J. L. ANDERSON, R. E. PUTNAM AND W. H. SHARKEY
382
electronegative portion of the activated complex dipole requires solvation, and again that mixed acetic acid-trifluoroacetic acid dimer is less suited for this purpose than trifluoroacetic acid. The magnitude of the effect of acetic acid on reaction rate is then presumed to be related to the degree to which negative charge develops on activation; that is, the more polar is the activated complex, the more
[CONTRIBUTION 1-0. 540 FROM THE C E X r R A L
Vol. 83
acetic acid will depress the rate of reaction. Since, however, acetic acid in some instances produces little or no rate depression in these polar reactions this second explanation can be accepted only with considerable reservation. Acknowledgment.-The authors are indebted t u the National Science Foundation for a grant in support of this research.
RESEARCH DEPARTMEST, EXPERIMEUTAL STATION, E.I. AND Co., WILMINGTON 98, DEL.]
DU P O V T DE xEMO'CRS
I. Synthesis from Cyclobutenes BY J. L. ANDERSON, K.E. P K J T N.WD . ~ ~\I-. ~ H. SIIARKEY~
Fluorodienes.
RECEIVED JUXE 8, 1960
A number of fluorodienes have been prepared by pyrolysis of cyclobutenes and cyclobutyl acetates. Reactions o f 1,1,&atetrafluorobutadiene with chlorine, bromine, sodium ethoxide, sodium thiophenoxide and peroxptrifluoroacetic acid arc described.
Thermal scission of the allylic carbon-carbon bond of cyclobutenes to give 1,3-dienes has been observed in a sufficient number of cases to suggest that it is a general reaction. A number of recently reported examples have been summarized by Vogel.2 In contrast to the ease of cleavage noted in the hydrocarbon series, hexafluorocyclobutene is resistant to thermal isomerization. Thus, pyrolysis of hexafluoro~yclobutene~ over active carbon a t 600-700' has been reported to give a mixture of the cyclobutene and hexafluorobutadiene with a maximum diene concentration of only 12%. We have found that fluorocyclobutenes bearing hydrogens on the ethylenic carbons undergo ring opening upon pyrolysis to give 1,3-dienes in excellent yields. When 3,3,4,4-tetrafluorocyclobutene was heated to 550-750', it was converted almost quantitatively to 1,1,4,4-tetrafl~orobutadiene.~ The reaction was carried out by addition of the cyclobutene to a hot tube packed with quartz rings as a heat transfer medium and kept a t a pressure of 5-25 mm. 1'2 --7
k-1 d
II 1 I , ,'i
--
( ' l ~ ' 7 = . \ LIl=('F: 'll~ tl
I!
4
The product gases were rapidly quenched in a cold trap. Identification of the product as 1,1,4,4-tetraHuorobutadiene was accomplished by spectral analysis and by the formation of derivatives. Infrared absorption at 1720 cin.-l confirmed the presence of difluorovinyl groups and absorption a t 3120 c m - l indicated vinyl hydrogens. Nuclear magnetic resonance (n.m.r.) spectra5 were most (1) T o whom inquiries regarding this paper should he addressed. (2) E. Vogel, Fovtschv. Chem. Forsch., 3 , 430 (1955). (3) R. K.Haszeldine and J. E. Oshorne, J . Chem. Soc., 3880 (1955). ( 4 ) (a) J. L. Anderson, U. S. Patent 2,743,303 (April 24, 1956); (b) J. D. Park, J. Abrams, 1 4 , Hein, D. N. Gray and J. R. Lacher, J . Org. Chem., 23, 1661 (1958), have also prepared small amounts of 1,1,4,4tetraauorohutadiene from CFz=CHI; they report a hoiiing point of -1.8' (584 mm.). ( 5 ) Spectra were obtained by means of a high-resolution nuclear magnetic resonance spectrometer and associated electromagnet, both
