Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfinic or sulfenic acids or salts thereof
Reexamination Certificate
2000-09-25
2002-10-08
Lambkin, Deborah C. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfinic or sulfenic acids or salts thereof
Reexamination Certificate
active
06462228
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for preparing fluorinated sulfinates and the use of the sulfinates obtained from the method as polymerization initiators, and particularly as initiators for the free radical polymerization of fluorinated monomers.
BACKGROUND OF THE INVENTION
Fluorinated sulfinates have utility as reactive intermediates and precursors for fluorochemical sulfonyl halides and perhalofluorocarboxylic acids and their esters. They are also useful as initiators in free radical polymerization reactions.
For example, U.S. Pat. No. 5,285,002 describes the use of fluoroalkyl sulfinates as a source of fluoroalkyl radicals in aqueous emulsion polymerizations. The resulting polymers contain a high level of perfluoroalkyl end groups, and when fluoroalkyl disulfinates are utilized, fluoroalkyl moieties are incorporated into the polymer backbone thereby yielding fluoropolymers with specific microstructural fragments which are derived from the fluoroalkyl disulfinate.
U.S. Pat. No. 5,639,837 discloses a process in which fluorine containing olefins are polymerized using an initiation system which is a combination of a fluoroaliphatic sulfinate or sulfinic acid and chlorate, bromate or hypochlorite ions. The resulting polymer contains fewer deleterious end groups and is more stable and/or easier to process.
Methods for the synthesis of fluorochemical sulfinates and their use as intermediates have been widely reported in the literature. For example, perfluoroalkane sulfinates can be prepared from the corresponding perfluoroalkanehalides via a dehalogenation and sulfination reaction, as reported in C. M. Hu, F. L. Quing, and W. Y. Huang,
J Org Chem,
1991, 2801-2804 and W. Y. Huang,
Journal of Fluorine Chemistry,
58, 1992, 1-8. Several reagent systems have been developed for use in this reaction, such as sulfite plus an oxidant, hydroxymethane sulfinate, thiourea dioxide and sodium dithionite. The use of sodium dithionite as dehalogenating and sulfinating reagent has also been reported by W. Y. Huang, B. N. Huang and W. Wang in
Acta Chim. Sinica
(
Engl. Ed.
), 1986, 178-184, and
Acta Chim. Sinica
(
Engl. Ed.
), 1986, 68-72. The later publication discloses that the reaction with an aqueous solution of the sodium dithionite is too slow for reactions involving water-insoluble perfluoralkyl bromides, and that cosolvents are needed to improve the mutual solubility of the various reactants and permit completion of the reaction within 30 to 35 hours. Mentioned cosolvents include acetonitrile, glycol and diethyleneglycol.
F. H. Wu and B. N. Huang,
Journal of Fluorine Chem,
67, 1994, 233-234 reported that if DMF, acetonitrile or alcohols are used as cosolvent, both polyfluoroalkyl iodides and polyfluoroalkyl bromides will react with sodium disulfite in neutral aqueous solution to give the corresponding sulfinates in good yield. In a similar manner, CF
3
CCl
3
reacts with sodium disulfite to give the corresponding sodium sulfinate. A disadvantage of preparing fluorinated sulfinates starting from the corresponding fluorinated iodide or bromide is that the resulting reaction product contains a large amount of by-products, particularly, inorganic salts which typically must be removed from the sulfinate.
U.S. Pat. No. 3,420,877 describes an alternative process for the preparation of fluorocarbon sulfinates. The preparation involves reacting perfluoroalkyl sulfonyl fluoride with an alkali metal sulfite or alkaline earth sulfite in an aqueous medium containing from about 10 to about 50 weight percent of a dissolved polar, inert organic solvent selected from the group consisting of dioxane, dimethoxyethane, di-n-butyl ether, tetrahydrofuran, and diethylene glycol diethyl ether. This process generally does not result in large amounts of salts that need to be removed from the resultant product, but requires use of a cosolvent that may be toxic and may have a negative impact on processes in which the sulfinate is ultimately employed, e.g., free-radical polymerization reactions.
