110
for 4 hr in methanol (25 ml) under a nitrogen atmosphere at which time all of the ketone had been converted to tosylhydrazone as shown by tlc. The solution was concentrated to 5 ml, added at 0" to NaBH4 (40 mp) in methanol (10 ml), stirred for 6 hr at room temperature, and heated at reflux for 1 hr. Removal of solvent and glpc at 170" gave all-trans-hydrocarbon X, retention time 18 min 18 sec; mass spectrum m/e 318.3285 (M+, C23H42).
6,lO-Dimethylundecan-Z-one(XI). Ketal 111 (100 mg) was dissolved in 25 ml of ethanol and hydrogenated over 20 mg of 5 % Pd/C. Filtration, addition of dilute phosphoric acid, evaporation of the ethanol, addition of water, extraction into ether, and evaporation of the ether gave saturated ketone XI. Anal. Calcd for C13H2$0:C, 78.4; H, 13.3. Found: C, 78.7; H, 13.2.
Synthesis and Polymerization of 1-Bicyclobutanecarbonitriles H. K. Hall, Jr.,I E. P. Blanchard, Jr., S. C . Cherkofsky, J. B. Sieja, and W. A. Sheppard Contribution No. 1596 from the Central Research Department, Experimental Station, E. I. du Pont de Nemours and Company, Wilmington, Delaware 19898. Received March 12, 1970
Abstract: 1-Bicyclobutanecarbonitrile and its bridge deuterated, 2,2-dimethyl, and 2,2,4,4-tetramethyl derivatives have been synthesized uia base-induced elimination reactions of the corresponding 3-chlorocyclobutanecarbonitriles or 3-cyanocyclobutyl benzenesulfonates. They readily undergo free-radical or anionic homopolymerizations to form high polymers containing 1,3-cyclobutane links in the chain. The tetramethyl polymer also contains ketenimine links, arising from propagation through N and caused by steric hindrance. Facile copolymerizations with the usual vinyl monomers also occurred, again incorporating cyclobutane rings into the polymer chain. The nature of the substituents at the 3 position determined their effect on polymerizability. The 3-methyl- and 2,2,3trimethyl-1-bicyclobutanecarbonitriles did not polymerize well with radicals, but anionic polymers could be made. The 3-phenyl derivative also did not polymerize well. On the other hand, 1,3-bicyclobutanedicarbonitrileand 3-chloro-1-bicyclobutanecarbonitrilepolymerized and copolymerized well under radical or anionic conditions. 1-Bicyclobutanecarbonitrile dimerized in solution at 80" and trimerized at 150".
R
ing-opening polymerization of compounds containing cyclopropane rings has been explored briefly in the past. Cyclopropane itself has not been reported to polymerize well, and 1, l-dimethylcyclopropane2 and isopropylcy~lopropane~ give only low polymers. Ketley, T a k a h a ~ h i Lishanskii,6 ,~ and their colleagues have shown that 1,l-dichloro-2-vinylcyclopropane polymerizes. Several bicyclic compounds containing three-membered rings also undergo polymerization. Pinazzi' has described low polymers from bicyclo[n. 1.O]alkanes and spiropentane is claimed to polymerize.8 Of direct interest in the present connection, Wiberg and coworkerss have shown that methyl and ethyl 1-bicyclobutanecarboxylate polymerize when left at room temperature. This series of articles will explore the synthesis and polymerization of selected bicyclic monomers and show that polymerization of bicyclo[x.y.O] compounds with opening of a strained single bond constitutes a new area of polymer (1) Address correspondence to this author at: Department ofChemistry, University of Arizona, Tucson, Ariz. 85721. (2) H. Pines, W. D. Huntsman, and V. N. Ipatieff, J. Amer. Chem. Soc., 7 5 , 2315 (1953). (3) W. Naegele and H. Haubenstock, Tefrahedron Left., 48, 4283 (1965). (4) A. D. Ketley, U.S. Patent 3,367,902 (1968). (5) T. Takahashi, I. Yamashita, and T. Miyakawa, Bull. Chem. Soc. Jap., 37, 131 (1964). (6) I. S. Lishanskii, A. G. Zak, R. F. Fedorova, and A. S. Khachaturov, Vysokomol. Soedin., 7966 (1965). (7) C. Pinazzi and coworkers, C . R . Acud. Sci., Ser. C, 266 (7), 433 (1968). (8) J. Brossas, P. Pinazzi, R . Cheritat, J. Brasse, and A. Pleurdeau, French Patent 1,469,121 (1967). (9) (a) K. B. Wiberg, G . M. Lampman, R. C. Ciula, D. S. Connor, P. Schertler, and J. Lavanish, Tetrahedron, 21, 2749 (1965); (b) K. B. Wiberg, Rec. Chem.Progr., 26, 143 (1965).
