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Sauron
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Nicodem Is Correct
A paper has turned up from Bull.Chem.Soc.Japan which details:
-- prep of KSH from methanolic KOH and H2S
- reaction of that solution with chloroform (vilent!)
- Use of crude potassium dithioformate solution in thioformylation without isolation
Paper is attached.
This is my modofocation of their procedure.
A solurion of KSH is prepared by mixing a solution of 46 g KOH (820 mmol) in 150 ml MeOH with 150 ml Ml MeOH which has been saturated with H2S and
containing a further 46 g KOH. Total KOH 1.64 mol. The solution is transferred to a 3 L flask equipped with a Dimroth condenser. The solution is
heated to 50 C and 30 g chloroform (250 mmol)added. The flask id dhaken constantly. An exothermic reaction sets in leading to violent boiling. After
ten minutes the mixture is cooled, KCl filtered off, and filtrate rotavaped to dryness. The crude potassium dithioformate can be thermolyzed to CS2
without further purification.
CHCl3 + 4 KSH -> HCSSK + 3 KCl + 2 H2S
Obviously do this in hood.
The oversize flask and efficient reflux condenser are necessary to avoid loss of reactants and solvent. The violence of the reaction may present a
scaleup problem.
Discontinue heating when the exotherm kicks in.
Attachment: BCSJ.pdf (538kB)
This file has been downloaded 967 times
[Edited on 28-5-2009 by Sauron]
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Sauron
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The theoretical yield from above ought to be 250 mmol CS2. That is 19 g. CS2 d 1.26 so about 15 ml.
To do this on a 1 mol CHCl3 basis use a 12 L flask, 120 g chloroform, and prepare KSH by mixing:
184 g KOH in 600 ml MeOH
and
184 g KOH in 600 ml MeOH saturated with H2S.
You will need one or more large efficient reflux condensers. Dewar condensers, double surface coil condensersAllihn condensers and Friedrichs
condensers all come to mind.
[Edited on 29-5-2009 by Sauron]
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len1
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| Quote: | The crude potassium dithioformate can be thermolyzed to CS2 without further purification.
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Is there a yield for this? Many compounds of C S and H have some CS2 in the decomposition - it does not sound like a high yielding process
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Nicodem
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At the moment I do not have the time to read the whole thread and find the citation regarding the dithioformate thermolysis, but Len's question makes
good sense, because if it is just a thermolysis and no other reagent (or air) is used, then you obviously need a redox reaction to transform HCSSK to
CS2.
Since it is unlikely for this compound to decompose to CS2 and KH or any such thing, then the formation of CS2 must be the consequence of a
disproportionation at the carbon. This means the stoichiometry between HCSSK and CS2 is 2 : 1. In practice this means half less CS2 than one would
hope for, and also the formation of the other disproportionation product(s). I have no idea what is the other disproportionation product, but one
option could be K2S and trithiane, or KSCH2SK (depending on which form is thermodynamicaly more favourable). Or maybe it's just a dirty thermolysis
with CS2 just as one of the many products?
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Sauron
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According to Reid, in extract posted upthread, potassium dithioformate melts with decomposition at 193 C. Dithioformic acid, solid, liberated from
above, melts with decomposition at 55-60 C. and as no pesky K is present we can work out the reaction:
HCSSH -> CS2 + H2
One mol HCSSK MW 116
gives one mol HCSSH 78 g
which theoretically gives 76 g CS2
The free acid must be decomposed as soon as prepared or it will polymerize.
Details on acidolysis are in Levi but are very likely to be similar to those for dithiocarbonate -> xanthis acid, which are in Mellor on Carbon
Part II. Cold dil aq mineral acod is used. Dithioformic acid is insoluble and ppts out as a buff colored powder.
Potassium ethyl dithiocarbonate (xanthate or xanthogenate)
KSC(=S)OEt
liberates xanthis acid HSC(=S)OEt
which falls apart in minutes at RT to CS2 and EtOH
The structural analogy to dithioformate and dithioformic acid is clear
HC(=S)SH
Under oxidizing conditions one might get COS and H2S but at 55 C? To be certain, do it under N2.
[Edited on 30-5-2009 by Sauron]
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Sauron
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Reid also states that CCl4 can be used in place of CHCl3 in this reactuin. He cites Leci again, same paper and a follow on.
I wonder what the stoichiometry is?