unusual in showing a broad, unresolvable band in the range of -575 to -315 c.p.s. for the fluorine resonance. At temperatures of -120 to -SOo the spectrum sharpened somewhat but not enough to be interpreted. Reaction of the diene with bromine gave 1,4-dibromo-1,1,4,4-tetrafluorobutene and the n.m.r. proton and fluorine spectra of this derivative were normal. In addition, an infrared spectrum of the dibromide showed the absence of a fluorinated double bond (no absorption a t 17201750 cm.-l). Oxidation of the dibromide produced bromodifluoroacetic acids6 In contrast to its reaction with bromine, tetrafluorobutadiene formed a tetrachloride when treated with chlorine under mild conditions. The cyclobutene used t o prepare 1,1,4,4-tetrafluorobutadiene was readily obtained from tetrafluoroethylene and acetylene by reaction of equimolar amounts of these compounds in a shaker tube a t 225'. Synthesis4a of tetrafluorobutadiene directly from tetrafluoroethylene and acetylene has also been accomplished by passing a mixture of these compounds through a pyrolysis tube maintained a t 600' and 1 atm. Undoubtedly the first product is the cyclobutene, which is cleaved to tetrafluorobutadiene a t the high reaction temperature. Tctrafluorobutadienc has also been
prepared by pyrolysis of l-acetosy-2,,,3,:~-tetrafluorocyclobutane, which is accessible from tetrafluoroetliylene and vinyl acetate.7 Presumably, loss of acetic acid fron: the cyclobutane leads to manufactured by I'arian Associates. Palo Alto, Calif., operating a t 40 M c . and approximately 10,000 gauss. Spectra were calibrated in terms of displacements in cycles per second (c.P.s.) from t h e proton resonance of H s 0 and the F resonance of CFaCOgH. Negative frequency displacements indicate resonances occurring a t higher field relative t o t h e reference. (6) E. L. hlartin and IV. IT. Sharkcy, TIiIs J o w R N A r . , 81, 5286 (19.59). (7) D. D. Coffman, P . L. Rarrick, R . D. Cramer and 11. S. Raasch, zbiii., 71, 490 (1948).
Jan. 20, 1961
FLUORODIENES FROM CYCLOBUTENES
383
tetrafluorocyclobutene, which isomerizes to the inhibitor. The bomb was cooled to -80' and charged, first with 80 g. of tetrafluoroethylene and then with 20 g. of diene a t the high temperatures (700-750') em- acetylene. The bomb was closed and heated to 225" for ployed. 12 hours behind a barricade. The bomb was cooled to room Pyrolysis of fluorocyclobutenes and fluorocyclo- temperature and tetrafluoroethylene, acetylene and octa- . liquid butyl acetates has been found to be applicable to fluorocyclobutanewere allowed t o escape s ~ o u ~ ~ JThe that remained (36.4 g.) was distilled to yield 34 5. the preparation of a variety of fluorodienes. The product (3570) of 3,3,4,4-tetrafluoroc~-clobutene,b.p. 54-56 , generality of the reaction is illustrated by the ex- nz5D 1.3086. amples in Table I. I n many cases, particularly A n d . Calcd. for C4F4H2: C, 38.11; H , 1.60; F, 60.29. those involving cyclobutenes with chlorine in the Found: C, 38.57; H , 1.59; F , 60.13. ring, much tar is formed. Other examples (noI-Chloro-3,3,4,4-tetrafluorocyc1obutene.-1,l- Dichlorotably 1-acetoxy-2,2,3,3-tetrafluorocyclobutane) py- 2,2,3,3-tetrafluorocyclobutane~(40 g . ) n-as added t o a solution of 40 g . of potassium hydroxide in 150 ml. of water and rolyzed cleanly without charring. the mixture was heated to boiling. The product that disMany of the cyclobutenes used were obtained tilled (b.p. 60-63") was collected in a trap cooled with ice. directly by cycloalkylation of fluoroolefins with Redistillation gave 17 g. (437,) of I-chloro-3,3,4,4-tetra5 ~ acetylenes. The structure of the products derived fluorocyclobutene, b.p. 59-60', ~ 2 1.3453. Anal. Calcd. for C4F4HCI: C, 29.93; H, 0.63. Found: from tetrafluoroethylene was assumed from the nature of the reactants. The structures of the C, 29.56; H , 0.83. 