FLUOROCARBON NITROGENCOMPOUNDS
June 5, 1962
2103
[CONTRIBUTION FROM THE DEPARTMENTS OF CHEMISTRY AND CHEMICAL ENGINEERING, UNIVERSITY OF FLORIDA, GAINESVILLE, FLA.]
Fluorocarbon Nitrogen Compounds. VIII. Mono-, Di-, Tri- and Tetra-acyl Derivatives, Oxadiazoles and w-Bromo Acyl Isocyanates' BY
JOHN
A.
xT0UNG, W I L L I A M
s. DTJRRELL~ A4ND R I C H A R D
D. DRESDNER
RECEIVEDSOVEMBER 6, 1961
X,K-Bis-(trifluoromethy1)-amides, RCON( C F S ) ~where , R = alkyl or perfluoroalkyl, 15ere made in good yield by the r e a Perfluoroacyl amides, RCOKHCORF, tion of acyl halides with the mercury derivative of bis-( trifluoromethy1)-amine were made by reaction of appropriate nitriles with acids, or amides with acid anhydrides or acid halides. Introduction of the second acyl group affected adversely most amide reactions; thus, CF3CONHCH3could be added to C3F0while ( CF3CO)&H could not, nor did metal derivatives of the latter react with acyl halides. Triacyl compounds could be made in certain cases by reaction of an N-bromoimide and an acyl halide. I n the presence of a fluorinated olefin, N-bromoperfluoroglutarimide underwent a free radical rearrangement t o 4-bromoperfluorobutyryl isocyanate. A tetrakis-( perfluoroacy1)-hydrazine was made, via the mercury derivative of CF3CONHNHCOCF3, which pyrolyzed readily to give an acid anhydride and a 2,S-bis(perfluoroalky1)-oxadiazole. Evidence indicates that a fluorocarbon diacyl diimide CFaCOS=NCOCFz was made by the reaction of IC1 with the mercury derivatives of the diacylhydrazine.
This paper describes the preparation and some reactions of several new types of fluorocarbon derivatives containing one or more acylamino groups and generally little or no hydrogen. Physical constants of these compounds are given in Table I and nuclear magnetic resonance assignments in Table 11. The synthesis of organic amides and related compounds usually depends a t some crucial point on the nucleophilicity of a nitrogen atom. With fluorocarbon compounds, the powerful inductive effect of fluorine greatly depresses the basicity of the nitrogen atom and thus makes methods based on reaction of a fluorocarbon amine with an acid derivative difficult or impossible (although, of course, fluorocarbon acid derivatives react readily with hydrocarbon amines) ; furthermore, no primary fluorocarbon amines of the type RfCFzNHz have been reported. Bis- (trifluoromethy1)-amine is too weak a base t o react as such with acyl halides:'; however, N,N-bis(trifluoromethy1)-amides can be made in good yield by the action of acid chlorides on the mercury derivative of the amine, as shown in Eq. 1. (CF3)2N-Hg-N( CFs)?
+ KCOCl ---+RCON( CF3)a
(1)
Allthough a few such amides have been isolated from electrochemical fluorination product^,^ the method illustrated gives improved yields and allows wide variation on the nature of R, including the use of hydrocarbon as well as of fluorocarbon acid halides. Compounds of the type where R = alkyl have not previously been described. They are not readily attacked by water, showing once again that compounds bearing both fluorinated and fluorine-free groups on nitrogen are apt to be hydrolytically stable as long as the nitrogen is tertiary and fluorine cannot be split off as H F from adjacent atoms.5 (1) This paper was taken in part from the Ph.D. Dissertatiou of W. S. Durrell, University of Florida, 1961, and was presented a t the 140th Kational Meeting of the American Chemical Society, Chicago, Ill., Sept. 3-8, 1961. The work was supported by the Army Research Office, and this paper may be used in whole or in part for a n y purposes of the United States Government. For the preceding paper in this series, see J. Am. Chcm. SOC., 89, 4553 (1960). (2) Present address, Peninsular ChemResearch, Inc., Gainesville, fila. (3)
J. A. Young. S. K.'Isoukalas and R . D. Dresdner, J. A m . Chem.
bo(., 80, 3604 (1958). ( 4 ) J. A . Young, 1'.C, Sinlitions ~ i i d1'. \V, IIoRman, ibid., 7 8 , 5637
(1926).
