Sauron
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Secondary CCl4 Preparation?
As well ought to know by now, CCl4 is produced by the direct chlorination of CS2 with dry Cl2 in the presence of a little I2 catalyst, in which case
the initial products are Cl3CSCl and S2Cl2/SCl2,
By following the procedures laid out by Rupp and Meyer, the sulfur chloride can be obtained exclusively as SCl2, which allows for easy fractionation.
The Cl3CSCl is then treated with Fe filings and quantitatively converted to CCl4.
Alternatively and more commonly FeCl2 is the catalyst and the products are CCl4 and sulfur chlorides, in which case fractionation is comples.
But in either case sulfur chlorides are the main byproduct and unless special steps are taken, S2Cl2 predominates.
According to Mellor, citing D.R.P. 72999 (1892) to A.Muller and H.Dubois, treating S2Cl2 with CS2 in presence of Fe or FeCl2 results in conversion to
CCl4 and S.
CS2 + 2 S2Cl2 -> CCl4 + 6 S
76 268 152 192
If this is so then the process overall is very efficient.
I need to obtain the old German patent.
But have no clue as to how or where.
Ullmann says this is real enough and industrially important:
Chlorination of carbon disulfide gives rise to a host of chlorinated products [19]. At temperatures between 5 and 30 °C and in the absence of iron,
iodine-catalyzed chlorination of carbon disulfide gives good yields of trichloromethanesulfenyl chloride [594-42-3]:
2 CS2 + 5 Cl2 ¾® 2 Cl3CSCl + S2Cl2
Depending on the degree of chlorination, some carbon tetrachloride [56-23-5], sulfur dichloride [10545-99-0], and thiophosgene [463-71-8] are also
formed.
In the presence of iron and metal chlorides and at higher temperature (70 – 100 °C), carbon tetrachloride and sulfur chlorides are exclusively
obtained [14]:
CS2 + 3 Cl2 ¾® CCl4 + S2Cl2
Further reaction of the sulfur monochloride [10025-67-9] with carbon disulfide produces more carbon tetrachloride and sulfur:
CS2 + 2 S2Cl2 B CCl4 + 4 S
These two reactions are the basis for the commercial production of carbon tetrachloride from the chlorination of carbon disulfide [20]. The reaction
with chlorine is very fast and proceeds to completion. Carbon disulfide and sulfur (I) chloride react more slowly. The stoichiometric reaction is
equilibrium limited at about 70 % at 90 °C.
[19] A. D. Raskina, B. A. Suvovov, V. I. Zetkin, Z. M. Kolesnikov, E. V. Zakharov, Zh. Prikl. Khim. 45 (1972) 672.
---------
But, being equilibrium limited to 70% @ 90 C, won't removing the precipitated S and adding more CS2 displace the equilibrium in favor of CCl4?
Note in the mass balance I added, a little CS2 generates a lot of CCl4
If 70% of S2Cl2 is converted to CCl4 in first run, then 21% of the remaining 30% will be converted in second, and 6.3% of the remaining 9% in the
third.
I suppose I ought to have paid more attention to the industrial side sooner.
[Edited on 11-2-2009 by Sauron]
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Sauron
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In another chapter (on halomethanes) Ullmann says:
"
Chlorination of Carbon Disulfide. The chlorination of carbon disulfide was, until the late 1950s, the principal means of producing tetrachloromethane,
according to the following overall reaction:
CS2 + 2 Cl2 ¾® CCl4 + 2 S (12)
The resulting sulfur is recycled to a reactor for conversion with coal or methane (natural gas) to carbon disulfide. A detailed look at the reaction
shows that it proceeds in stages corresponding to the following equations:
2 CS2 + 6 Cl2 ¾® 2 CCl4 + 2 S2Cl2 (13)
CS2 + 2 S2Cl2 B CCl4 + 6 S (14)
The process developed at the Bitterfeld plant of I.G. Farben before World War II was improved by a number of firms in the United States, including FMC
and the Stauffer Chem. Co. [74][75][76], particularly with respect to purification of the tetrachloromethane and the resulting sulfur.