1-Hydroxymethyl-3,3,4,4-tetrafluorocyclobutene .-In cyclobutenes derived from chlorotrifluoroethylene, a 148-1111. stainless steel high-pressure tube were placed 40 1,l-dichloro-2,2-difluoroethylene and methyl pro- g. of propargyl alcohol, 0.5 g. of hydroquinone and 3 drops piolate were assumed to be similar to the previously- of a terpene inhibitor. The bomb was cooled t o -80°, described products8 obtained from the same ole- evacuated, charged with 35 g. of tetrafluoroethylene and to 175' for 16 hours. The liquid product was distilled fins and phenylacetylene. In the case of the cyclo- heated t o yield 19 g . (35%) of l-hydroxymethyl-3,3,4,4-tetrabutane prepared from vinyl acetate and chloro- Buorocyclobutene, b.p. i4' (20 mm.), ? z Z 5 ~1.3i63. trifluoroethylene, the structure of the product Anal. Calcd. for C ~ F ~ H G C, O : 38.48; H , 2.58. Found: is presumed to be l-acetoxy-2,2,3-trifluoro-3-C, 38.04; H , 2.97. chlorocyclobutane on the basis of its proton This procedure was used in preparing the cyclobutenes nuclear magnetic resonance spectrum. The spec- that follow. l-Methoxycarbonyl-3,3,4,4-tetrafluorocyclobutene.trum contains a doublet for the methylene hydro- From 40 g. of tetrafluoroethylene containing 3 drops of a gens and this fact is best explained by assuming the terpene inhibitor and 25 g. of methyl propiolate heated methylene group to be adjacent to the CClF 16 hours a t 190" there was obtained 18.5 g. (347,) of 1methoxycarbonyl-3,3,4,4-tetrafluorocyclobutene, b .p. 140', group. We have found 1,1,4,4-tetrafluorobutadieneto 12261) 1.3718. Calcd. for CGH4F4O2: C, 39.14; H , 2.19. Found: be a very reactive compound. With sodium C,Anal. 39.26; H , 2.51. ethoxide in ethanol i t gave a product that was 1-Phenyl-3,3,4,4-tetrafluorocyclobutene .-Phenylacetylconverted to diethyl succinate by hydrolysis. ene (40 g.), tetrafluoroethylene (40 g.) and a terpene in//
I
CFz
CH
NaOEt
-+
EtOH
mixture of ethers and olefins
Hz0 CHzCOzCzH5
-+ ,
CH2COzCzHs
hibitor (3 drops) were heated 16 hours a t 160". Distillation of the reaction mixture gave 60 g. (7376) of I-phenyl-3,3,4,4-tetrafluorocyclobutene, b.p. 88-89' (16 mm.), XZ5D 1.4823. Anal. Calcd. for C I ~ F ~ H C, G : 59.41; H , 2.99: F , 37.60. Found: C, 59.25; H, 3.14; F, 37.9.
l-Methoxycarbonyl-3,3-difluoro-4,4-dichlorocyclobutene.
NaHFz and diethyl ether were isolated as side -l,l-Dichloro-2,2-difluoroethylene (50 9.) and methyl products. Use of sodium thiophenoxide in place propiolate (35 g.) were heated 16 hours a t 190'. From the reaction mixture there was obtained 26 g. (32%) of cycloof sodium ethoxide gave C F ~ = C H C H Z C F ~ S C ~ butene, H ~ b.p. 88' (22 mm.), n z j 1.4446. ~ as the only product. Reaction of tetrafluoroAnal. Calcd. for C ~ H ~ F ~ C I T C,O33.28; ~: H , 1.84; C1, butadiene with peroxytrifluoroacetic acid yielded 17.53. Found: C, 33.20; H, 2.11; C1, 17.5. fumaric acid. The route by which fumaric I-Methoxycarbonyl-3,3,4-trifluoro-4-chlorocyclobutene .acid was formed is not known, but 1,4-addition of From 50 g. of chlorotrifluoroethylene and 40 g. of methyl hydroxyl radicals followed by hydrolysis is a propiolate heated a t 190' for 16 hours there was obtained ~ 30 g. (35%) of material of b.p. 64' (25 mm.), n Z 514083. possibility.
