Purification of perfluorosulfonyl fluoride perfluorovinyl ethers by thermal decomposition of unstable isomers
The separation of primary perfluorosulfonyl fluoride perfluorovinyl ethers from their isomers by selective pyrolysis and the preparation of copolymers of tetrafluoroethylene from the purified isomers is disclosed.
Latest E. I. Du Pont de Nemours and Company Patents:
In the Examples which follow, all parts are by weight unless otherwise indicated.
EXAMPLE 1 Preparation of PSEPVE ##STR18##The addition product of two moles of hexafluoropropylene oxide (HFPO) to one molecule of fluorosulfonyldifluoroacetyl fluoride (diadduct) is prepared as taught in U.S. Pat. No. 3,301,893. ##STR19##
A reaction flask was charged with 1,800 g of anhydrous Na.sub.2 CO.sub.3 (dried over silica gel). The slurry was heated to 165.degree. and 4,983 g of the diadduct was added with vigorous stirring over 8 hours. The PSEPVE was continuously removed from the reaction via a liquid-liquid separator. The crude PSEPVE (4052 g) was washed once with water and steam distilled to give 3,712 g of wet PSEPVE plus 259 g of an unidentified residual oil. The steam-distilled PSEPVE was dried over silica gel and distilled to obtain 2,903 g. PSEPVE normal b.p. 132.degree.-134.degree. C. The distilled PSEPVE was further purified by passing it through a column of silica gel and storing it over silica gel.
The factors effecting yields are dryness of reactants, temperature, and contact time. Secondary isomers are often present when PSEPVE is prepared by this route.
EXAMPLE 2A dry 30 ml. stainless steel cylinder is charged with 1 g. of previously dried (heated 20 hours at 400.degree. C. in vacuo) "Darco," commercially available activated carbon, and is cooled to -180.degree. C. and evacuated. There is then introduced 8.7 grams of hexafluoropropylene peroxide and 8.7 g. of pentafluoropropionyl fluoride. The mixture is slowly warmed to room temperature and kept at room temperature for 2 days. On workup, there is obtained 7.8 g. of perfluoro-2-propoxypropionyl fluoride having a boiling point of 55.degree. to 57.degree. C. Both epoxide and perfluoropropionyl fluoride are recovered in nearly equal amounts indicating that the product is formed by interaction of acid fluoride and epoxide.
Perfluoro-2-propoxypropionyl fluoride so prepared is also charged into a polyethylene bottle equipped with a Dry Ice condenser. There is then added 15 weight percent, based on the weight of the acid fluoride of water. The reaction mixture is neutralized to phenolphthalein end point with 10 N KOH in water and was evaporated in dryness at 35.degree. C. The dry mixture of potassium perfluoro-2-propoxypropionate and potassium fluoride is further dried in vacuo at 100.degree. C. The resulting mixture is placed in a glass reaction vessel equipped with a Dry Ice trap. The vessel is heated to 185.degree. to 215.degree. C. for a period of 24 hours. Perfluoro(propyl vinyl) ether is obtained on distillation of the product in the trap.
EXAMPLE 3Copolymer of TFE/PPVE is prepared by the following procedure:
Into an evacuated stainless steel 100 ml. autoclave fitted with a magnetically driven stirrer is placed a solution of 9 g. of perfluoropropyl perfluorovinyl ether (0.034 mol) in 64 ml. of perfluorodimethylcyclobutane. The solution is heated to 60.degree. C., whereupon tetrafluoroethylene is admitted to the autoclave until a pressure of 268 psig is attained. To the rapidly stirred mixture is added approximately 10.sup.-4 mol of N.sub.2 F.sub.2 diluted with nitrogen. The contents of the autoclave are heated and stirred for 1 hour at 60.degree. C., and then cooled and gaseous materials vented off. The solid polymer obtained weights 15.0 g. and had a melt viscosity at 380.degree. C. of 3.6 .times. 10.sup.4 poises. Films of the copolymer pressed at 350.degree. C. and 20,000 psi platen pressure are tough, clear and colorless. Infrared analysis of the resin indicates the presence of 9.7 wt. percent perfluoro (propyl vinyl) ether.
EXAMPLE 4 Polymerization of PSEPVE and TFEThe Polymerization system consisted of a 3-gallon jacketed stainless steel autoclave with a helical agitator. A water cooled container and a wet-ice trap followed by a Dry-Ice trap were provided in the vent line from the reactor to condense the reaction monomer solution during boil-out. The charge to the reactor consisted of a total of 13,342 grams total, comprising by weight percent 52.2 percent PSEPVE with no iso-PSEPVE 2.0 percent, hydro-PSEPVE, ##STR20## and 45.8 percent "Freon"-113.