N-Acylamides, or imides, can be made by reaction of an amide with an acid anhydride,6 but a purer and more easily isolated product is obtained by reaction of an acid with a nitrile. For instance, (CF3CO)zNH made from trifluoroacetamide and trifluoroacetic anhydride was originally reported to be a liquid at room temperature.6 In our hands, this reaction gave a product melting a t about 'TO', but the material resulting from reaction of CF3COOH and CF3CN gave a melting point of 85'. This imide was very hygroscopic. h fairly detailed study of the acid-nitrile reaction and its mechanism is described in a forthcoming paper; for preparative purposes reaction of equimolar quantities of acid and nitrile for 1-4 hours a t 150' in the presence of a few per cent. of H2S04is recommended. The second trifluoroacetyl group strongly decreased the nucleophilic activity of the amide. No base-catalyzed addition of (CFaC0)*NH to C3F6 could be obtained, although CF,COXHCH, gave a 75y0 yield of its respective adduct. Reaction of the sodium derivative of CF3CONHCHa with CF3COC1 gave a fair yield of the N,N-diacyl compound, but no reaction occurred between CF3COC1 and the sodium, mercury or silver derivatives of (CF3C0)2NH. Fluorine-containing tertiary amides, (KCO)3N, have not been reported. As mentioned above, they could not be prepared from fluorocarbon secondary amides. Two compounds of this general nature were obtained, however, from an unusual reaction involving N-bromoperfluoroglutarimide and an acyl bromide, as shown in eq. 2 . This reCO(CF&CONBr
+ IiCOBr --+
I .
CO(CF2)sCOSCOK $- Rr? ( 2 ) L-1
actioti was successful with benzoyl bromide and perfluoroglutaryl chloride, but since no reaction took place when CF3COBr or C7FISCOBr was used, i t does not seem to be a general method of preparation.' ( 5 ) The adduct of pyrrole and tetrafluoroethylene is hydrolytically stable (D. C. England, L. R . Melby, hl. A. Dietrich and R . V. Lindsey, Jr., i b i d . , 89, 5116 (1R60)), as is the ethylene adduct of (CFa)zNRr (unreported work, this Laboratory) (6) G. H. Smith, U. S. Patent 2,701,814 (19.55). (7) A corresponding reaction with ( C F C 0 ) z S B r was n o t a t t e m p t e d because the N-bromoimide could not be synthesized.
2106
J. -1. YOUNG, K'. S. DURRELL ASD R. D. DRESDNER
lTol. 84
TABLE I FLUORINE-CONTAINING AMIDE,IMIDEAND ISOCYANATE COMPOUXDS B . p . , O C . (mm.)
Compound
145 (760) 90 (60) 118 (760) 115-116 (760) 30 (760)' 66 (760) 95 (90) 85 (2.5)
(CFICO ) z h " CFaCOSHCOCH, (CFaCO)zNCH3 CFaCOK( CHz)CFzCHFCIi3 CF3CoK( CFa)z CHsCON( CFZ)2 CsHbCOhT(CF3)t CO( CFi)sCOKCOCsHb
u
CO( CFe)sCOSCO( CFz)sCONCO( CF*),CO I
u
1
M.p., " C .