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watson.fawkes
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A completely different way
This method applies mostly only to Sauron, but I'm sure that the Thai Rayon plant in Angthong Province has CS2 on premises. If they sell it officially, it's likely to be by the drum.
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Sauron
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This review has popped up, right on point.
Ita states that purer HCSSK is obtained when the reaction is run in mrthanol tather than ethanol and that the reaction should be done under an inert
atmosphere.
Read along with me,
Attachment: Pages from rc45.pdf (645kB)
This file has been downloaded 1544 times
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Sauron
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References 15 abd 16 from the Russian reciew above are actually two short notes back to back on a single page from same authors, covering potassium
dithioformate and dithiofomic acid respectively.
Naturwissenschaften, 58 (1), p.53 (1971)
G. Gattow, M. Dräger and R. Engler
Über Dithioformiate
Attached.
Apparently the salt dimerizes ar its mp to sulfide KCSSSCK rather than fragmenting. That is (KC(=S)2S. This is a liquid d 1,74.
I am stiill reading so the other shoe has not dropped yet. What does duthioformic acid do at the mp?
In the free acid mass spec peaks correspond to the diner, the monomer, and CS2, which sounds promising. HCSSH is monomer, (HCSS)x the polymer, the
dimeric disulfide x=2. Not the same as with the salt. In both cases H2 is extruded as I surmised.
Note that the polymerization is fairly rapid at RT, see Todd's paper (JCS 1837 for timeline of MW growth over 24 h. So the acid is stored as the salt,
liberated w/dil HCl and thermolyzed at once at 60 C or whatever gives best yie;d of CS2.
Attached
Attachment: nat71.pdf (137kB)
This file has been downloaded 535 times
[Edited on 30-5-2009 by Sauron]
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Formatik
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Since the work of Levi [1] concerning dithioformates, these salts have been only briefly mentioned in the literature [2, 3]. By the described
method of preparation one obtains however a strongly impure product.
K[HCS2] (Mp. = 196°C, decomposition under formation of K2CS3; d20/4= 1.737 g/cm³) was prepared by the reaction of chloroform with a methanolic
solution of K2S under the absence of air; from the concentrated down solution, the substance crystallized out in the cold. - The tetraphenylarsonium
salt [.phi.4 As] [HCS2] (Mp. = 191-193°C, dec.: d20/4 = 1.39 g/cm³) results as a barely soluble precipitate by the addition of [.phi.4 As]Cl to an
aqueous solution of K[HCS2], and it can be recrystallized from water.
Aqueous solutions of the [HCS2](-) ion show visible and UV-range absorptions at 225, 331, and 386 nm.
IR spectrum of K[HCS2]: .... [spectral data for the potassium and tetraphenylarsonium salt]
Dithioformates and dithioformic acid, whose existence was first pointed out by Levi [1], are only briefly mentioned in the following literature
[2,3].
Dithioformic acid was precipitated from an aqueous solution of K[HCS2] by the addition of dilute hydrochloric acid. It is as opposed to formic acid
and monothioformic acid [5], barely soluble in water. Aqueous sodium hydroxide as well as tetrahydrofuran and dioxane solubilize the free acid well;
in ether, chloroform and benzene it has only low solubility.
The weak yellowish, X-ray amorphous acid [HC(S)(SH)]x melts at 55-60°C. In the mass spectrum, aside the molecule peak at m/e = 234 (x=3), there are
peaks at m/e= 156 (x=2), 78 (x=1) and 76 (CS2). Solutions of dithioformic acid in diethyl ether show in the UV-range absorption at 295 nm.
IR spectrum of dithioformic acid: [spectral data concerning the said compound and its ethyl and methyl ester briefly]
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Sauron
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Thank you, formatik.
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Sauron
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To recap, it appears that potassium duthioformate does not thermolyze to CS2 but that dithionic acid might well.
Also treating the acid with aqieous NH3 obtains thioformamide, and Wilstatter and Wirth (posted above) report that the hydrochloride of that compound,
prepared with HCl gas in ether, does thermolyze to CS2.
Is this competitive with acetylebe and S? That depends on circumstances. Os chloroform readily available and cheap? If so then just maybe this is a
viable alternative.
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Rattata2
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| Quote: | | [quote=Sauron]Potassium Ethyl Xanthate is pricier than I remembered, so its decomposition, while facile and efficient, is not an economical way to
obtain CS2. |
This post gave me an idea..how about the decomposition of cellophane or rayon to obtain CS2? That stuff is dirt-cheap and used everywhere..and is a
xanthate 
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