. The yield of ammonium pyrosulphate was 89%.



descent: In 1960's Gmelin these are listed as references for H₂S₂O₇ from FeSO₄^.7H₂O :

J.Chim.phys., 45.1948;55-63 and J.Chim.phys., 46.1949;118-119

--psyloxy--

[psyloxy]

Again from Mellor's Modern Inorganic Chemistry, rev. ed. 1951 this time p 461-462:

The most efficient catalyst is platinum in presence of which the reaction proceeds quickly and almost to completion at 400°.



Sulphur dioxide and oxygen are dried by passing through wash-bottles containing concentrated sulphuric acid and then mixed at the entrance to a hard glass tube containing platinized asbestos which is heated to a temperature of about 400°. Sulphur trioxide is formed in white clouds which condense, in a freezing mixture, if the apparatus is absolutely dry, in the form of silky needles.

--psyloxy--

[Organikum]

The alchemists' method is starting from FeSO4 hydrate which in our days is very cheap and is sold in every agricultural chemicals shop. In my country it is called "green stone". Green FeSO4.xH2O is allowed to stay for several days/weeks on air when it is oxydized to the pale-yellow Fe(OH)SO4. Scatter it on a newspaper, place in a not very dry place and wait. The so obtained Fe(OH)SO4 is pyrolized at 700 deg.C and it decomposes in Fe2O3 and oleum H2S2O7. The problem is that you'll need a ceramic, or better porcelaine, alambic.

My problem here is that I cant get this balanced even when correcting the Fe(OH)SO4 to the correct Fe(OH)2SO4 what is the real product of oxidation of ferrous sulfate in moist air.

From the Wikipedia:
".... in a technique similar to the original alchemical processes. Pyrite (iron disulfide, FeS2) was heated in air to yield ferrous sulfate, FeSO4, which was oxidzied by further heating in air to form ferric sulfate, Fe2(SO4)3, which when heated to 480°C decomposed to ferric oxide (Fe2O3) and sulfur trioxide, which could be passed through water to yield sulfuric acid in any concentration."
(emphasis added by me)

Looks much better to me - more balanced so to say....

ORG  

[Lestat]

Org, better edit to say pass SO3 through H2SO4 instead of water, otherwise nastiness in most abundant quantity is going to happen. We wouldn't want newbees thinking it is saffe to mix SO3 and water now would we

[psyloxy]

J.Chim.phys., 45.1948;55-63 and J.Chim.phys., 46.1949;118-119 don't have any other information on the subject they were cited for in Gmelin than

"Pyrosulphuric acid can be prepared by overheating ferrous sulphate containing water of crystallization (FeSO₄^.7 H₂O)."
Of course no reference is given for that statement, and I couldn't find any others with crossfire.

The first one is a lenghty French article dealing with the determination of the molecular structure of some organic and inorganic substances using Raman spectroscopy. The 1949 article is an English advertisement for the French one.

--psyloxy--

[lugh]

Muller's article on sulfuric acid and sulfur trioxide from the fourth edition of Kirk-Othmer Enclyclopedia of Chemical Technology:

[psyloxy]

Thermochim.Acta, 114.1987;281-286

"K₂S₂O₇ was prepared by decomposing E.Merck K₂S₂O₈ (98%) at 280°C for 4 h. The aqueous solution of the product showed the absence of persulfate by starch-iodide as well as MnSO₄ tests. The melting point of the product was found to be 415°C, as compared to 410°C arlier reported in the literature. Acidimetric analysis showed 98,9% ⁺ 0,8% K₂S₂O₇"

--psyloxy--