85
39-41
95-lOO(1.5)
Infrared carbonyl assignment, p a
Yield, % '
5.64,5.74 5.60,5.i9 5.74 5.73 5.55 5.60 5.50. 5.77 5.56.5.83
75 80 62 95 60
5.45,5.78
28
80-100h
80-1 0Ob 25-30
95 CCF3CO),Nz 108 (760) 5.3,5.5 60-50 CF,CON=NCOCF3 6-8 (80) 5 . 3 , 5.5 (4.39),5.50 100 Br( CFz)3COiXC0 42 (30) 98-100 5.90 Br( CF*):,CONHZ a Infrared spectra were taken on a Perkin-Elmer double bemi instrument where bauds are reported to three figures, a n d on a Beckman Infracord where only two figures are given. A 5-cm. cell a t a pressure of about 10 mm. was used for gas samples. * Paper in preparation. c See ref. 4. d Purity only ca. 80%. TABLE I1 Fl9
5.57
(CF~CO~ZKCH~ CHzCOr\;( CF8)z C~HSCOIL'( CF8)z CO( CFz)3CONCsHs L
NUCLEAR MAGNETIC RESONANCE SPECTRA^
A
-
a b CO( CFz)aCONCO( CFn)aCOKCO( CI%)3CO L-J
a
1
-21.3 -21.5 42.1
b a
2 2
57 1 41 7
2 non-equiv. quartcts Singlet Singlet Triplet Pentet Singlet
Singlet Triplet Pentet d Singlet Singlet 1 Singlet 1 1 Singlet Triplc triplrt 1 1 Triplct 1, I Triplet C 1 Triple triplet 1 1 Triplet 1) 1 Triplet C 1 Kuclear magnetic resonance spectra wcrc taken on a Varian Associates instrument operating a t GO inc. arc given in p.p.m., high field positive sign, relative to an external standard of CF3COOH. c
d
a
b
b
1
C
2 4 1
Tetraacylated hydrazines have apparently not been previously described in the literature. At least with perfluoroacyl substituents, they seem to be generally accessible in excellent yield by the iollowing series of reactions. Hg( OAc)2 IZFCOCI RFCOSHSHCORF---> (lt~C0S)zHg -+ ( R F C O ) ~ S Z( 3 )
Following this procedure, it was not necessary to isolate the monohydrazide, which is difficult to purify when R = CF3, and all the steps were virtually quantitative. The mercury derivative was a white, finely divided, amorphous solid, insoluble (except with reaction) in all solvents tested and probably therefore a polymeric rather than a chelated form. If carefully dried, i t was very stable thermally, decomposition setting in only
46.7 49 0 55 6 -2 1 f2 0 +4 1 + l O c, -14 2 40 1 38 7 -15 1 42 1 42 2
Clicinical s l d t s
above 350' and becoming rapid a t 400'. The products were mainly metallic mercury, nitrogen, carbon monoxide and C2Fs, but a small amount of material boiling a t approximately 70' was formed whose infrared spectrum was identical with that of the (CF3C0)4N2pyrolyzate discussed below. The tetraacyl compound was easily obtained by reaction of the mercurial with CF3COC1a t 50' for eight hours. Of the four acyl groups, two could be removed by reaction with alcohol, giving the diacylhydrazine plus an ester, while three of the four could be titrated with aqueous base to a phenolphthalein end-point. (CF8CO)rSz
+ EtOH + 2CFaCOOEt + CFaCOSHKHCOCF3
(4)
The structure of the compound is not rigorously proved, since i t could be either the N,N,N',N'tetraacylhydrazine I or an imido ester (11).
June ,5, 1962
FLUOROCARBON XITROGEX
D
0
O
/- -\ CCFI CFyC \ / X-S
I
0
/- -\
CFsC
\
0
/
CCR
0
I1
Structure I seems the more probable. As can be seen in Table I, all the perfluoroacyl compounds listed, as well as esters such as CF,COOEt, show carbonyl absorption between 5.5 and 5.9 p . Structure I would be expected to show only this absorption, while structure I1 should show in addition to the carbonyl band an absorption due to the C=NN=Csystem. For instance, the oxadiazole
7
-
0
1
CF3C=N-N=CCF3 has a moderately strong doublet a t 6.2, 6 . 3 which ~ can be assigned t o that system. The actual spectrum of the tetraacyl compound shows the expected carbonyl doublet a t 5.3, 5.5p, but no absorption in the 6-7 p region. While i t is true that pyrolysis of (CF3C0)4N2, as described below, can be more easily rationalized on the basis of structure 11, the infrared evidence strongly supports structure I. Both the infrared and n.m.r. spectra indicate that (CF3C0)4N2 is a rather unusual molecule. In addition to the 5.3 and 5 . 5 ~absorptions in the infrared there are two weak bands a t 5.2 and 5.8p which cannot be dismissed as being due to impurities since the compound was estimated chromatographically to be a t least 98% pure. Other strong infrared peaks are present a t 7.3, 8.0, 8.3, 8.7, 9.0, 9.3, 11.3 and 1 3 . 