SYNTHESIS OF 3,4-DICHLORO-2,2,5,5-TETRAFLUORO2,5-DI HYDROFURAN AND 4-HYDROXY-2,3-DICH LORO4,4-DI FLUORO-2-BUTENOIC ACID ?-LACTONE E D W A R D
5 .
BLAKE
A N D
Monsanto Research Corp., Dayton, Ohio
J O H N
L .
S C H A A R
45407
Preparative methods for the two titled compounds by the reaction of SF1 with dichloromaleic anhydride and dichloromaleic acid are reported. Prior synthesis of the tetrafluoro compound using the anhydride is better defined and improved by use of the acid. The tetratluoro compound is an intermediate for the synthesis of tetrafluorooxydiacetic acid, which is an important intermediate in exploratory polymer synthesis.
ADVANCES in technology and the extreme conditions im-
20.5.C.). The dichloromaleic acid was prepared by dissolving the dichloromaleic anhydride in water a t the boiling point, removing the water in a rotating evaporator below 60" C. to a paste, redissolving in ether, drying over sodium sulfate, removing the ether below 50° C., and finally drying in a vacuum desiccator over phosphorus pentoxide (melting point corrected, 111-13" C.). The toxicity hazards of sulfur tetrafluoride (Smith, 1962) and of anhydrous hydrogen fluoride (Sax, 1957) are re-emphasized. General Procedure for Preparation of 3,4-Dichloro-2,2,5,5tetrafluoro-2,5-dihydrofuran and 2,3-Dichloro-4,4-difluoro-4hydroxy-2-butenoic Acid ?-Lactone. Condition details and results of the individual experiments are summarized in Table I. In general, the autoclave was charged with the solid reactants, checked for leaks under nitrogen pressure, cooled in dry ice-acetone mixture, and evacuated to facilitate charging with SF,. The SF4 was charged by weight from a laboratory cylinder. On completion of the reaction, the autoclave was allowed to cool and the SOFr, H F , and excess SF4 were vented into a caustic trap. The liquid reaction mixture was poured into a stainless steel beaker, bubbled with nitrogen, and poured through a thin layer of glass wool for a crude yield. The reported yields of the two identified components were determined by quantitative gas chromatography. The two named compounds were separated initially by mers are stable in air to 350" and are resistant to fuming distillation through a 42-inch Todd column packed with nitric acid (Brown, 1960). glass helices. The tetrafluoro compound was then carefully Insertion of oxygen in the perfluoroalkylene chains in washed with dilute potassium carbonate and redistilled the above perfluoropolytriazine polymer should impart (b.p. 74°C.) (Hasek et al., 1960; b.p. 73 t o 74°C.) (ng improved flexibility. For this type of polymer the 1.3611; 99.4% pure as shown by GLC). Redistillation oxydiperfluorodicarboxylic acids are critical intermediates of the lactone yielded a product 99.65 pure (b.p. 124"C., of considerable interest. The objective of this paper is ng 1.4318). The infrared showed absorption a t 5.5 microns to define improved conditions for the synthesis (Hasek et al., 1960) of 3,4-dichloro-2,2,5,5-tetrafluoro-2,5-dihydro- (carbonyl), 6.1 microns (double bond), two bands 7.7 and 8.1 microns (aliphatic CF,), and a group of bands a t furan which, by oxidation, is readily converted to tetraapproximately 8.7 microns (lactone ring oxygen). A major fluorooxydiacetic acid, O(CF?COOH)?.The y-lactone is a uncoupled N M R resonance was observed a t +7.3 p.p.m. coproduct in this synthesis. (as referenced to CF,COOH)- which is in the region for Experimental the CF2 environment of the proposed structure. Analysis. Analyses were carried out on an F&M 500 Chemicals. The sulfur tetrafluoride was used as obtained Model gas chromatograph fitted with a 6-foot column in lecture bottles from the Matheson Co., Inc. packed with a 20% Xe 60 on Diatoport S. The operation Dichloromaleic anhydride (Aldrich Chemical Co.) was conditions were: injection block 100°C., column 30" to recrystallized from toluene (melting point corrected, 118.5-
posed by exploration in space have impressed severe demands on polymers and elastomers. Significant improvements are needed in thermal stability, retention of strength a t elevated temperature, resistance to oxidation and degradation by fuels, etc. One approach to this problem being actively pursued is the elimination of hydrogen from the polymeric material by replacement of the C-H bonds with more stable C-F bonds. Teflon has been known for some time, but it exhibits no elastomeric character. Teflon's rigidity is the result of crystallinity arising from the interaction of the long chains and not from an inherent rigid structure. Interruption in the length of the long perfluoroalkylene chains by insertion of highly aromatic heterocyclic groups should destroy the crystallinity and impart elastomeric properties. Brown is actively engaged in applying this approach to perfluoroalkylene systems interspersed with triazine groups-for example, these poly-
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I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Table 1. Reaction of Dichloromaleic Acid and Anhydride with SFI
Run No. 1 2 3 4
5 6 n
8 9 10
Dichloromaleic anhydride
Reactants, Mole Dichloromaleic acid
Autoclave Temp.,
SF,
0.25 0.25 0.25 0.25 0.333
... ... ... 0.15 0.10
Yield, 5; by GLC TetraDifluorofluor0 y -lactone compd. compd.
