was added dropwise at O", with stirring. After stirring at 0" for 5 min., t h e solution was allowed t o warm t o room temperature, and the silver salts and silver metal were filtered off. Acidification of t h e filtrate and extraction with ether gave, after removal of t h e ether under reduced pressure, 0.49 g . (90%) 0.f pale yellow oil, XZoD 1.5412. T h e infrared spectrum was identical with t h a t of t h e trans isomer described xbove escept in t h e 1830-1260 crn.-' region where t h e cis cornpouncl had two bands of approximately equal intensity a t 1232 and 1256 cm.-' while t h e trans isomer had a somewlint stronger band a t 1236 cm.-l with a shoulder a t 1255 tin.-'. This difference appeared in several preparations of each compound. T h e amide prepared from 0.21 g . (0.0011 mole) of t h e acid by the method employed for t h e transamide was obtained as 0.18 g. (86% yield), m.p. 155.5-157'. Recrystallization from ethylene chloride gave 0.12 g. of cisamide, m.p. 158-158.5". T h e m.p. was not changed b y further recrystallization. ,4 mixed m . p . with t h e transamide was 151.5-154O. Anal. Calcd. for CI2HljNO: C , 76.2; H , 8.0; li,7.4. Found: C , 76.2; H , 8.0; N, 7.4.
Conversion of cis( ?)-and trans( ? )-3-Phenylcyclopentaecarboxylic Acid to 3,4-Benz-2-ketobicyclo[3.2.1]octane (IX). --A mixture of the cyclopentanecarboxylic acid and polyphosphoric acid was stirred intermittently a t room temper:tture for 3 hr. and then on a steam-bath for 1-1.5 h r . Tlic reaction mixture was then poured into 100 mi. of ice-wttcr and extracted with ether. T h e ether solution vas extracted with 10% sodium carbonate t o remove a n y unreacted acid a n d , after drying, the solvent was distilled off under retliiced pressure. From 1.4 g. (0.0074 mole) of Iruns-c:irbos!.lic acid and 16 g. of polyphosphoric acid was obtnincd U.99 g . (78y0)of IX as a light red oil, nZ5D1.5798 (repcirtcd341.577). From 0.62 g. (0.0027 mole) of cis-acid and 7 . 1 g. of polyph(1sphoric acid was obtained 0.40 g. (85%) of red IX, YZ% 1.5791. I n each case t h e infrared spectr:t had strong carbonyl stretching absorption at 1692 cm.-l. T h e spectrurii of t h e sample from t h e cis-acid differed from t h a t of the trans only by a weak band at 1775 cm.-l. In each case the 2,4-dinitrophenylhydrazonerecrystallized from dioxane h:itl m.p. 250.5-251.5" (reported34 248-249" ) . URBAX.4, ILL.
[CONTRIBTJTION FROM THE N O Y E S CIIEMICAL
LABORATORY, UNIVERSITY
O F ILLIKOIS]
Chemistry of Spiropentane. 11. The Chlorination of Spiropentane U Y DOUGLAS E. APPLEQUIST, GEORGEF. FANTA AND BERTELW.HEXRIKSON RECEIVED SEPTEMBER 14, 1959 T h e product mixture obtained by free-radical chlorination of spiropentane has been shown t o consist in part of t h e nprinal substitution product, chlorospiropentane, b u t mainly of chlorides which can be accounted for by initial ring-opening 4-chlnro-2-chloroattack of a chlorine atom on carbon. T h e latter products include 1,l-bis-(chloromethyI)-cyclopropane, methyl-1-butene and 1,2,4-trichloro-2-ehloromethylbutane.