3 ~ . With regard t o the F19n.m.r. spectrum, structure I would seem to make all fluorines equivalent, predicting a single peak, while structure I1 should probably give two peaks of equal intensity with closely similar chemical shifts. The actual spectrum shows four separate peaks of identical shape and size, closely but not symmetrically spaced with no fine structure resolvable a t 60 mc. Since there is no chance for spin-spin coupling in the molecule, this four-peak spectrum does not furnish much information regarding choice between I and 11. The presence of four peaks may be due to double bond character in the C-0 and C-N bonds, leading to hindered rotation and the possibility of &-trans isomerism involving the CF3 groups and the 0-C-N-C-0 plane. Canonical structures illustrating this possibility can be written ; however, hindered rotation should lead to a temperature-dependent n.m.r. spectrum, while no change was actually observed in a spectrum taken a t 100'. Comparison of the magnitude of the observed chemical shifts with those of reference compounds was also inconclusive. Trifluoromethyl
70-1
groups in CF3C===N-N=CCF3, resembling structure I , and in (CF3C0)*0,resembling structure 11, gave chemical shifts of, respectively, 10 and zero p.p.m., both of which values are included in the range of chemical shifts exhibited by the tetraacyl compound. Pyrolysis of (CF3C0)4N2 took place very smoothly a t 325' to give trifluoroacetic anhydride
+
COMPOUNDS
2107
and 2,5-bis-(trifluoromethyl)-oxadiazole.Although little effort was made to find optimum conditions, conversions were obtained as high as 89% for the anhydride and (37% for the oxadiazole. The reaction sequence shown in eq. 3, followed by pyrolysis t o the oxadiazole, is very similar to the classic ring closure of organic diacyl hydrazines with acetic anhydride to give oxadiazoles, although in the latter case the tetraacyl compounds have not been isolated, and seems to constitute a general route to oxadiazoles bearing perfluoroalkyl substituents in positions 2 and 5.a By oxidation of diacylhydrazines, Cramerg has synthesized several diacyldiimides, RCON=NCOR. I t was hoped that an analogous reaction could be applied to CF3CONHNHCOCF3, but negative results were obtained under a wide variety of conditions on attempted oxidation of either the diacylhydrazine or its mercury derivative, free nitrogen being eliminated very readily. The best results were achieved by reaction of the mercury derivative with iodine monochloride in CC14 a t about 10-20'. Using continuous fractionation a t reduced pressure during the reaction, a product was isolated in approximately 30-50~oyield which, although it contained about 20% CC14 as estimated both by molecular weight and by infrared spectrum, was a red vapor or blood-red liquid. The color was quickly discharged when the material was exposed to heat or t o ultraviolet irradiation, giving only C2Fe and noncondensable gases. It seems quite probable that this was actually the diimide, CF,COh'= NCOCFa, but the compound was not obtained in pure enough form for characterization. If the identification is correct, it would seem that the fluorocarbon diacyldiimides are even less stable than the hydrocarbon analogs. The N-bromoamine (CF3)2NBris known to add easily to olefins,3 including the fairly unreactive C3FB. On the other hand, N-bromopeduoroglutarimide underwent no addition to C3F6 or to CF2=CFC1 with either peroxide or ultraviolet initiation; however, an interesting rearrangement did occur under these conditions which did not take place in the dark or in the absence of an olefin. Since the necessity of initiation by peroxide or irradiation indicates a free radical mechanism, a parallel was a t first inferred between this rearrangement and the reaction of a fluorocarbon imide with silver difluoride,lO which is thought to proceed by initial abstraction of hydrogen, followed by attack of fluorine on carbonyl carbon to give an acid fluoride and RrCON :, the latter rearranging to an isocyanate. A similar mechanism for the N-bromoimide rearrangement would lead to BrCO ( CF2),N=C=O. No labile bromine could be found, however, and the product was eventually identified as 4-bromopeduorobutyryl isocyanate, Br(CF2),CON=C=O. The fission of a carbon-carbon bond in a fluorocarbon derivative under such mild conditions is re(8) Since the submission of this paper, compounds of this type have been reported by H. C. Brown, cf a!., J. Org. Chem., 26, 4407 (196l), and Chambers and Coffman, i b i d . , 26, 4410 (1961). (9) 11. Cramer, J . A m . Chem. SOC.,79, 6215 (1957). (10) J. A. Young, W. S. Durrell and R. D. Dresdner. { b i d . , 82, 4569
(1960).