Reaction Conditions
0.25 0.25 0.25 0.05 0.03
c.
Pressure, p.s.i.g.
Time, hr.
Uol.,
ml."
0.60 0.58 0.585 0.637" 0.823
300 300 300 300 300
422* 4700' 4729O 5023' 6300' 6005'
16 16 16 16 10
1390 122 122 122 133
...
0.925 0.990 0.925 0.76 0.768
300 200 300 250 300
833O 3201° 37335 5480° 5426'
15 16 16 16 16
1390 310 310 122 122
< 10.0
10.4 27.8 7.4 45.8
39.2 74.2 75.1 51.8
75. 27.2 19.3 36.7 26.4 77.2 33.1 2.3 5.7 6.3
-
Total uolume including fittings. 'Pressure calculated on basis of 1 mole anhydride + I mole S F , 1 mole product + 2 moles gaseous by-products; 1 mole acid + 3 moles SF, 1 mole product + 5 moles gaseous by-products. ' Hastelloy C autoclave, others stainless steel. Passed S F , through glass uool on charging autoclave to remow possible traces of HF. Measured pressure.
-
150°C., a t 7.9"C. per minute, detector block 180"C., detector current 150 ma., helium flow 60 ml. per minute, and sample size 1.5 p l . Calibration curves of the two pure components, 3,4-dichloro-2,2,5,5-tetrafluoro-2,5-dihydrofuran (99.4%) and 2,~3-dichloro-4,4-difluoro-4-hydroxy-2butenoic acid y-lactone (99.6%), were plotted, giving a linear response, using pe,ak height ratios of pure compounds over internal standard us. concentration. The concentration range was 20 to 80%, using p-xylene as an internal standard. I n addition to the above two compounds, there were as many as 11 unidentified components. I n the majority of the analyses only three or four of the unidentified components were present in significant amounts. Results and Discussion
I n a previous publica.tion (Hasek et al., 1960), the synthesis of 3,4-dichloro-2,2!, 5,5-tetrafluoro-2,5-dihydrofuran was reported in a 46% yield by the reaction of dichloromaleic anhydride (0.20 mole) with SF, (0.47 mole) a t 300°C. for 10 hours in a Hastelloy or stainless steel autoclave having a capacity between 80 and 1000 ml. Apparently the paramount importance of pressure in this specific SF, reaction was not recognized, as the autoclave size was not identified with the experiment. As a consequence, prior to achieving the reported 46% yield, the authors carried out an inordinate number of unnecessary experiments. Other workers (Greenwald et al., 1968) repeating the same procedure obtained a 21% yield of the 3,4-dichloro-2,2,5,5-tetrafluoro-2,5-dihydrofuran only by the incorporation of BF:, as a Lewis acid catalyst and with a prolonged reaction time. Obviously, if pure dichloromaleic anhydride is used, the reported preparative.method for the tetrafluoro compound (46%) can be duplicated only if the correct autoclave size for a given batch charge is chosen (run 5 ) . Furthermore, the authors have found that the yield of the tetrafluoro compound can be increased significantly (from 46 to 75%) by substitution of dichloromaleic acid for the anhydride (cf. runs 5 , 8, and 9). The yield with either the acid or anhydride is a function of temperature and pressure. However, run 9 indicates that when the acid is employed in a limited autoclave volume, it should be possible to operate a t
a lower temperature. The effect of very low pressure with both the anhydride and the acid is further observed in runs 1 and 6. I n these runs the r-lactone becomes the major product and is obtained in yields above 75%. This is an excellent preparative route to the y-lactone. Mass spectrometric analysis of a gas sample vented from run 5 showed the mole per cent components as SOF2(93), SF4(7). There was no detectable SO, or H F . These data suggest a stepwise conversion of the dichloromaleic anhydride to the difluoro-?-lactone subsequently converted to the tetrafluoro compound, catalyzed by H F generated by the dichloromaleic acid. The more highly polarized keto group of the dichloromaleic anhydride promotes its reaction with SF4 under milder conditions than are required for the difluoro-y-lactone. The following probable mechanism is suggested:
I
11
Ill
I\
Compound I expels SOF, to produce the ion pair (11), which collapses to the difluoro-?-lactone (111). The y-lactone is converted to the tetrafluoro compound (IV) catalyzed by HF. Acknowledgment
The authors acknowledge the assistance of Joseph Satanek, Jr., with the SF4 reactions, D. 0.Douglas and F. D. Crabtree with the GLC analyses, N . F. Hodgson with the mass spectrometric analysis, and J. E. Strobe1 with N M R analysis. Literature Cited
Brown, H . C., J . Polymer Sci. 44, 9 (1960). Greenwald, J.R., Grindahl, G.A., Kim, Y.K., Pierce, 0. R., Abstracts, Division of Fluorine Chemistry, 156th Meeting, ACS, Atlantic City, N. J., September 1968. Hasek, W. R., Smith, W. C., Engelhardt, V. C., J . A m . Chern. Soc. 82,543 (1960). Sax, N.I., "Dangerous Properties of Industrial Materials," Reinhold, New York, 1957. Smith, W. C.,Angew. Chern. I n t e n . Ed. 1 (€9,467 (1962).
RECEIVED for review January 7, 1969 ACCEPTED April 4, 1969 VOL. 8 NO. 2 JUNE 1969
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