Journal of the American Chemical Society
chemistry. The present article deals with l-bicyclobutanecarbonitriles. Synthesis of Monomers. Convenient access to most of the required compounds was provided by cycloaddition of allene or 1,l-dimethylallene to acrylonitrile. lo Conversion of the resulting methylenecyclobutanecarbonitriles to the corresponding 3-methyl-lbicyclobutanecarbonitriles has already been described by Blanchard and Cairncross. l 1 Alkyl groups at the reaction center usually diminish polymerizability, so we wished to prepare the corresponding compounds lacking the 3-methyl substituent. We used oxidation with sodium metaperiodate-osmic acid12for 3-methylenecyclobutanecarbonitrile, and the more reactive ozone for the hindered and less-soluble 2,2-dimethyl compound lo to obtain 3-oxo-1-cyclobutanecarbonitrile and 2,2-dimethyl-3-oxo-1-cyclobutanecarbonitrile. Exhaustive methylation of either of these compounds using sodium hydride and methyl iodide in N-methylpyrrolidone solution gave 2,2,4,4-tetramethyl-3-oxocyclobutanecarbonitrile. Reduction of the three ketones by sodium borohydride in water gave the corresponding alcohols in good yields. 3-Hydroxycyclobutanecarbonitrile was smoothly converted by thionyl chloride to 3-chlorocyclobutanecarbonitrile,13 while the methylated hydroxynitriles were converted to the corresponding benzenesulfonates using benzenesulfonyl chloride in (10) H. N. Cripps, J. K,Williams, and W. H. Sharkey,J. Amer. Chem. Soc., 81, 2723 (1959). An equal volume of benzene was added to
moderate the reaction of allene and acrylonitrile. (11) E. P. Blanchard and A. Cairncross, ibid., 88, 487 (1966). (12) F. F. Caserio, Jr., and J. D. Roberts, ibid., 80, 5837 (1958). (13) W. A. Neville, D. S. Frank, and R. D. Trepka, J . Org. Chem., 27, 422 (1962).
1 93:l 1 January 13, I971
J
+
-
rcN
+CN
--+
O+CN
I
pyridine. Treatment of the chloro- or benzenesulfonyloxy nitriles with strong bases gave the corresponding bicyclobutanes in good yields. Potassium tert-butoxide in ether was preferred but sodium hydride or sodium amide in polar solvents could also be used. Although previous investigators have used bromides and iodides in such syntheses, both isomers of the chloronitrile appear to be highly, and about equally, reactive. A recent articleI4 described the 2,2,4,4-tetramethylbicyclobutane ester corresponding t o our nitrile. 3-Oxocyclobutanecarbonitrile was used t o prepare three other bicyclobutanecarbonitriles. Treatment with H C N gave the cyanohydrin which with triphenylphosphine and carbon tetrachloride l5 gave l-chloro1,3-~yclobutanedicarbonitrile. This was readily dehydrochlorinated by strong bases t o give 1,3-bicyclobutanedicarbonitrile. CN
CN
-
111 CN
HO+CN
--+
L
CI+CN
--+
@
J
FN
F1
OC,H,-tert
OC,H,-tert CN
CN H
Y‘C”
The cyano ketone with PCIj at 0” reacted preferentially at the carbonyl group t o give the 3,3-dichloro derivative, which on dehydrochlorination gave 3-chloro1-bicyclobutanecarbonitrile. CN I
CN
CN
I
I
O”P”9 0
c1
c1
c1
Treatment of 3-oxocyclobutanecarbonitrile with phenylmagnesium bromide followed by aqueous hydrogen chloride and base gave 3-phenyl-1-bicyclobutanecarbonitrile. CN f”
I
CN I
The cycloaddition of ketenes t o vinyl ethersl5 was used to prepare an extensively bridge-deuterated l-bicyclobutanecarbonitrile for future spectroscopic studies (14) C. Burridge and D. P. G.Hamon, Chem. Commun., 206 (1968). (15) J. B. Sieja, J . Amer. Chem. Soc., 93, 130 (1971).
