Sciencemadness Discussion Board - Production of thionyl chloride using... hexavalent chromium?

Production of thionyl chloride using... hexavalent chromium?

Ionic Chemist - 13-5-2013 at 13:32

Recently I've been working on novel ways to produce acyl chlorides. One method utilizes alkenyl esters after a multistage process. However, the method I am really wondering about is the more travelled route, the chlorination of carboxylic acids using thionyl chloride; specifically the production of the thionyl chloride itself.

I am aware that thionyl chloride can be synthesized by oxidation of sulfur dichloride by sulfur trioxide, yielding thionyl chloride and sulfur dioxide. But I am wondering if it is only sulfur trioxide that can be utilized for the oxidation, what about the use of hexavalent chromium compounds (yes I know about the carcinogenicity), compounds such as chromium trioxide, or even chromyl chloride. This comes about because of the aggressive nature of the chromium (VI, Cr⁶⁺) oxidizing agents, couldn't they be used to oxidize sulfur chlorides to yield thionyl chloride or at best sulfuryl chloride and producing trivalent chromium (III, Cr³⁺) compounds as a byproduct?

Thank You......

woelen - 16-5-2013 at 04:00

I'm not sure about that. I have found that hexavalent chromium is very reluctant to oxidizing compounds when no hydroxyl groups are present.

Thionyl chloride is a strong reductor itself, it contains sulphur in oxidation state +4. When CrO3 is added to that, then you get SO2 and CrO2Cl2 (red vapor, red solution). As soon as a little water is added, the chromium is converted to green trivalent chromium in an explosively violent reaction. Without water, however, no redox reaction occurs. Of course, my experiment is not with S2Cl2 as reductor, but it might be that this behavior of hexavalent chromium is common in all environments where no water (or more general, hydroxyl groups) are available.

AJKOER - 16-5-2013 at 08:29

Now, as per Wikipedia on Thionyl chloride (http://en.wikipedia.org/wiki/SOCl2 ) to quote:

"The major industrial synthesis involves the reaction of sulfur trioxide and sulfur dichloride:[3]

SO3 + SCl2 → SOCl2 + SO2 "

so a convenient path to SO3 could help with SOCl2. I did come across a source citing the formation of SO3 from the action of HNO2 on SO2. To quote (source link: http://nitrogen.atomistry.com/nitrous_acid.html ):

"On the other hand, many reducing agents are oxidised, the primary decomposition being:

2HNO2 = 2NO + O + H2O

Stannous chloride is converted into stannic chloride, sulphuretted hydrogen into sulphur, sulphur dioxide into sulphur trioxide. "

Unfortunately, no other direct confirmation of the reaction of HNO2 on SO2 gas, but this is not that surprising as Nitrous acid is reputedly a stronger oxidizer than Nitric acid (see, for example, "The Encyclopaedia Britannica: latest edition. A dictionary of arts ..., Volume 5, page 513, link: http://books.google.com/books?id=14FGAQAAIAAJ&pg=PA512&a... ).

However, per this comment from Atomistry (http://nitrogen.atomistry.com/nitrous_acid.html ) to quote:

"Sulphurous acid shaken with nitrous acid yields hydroxylamine-disulphonic acid:

HNO2 + 2 H2SO3 ⇔ OH.N.(SO2OH)2 + H2O"

so the exact manner to effect the SO3 gas creation is a little unclear to me. Will simply bubbling very hot SO2 (to limit H2SO3 and H2SO4 formation) through HNO2, followed by collecting and drying the exit gases work?

Note, one can form HNO2 as follows (same source):

"5. Nitric oxide passed into nitric acid reduces the latter to nitrous acid:

HNO3 + 2NO + H2O = 3HNO2."

So even concentrated Nitric acid is not required in this preparation and given the instability of HNO2, probably not advised.

I hope in spite of my lack of thorough documentation (meaning at least two confirming sources), some may find my suggested preparation of SO3 leading to Thionyl chloride interesting.

[Edited on 16-5-2013 by AJKOER]

ScienceSquirrel - 16-5-2013 at 09:49

You could bubble sulphur dioxide through dilute nitrous acid until the cows* come home, you are not going to get sulphur trioxide. Dilute suphuric acid maybe, sulphur trioxide gas, no.