Although spiropentane(I) has been known for a number of years,l no substituted spiropentanes are known except the perdeuterated spiropentane.3 Since the standard preparation of spiropentane by dehalogenation of pentaerythrityl tetrahalides is
CHzCI CH? lj ClCH?CH&CH:CI
~~~~~
I11
IT
1
CICH2CHrCCHpCl I c1
xr
C h ~ i i i .23, ,
spiropentane with lithium in tetrahydrofuran followed by ethanol (78y0yield) and by its n.m.r. and infrared spectra. The n.m.r. spectrum (60 mc.) showed a quartet of nearly equal signals centered a t 1.48 p.p.m. from water and spaced 3 cycles apart, which was assigned to the hydrogen a to the chlorine. There was a triplet (areas approximately 1:2 :1,with the central signal nearly resolved into two) a t 3.38 p.p.m., spaced G cycles apart, which was assigned to one of the &hydrogens; and there was a quartet centered a t 3.63 p.p.m., spaced successively 3,2 and 3 cycles apart, which was assigned to the other @-hydrogen. The foregoing signals constitute a typical first-order threeproton spectrum in which all three protons are different.6 In the present case, the two a-p coupling constants are 3 and G c.p.s. and the F-P coupling constant is about 5 C.P.S. The methylenes of the unsubstituted ring were represented by a strong signal a t 3.82 p.p,m., with shoulders partially resolved on each side. The quartets for the phydrogens were found to be partially superimposed a t 40 mc., making interpretation difficult. Spiropentane itself showed a single sharp signal a t 4.04 p.p.m. The infrared spectrum of chlorospiropentane showed no C-C absorption, and contained
(1945). (4) H. B. Hass and H. Shrchter, ibid.,75, 1382 (1953).
( 5 ) J . A. Pople. XV. G. Schneider and H. J . Bernstein, "High-resolution Nuclear Magnetic Resonance," IlcGraw-Hill Book C o . , I n c . , iXew I'ork, N. Y . ,1959, p. 130.
I
I1
not readily extended to the synthesis of spiropentane derivatives, a promising approach to the preparation of such derivatives appeared to be direct free-radical substitution reactions on spiropentane, analogous to the reported successful chlorination3 and nitration4 of cyclopropane. This paper reports a study of the free-radical chlorination of spiropentane, a reaction expected to yield chlorospiropentane (11), which was desired for an investigation to be described in a future publication. Photoinduced chlorination of spiropentane in the gas phase was studied with spiropentane to chlorine mole ratios of 10:l to 30:l with provision for removing chlorinated products as they formed. Distillation and gas chromatography of the reaction mixture revealed that there were four major products, which are here assigned the structures 11-V. The structure of chlorospiropentane (11) was assigned on the basis of its analysis, its reduction to (1) D. 13. hpplequist, G. F. F a n t a and B. W', Henrikson, J . O i g . 1715 (195S), and references cited therein. ( 2 ) 11, 0 . House, R . C. Lord and H . S.R a o , ibid.. 21, 1487 (105(i). (3) J. D. Roberts and P. €1. Dirstine, ' h i s JOURSAL, 67, 1281
CHLORIXATION OF SPIROPENTANE
May 5 , 1960
2369
TABLE I all of the peaks found in the spectrum of spiropentane. COMPOSITIONS OF PRODUCTS FROM VAPOR-PHASE CHLORTKAThe structure of 1,l-bis-(chloromethylj-cycloTIOS OF SPIROPENTANE Experiment Ab B C D propane (111) was indicated by its n.m.r. spectrum Conditions" T w o sunTwo sunOne sunDarknes3, (40 mc.), which showed two equal, unsplit signals lamps, one lanips lamp 1160 heat lamp a t 1.15 and 4.04 p.p.m.; by the infrared spectrum, Products, mole 7; which showed no double-bond absorption and resembled strikingly the spectrum of 1,l-bis-(bromoI1 43 2 43 2 36 2 9 6 methyl)-cyclopropane6; by its failure to react with I11 3 8 8 8 25 1 63 4 neutral permanganate; and by its inertness to IT' 35 8 30 9 25 6 18 6 powdered potassium hydroxide, which was in fact T' 15 7 9 7 8 9 4 8 used to isolate I11 in pure form. VI" 1 2 1 5 1 8 -1 2 The unsaturated dichloride I V gave a positive a See Experimental for further details. * The spiropenpermanganate test and showed infrared absorption tane used in run A was only about 88% pure, being cona t 1642 cm.