CN
inversion
H
D D
D
of the polymer. 3-tert-Butoxycyclobutanone,prepared by cycloaddition of ketene t o tert-butyl vinyl ether, was almost completely deuterated using NaOCH3 in D20-THF. The little remaining hydrogen was largely cis to tert-butoxy, which could be understood on the basis of preferential deuteration of a flat enol on the less-hindered side. Addition of H C N also occurred with CN- attacking the less-hindered side. The hydroxyl and tert-butoxyl were replaced with complete inversion to give only the cis-dichloride. Only the chlorine a t o cyano in the dichloronitrile was replaced by 1 equiv of tributyltin hydride, as expected because of resonance stabilization of the intervening radical, to give cis- and trans-3-chlorocyclobutanecarbonitriles. Reaction of the cis-trans mixture with base led t o bridge-deuterated 1-bicyclobutanecarbonitrile. The hydrogen visible in the nmr spectrum, other than the bridgehead, was at the exo position. Another elimination reaction t o form 1-bicyclebutanecarbonitrile was the thermolysis of the sodium salt of 1-cyano-3-chlorocyclobutanecarboxylic acid. Sieja, et a!.
Polymerization of 1-Bicyclobutanecarbonitriles
112
@ 0
Journal of the American Chemical Society
/ 93:l 1 January 13, 1971
o m
e 0m
113
N
: 2 d
00
'9
0
b.
?m
R
rW
I\o
N
N
ri
-
m 0
E
mo
E
m
IC)
0
M
R
8
8
\o
I-
? 0
e,
r= .-*
S
E
e
E ff
e
d
a
€4
z
3
B
2
x *
a
.-.-0
v)
9
9
T d
Q 8 9
m
m
hi
e, r3
r3
E 0
e
.-*
-
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9 m
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.-b 8
x
4
IC)
00
0
e, .-* .-LC
0
a
2,
m IC)
I-
0
Sieja, et al. 1 Polymerization of 1-Bicyclobutanecarbonitriles
114
-0-Or X CN
However, thermolysis of 3-cyanocyclobutyl acetate led only t o vinyl acetate and acrylonitrile. The foregoing syntheses of the bicyclobutane ring all involved a 1,3-elimination reaction of a cyclobutane derivative. It was of interest t o determine whether the bicyclic structure could be constructed by fusing a new cyclopropane ring to one already present. Epoxidation of 4-pentenenitrile gave the epoxide which on treatment with sodium amide in refluxing tetrahydrofuran gave only 2-(hydroxymethyl)cyclopropanecarbonitrile. Thionyl chloride transformed this without rearrangement into 2 -(chl oromet hyl)cyclopropanecarbonitrile, which, when treated with strong base, gave no l-bicyclobutanecarbonitrile under conditions where 3-chlorocyclobutanecarbonitrile gave high yields.