The polymerization kettle was kept at a pressure of 90 psig and a temperature of 45.degree. C. for three hours using 200 rpm agitation. A solution of perfluoropropionyl peroxide in the amount of 0.115 g. per cc. of "Freon"-113 was prepared, 2.5 cc. of solution was added initially and 0.5 cc. of solution was added each half hour for 21/2 hours.
The yield was 1040 grams of polymer of equivalent weight of 1,095 with a melt flow of 3.6 g. per 10 minutes and a water absorptivity of 31.6 percent.
EXAMPLES SHOWING THE SEPARATION OF ISOMERS EXAMPLE 5The primary isomer PPVE and the other isomers incidental to production of the primary isomer according to the method of Example 2 were passed through a tube over sodium carbonate at the temperatures indicated. The average contact time over sodium carbonate was 22 seconds. The feed and product concentrations of the undesirable isomer are listed in addition to the percent product recovery of the desirable isomer.
______________________________________ % ofA in CF.sub.3 CF.sub.2 CF.sub.2 OCFCF.sub.2 (PPVE) Temp. Feed Product Product Recovery ______________________________________ 250 0.66 0.61 95% 280 0.50 0.23 -- 300 0.65 0.10 97% 300 0.37 0.10 90% 300 0.37 0.08 95% 300 0.37 0.10 97% 300 0.37 0.07 93% 300 0.37 0.08 97% 300 0.37 0.15 91% 320 0.26 0.10 88% ______________________________________ ##STR21##
A stainless steel tube four inches in diameter and five feet long was filled with ten pounds of anhydrous sodium carbonate. The tube was heated to 300.degree. C. and the sodium carbonate fluidized. Then 11.5 pounds of PPVE containing 0.65 percent iso-PPVE was fed through the tube in 68 minutes. The PPVE recovered weighed 11.2 pounds and contained 0.10 percent iso-PPVE.
Analogous experiments were performed using potassium carbonate, glass beads or stainless steel mesh in place of the sodium carbonate. However because of ease in handling, heat transfer, etc., the use of carbonate is preferred.
EXAMPLE 7The following is an example of the selective pyrolysis resulting in the removal of (perfluoro-3,6-dioxa-5-methyl-7-octene-sulfonyl fluoride (I) from perfluoro-3,6-dioxa-4-methyl-7-octene-sulfonyl fluoride (II). They are prepared by the process of Example 1. ##STR22##
A vertically mounted glass tube 12 inches .times. 1 inch OD was filled with glass beads and topped by a pressure equalizing dropping funnel. The outlet of the tube was connected to a trap cooled to -78.degree. C. The apparatus was flushed with nitrogen and 10 g of crude (II) containing some (I) was added to the funnel. The glass tube was heated to 300.degree. and the sample added in 4 minutes. The recovered product, 8.5 g, was a colorless liquid. Gas chromatographic analysis showed that no more (I) remained.
EXAMPLE 8A perfluorinated vinyl ether mixture was passed through a 12 inch by 1 inch diameter glass tube heated by a split tube furnace. The vinyl ether mixture vapor was carried by a stream of nitrogen through the glass tube and multiple cold traps in which the reaction product was collected.
The tube was heated to 300.degree. and 6.00 g of a mixture containing 83.3 percent perfluoro (3-oxa-1-octene) and 16.7 percent perfluoro-(3-oxa-4-ethyl-1-hexene) passed through the tube in 8 minutes. Infrared spectral analysis of the vinyl ether product showed it to be a mixture of 98 percent perfluoro (3-oxa-1-octene) and 2 percent perfluoro-(3-oxa-4-ethyl-1-hexene).
EXAMPLE 9Using the apparatus and procedure of Example 8, the tube was heated to 275.degree. and 2.30 g. of a mixture containing 87.0 percent perfluoro(3-oxa-1-octene) and 13.0 percent perfluoro(3-oxa-4-ethyl-1-hexene) passed through the tube in 4 minutes. Infrared spectral analysis of the vinyl ether product showed it to be all perfluoro(3-oxa-1-octene).
EXAMPLE 10Using the apparatus and procedure of Example 8, the tube was heated to 275.degree. and 2.30 g. of a mixture containing 87 percent perfluoro(3-oxa-1-octene) and 13 percent perfluoro(3-oxa-4,5-dimethyl-1-hexene) passed through the tube in 3.5 minutes. Infrared spectral analysis of the vinyl ether product showed it to be all perfluoro-(3-oxa-1-octene).