"OS
J .I.YOUNG,\I-.S.DURRELL .IND
markable, but the reaction is unmistakably similar to the rearrangement of N-bromosuccinimide, reported several years ago to proceed under comparable conditions.11s12The mechanism of these reactions has not been elucidated, but may possibly resemble that proposed quite recently for the free radical rearrangement of cyclopropanols. I s
R. D. DRESDNER
Vol. 83
about % 1. of dry toluene and dried to give 290 g. of CFJCONHNCOCFa, m.p. 17k176". The mercury derivative was prepared by dissolving 33 g. (0.15 mole) of CF3CONHNHCOCF3in 250 ml. of water and adding 43 g. (0.15 mole) of mercuric acetate in 150 ml. of water, acidified slightly with acetic acid. T h e very insoluble but extremely finely divided precipitate was filtered a t 50" or so to decrease viscosity, through a medium grade sintered glass filter, left overnight on a clay plate, then vacuum dried for several hours a t room temperature. Application of heat before drying was completed resulted in some decomposition. Experimental Anal. Calcd. for C4F6HgN202: Hg, 47.5. Found: Hg, Reaction of Acyl Halides with [(CF3)2N]2Hg.-About 0.2 47.9. mole of the mercurial3 and 0.4-0.6 mole of the appropriate Trifluoroacetyl chloride (38 g., 0.29 mole) and 50 g. of a acid chloride were sealed in glass and allowed to warm to room temperature. A short heating period a t 40" initially fluorocarbon solvent boiling a t about 50' were condensed into a pressure vessel containing 57 g. (0.14 mole) of thoremployed was found t o be unnecessary. Distillation then oughly dried (CF3CON)2Hg. After sealing, the vessel was gave the amides. N,N-Bis-(trifluoromethy1)-trifluoroacetamidewas identi- rocked for 14 hours a t 50". Volatiles were then removed by pumping and fractionated to give the product, 53 g. (CF3fied by comparison of a n infrared spectrum with that of a CO)rNz. known ample.^ N,N-Bis-(trifluoromethy1)-acetamide:Anal. Calcd. for Anal. Calcd. for C8Fl*N2O4:C, 23.1; F, 54.8; S , 6.7; CJ?&r\TO: mol. wt., 195; N , 7.22. Found: mol. wt., 194; neut. equiv., 138. Found: C, 23.4; F, 55.2; N, 5.9; neut. N, 7.41. equiv., 138. N,N-Bis-( trifluoromethy1)-benzamide: Anal. Calcd. for 2,5-Bis-(trifluoromethyl)-oxadiazole.-Eighteen grams C9F6H6h-O: N, 5.40. Found: hT,5.72. (0.043 mole) of (CF3C0)4T';2was dropped into a vertical Synthesis of Imides.-The acid-nitrile and amide-anhyPyrex column packed with glass helices and heated to 325 =t dride reactions are described in detail in a forthcomine DaDer. 5", over a period of 18 minutes. T h e exit vapors were cunN-Acetyltrifluoroacetamide: Anal. Calcd. for UC'aFiH4- densed in cold traps and subsequently fractionated to give 8 NOz: C , 31.0; H, 2.6; N, 9.0. Found: C, 31.2; H , 2.8; g. (890/o) of (CF3CO)20,identified by boiling point, molecS , 8.6. ular weight and infrared spectrum, and 6 g. (67%) of N-Methyl-N-trifluoroacety1trifluoroacetamide.-To a --O----, slurry of 0.1 g. atom of sodium sand in 300 ml. of tetrahydroCF3C=N-N=CCF3, identified by molecular weight and furan, 13.7 g. (0.1 mole) of CF3CONHCH3dissolved in a comparison of its infrared spectrum with that of an ausmall amount of tetrahydrofuran was added with stiring thentic specimen. and cooling. Then 13.2 g. (0.1 mole) of CF3COC1 was conBelow 275', little pyrolysis took place; a t 400°, products densed into the cooled solution, which was stirred overnight resembling those from the pyrolysis of trifluoroacetic anand finally brought t o reflux. Filtration and fractionation hydride, that is, CF3COF, COFz and (-CF*-)n, were found. gave 5.0 g. of (CF3C0)2NCH3. The secondary amide was Bis-( trifluoroacety1)-diimide.