-'. Its n.m.r. spectrum (40 mc.) taminated mainly by 2-methyl-1-butene. The product contained a t least eleven unidentified compounds, showed two barely unresolved olefinic proton therefore amounting to about 13.5Yc of the product mixture. The signals a t -0.51 and -0.31 p.p.m., an unsplit values shown in the table represent composition of the prodpeak a t 0.71 p.p.m. due to the allylic -CH&l, a uct mixture exclusive of these unidentified substances. T h e spiropentane used in runs A-D contained about 1.6, triplet a t 1.13 p.p.m. (separated about 6 c.P.s.) due to the other -CH2C1, and a triplet a t 2.12 p.p.m. 1.7, 0.7 and O.l%, respectively, of methylenecyclobutane. (separated about 7 c.P.s.) due to the remaining to become warmer upon strong irradiation (Budde allylic -CH2-. effect'). The runs A to D are therefore probably The structures of I11 and I V were futher confirmed by demonstration of their anionotropic arranged in descending order of actual reaction relationship through zinc chloride-catalyzed iso- temperature, and the variation in product compomerization. A mixture of 10.2% I V and 86.2% sition is possibly to be ascribed to the temperature I11 upon treatment with solid zinc chloride for effect. Two effects are notable: (1) The formation 100 hr. a t room temperature isomerized to a mix- of chlorospiropentane (11, is favored by strong ture containing 31.8% IV, 7.3% I11 and 58.G% of a irradiation (higher temperatures) ; and ( 2 ) the new substance assigned the expected6 structure VI. product of single ring opening (111) is favored with The n.m.r. spectrum (40 mc.) of the new compound respect to double ring opening (IV and V) by lower was in agreement with structure VI, showing a temperatures. A mechanistic scheme which accounts for the sharp signal for -CH2C1 a t 0.99 p.p.m. and a comforegoing observations is shown in Chart I. There appears to be no convenient explanation for the
-
Chart I
VI
plex pattern for the ring methylenes a t 2.0-3.1 p.p.m. Compound V I was also found among the products of chlorination of spiropentane to the extent of about 1%, but i t may have arisen in whole or in part from methylenecyclobutane which was known to contaminate the spiropentane. The tetrachloro compound V was identified by its reduction with lithium aluminum hydride to a mixture of 2-methylbutane and 2-methyl-l-b~tene; by its infrared spectrum, which showed no C=C or C-CHZ absorptions; and by its n.m.r. spectrum (40 mc.), which showed unsplit (0.83 p.p.m.) and triplet (0.95 p.p.m., J E 7.5 c.P.s.) signals for -CHzCl and a triplet (2.27 p.p.m., J E 7.5 c.P.s.) for the remaining methylene. I t was found that the products 11-V were obtained in different proportions, depending upon the temperature and intensity of irradiation. It was found, in fact, that the same products were obtained by a purely thermal chlorination (reaction D), although the reaction was slower. The product compositions from the various vapor-phase chlorinations are summarized in Table I. An attempt was made to make the reaction temperatures identical in runs C and D, but i t is probable that the temperature in the reaction zone in run C was higher due to the known tendency of chlorine (6) D . E. Applequist and J. D . Roberts, THIS J O U R N A L , 78, 874
(1956).
I
1
111 CHzCI I
CICH,CH,CCH,CI
v
c1
ring-opened products 111-V except the attack of chlorine atom on carbon as shown. The ring opening of radical VI1 to yield completely openchain products finds analogy in the formation of allylcarbinyl chloride by photochlorination of methylcyclopropane.8 (7) G. B . Kistiakowsky, "Photochemical Processes," T h e Chemical Catalog Co., Inc., (Reinhold Publ. Corp.), S e w York, S. Y.,1928, p.
138. (8) J. D. Roberts and R. H. Mazur, THIS JOURNAL, 78, 2509 (1951).