Properties. 1-Bicyclobutanecarbonitriles were colorless liquids, distillable below 1 mm. As discussed further below, they may be polymerized by light and/or air and undergo thermal transformations, but they could be stored almost indefinitely at -80". At this temperature they were all crystalline; l-bicyclobutanecarbonitrile melted at - 27 ', Homopolymerization. The bicyclobutanecarbonitriles which lack alkyl or aryl substituents at the 3 position readily underwent radical-initiated polymerizations in solution in the presence of chain-transfer agents, in suspension, or in emulsion t o give high molecular weight polymers. Qualitatively, bicyclobutanecarbonitrile was as reactive as acrylonitrile. Methyl groups at C-2 and C-4 did not slow the rate of polymerization appreciably. Anionic polymerizations of these monomers were carried out using butyllithium in tetrahydrofuran, but it was more difficult t o obtain high molecular weight, colorless products by this mode of initiation. The 3-methyl-1-bicyclobutanecarbonitrilespolymerized under these conditions. The homopolymer results are given in Table I. Copolymerizations. 1-Bicyclobutanecarbonitrilecopolymerized readily with various vinyl monomers such as styrene and methyl methacrylate under radical
-CH,CH+ I X
for cyclopropyl hydrogens could be seen. Also Dr. R. C. Ferguson detected no cyclopropyl hydrogens using a 220-MHz nmr spectrometer. The observation of two methyl nmr signals in solutions of the homopolymer of 3-methyl-1-bicyclobutanecarbonitrileleads t o the conclusion that both cis and trans links are present. Poly-1-bicyclobutanecarbonitrilemelts at 370", followed immediately by decomposition according t o DTA, and stays white and unchanged well above 300" in air. The other cyanopolymers are also high melting (>300°) and thermally stable. Poly-l-bicyclobutanecarbonitrile showed a low degree of crystallinity by X-ray analysis. The cyanopolymers dissolved in polar liquids such as N,N-dimethylacetamide, y-butyrolactone, and N-methylpyrrolidone. Poly-3-methyl-1-bicyclobutanecarbonitrilepossessing an inherent viscosity of 1.0 was amorphous. It was soluble in trifluoroacetic acid and hexafluoro-2-propanol. Chemical Reactions of 1-Bicyclobutanecarbonitriles. Blanchard and Cairncross have shown that 3-methyl-lbicyclobutanecarbonitrile exhibits remarkably diverse reactions. We have briefly explored selected reactions with 1-bicyclobutanecarbonitrile. Addition of bromine to 1-bicyclobutanecarbonitrile gave rapidly and quantitatively a 3 : l mixture of cisand trans-dibromides. Treatment of this mixture with magnesium in T H F regenerated a good yield of l-bicyclobutanecarbonitrile. e
(16) H. K. Hall, Jr., C. Smith, E. Blanchard, Jr., S. Cherkofsky, and J. Sieja, J. Amer. Chem. SOC.,93, 121 (1971).
93:l
+
Br2
-+
B r a c Br N
3
e
C
N
Free radicals other than growing polymer chains also added smoothly t o the strained central bond of 1-bicyclobutanecarbonitrile. Treatment with tert-butyl mercaptan gave approximately equal amounts of cis- and trans-3-tert-butylthiocyclobutanecarbonitrile. At most, 6.5% of the product formed by addition of thiyl radical to the 1 position was observed, in contrast e
conditions t o give a new class of high molecular weight copolymers, This represents a new method for incorporating rings into chains of carbon atoms. The polymerizations are described in Table 11. Moreover, 1-bicyclobutanecarbonitriles copolymerized with each other and with other bridgeheadsubstitutedI6 bicyclobutanes t o give another new class of high molecular weight copolymers. The infrared spectrum of the polymers was compatible only with a 1,3-cyclobutane ring: no evidence
N
Nucleophiles reacted at the 3 position as expected. Thus, methoxide added t o I-bicyclobutanecarbonitrile to give a 2 : 1 isomer mixture of 3-methoxycyclobutanecarbonitrile.