* If you do not like cows insert the large domestic animal of your choice here; sheep, goats, llama, camels, etc, etc.

AJKOER - 16-5-2013 at 12:22

Quote: Originally posted by ScienceSquirrel

You could bubble sulphur dioxide through dilute nitrous acid until the cows* come home, you are not going to get sulphur trioxide. Dilute suphuric acid maybe, sulphur trioxide gas, no......

ScienceSquirrel:

I am not sure I share your zeal. By the way, dilute HNO2 is not expressly mentioned so it is possible one could be employing an acidified nitrite. Perhaps passing steam and SO2 over mildly heated NaNO2 (a reaction paralleling the creation, in low yield, of Cl2O from Cl2 and steam over heated NaOH or Na2CO3, for example, an actual commercial process).

I did find it interesting that per this source ("Inorganic Chemistry" edited by Arnold F. Holleman,.., page 676, link: http://books.google.com/books?id=Mtth5g59dEIC&pg=PA676&a... ) the reverse reaction, namely, the products of hydrolysis of hydroxylamine-disulphonic acid, is reported not to include H2SO3, but H2SO4. This would interestingly, however, be consisent with the formation of SO3 (as claimed) and H2SO4 in the forward reaction.

There is even more uncertainty, in my mind, cause by the following cited reaction in the second reference (page 657):

HNO2 + 2 H2SO3 + H2O --> NH2OH + 2 H2SO4

where the precise temperature for this reaction is not specified. Now, this is in contrast to the reaction that occurs upon shaking a solution of SO2 (or H2SO3) in HNO2 at, I suppose, room temperature in the first reference. To quote precisely:

"Sulphurous acid shaken with nitrous acid yields hydroxylamine-disulphonic acid:

HNO2 + 2 H2SO3 --> OH.N.(SO2OH)2 + H2O"

(As an additional reference on the above see page 558 at http://books.google.com/books?id=5NU5AQAAIAAJ&pg=PA558&a... )

Now, note the disappearance of NH2OH from the preceeding equation. But, the second reference also cites the following reaction on page 676:

NH2OH +3 SO3 --> NO(SO3H)3

that is, NH2OH can and is consumed by SO3, so if the hydroxylamine-disulphonic acid is formed as indicated, so could also be SO3!

However, as I am unclear of reaction conditions for these reactions (temperature for one), the above is certainly not a completely confirmatory evident, but does keep my wishful thinking alive.

[Edited on 17-5-2013 by AJKOER]

MrHomeScientist - 16-5-2013 at 13:39

Instead of relying on "wishful thinking," why not try the experiment yourself? Certainly sounds simple enough. Experimental evidence is much more valuable than a passing mention (without reference) on an obscure website.

halogen - 16-5-2013 at 14:14

It's not zeal it's that water is inimical to SO3.

AJKOER - 16-5-2013 at 17:06

MrHomeScientist:

Please review my revised comments.

To be honest, I am still not particularly clear on the reaction chain. The reaction temperature could be anywhere from 0 C to 100 C. The reactants, as I gave some insight, could be gas on a solid or aqueous.

Awaiting someone with experience/knowledge in these reactions before even thinking on a synthesis route.

The good news if I happen to be correct, a safer/easier path to SO3 is a significant development for all of us. I would prefer not to argue my case, but just gather further research and experience from our members. Whoever succeeds first in an actual synthesis, great, I seek no particular recognition. Lets just call it the Nitrous acid path to SO3.

woelen - 16-5-2013 at 22:57

There is no nitrous acid path to SO3, at least, not in this universe

AJKOER - 17-5-2013 at 05:52

Axehandle:

What was reference for equation (d) below because it does claim the formation of SO3 in the Lead Chamber process (http://www.sciencemadness.org/talk/viewthread.php?tid=2824 )?

Quote: Originally posted by axehandle

I was going to hold on to this a bit further - until I have more observations to report - but I decided otherwise since the more that try the process, the more improvements might be invented - and many of you may have suggestions and ideas to optimize the process.