2370
D. E. APPLEQUIST,G. F. FANT.IA N D €3. IY.HEXRIKSON
The free-radical displacement on carbon t o form VI1 is a seldom observed class of reaction. In fact, there appear to be no thoroughly established examples of such displacements on tetrahedral carbons in open chains or unstrained rings, although some possible cases have been discovered and given preliminary examination.9 On the other hand, it appears likely that free-radical displacements on cyclopropane carbon are more common, being quite well established in thermal iodine addition, l o and by analogy probable for other halogen additions t o c y c l o p r ~ p a n e . ~The ~~~ photosensitized polymerization of cyclopropane has been thought to proceed by a radical displacement on carbon,12 but the more recently demonstrated complexity of the polymer makes such a conclusion d u b i ~ u s . ’ ~Free-radical additions to cyclopropanes are certainly less facile than additions to olefins, as shown by the relative unreactivity of cyclopropane toward halogens,Il and by the failure of cyclopropyl cyanide, methyl cyclopropyl ketone and phenylcyclopropane to undergo radical-initiated polymerization. 12b The variation of product composition with intensity of illumination (Table I), if the effect is simply a temperature effect as assumed, is accounted for in terms of the mechanism of Chart I if the activation energy for hydrogen abstraction to form spiropentyl radical is higher than that of the ring opening to form VII, and if the activation energy for opening the second ring (in VII) is greater than that for formation of I11 from VII. The latter relationship appears reasonable, b u t the former is in contrast with the results of the thermal chlorination of c y ~ l o p r o p a n e , ~where higher temperatures favored ring opening over substitution and temperatures over 500 were necessary to make ring opening a major reaction. A possible source of difference between spiropentane and cyclopropane is in the strain energies, but that of spiropentane (59 kcal.)14 is only about twice that of cyclopropane (29 kcal.)I5 if the same, value of the C-C bond energy is used to obtain the empirical strains from the heats of combustion. (The figures shown were calculated using 82.4 kcal. as the C-C bond energy and 170.4 kcal. as the heat of sublimation of graphite.) If a larger value of the C-C bond energy is more appropriate for the hypothetical unstrained spiropentane, as seems reasonable in view of its branched structure,I6 then the strain in spiropentane would be more than twice that in cyclopropane, and the opening of the first ring by a chlorine atom would be facilitated. Another effect which might contribute to the (9) (a) R. A. Herrmann and R . M. Noyes, THISJ O U R N A L78, , 5764 (1956): (b) R. A. Holroyd and W. A. Koyes, Jr.. i b i d . , 76, 1583 (19.54); (c) H . G. Oswin, R. Rebbert and E. W. R. Steacie, Can. J . Chem., 33, 472 (195.3. (10) R. A. O g g . Jr., and W. J. Priest, J. Chem. P k y s . , 7 , 736 (1939). (11) M . S. Kharasch, M. 2. Fineman and F. R. Mayo, THISJOURN A L , 61, 2139 (1939). (12) (a) H . E. Gunning and E. W. R. Steacie, J . Chom. P h y r . , 17, 351 (1949); (b) G. S. Hammond and R. W. Todd, THISJOURNAL, 76, 4081 (1954). (13) K . J. Ivin, J . Chem. Soc., 2211 (1956). (14) F. M . Fraser and E. J. Prosen, J . Research Natl. Bur. Standards, 64, 143 (1955). (15) J. W. Knowlton and F. D. Rossini, ibid.. 43, 113 (1949). (18) G. E. K . Branch and M. Calvin, “ T h e Theory of Organic Chem. istry,” Prentice-Hall, Inc., New York, N. Y..1941, p. 274.
ease of ring opening of spiropentane is resonance stabilization (ionic or otherwise) of the transition state leading to 1’11, analogous to that which would account for the unusually fast decomposition of bis-cyclopropylacetyl peroxide. l7 It is difficult to see how such stabilization could be stereoelectronically favorable in the spiropentane ring opening, since the orbital which contains the odd electron in VI1 would be nearly orthogonal to the bentbond orbitals of the undisturbed three-membered ring in the transition state for formation of VII. AS a further confirmation of the free-radical mechanism shown in Chart I, it has been shown that the products 11-V are also formed in liquid phase chlGrinations in sealed tubes, using excess spiropentane as solvent, and that the formation of all of these products in the liquid phase is strongly enhanced by light or by trichloroacetyl peroxide (which decomposes rapidly a t room temperature). The yields, based on chlorine used, are shown in Table 11. Several unidentified products were TABLE 11 YIELDSOF PRODUCTS FROM LIQUID-PHASE CIILORISATIOS OF SPIROPESTAXE E Experiment Conditions
F
Tutal darkness, Total darkness no peroxide, peroxide, 24 hr. 4 hr.” Products, mole Yo
G Light 5 lir.