-To a flask fitted with stiralso prepared (3 g.) by fractionating a mixture of 0.05 mole rer, dropping funnel and a good fractionating column was each of pyridine, CFaCOCl and CFaCONHCH3,after reac- added 13.0 g. (0.031 mole) of (CF3CON)zHgand 100 ml. of tion overnight at room temperature. carefully dried carbon tetrachloride. Reflux was established Anal. Calcd. for Cd?&S02: C, 26.9; H , 1.3; S , 6.3. a t 80 mm. pressure, and 9.0 g. (0.055 mole) of dry iodine Found: C, 27.2; H , 1.5; N, 6.0. monochloride in 50 ml. of dry CCl, was added a t such a rate N-Benzoylperfluorog1utarimide.-Thirteen grams (0.043 that little or no unreacted IC1 solidified on the cold finger of The reflux mole) of N-bromoperfluoroglutarimide and 7.5 g. (0.043 the condenser, which was kept a t about -40'. temperature dropped gradually from 16 to 6" and vapor was mole) of benzoyl bromide were mixed and heated a t 90' a t taken off slowly into a cold trap as long as the reflux was about 45 mm. pressure for 4 hours. Fractionation gave 8 g. dark red and the reflux temperature did not exceed 8'. The of the hygroscopic tertiary amide. The n.m.r. spectrum product so obtained was estimated to contain about 17y0 showed that the perfluoroglutarimide ring was still intact. cc14 both by molecular weight measurements (mol. wt.: Anal. Calcd. for C12F&NO3: N, 4.3. Found: N, 4.5. (CF3CON)z, 222; CC14, 154; product, 210) and by estimaN ,N,N',N'-Bis-(perfluoroglutaryl)-perfiuoroglutardi- tion of CCl4 content from the intensity of the 12.6 p line in amide.-Twenty-one grams (0.07 mole) of N-bromoperfluorothe infrared. Short exposure of samples sealed in glass to glutarimide and 9 g. (0.033 mole) of perfluoroglutaryl chlo- either ultraviolet exposure or to a temperature of 100' disride were heated together a t 100' for 3 days, with a slight charged the red color completely, leaving as the only convacuum maintained. Vacuum fractionation gave 6 g. of densable material a colorless gas or solid subliming a t CO( CF2)3COFCO( CF2)3CONCO(CFz),CO. The n.m.r. low pressures and showing bands attributable only to C Z F ~ L--L---J in its infrared spectrum. spectrum showed two cyclic perfluoroglutarimido rings and N-Methyl-N-( 2-H-perfluoropropy1)-trifluoroacetamide.one linear perfluoroglutaryl group. ;In excess of methylamine was bubbled into ethyl trifluoroacetate a t room temperature. Fractionation then gave A n d . Calcd. for CijF18S206:N, 4.3. Found: S , 4.7. Tetrakis-( trifluoroacety1)-hydrazine.--I solution of 180 CFICONHCHBin about 807, yield. A n d . Calcd. for C3F3HaX0:C, 28.4; H , 3.2; h-,11.0. g . (12 6 moles) of ethyl trifluoroacetate in 200 ml. of absolute Found: C, 28.6; H , 3.4; K , 10.9. ethanol was stirred and 45 g . (1.40 moles) of anhydrous hyhydrazine in 150 ml. of absolute ethanol added dropwise with Four grams (0.17 g. atom) of sodium metal was heated intermittent cooling. After standing overnight, alcohol was with 168 g. of CF3COKHCH8until it had dissolved. Thi:, removed under a water-pump vacuum a t room temperature solution was treated with 40 g. (0.25 mole) of CFsCF=CF? in a rocking autoclave a t 80" for 40 hours. O n cooling and until the sirupy residue began to crystallize. Trifluoroacetic acid, 200 g . , was then added to dissolve most of the