In a first step, carbon disulfide dissolved in tetrachloromethane is induced to react with chlorine at temperatures of 30 – 100 °C. Either iron or
iron(III) chloride is added as catalyst. The conversion of carbon disulfide exceeds 99 % in this step. In a subsequent distillation, crude
tetrachloromethane is separated at the still head. The disulfur dichloride recovered from the still pot is transferred to a second stage of the
process where it is consumed by reaction with excess carbon disulfide at ca. 60 °C. The resulting sulfur is separated (with cooling) as a solid,
which has the effect of shifting the equilibrium in the reactions largely to the side of tetrachloromethane. Tetrachloromethane and excess carbon
disulfide are withdrawn at the head of a distillation apparatus and returned to the chlorination unit. A considerable effort is required to purify the
tetrachloromethane and sulfur, entailing hydrolysis of sulfur compounds with dilute alkali and subsequent azeotropic drying and removal from the
molten sulfur by air stripping of residual disulfur dichloride. Yields lie near 90 % of the theoretical value based on carbon disulfide and about 80 %
based on chlorine. The losses, which must be recovered in appropriate cleanup facilities, result from gaseous emissions from the chlorination
reaction, from the purification systems (hydrolysis), and from the molten sulfur processing.
The carbon disulfide method is still employed in isolated plants in the United States, Italy, and Spain. Its advantage is that, in contrast to
chlorine substitution on methane or chlorinating cleavage reactions, no accumulation of hydrogen chloride or hydrochloric acid byproduct occurs."
[74] Food and Machinery Corp., US 3 109 866, 1963 (E. Saller et al.).
So my surmise about the manipulation of the equilibrium in the second step was correct.
Industrially, though, they are skipping the CSCl4 (Cl3CSCl) step and using Fe or FeCl3 catalyst so that they have a fractionation of CCl4 and S2Cl2.
Whereas I would use I2 catalyst and do easy fractionation of CSCl4 from SCl2 (AKSO process) then convert the CSCl4 to CCl4 with Fe, avoiding all that
tedious purification for the bulk of the CCl4 product. But then I am talking bench scale. Then convert the 2 SCl2 to S2Cl2 + Cl2 and convert that to
CCl4 and S.
[Edited on 11-2-2009 by Sauron]
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chemrox
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CS2 + 2 S2Cl2 -> CCl4 + 6 S
76 268 152 192
I copied the above from your first post on this. What do the lower numbers represent or mean?
So do you think you have you arrived at a lab scale process you're ready to try?
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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Sauron
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That is the overall equation for two step process from CS2
See the 2 equations in the Ullmann quote? Add them and cancel terms that are on both sides.
The lower numbers are MWs for mass balance
The two equations add to be
3 CS2 + 6 Cl2 -> 3 CCl4 + 6 S
Now factor out the common multiple 3 and you have the equation at top.
The lab prep I have long admired is the chlorination of CS2 at room temp, without sunlight and with I2 rather than Fe catalyst.
Cl2 is completely absorbed at least till near the end.
The best way of judging the end is by volume, which should be 2X starting volume.
You will have a mix of Cl3CSCl (high boiling) and sulfur chlorides (S2Cl2 and SCl2, one high boiling and other low boiling.
AKSO patents I have posted before teach how to force the sulfur chlorides all to SCl2 low boiling compound, which facilitates fractionation from the
trichloromethyl sulfenyl chloride.
Now you have pure Cl3CSCl (which can be rewritten CSCl4) and pure SCl2.
Treat the CSCl4 w/Fe filings and you have CCl4
Reconvert the unstable SCl2 to S2Cl2 per AKSO
Add CS2 (1 eq) to 2 eq S2Cl2 at 60 C and stir.
S precipitates and CCl4 forms to extent of 70%
That is an equilibrium rxn
Filter off S after cooling and add more CS2, heat and stir, same effect. Now 91% Repeat again, >97%. Purify the CCl4 by dil basic hydrolysis then
dry by azeotropic distillation.
Industrially they settle for about 90-93% overall on CS2 basis. In the lab we can do a little better.
Industrially they use Fe or Fe (III)Cl catalyst and so have only CCl4 and S2Cl2 to contend with, but there is always some SCl2 to complicate things.
I have previously posted facile preps for Cl3CSCl, so there is no need to repost here.
CS2 is the more usual starting material.
MeSCN has the advantage of producing a good crop of precipitated crystalline cyanuric chloride in first stage of chlorination. Once CC no longer falls
out, continued chlorination produces a mixture of sulfur chlorides, thiophosgene and Cl3CSCl, which on further chlorination all give CCl4 (except for
the S chlorides which are separated and processed with CS2.)
If you make your own MeSCN this is about as cheap as making CCl4 from CS2. The advantage will be for those who cannot buy CC (TCT) but want some and
also need CCl4.
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