EXAMPLE 11Using the apparatus and procedure of Example 8, the tube was heated to 275.degree. and 6.1 g of a mixture containing 90.6 percent perfluoro(3,6-dioxa-5-methyl-1-nonene) and 9.4 percent perfluoro(3,6-dioxa-4-methyl-1-nonene) passed through the tube in 21 minutes. The vinyl ether product was converted by reaction with cesium fluoride, dimethyl formamide and water to a mixture of 98.8 percent perfluoro(3,6-dioxa-5-methyl-2-hydrononane) and 1.2 percent perfluoro(3,6-dioxa-4-methyl-2-hydrononane) showing that the percentage of perfluoro(3,6-dioxa-4-methyl-1-nonene) in the vinyl ether mixture had decreased from 9.4 percent to 1.2 percent upon heating.
EXAMPLE 12Using the apparatus and procedure of Example 8, the tube was heated to 275.degree. and 8.5 g of the same mixture used in Example 11 passed through the tube in 3.0 minutes. The vinyl ether product, 6.9 g, was treated as in Example 12 to give a mixture of 97.8 percent perfluoro(3,6-dioxa-5-methyl-2-hydrononane) and 2.2 percent perfluoro(3,6-dioxa-4-methyl-2-hydrononane) showing that the percentage of perfluoro(3,6-dioxa-4-methyl-1-nonene) in the vinyl ether mixture had decreased from 9.4 to 2.2 percent upon heating.
The purified isomer is useful at least in preparing copolymers with TFE having utility as self-supporting films and molded articles. The copolymers of TFE and the purified isomers are melt fabricable.
Claims
1. In the process for the preparation of perfluorosulfonyl fluoride perfluorovinyl ethers having the formula ROCF=CF.sub.2, where R is a sulfonyl fluoride-containing fluorinated alkyl radical having three to 15 carbon atoms, wherein mixtures of the primary isomer and other isomer thereof having the same number of fluorine and oxygen atoms per molecule as the primary isomer are present, the improvement comprising an additional heating of said mixture consisting essentially of said isomers at a temperature of between 250.degree.-350.degree. C. to selectively destroy said other isomer and separating the purified primary isomer from the products of the destroyed isomer, the --OCF=CF.sub.2 group of the primary isomer being connected to a CF.sub.2 group in R and the --OCF=CF.sub.2 group of said other isomer being connected to a secondary or tertiary carbon atom.
2. Process of claim.[.1.]..Iadd.3.Iaddend.wherein the primary isomer is perfluoro-3,6-dioxa-4-methyl-7-octene-sulfonyl fluoride and there is also present in the mixture the isomer perfluoro-3,6-dioxa-5-methyl-7-octene-sulfonyl fluoride..Iadd. 3. In the process for the preparation of perfluorosulfonyl fluoride perfluorovinyl ethers having the formula ROCF=CF.sub.2, where R is a sulfonyl fluoride containing fluorocarbon group of three to 15 carbon atoms which may optionally contain one or more ether linkages or chlorogroups with the proviso that the carbon atom of R bonded to the oxygen is also bonded only to atoms from the class consisting of carbon and fluorine, wherein mixtures of the primary isomer and other isomer thereof having the same number of fluorine and oxygen atoms per molecule as the primary isomer are present, the improvement comprising an additional heating of said mixture consisting essentially of said isomers at a temperature of between 250.degree.-350.degree. to selectively destroy said other isomer and separating the purified primary isomer from the products of the destroyed isomer, the --OCF=CH.sub.2 group of the primary isomer being connected to a CF.sub.2 group in R and the --OCF=CF.sub.2 group of said other isomer being connected to a secondary or tertiary carbon atom..Iaddend.
| 3041317 | June 1962 | Gibbs et al. |
| 3282875 | November 1966 | Connolly et al. |
| 3301893 | January 1967 | Putnam et al. |
| 3492348 | January 1970 | Bondakian et al. |
Type: Grant
Filed: Jun 28, 1976
Date of Patent: Feb 7, 1978
Assignee: E. I. Du Pont de Nemours and Company (Wilmington, DE)
Inventor: Paul R. Resnick (Wilmington, DE)
Primary Examiner: Norman Morgenstern
Application Number: 5/700,068
International Classification: C07C14308; C07C14370;