monoventing of the autoclave no olefin was recovered. Fractionahydrazide and 420 g. (2.0 moles) of (CF3C0)20 added with tion gave 52 g. of adduct, 1.3170. The complex n . m . r . stirring, under an ice-water-cooled reflux condenser. As peak for the lone proton indicated that the direction of addircaction took place, the solution first became clear, with subtion mas that shown in the formula C F ~ C O N ( C H : I ) C F ~ sequent crystallization of the diacyl compound. -4fter the CHFCFI. reaction had stood overnight, trifluoroacetic acid and excess 4-Bromoperfluorobutyryl Isocyanate.-Fifteen grams anhydride were removed (under vacuum toward the last). (0.05 mole) of A--bromoperfluoroglutarimide and 5 g. (0.03 The crude diacylliydrazine was then recrystallized from mole) of CF3CF=CF2 were sealed in glass and left in direct sunlight for 4 days, although there was no apparent further (11) H. W. Johnson and I ) . E . Buhli:z, J . A m . Chem. Soc., 79, change after the first day. Fractionation of the product 75:3 ( l g A 7 ) ; 8 0 , 31.50 (19581. resulted ixi recovery of all the olefin sild a quantitative yieltl of Br( CF2)gCONCO. The acyl isocyanate reacted alrriosl (12) J. C. hlarrin and P. D. Bartlett, ibid., 79, 2533 (19.57). C . H d o P u y . G M. 1)nypen and J . W. Hnusser, i b i d . , 88, 3166 explosively with water, but the solution gave no test fbr Br(19U1). Reaction bf the same quan$ities of reactanta with 1 g . rff
FLUORIXATED h'a?ZS-OLEFIXIC
June 5, 1962
benzoyl peroxide a t 100' gave comparable results, and quantitative rearrangement was also obtained when CIFB was replaced by CFZ=CFCl and the mixture exposed to sunlight. Substitution of (CF,CO),O for the olefin or exposure of the N-bromoimide alone to sunlight gave a little free bromine but recovery of most of the bromoimide, with no rearranged product. Because of the extreme reactivity of the acyl isocyanate, it was identified by indirect methods, as follows. A small sample of the isocyanate was allowed to stand 2 weeks in an ether solution of benzyl alcohol. Evaporation of the solvent left a solid which on recrystallization from cyclohexane melted a t 76.5 to 78.5'. Anal. Calcd. for BrClsF6H8N03: C, 35.2; H , 2.0; X, 3.4. Found: C,35.7; H , 2 . 3 ; S , 3.0.
[CONTRIBUTION FROM
THE
2109
ACIDS
The white solid formed on reaction of the acyl isocyanate with water, after washing and recrystallization from benzene, melted a t 98 to looo. Anal. Calcd. for BrCaFsHzSO: Br, 29.2; N, 5.1. Found: Br, 26.914; N, 5.0.
Acknowledgments.-The authors are indebted to Dr. Wallace Brey for interpretation of the n.m.r. spectra, and to Dr. Henry C. Brown for a comparison infrared spectrum of 2,5-bis-(trifluoromethyl) -0xadiazole. (14) Although t h e bromine value for this compound is low, it is felt that the complete body 01 evidence strongly supports the proposed structure for t h e rearranged product.
DEPARTMENT OF CHEMISTRY, PURDUE VNIVERSITY, LAFAYETTE, IND.]
Stereochemistry of the Diels-Alder Reaction. 111. Fluorinated trans-Olefinic Acids as Dienophiles BY H. P. BRAENDLIN, A. 2. ZIELINSKI~ AND E. T. RICBEE RECEIVED JUNE 29, 1961 Adducts between cyclopentadiene and acids of the general formula trans-RrCH=CHCOzH were prepared. Bromination in chloroform was shown to be a good adduct isomer determination method, revealing a consistent carboxy-exo to carboxy-endo relationship of 2 : 1. In some instances of adduct hydration, skeletal rearrangement was observed.
