Sept. 20, 1957
PREPARATION OF PERFLUOROALKYL PROPENYL KETONES
4983
[CONTRIBUTION FROM MATERIALS LABORATORY, WRIGHTAIR DEVELOPMENT CENTER,AIR RESEARCH A N D DEVELOPMENT COMMAND]
Unsaturated Ketones. I. The Preparation and Polymerization of Perfluoroalkyl Propenyl Ketones1 BY DOUGLAS A. RAUSCH,LESTERE. COLEMAN, JR.,
AND
ALANM. LOVELACE
RECEIVED NOVEMBER 13, 1956 A series of perfluoroalkyl propenyl ketones has been prepared and their preparation has been described in detail along with the infrared and ultraviolet absorption spectra. Some polymerizations and copolymerizations of these new monomers have been described and the properties of a variety of new copolymers have been recorded.
This Laboratory has undertaken a study of the preparation and polymerization of a,@-unsaturated ketones. This paper deals with the synthesis and polymerization reactions of a series of three perfluoroalkyl propenyl ketones. Monomer Synthesis.-It has been shown previously that Grignard reagents react readily with peduorocarboxylic acids t o give alkyl perfluoroalkyl ketones in good yields2 Therefore, i t was assumed that P, y-unsaturated ketones could be prepared by treating perfluorocarboxylic acids with allylmagnesium bromide and that these ketones could be rearranged to the a$-unsaturated derivatives. Accordingly, three moles of allylmagnesium bromide were added to one mole of CsF7C02H or to two moles of C3F7C02Li in ether to yield fraction I (b.p. 10C-115°) and fraction I1 (b.p. 116.7'). Infrared absorption spectra of the two fractions showed that fraction I had two sharp carbonyl absorption bands, on eat 6.64 p and the other a t 5*78p, while fraction I1 had a single carbonyl absorption band a t 5.78 p. Both fractions showed a strong C= C band a t 6.11 p . Haszeldine3 has reported that fluorine-containing ketones having the structure RfCOCH2- have a strong carbonyl absorption frequency a t 5.65 p . Fraction I, therefore, contains C3F7COCH2CH=CH2 (A) accounting for the absorption frequency a t 5.64 p . Since the number of possible hyperconjugation structures is two for A and three for C~F~COCH=CHCHS (B), the a,@B,r equilibrium of the unsaturated ketone should favor the c~,P-derivative.~Therefore, A should isomerize to the conjugated system B, thus shifting the carbonyl absorption frequency to the longer wave length 5.78 p . Refractionation of fraction I after standing several weeks yielded almost entirely fraction I1 (B). The conjugated structure of B has been confirmed by nuclear magnetic resonance spectrum. Therefore, the reaction of CyF7C02H or its lithium salt with allylmagnesium bromide produces the p, y-unsaturated ketones which rearrange slowly to the a,,&-unsaturatedderivatives. Compound B was obtained in 40-50% yields using both procedures. Similar yields were obtained using both CF3C02Hand n-C7F&02H. These a,@unsaturated ketones also showed the strong carbonyl absorption frequency a t 5.78 p and the C=C absorption frequency a t 6.11 p . The physical con-
stants of the a,@-unsaturatedketones are shown in Table I. As shown in Table 11, the fluorine-containing ketones have the characteristic ultraviolet absorption spectra of unfluorinated vinyl ketones. It can be seen that as the electron-attracting power of the terminal group R increases, the K- and R-bands are displaced to longer wave lengths. However, the K-band is only displaced to 237 mp when R is CF3 while wc3F.1and n-C7F16 causes a shift to 242 mp. This indicates that the electron-withdrawing effect of n G F 7 and n-C7F16 are about equal but greater than that of CF3. Henne and Fox6 have previously shown by determining the ionization constants of C3F7C02H and CF3C02H that the C3F7 group is more electron withdrawing than the CF3 group. Polymerization.