Also, I can't resist the temptation of bragging about finally finding a successful, simple way of making H2SO4 with easily obtained tools and chemicals...

The Lead Chamber Process, invented in 1746 by the Brit John Roebuck, was the first feasible industrial manufacturing process for H2SO4, and wasn't replaced with the contact process (using a Pt catalyst to oxidize SO2 to SO3

until the first half of the 1900s. Lots of historical information exists online, I won't go into the historical aspect more than strictly necessary.

In the lead chamber process, 7 part sulfur (note 2) is burned together with 1 part sodium or potassium nitrate inside a lead-lined chamber (note 1) with water covering the floor. SO2 is generated in abundance together with lesser amounts of NO from the saltpetre. Over time (several hours in my experience) the NO catalyses the oxidation of the gaseous SO2 to the trioxide SO3; which combines with the water on the floor, as well as with water vapour (note 2) inside the chamber, to form dilute H2SO4. The reaction mechanism is described by the following, unbalanced reactions:

(a) 3S(s) + 2KNO3(s) --> K2S(s) + 2SO2(g) + 2NO(g) ;sulfur + KNO3 reaction
(b) S(s) + O2(g) --> SO2(g) ;combustion inside the chamber
(c) 3NO(g) + 3/2O2(g) --> 3NO2(g) ;spontaneous at NTP
(d) 3NO2(g) + 3SO2(g) --> 3SO3(g) + 3NO ;catalyzed oxidation
(e) SO3(g) + H2O(l) --> H2SO4(aq) ;absorption

In (a,b) 1 part of the sulfur combined with the nitrate during the combustion, and the other 6 parts combines with oxygen from the air inside the chamber. (c, d) constitute the catalyzed step.
.............

Interestingly, the chemistry per Wikipedia (https://en.wikipedia.org/wiki/Lead_chamber_process ) does NOT cite the formation of SO3. This reference (http://books.google.com/books?id=Mjs-CN_gFJ0C&pg=PT1240&... ), however, clearly states that the Lead Chamber process consists of reacting NO, NO2, steam (these last three are precisely the products on heating HNO2) and air in a large lead-lined reaction chamber. The NO2 is said to readily oxidize the SO2 to SO3 and NO. Another source (see page 290 at http://books.google.com/books?id=Qdp-AAAAIAAJ&pg=PA289&a... ) interestingly notes the formation of nitrogen in the complete absence of water via the reaction:

3 SO2 + N2O3 --> N2 + 3 SO3

Apparently, the following reaction is well accepted and documented relating to acid rain formation, from the burning of nitrogen containing compounds in the presence of Sulfur and O2 (no sunlight):

NO2 + SO2 --> NO + SO3

See, for example, "General, Organic, and Biochemistry Media Update", by Ira Blei, George Odian, page 208 at http://books.google.com/books?id=FziEIenSCTAC&pg=PA208&a... . However, a more advanced source (see "Theoretical and Modeling Studies of the Atmospheric Chemistry of Sulfur ..." by Hazem S. El-Zanan at http://books.google.com/books?id=gRFwpGlNZ1kC&pg=PA73&am... ) reveals considerable recent research, complexity and new opinions on a photolysis route. Interestingly, however, per page 73, the author notes, to quote, "Mueller et al (2000)[64] suggested at high pressure the SO3 formation via SO2 + NO2 --> SO3 + NO becomes important.", which makes sense if the reaction temperature is held to below the boiling point of SO3 (45 C).
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So the question is can SO3 be formed and isolated from water to avoid the formation of H2SO4 in some revised preparation based on NOx?
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Note, the yet to be determined revised process, I was referring to, could possibly be based, per my above reference:

"whereas stronger solutions [referring to Nitrous acid] at higher temperatures decompose according to the equations

2HNO2 ⇔ N2O3 + H2O ⇔ NO + NO2 + H2O "

Intuitively, there is some rationale here as by simply rewriting (per above):

SO2 + 2 HNO2 → H2SO4 + 2 NO

as:

SO2 +[NO + NO2 + H2O] → H2O + SO3 + 2 NO

and upon limiting the water (as vapors perhaps):