Anal. Calcd. for CcH4F~C102: C, 35.93; H , 2.01; C1, Found: C, 36.29; H , 2.21; C1, 17.97. not isolated l-Acetoxy-l-methyl-2,2,3,3-tetrafluorocyclobutane .CIiCOzH .I tiiilture of 140 g. of isopropenyl acetate, 40 g. of tetraII fluoroethylcne and three drops of a terpene inhibitor was HOICCH heated to 190' for 3 hours. The product was distilled t o Cycloalkylatiori reactions of 1,1,4,4-tetrafluoro- give 32 g. (-llcc)of l-acetoxy-l-niethyl-2,2,3,3-tetrafluorobutadiene are described in an accompanying paper.g cyclobutene, b.p. 137", ~ Z Z D1.3646. Anal. Calcd. for C7H8F402:C, 42.01; H, 4.02. Found: Experimental1o C, 42.49; H, 4.60. 3,3,4,4-Tetrafluorocyclobutene."-To a 400-ml. stainless .--Vinyl steel high-pressure bomb was added 3 drops of a terpene1% acetatel-Acetoxy-2,2,3-trifluoro-3-chlorocyclobutane (140 g.) and chlorotrifluoroethylene (47 g.) were heated to 215' for 3 hours. The reaction mixture was dis(8) J. D. Roberts, G. B. Kline and H. E. Simmons, Jr., THIS JOURtilled to obtain 30 g. (37Y0) of l-acetoxy-2,2,3-trifluoro-3N A L , 75, 4765 (1953); E. J. S m u t n y a n d J. D. Roberts, ;bid., 77, 3420 chlorocyclobutane, b.p. 163-164', ~ S 1.3921. D (1955).
CFz=CHCH=CF?
+ [HOCFzCH=CHCFzOH] +
(9) R. E. P u t n a m , J. L. Anderson and W. H. Sharkey, ibid., 83, 386 (1961). (10) All melting points and boiling points are uncorrected. (11) T h e authors are indebted t o Dr. B. C. Anderson of this Labordt o r y for preparation of tetrafluorocyclobutene b y this method.
1i.68.
(12) Added t o inhibit polymerization of the fluoroolefin. Tetratluoroethylene should always be inhibited as otherwise it presents an explosion harzard. Terpenes t h a t are effective include dipentene and tcrpinolene.
384
J. L. ANDERSON,R. E. PUTNAM AND 1 %'. H. SHARKEY
Vol. 83
CJ
c4
Y Y
v
u I1
Jan. 20, 1961
FLUORODIENES FROM CYCLOBUTENES
Anal. Calcd. for CaHaFaOrC1: C, 35.57; H, 2.99. Found: C, 36.01; H , 3.30.