--Homopolymerization of the fluorine-containing unsaturated ketones could not be accomplished using either bulk, solution or emulsion recipes. These ketones did, however, undergo copolymerization with a variety of vinyl monomers such as acrylonitrile, ethyl acrylate, styrene and vinyl acetate. Properties of these copolymers are listed in Table 111. Peduoropropyl propenyl ketone has also been copolymerized with m-trifluoromethylstyrene and 1,l-dihydropeduorobutyl acrylate. Products were a white powder and a sticky gum, respectively. Incorporation was confirmed by infrared analysis. No further characterization was made. An attempted copolymerization of the perfluoropropyl propenyl ketone with benzalacetophenone in a bulk recipe failed to give any polymeric product. nButyl vinyl ether copolymers could not be prepared using either bulk or emulsion recipes. In the attempted copolymerization of the perfluoroalkyl propenyl ketones with maleic anhydride only maleic acid was isolated. An attempted Diels-Alder reaction yielded the same product. As a group, the peduoroalkyl propenyl ketones exhibit polymerization reactivity similar to that of other P-substituted-a$-unsaturated ketones such as benzalacetopherione and its analogs.6 Incorporation of the ketones with acrylonitrile and ethyl acrylate is small, whereas large amounts of ketone are incorporated with styrene. One noticeable difference between the fluorine-containing ketones and benzalacetophenone or benzalacetone is the
(1) Presented before the 130th Meeting of the American Chemical Society, Atlantic City, N. J., September 10-21, 1950. (2) K. T.Dishart and R. Levine, THIS JOURNAI, 7 8 , 2268 (1956). (3) R. N. Haszeldine, Notrrre, 166, 1028 (1951). (4) E. R. Alexander, "Principles of Ionic Organic Reactions," John Wiley & Sons, Inc., New York, N. Y.,1950, p. 281.
( 5 ) A. L. H e m e and C. J. Fox, THIS JOURNAL, 13,2323 (1951). (0) (a) C. S. Marvel, W. R. Peterson, H. K. Inskip, J. E. McCorkle. W. K. Taft and B. G. Labbe, l n d . Eng. Chem., 46, 1542 (1953); (b) C. S. Marvel, J. Quinn and J. S. Showell, J . Org. C h o n . , 18, 1730 (1953); (c) C. S. Marvel. L. E. Coleman, Jr., and G. P. Scott, ibrd.. 20, 1785 (1955).
x.
4954
DOEGLAS I ~ A U S CLESTER H, E. COLE~IAN, JR.,
AND
ALANM. LOVEL.4CE
VOl. 79
TABLE I PHYSICAL PROPERTIES OF UNSATURATED KETONES,RfCOCH=CHCH8 Rr
OC.
B.p.
h1m.
85-86 757 CFa n-C3F; 116.7 745 5 n-CiFls 55.0-55,5 a Analysis were carried out by the
1.3583 1.189 1.33 1.3400 1.366 1.37 1.3340 1.624 1.30 Schwartzkopf Microanalytical
TABLE I1 ULTRAVIOLET S P E C T R A O F ~u,~-UNSATCRATED KETOSES, R CO CH=CH CH3 R
Xmax
CH3 CF3 n-CaF7 n-CiHls
224 23 7 242 242
K-band
Carbon, % Calcd. Found
ARf
d20,
Xz0D
R-band Xmax
E
9 750 1 800 5.600 5 800
313 5 322 322 322
E
38 20 45 50
Analyses Hydrogen, % Calcd. Found
3.62 3.40 43.45 43.32 35.39 2.10 2.18 35.29 1.14 1.20 30.14 30.13 Laboratory, Woodside, S. J.
Fluorine, % Calcd.
Found
41.30 55.88
41.40 65.68 65.10
65.07
hydrolyzed by pouring into ice-concentrated hydrochloric acid. The ether layer was separated and the water layer extracted with three 100-ml. portions of ether. T h e conibined ether layers were dried over Drierite and distilled to remove the ether; the residual liquid was then dried over phosphoric anhydride and fractionally distilled through a n efficient column. I n each case, a lower boiling fore-cut was obtained which upon redistilling after several weeks of standing yielded additional propenyl ketone. An alternate procedure for t h e ketone preparation was accomplished by treating equivalents of perfluorocarboxylic
TABLE I11 BULKPOLYMERIZATIONS OF PERFLCOROALKYL PROPESYL KETONES KITH VINYL MONOMERS
Comonomer
Acrylonitrile Ethyl acrylate Vinyl acetate Styrene Acrylonitrile Ethyl acrylate Vinyl acetate Styrene
Polym. time hr.
