Chemistry of inorganic compounds – Halogen or compound thereof – Sulfur containing
Reexamination Certificate
2001-11-01
2004-07-20
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Sulfur containing
C423S467000, C423S24000R, C423S24000R
Reexamination Certificate
active
06764670
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to providing pure sulfur tetrafluoride (SF
4
). More particularly, it relates to the removal of thiothionylfluoride (S═SF
2
) from SF
4
by contacting the impure SF
4
with a high surface area material, such as activated carbon.
Sulfur tetrafluoride is an extremely useful fluorinating agent, which is particularly suited for the fluorination of oxygen-, sulfur- and nitrogen-containing groups bonded to non-metal or metal atoms. See, e.g., U.S. Pat. No. 3,950,498 to Appel et al. According to a publication of Air Products and Chemicals, Inc. (http://www.airproducts.com/fluorination/sulfur.asp; 2001), SF
4
is particularly useful for deoxofluorinating aldehydes, ketones and carboxylic acids in the presence of hydrogen fluoride (HF) and other Lewis acid catalysts.
SF
4
can be produced by a variety of methods. For example, U.S. Pat. No. 2,992,073 to Tullock describes a process for producing SF
4
comprising reacting an alkali metal fluoride (wherein the alkali metal is Na, K, Rb or Cs) with a chlorine-supplying reactant (e.g., elemental Cl, etc.) and sulfur-supplying reactant (e.g., elemental S, etc.).
U.S. Pat. No. 3,950,498 to Appel et al. describes a process for the production of sulfur tetrafluoride, wherein sulfur tetrachloride or mixtures consisting of sulfur dichloride and chlorine are reacted with hydrogen fluoride in the presence of a carbon tetrahalide to provide SF
4
.
A problem with existing methods for manufacturing SF
4
is the production of undesirable byproducts that contaminate the SF
4
. Such impurities can hinder the usefulness of SF
4
as a fluorinating agent.
Thiothionylfluoride is a particularly undesirable SF
4
contaminant. Thiothionylfluoride is typically observed in SF
4
compositions at concentrations of 5% or more. Although thermally stable, S═SF
2
can undergo a disproportionation reaction to produce elemental sulfur when using SF
4
as a raw material. The elemental sulfur byproduct can interfere with the SF
4
chemistry and foul the processing systems.
Seel, “Lower Sulfur Fluorides” in 16
Adv. Inorg. Chem. Radiochem,
297, 303-304 (1974), describes a process for converting pure S═SF
2
to SF
4
and elemental sulfur using catalysts, such as HF or BF
3
. Although Seel does not address the problem of removing S═SF
2
from SF
4
, the inventor is aware of a proprietary process for removing S═SF
2
from SF
4
, which employs the same chemistry as described by Seel to disproportionate S═SF
2
to form S
8
and SF
4
using HF (or BF
3
). However, this process is both inefficient and dangerous because it causes significant losses of SF
4
and requires using large quantities of HF. The HF catalyst becomes deactivated during the disproportionation, because of the formation of the salt SF
3
+HF
2
−
(BF
3
catalyst becomes deactivated by formation of the analogous salt with SF
4
). Thus, in order to have sufficient free HF present to initiate the disproportionation of S═SF
2
, at least 30 mole % of HF must be mixed with the contaminated SF
4
. While this method produces SF
4
free of impurities, about 20-25% of the SF
4
is unrecoverable from the HF. The proprietary process is dangerous in that it involves handling large quantities of liquid anhydrous HF. HF is a gas under standard conditions, and reacts violently with many materials including glass. It can permeate large areas rapidly, and is extremely dangerous to humans. It is, therefore, desirable to avoid handling large quantities of HF.
The use of high surface area materials, such as activated carbon, zeolites, and silica, for separation processes is known. However, the inventor is not aware of any prior art disclosing the use of high surface area materials for removal of S═SF
2
from SF
4
.
Accordingly, it is desired to provide a safer and more efficient process for removal of S═SF
2
from SF
4
.
All references cited herein are incorporated herein by reference in their entireties.
BRIEF SUMMARY OF THE INVENTION
The invention provides a process for removing thiothionylfluoride from a composition containing sulfur tetrafluoride and an initial concentration of thiothionylfluoride. The process comprises: contacting the composition with an activated carbon; reacting at least a portion of the thiothionylfluoride to form elemental sulfur; and recovering a purified composition containing the sulfur tetrafluoride and the thiothionylfluoride at a reduced concentration less than the initial concentration.
Also provided is a process for removing thiothionylfluoride from a composition containing sulfur tetrafluoride and an initial concentration of thiothionylfluoride, which process comprises: contacting the composition with a metal oxide-free material having a surface area of at least 400 m
2
/g; reacting at least a portion of the thiothionylfluoride to form elemental sulfur; and recovering a purified composition containing the sulfur tetrafluoride and thiothionylfluoride at a reduced concentration lower than the initial concentration.
REFERENCES:
patent: 2992073 (1961-07-01), Tullock
patent: 3000694 (1961-09-01), Smith et al.
patent: 3393977 (1968-07-01), Langer
patent: 3950498 (1976-04-01), Appel et al.
patent: 4082839 (1978-04-01), Eibeck et al.
patent: 634467 (1962-01-01), None
Air Products and Chemicals, Inc. Publication (www.airproducts.com/fluorination/sulfur.asp;) 2001 Seel, “Lower Sulfur Fluorides” in 16Adv. Inorg. Chem. Radiochem, 297, 303-304 (1974) no month.
Air Products and Chemicals Inc.
Leach Michael
Nguyen Ngoc-Yen
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