CN
Journal of the American Chemical Society
C
C
N
+
tert-BUSH
-----t
tert-BuS@CN
to the results of Blanchard and Cairncrossll on 3-methyl-1-bicyclobutanecarbonitrilewho found addition of thiyl radical predominantly at the 1 position. Electrophiles added only sluggishly t o l-bicyclobutanecarbonitrile. Thus, hexafluoroacetone, which reacted vigorously with the 3-methyl derivative, barely reacted with 1-bicyclobutanecarbonitrile. It seems reasonable that the 3-methyl substituent stabilizes positive charge in several of the reactions studied previously. Heating 1-bicyclobutanecarbonitrile neat or in solution at around BO", in either case in the presence of a
January 13, 1971
115
free-radical inhibitor, gives the tail-to-tail dimer. At higher temperatures, approximately 150O, the formation
of a trimer predominates. The structure, on the basis of ir, nmr, and mass spectra, is thought to be
Experimental Section Routine Procedures. The following analytical gc columns were used: A, 1 M 20% butanediol succinate on 60-80 NAW Chromosorb W at 175"; B, 2-ft 10-207J silicone gum nitrile XE-60 on 60-80 Gas Chromosorb R a t 150"; C, 1 M 2 0 x fluorosilicon on 60-80 Gas Chromosorb R; D, capillary column, Squalane. A tricyanoethoxypropane column was also found useful with nitriles. The percentage composition was taken directly from the areas under the peaks. A wet test meter from American Meter Co. was used to measure H1evolution. Capillary melting points were taken on a Thomas-Hoover apparatus and were corrected by use of standard substances. Melting points when given t o 0.1" or mixture melting points were taken on a Thomas-Hoover apparatus whose thermometer had been calibrated against the supplier's standard samples. Those reported to 1 were taken on a Fisher-Johns block. Nmr spectra were interpreted from intensities (i 15%) and reference chemical shifts. Deuteration was used to locate hydroxyls. Because of cis-trans mixtures and complex spectra generally of cyclobutanes, spin-spin splitting was interpretable in only a few cases. The numbers given for multiplets are the centers of the integration trace for the given envelope. All values are in S units. Spectra were usually run in DCC& solution on a Varian A-60 spectrometer. Abbreviations used are: (s) singlet; (d) doublet; (t) triplet; (4) quadruplet; (p) pentuplet; (m) multiplet. Infrared spectra were determined routinely using a Perkin-Elmer No. 21 instrument. Abbreviations used are: s, strong; m, medium; w, weak. 3-Oxocyclobutanecarbnitrile. A 5- l., four-necked flask fitted with an efficient motor-driven stirrer, an air-cooled reflux condenser, and a thermometer was immersed in a large pail filled with ice. In it were placed 260 g (2.79 mol) of 3-methylenecyclobutanecarbonitrile,1° 3.5 1. of water, and 250 ml of ether. The mixture was cooled with stirring to 5-8" and 0.50 g of osmic acid (caution: very poisonous) was added and rinsed in with a little water. Over 4-5 hr, sodium metaperiodate (1360 g, 6.37 mol) was added in small portions with continued stirring at 5-8". A gentle nitrogen bleed was applied and the mixture was stirred overnight while the ice was gradually allowed to melt in the pail and the mixture came to room temperature. At this point, the reaction mixture should be a slurry of white salts in an aqueous phase, and no organic phase should be present. When necessary, a little additional water was added to get a filterable slurry. The mixture was filtered, and the salts were washed thoroughly with chloroform and discarded. A continuous liquid-liquid extractor was set up, and the water extract was extracted continuously overnight with the chloroform. The chloroform extract was boiled down and was heated on the steam bath under house vacuum and finally under aspirator vacuum to remove the chloroform. The clear, dark-gray residue was dissolved in 800 ml of tetrahydrofuran, 10 ml of mercury (caution: add carefully to avoid breaking the flask) and 17 g of silver carbonate were added, and the mixture was stirred under reflux overnight with a motor-driven stirrer. The flask was wrapped with aluminum foil to protect it from light. The mixture was filtered and the salts and mercury rinsed with tetrahydrofuran. The tetrahydrofuran was evaporated and the residue was distilled through a Claisen head using an oil bath, magnetic stirrer, and full pump vacuum. The product distilled smoothly at 58-62' (0.30 mm) and solidified as a white solid in the receiver. At the very end, the temperature rose to 71" and a yellow solid began coming over. The distillation was terminated before it entered the O