-
Conversion,
48
35 25 25
i
55
7
-
40
i
25 40 50
7
-
48 c
Inherent viscosity (benzene)
Softening point, OC.
Change ratio ketone/ comonomer
Perfluorornethyl propenyl ketone > 276 40/60 0.8" 30/70 0.9 90-95 40/60 0,5 145-150 40/60 Perfluoropropyl propenyl ketone 0.SAa > 275 40/60 30/70 0.57 83-88 40/60 0.30 140-145 40/60
Fluorine,
70
Trace 3.7 23.6 14.0 Trace
7.5 36.8 27.5
Ketone incorp. wt. 70
Appearance of polymer
5b
Powder Gum Powder Powder
9
57 34
5b 13
65 50
Powder Gum Powder Powder
Perfluoroheptyl propenyl ketone m 7 45 1.7" >27,5 40/60 4.4 Powder Acrylonitrile Ethyl acrylate I 3j 30/70 15.5 24 Gum Powdcr Vinyl acetate 48 40 0.i 75--80 40/60 49.4 in 7 50 0.3 130-135 40/60 33.6 52 Powder Styrene Inherent viscosity determined in N,N'-dimethylforniamide. * Estimated from infrared spectrum. copolymer formation of the former with vinyl ace- acid and metallic lithium in a small quantity of ether t o gike lithium perfluorocarboxylate. A4fter addition of one tate. Benzalacetophenone and similar ketones did the liter of ether t o two moles of the lithium salt, the solution not yield copolymers. was cooled in a n ice-bath and three moles of allylmagnesium In comparing the reactivity of the three ketones bromide in three liters of ether was added dropwise with described in this paper, it was observed that as the stirring. The reaction was run overnight at room temperaand the mixture was worked up as described above. size of the perfiuoroalkyl group increased, the reac- ture Using either procedure, the yields of the perfluoroalkyl tivity increased and the rate decreased. An esti- propenyl ketones were 40-50%. mation of the reactivity ratios of the fluorinePolymerization.-Bulk, solution and emulsion recipes containing ketones with styrene (311) indicated were used. Bulk polymerizations were run at 60" with benperoxide as catalyst. For solution polymerization, that the perfluoropropyl- and perfluoroheptyl- zoyl benzene or N,N'-dimethylformamide was used as solvent. derivatives were similar ( r l = 0.5-0.7; r2 = 0) The emulsion recipes consisted of Office of Synthetic Rubber while the perfluoromethyl propenyl ketone ( ~ 1= soap, potassium persulfate as initiator and dodecyl niercap1.0; ~2 = 0 ) was less reactive. On an over-all tan as modifier. Occasionally Dupanol M E was used a< n emulsifier. Reactions were run at 50". I n all cases, basis, perfluoropropyl propenyl ketone indicated ascrew cap bottles were used with Buna i Y type gaskets. optimuni utility as a comonomer. A forthcoming The incorporation of the propenyl ketones into copolypaper will discuss the copolymerization of these mers was determined by elemental analysis and confirmed by the infrared absorption frequency of the ketone carbonyl ketones with various 1,3-dienes. band which shifted from 5.78 p in the monomer t o 5.65Experimental 5.70 p in the polymer. Three moles of allylmagnesium bromide in two liters of Acknowledgment.-The authors would like to (liethyl ether was prepared in a cyclic reactor.7 express their appreciation to the Analysis ant1 One mole of perfluorocarboxylic acid in a n equal volume Measurement Branch, Materials Laboratory, for of ether was added dropwise with stirring t o the Grignard their assistance in obtaining the infrared and ultrareagent which was cooled in a n ice-bath. After stirring overnight a t room temperature, the reaction mixture was violet spectra and to the Varian Associates for the
-
r-
17) 11.S. Kharasch and 0. Reinmuth, "Grignard Reaclions of L-onmetallic Substances Frentice-Hall, I n c . . Y e w York, N . lr.,1954, p . 23 I '
nuclear magnetic resonance spectrum and interpretdtion. IVRIGHT-PA~TERSON FORCE BASE,OHIO