385
30 g. of bromine in 75 ml. of chloroform. The mixture was stirred at room temperature for 5 hours. It was then distilled to give 32 g. (84%) of 1,4-dibromo-l,l,4,4-tetral-Chloromethyl-3,3,4,4-tetrafluorocyclobutene .-A mixture of 16 g. of l-liydroxymethyl-3,3,4,4-tetrafluoro- fluorobutene, b.p. 105-107', n 2 5 ~ 1.4183. The absence cyclobutene, 50 ml. of ether and 10 drops of pyridine was of 1,2-isomer was indicated by lack of infrared absorption a t 1720-1750 cm.-1 which is characteristic of a difluoroheated under reflux and to it was added dropwise 12 g. of thionj-l chloride in 50 ml. of ether. Heating under reflux vinyl group. The n.m.r. proton and fluorine spectra were was continued for 30 minutes. Distillation of the reaction normal. A single hydrogen peak occurred a t 58.7 C.P.S. and a single fluorine peak occurred a t - 1270 C.P.S. mixture gave 15 g. (8670) of l-chloromethyl-3,3,4,4-tetrafluorocyclobutene, b.p. 117', n% 1.3771. Anal. Calcd. for C4H2F4Br2:C, 16.81; H, 0.71; Br, Anal. Calcd. for CbFdH8Cl: C, 34.41; H, 1.73; C1, 55.96. Found: C, 16.45; H , 0.91; Br, 56.26. 20.32. Found: C,34.56; H,2.03; C1,20.47. Reaction of 1,1,4,4-Tetrafluorobutadiene with Sodium Preparation of Dienes from Cyclobutenes. 1,1,4,4- Ethoxide.-A solution of sodium ethylate was prepared in Tetrafluorobutadiene .-The following example is illustrative a heavy-walled glass bottle by adding 2.3 ,g. of sodium of the procedure used in the preparation of fluorodienes from to 50 ml. of ethanol. After cooling to -10 , 12.6 g. (0.1 mole) of tetrafluorobutadiene was added. The bottle cyclobutenes (see Table I). The pyrolysis system used consisted of a dropping funnel was capped and heated on a steam-bath for 2 hours during which time a white solid separated. The solid was sepaattached to a vertical tube 2 feet long and 1 inch in diameter packed with pieces of 8-mm. quartz tubing cut into 0.25- rated on a filter, washed with ether, and dried in vacuum inch lengths. A thermocouple well was introduced up the a t 65'. I t was identified as sodium hydrogen fluoride center of the tube, its end being located approximately a t (neutral equivalent calcd. 62 found 60), and the amount the center of the packing. The tube was heated by means isolated (6 g.) corresponded to the removal of two equivaof a Hevi Duty Electric Co. 110-volt electric furnace, type lents of fluoride ion from the diene. After distillation of the alcohol ( 5 g. of diethyl ether and 70. The temperature a t the center of the packing (also the center of the furnace) is the temperature that is specified much H F in forerun), the residual oil was treated with water in Table I. The lower end of the pyrolysis tube was con- and then extracted with ether. The ether extract was dried nected in series to a solid carbon dioxide-cooled trap, a liquid over sodium sulfate. Distillation gave 8 g. (4770) of dinitrogen trap, a manometer, and an efficient vacuum pump. ethyl succinate, b.p. 70-75' (4 mm.). The structure of The material to be pyrolyzed was added dropwise at a rate the product was proved by comparison of its infrared spectrum with that of an authentic sample. of 0.5 to 1.0 ml. min.-l. Phenyl 1,1,4,4-Tetrafluoro-3-butenylSulfide.-Sodium Pyrolysis of 56 g. of 3,3,4,4-tetrafluorocyclobutene a t 700' and 10 mm. in the above system gave a total of 55 g. methoxide (6.4 g., 0.1 mole), anhydrous methanol (100 of condensate divided equally between the two traps. The mi.) and thiophenol(11 g., 0.1 mole) were added to a heavycondensates were combined and distilled through a low- walled glass bottle. The mixture was cooled to -80' Al- and 12.6 g. (0.1 mole) of tetrafluorobutadiene was added. temperature still, all of the material boiling a t 4-5'. though elemental analyses of tetrafluorobutadiene were not The bottle was capped and heated to 95" for 3 hours. The obtained, they were obtained for the derivatives described reaction mixture was distilled. As the solution was concentrated, the sodium fluoride that precipitated was resubsequently. moved by filtration. The fraction boiling a t 57" (3 mm.) Preparation of Dienes from Acetoxycyclobutanes. 1!1,4,4Tetrafluorobutadiene.-The following procedure IS 11- was collected (12 g., 51%). An infrared spectrum of the lustrative of that employed in the preparation of fluoro- material showed it to be phenyl 1,1,4,4-tetrafluoro-3-butenyl sulfide. The spectrum had a strong band a t 1755 cm.-l dienes from cyclobutyl acetates. Fifty grams of 1-acetoxy-2,2,3,3-tetrafluorocyclobutane (CFs=C