SO2 + [NO + NO2] --?--> SO3 + 2 NO

Time, pressure, uv, O2 and the possible presence of some H2O and HNO3, may promote the photolysis reaction. Note, previously on Sciencemadness, I cited a reference to gas phase reaction with NO, NO2 and ammonia given as follows:

(2)NO2 + (2)NO + (4)NH3 --> (2)NH4NO2 + (2)H2O + (2)N2

To quote: "Dry ammonia gas reacts with the nitrogen dioxide and nitric oxide, at room temperature. (reaction investigated by Marcellin Berthelot)". I also recall an observation that a mixture of NO and NO2 gases actually forms a cloud of white Ammonium nitrite.

So, does wishful thinking continue on the formation and isolation of SO3 from water via HNO2 (and/or from its decomposition products) under some conditions, or is it still in a universe far, far away?
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Barring major developments, I feel it is inappropriate to continue a theoretical/new synthesis discussion on SO3, at this time, on this thread. Part of my reasoning is that if the original cited SO3 creation is, for example, occurring, it could even be the result of the formation of an aerosol in the presence of SO2, NO, NO2, HNO3, O2, water vapor..., and associated chemistry occurring there with. Obviously, the level of such chemistry, doesn't belong on this thread.

[Edited on 18-5-2013 by AJKOER]

AJKOER - 6-7-2013 at 10:43

Quote: Originally posted by AJKOER

... I did come across a source citing the formation of SO3 from the action of HNO2 on SO2. To quote (source link: http://nitrogen.atomistry.com/nitrous_acid.html ):

"On the other hand, many reducing agents are oxidised, the primary decomposition being:

2HNO2 = 2NO + O + H2O

Stannous chloride is converted into stannic chloride, sulphuretted hydrogen into sulphur, sulphur dioxide into sulphur trioxide. "

OK, came across a very authoritative reference, IMHO, "Nitrosation Reactions and the Chemistry of Nitric Oxide", by D.L.H. Williams, mostly available online for free at http://books.google.com/books?id=BVv0Lytq8foC&pg=PA14&am... that some may find informative.

Per this source, my first general comment on pathways for nitrosation reactions is that apparently the chemistry involved is complex and to some extent unsettled with varying pathways and numerous studies. Nevertheless, moving forward, the author does cite interestingly the following reaction, as Equation 35 on page 16:

2 [NO+] + 2 [SO3 2-] = 2 NO + SO3 [35]

This would be a confirmation of the comment cited in Atomistry.com, however, the Nitrosonium cation may be in an organic solvent (the author list at the bottom of page 14, for example, nitromethane, toluene and acetonitrile) given its affinity for hydrolysis.

Also, the author, per equation [7] on page 2, notes that the Nitrosonium cation NO+ is most likely only present in highly acidic environments:

HNO2 + H3O+ <---> [NO+] + 2 H2O [7]

usually created in situ, as per example, from the action of HCl on NaNO2.

Assuming Equation [35] is cited as it is based on actual observations, one may take arguably the reference to Nitrosonium cation as short-hand for other pathways in other environments (like highly ionic low pH aerosols).

Bottom line, the reaction for the creation of SO3 via HNO2 may indeed occur, but no definitive support for a largely aqueous path in accord with the opinions of Woelen and others.
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[EDIT] An alternative path to SO3 suggested by the equation:

2 [NO+] + 2 [SO3 2-] = 2 NO + SO3

is that by passing NOCl gas over (and not through) an aqueous solution of Sulfurous acid (or, over SiO2 saturated with H2SO3) may form some condensation of SO3 on the cool sides of the reaction vessel. Speculated reaction:

2NOCl (g) + SO2 (g) + H2O (vapor) --> 2 NO (g) + SO3 (s) + 2 HCl (g)

Note, as:

NOCl + H2O --> HCl + HNO2

this reaction is still based on Nitrous acid pathways. More specifically, to quote from the author per page 3:

"As to whether acidic solutions of Nitrous acid react via N2O3, NO+ or XNO will depend on a number of factors particularly the pH, [HNO2], and the nature and concentration of the X-."

[Edited on 7-7-2013 by AJKOER]