Accordingly, there continues to be a need for an improved process for preparing fluorinated sulfinates that does not require the use of toxic solvents and preferably does not require further processing or purification of the resulting reaction mixture. It is further desirable to improve the yield of the fluorinated sulfinate.
SUMMARY OF THE INVENTION
The invention provides a process for preparing a fluorinated sulfinate product which comprises the steps of:
a) providing a reaction mixture comprising:
(1) water;
(2) dehalogenating and sulfinating reagent; and
(3) fluoroaliphatic sulfonyl fluoride represented by the formula
(I): R
f
—[SO
2
F]
n
(I)
wherein:
R
f
represents a fluoroaliphatic group, and
n is a number of 1 to 4, and typically is 1 or 2; and
(4) at least one of the materials selected from the group consisting of (i) fluorinated surfactant, and (ii) organic cosolvent comprising, as the major component by weight of the organic solvent, alcohol having a boiling point of less than 110° C. at 760 torr;
b) heating the reaction mixture to a temperature between about 50° C. and 100° C. until the desired product yield is achieved; and
c) where the organic cosolvent is employed in the reaction, optionally removing residual organic cosolvent from the resultant reaction mixture to achieve the desired level of product purity.
In a preferred embodiment, the invention provides a process for preparing a fluorinated sulfinate product comprising reacting in water, at a temperature between about 50° C. and 100° C.: (a) the fluoroaliphatic sulfonyl fluoride represented by formula (I) described above; with (b) a dehalogenating and sulfinating reagent; in the presence of the fluorinated surfactant, and without organic cosolvent until the desired yield of the product is achieved.
In another aspect, the invention provides a method of using the fluorinated sulfinate product obtained by the above-described processes as an initiation system for a free radical polymerization process.
In a preferred embodiment, the method may be used to prepare fluorine-containing polymers and comprises polymerizing, under free radical conditions, an aqueous emulsion or suspension of a polymerizable mixture containing the fluorinated sulfinate product and an oxidizing agent capable of oxidizing said tne fluorinated sulfinate compounds in the fluorinated sulfinate product to their corresponding sulfonyl radicals.
The invention provides a process for the preparation of fluorinated sulfinates using fluoroaliphatic sulfonyl fluoride that reduces or eliminates the need for organic cosolvents (such as dioxane, acetonitrile or 1,2-dimethyoxyethane) that may be toxic and/or interfere in reactions in which the fluorinated sulfinate product is used as a precursor, intermediate or initiator thereby eliminating or reducing the need for subsequent purification of the fluorinated sulfinate product. The invention accomplishes this improvement while providing comparable or improved yields to prior art processes.
DETAILED DESCRIPTION
Organic cosolvent may be used in the process either with or without fluorinated surfactant. The invention also includes reactions which do not use any organic cosolvent and employ only the fluorinated surfactant. The fluorosulfinate product largely comprises the fluorosulfinate derivatives of the fluoroaliphatic sulfonyl fluoride(s) used in the reaction mixture. Typically, the fluorosulfinate product will comprise at least about 50 weight percent and preferably at least about 70 or 80 weight percent fluorosulfinate compounds, based on the total weight of the fluorosulfinate product. The balance of the composition of the fluorosulfinate product is largely constituted of the sulfonate derivatives of the fluoroaliphatic sulfonyl fluoride(s) used to prepare the reaction mixture.
Representative fluoroaliphatic sulfinates that can be obtained with the process of the invention include the following:
CF
3
SO
2
Na
C
8
F
17
SO
2
Na
CF
3
C(Cl)
2
CF
2
SO
2
K
Cl(CF
2
)
8
OC
2
F
4
SO
2
Na
NaO
2
SC
8
Jordan Robert H.
Lambkin Deborah C.
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