The steric course of the Diels-Alder reaction have been observed to exert considerable endo dibetween a cyclic conjugated diene and a dienophile rection. Finally, studies with acrylic corn pound^^^ ,0 was stipulated by Alder and Stein to result in the have revealed that, a t least in these systems, product with maximum overlap of double bonds2 two a-substituents can compete with each other This was extended by Alder and Windemuth to for the endo position even if one substituent is include the formation of products wherein maximum not electronegative. Thus, acrylonitrile, acryloverlap of unshared electron pairs is ~ b s e r v e d . ~amide and methacrylic compounds give cycloThus, dienophiles carrying an electronegative pentadiene adducts with large percentages of the substituent near the olefinic linkage were said isomers having hydrogen or methyl endo. Since the mechanism of the Diels-Alder reaction to react with cyclic conjugated dienes to give predominantly the adduct with the substituent is still obscure, the driving forces behind these in the endo position of close proximity to the double anomalies are also unexplained. It is possible bond formed by the diene portion of the molecule. that the behaviors of the three groups of ethylenic However, exceptions to this rule are being observed dienophiles, cis- and trans-a,@- and a,a-disubstiwith increasing frequency. Not only have cis- tuted ethylenes, differ essentially. Whereas aa,P-disubstituted ethylenes, such as maleic an- methyl may compete with a-carboxy for the endo hydride, been known for some time to give both position, trans-0-methyl appears to be unable to endo and ex0 product^,^,^ but also in trans-olefin do so : trans-crotonyl chloride adds to cyclopentaaddition both substituents have been found to diene with the methyl group exclusively exo7; vie for the endo position to give mixed adduct^.^ trans-4,4,4-trifluorocrotonic acid, on the other In most cases of such mixed addition of trans-a,p- hand, gives an adduct mixture (I) which was disubstituted ethylenes to a cyclic conjugated indicated to have a cirboxy-exo (Ia) to carboxydiene both substituents carried double bonds, endo (Ib) ratio of 2 : 1.5e i . e . , two a-electron systems were in competition. Recently, however, also trans substituents lacking x-electrons, such as t r i f l u ~ r o m e t h yand l ~ ~ halogen,5f (1) Present address: Politechnike Szczecinska, Wgdzial Chemiczny, Szczecin. Poland. (2) K. Alder and G. S t e i n , Angew. Chem., 6 0 , 510 (1937). (3) K . Alder and E . Windemuth, B e y . , 71, 1939 (1938). (4) (a) A. Wassermann, J. Chem. Soc., 1511 (1935); 612 (1942); Trans. Faraday Soc., 3 4 , 128 (1938); 3 6 , 841 (1939); (b) K. Alder, e f al., A n n . , 626, 247 (1936); 666, 1, 58 (1950); (c) H. Kwart and I. Burchuk, J . A m . Chem. S o c . , 7 4 , 3094 (1952); (d) D. Craig, e f al., ibid., 7 3 , 4889 (1951). 7 6 , 4060 (1954); (e) J. A. Berson, e l al., ibid., 76, 1721 (1953); 7 8 , 6049 (1956). ( 5 ) (a) C. S. Rondestvedt and J. C. Wygant, J . Org. Chem., 17, 975 (1952); J . A m . Chem. S O L . 73, , ,5785 (1961); (b) C. D . VerNooy and C. S . Rondestvedt, ibid.,77,3583 (1955); C. S . Rondestvedt and C. D . VerNooy, ibid., 1 7 , 4878 (1955); (d) F. Winternits, M. Mousseron and 0. Rouzier. Buil. sot. chim. France, 170 (1955): (e) E. T.McBee, G. Rsll and C. W. Roberts, J . A m . Chem. Soc., 7 8 , 3388 (1956); (r) K . Alder, R. Hartmana a d W.Rot& A n n . , 613,6 (1968).
c.
I
\
COzH
Ia
COzH
Ib
I t has now been found that this ratio is not only reproducible but applies also to cyclopentadier e adducts of other fluorinated acids of the formula RfCH=CHC02H. The compounds C3FCH=C(6) (a) J. S. Meek and W, B. T r a p p , J. A m . Chem. SOC.,79, 3909 (1957); (b) W.R. Boehme, E. Schipper, W. G. Scharpf and J. Nichols, ibid., 8 0 , 5488 (1958); (c) K. Alder, K. Heimbach and R. Reubke, Ber., 91, 1516 (1958); (d) M. Schwarz and M . h l a i e n t h a l , J . Ovg. Chem., S6, 499 (1960); ( e ) J. A. Berson, et ai.. J . A m Chem. Soc , 82, 5501 (1960); Tetrahedron Letters, No. 4 , 131 (1961). (7) K. Alder and G. Stein, Ann., 611, 187 (1934).