receiver. The ketone weighed 196 g (7473 and was rather unstable. It should be stored under nitrogen in a freezer. It melted at 49.0-50.0" (lit.10 mp 50"); ir 5.55 (C==O),4.45 p (-CN); nmr 6 3.47 (m). 3-Hydroxycyclobutanerbonitrile. To a stirred solution of 2.25 g (0.060 mol) of sodium borohydride in 50 ml of water was added with stirring a warm slurry of 19.0 g (0.20 mbl) of 3-oxocyclobutanecarbonitrile in 50 ml of water. The reaction was mildly exothermic and judicious ice cooling was used to maintain the temperature at 35 '. After the addition was complete, the solution was stirred at room temperature for 4 hr and was extracted continuously overnight with chloroform. The chloroform extract was dried and distilled t o give 16.79 g (86.5z) of colorless liquid: bp 70-71" (0.33 mm); ir 2.95 (-OH), 4.46 p (-CN); nmr 6 2.62 (m, 5 H, ring protons), 4.27 (m, 2 H, CHOH). Anal. Calcd for C5H,0N: C, 61.84; H, 7.27; N, 14.42. Found: C,61.52; H,7.26; N, 14.18. The compound was a 70:30 cis-trans mixture as established by gas chromatography on column A. 3-Chlorocyclobutanecarbonitrile. A 5 0 0 " four-necked flask was equipped with a mechanical stirrer, thermometer, 2 5 0 " addition funnel without a pressure equalizing side arm, and an efficient condenser. From the top of the condenser was arranged in series an ice-cooled trap, a calcium sulfate drying tower, a Nujol bubbler, and a gas scrubber. T o the flask was added 97 ml (1.36 mol) of thionyl chloride. To the funnel was added a solution of 5 ml of dimethylformamide in 97 g (1 mol) of 3-hydroxycyclobutanecarbonitrile. The contents of the funnel were added to the flask over 45 min at about 55'. The mixture was then heated to 100-105° for 1 hr until no more sulfur dioxide was evolved. The mixture was cooled and distilled to give 93.9 g (81%) of product containing trace amounts of D M F and about 1 of a low boiler: bp 48-51" (1.9 mm); 98" (28 mm); ir 4.44 p (-CN); nmr 6 2.87 (m, 5 H; ring protons), 4.68 (m, 1 H, CHCI). And. Calcd for CbHBNCI: C, 51.96; H, 5.23; C1, 30.68. Found: C,52.04; H, 5.59; C1,30.70. The purity was 97.9% as established by gas chromatography on column A. Column B resolved this to an 83:17 mixture of cistrans isomers. 1-Bicyclobutanecarbonitrile. A 1-1. glass flask fitted with a stirrer, condenser, and nitrogen bleed was dried with a heat gun and cooled under nitrogen. Under a nitrogen atmosphere, there was placed in the flask 62.4 g (0.54 mol) of 3-chlorocyclobutanecarbonitrile and 600 ml of ether. The mixture was stirred and cooled to 12", at which temperature 66.0 g (0.588 mol) of potassium tert-butoxide was added portionwise over 8 min. Stirring at 12" was continued for 15 min. About 20 g of powdered solid carbon dioxide was added, and then water was added 1 ml at a time until the salts coagulated (not >5 ml). About 10 g of magnesium sulfate and 0.40 g of phenothiazine were added. The reaction mixture was filtered cold under nitrogen pressure through diatomaceous earth using a coarse sintered-glass filter, followed by three rinses of fresh ether. Ether was evaporated from the filtrate under house or gentle water vacuum at 35-45'. The residue along with additional phenothiazine was redried if necessary and transferred to a distillation flask fitted with a Vigreux head. The remaining ether was removed with the bath at 25" without cooling water in the condenser. When the pressure decreased to 8 mm, cooling of the condenser with water and of the receiver with ice-methanol was begun. Almost all the tert-butyl alcohol was removed in this way. The distillate was examined by gc to ensure that no bicyclobutanecarbonitrile was present. When it was, the inhibitor was added, alcohol was evaporated, and the residue was returned to the distillation flask. With the bath at