Products, mole 70 0.9 26 4 4 20 52 0 18 2 l V 0 5 VI 0 0 0 Unidentified 1.5 9 5 a Because of the speed at which trichloracetyl peroxide decomposes at room temperature, t h e reaction was probably complete in much less time, but darkness prevented visual observation of chlorine disappearance. See Experimental for details.
I1 I11 Iv
-
formed in these reactions even though the spiropentane was 97.5% pure or better, but such products would be expected in this situation where initial products are not removed from the reaction mixture. None of these extra products have been investigated further. Acknowledgment.-This research was supported in part by a grant from the Petroleum Research Fund administered by the American Chemical Society. Grateful acknowledgment is hereby made to the donors of said fund. We are indebted t o Prof. Martin Saunders for a GO mc. n.m.r. spectrum, to Mr. Ben Shoulders for the 40 mc. n.m.r. spectra, to Mr. Paul McMahon and Mrs. Mary Verkade for the infrared spectra, and to Mr. Josef Nemeth, Miss Claire Higham, Lfiss Jane Liu and hlrs. Ruby Ju for microanalyses. Experimental18 Vapor-phase Chlorination of Spiropentane. Reaction C, O n e Sunlamp.-The chlorination apparatus was modeled (17) H. H a r t , J. M. Sandri and D. P. Wyman. Abstracts of the 131st Meeting of the American Chemical Society, Miami, Fla., April, 1957. p. 65-0. (18) Boiling points are uncorrected. Infrared spectra were measured with a Perkin-Elmer model 21B spectrophotometer with sodium chloride optics. Gas chromatography was done with a Perkin-Elmer model l54B vapor fractometer, using helium as the carrier gas.
May 5, 1960
CHLORINATION OF SPIROPENTANE
237 1
(THF) which had previously been distilled over lithium aluafter t h a t used by Roberts a n d Mazur for t h e chlorination of minum hydride. T h e contents of t h e flask were cooled t o cyclobutane.8 T h e light source was a 275 w. sunlamp approximately -35", and a solution of 1.4 g . (0.0136 mole) placed about 0.5 c m . from t h e glass spiral. Spiropentane' of spiropentyl chloride (98.4y0 pure b y vapor chromatog(27.3 g., 95.2% pure by vapor chromatography) was placed in the boiler and heated until t h e entire apparatus was filled raphy) in 9.1 ml. of T H F was then added over a two-hour period while the entire system was stirred and kept under a n with vapor as evidenced b y rapid condensation at t h e Dry Ice condenser. Chlorine was then admitted t o the system, atmosphere of helium. After 23 hr. at -35 t o -15", the reaction mixture was decomposed by the addition of 5 ml. of the number of moles per minute being governed by a caliabsolute ethanol. The entire system was then swept with a brated flow-meter. The ratio of chlorine to hydrocarbon slow stream of helium for 20 hr. t o yield 6.37 g. of liquid in was held at approximately 1:30 throughout the reaction. the Dry Ice t r a p . Analysis of this liquid by vapor chromaThe reaction was stopped a t the end of 6 hr. when the temtography (didecyl phthalate column) showed a low-boiling perature of the liquid in t h e boiler reached 100'. Distillaliquid t o be present in addition t o T H F . A pure sample of tion of t h e crude reaction mixture through a 4.5-ft. modified this component was collected b y vapor chromatography and Podbielniak column1gyielded spiropentane ( I ) (b.p. 38.5'); was shown t o have a n infrared spectrum identical t o t h a t of spiropentyl chloride (11)( b . p . 93-99'); a misture of 111, IV and VI (b.p. 160-180°); and 1,2,4-trichloro-2-(chloromethyl)- spiropentane. The calculated yield of spiropentane was butane (V) (b.p. 76.5-78" (2 mm.)). T h e mixture of 111, 78%. Reduction of 1,2,4-Trichloro-2-( chloromethy1)-butane (V) I V and V I was analyzed by vapor chromatography (didecyl with Lithium Aluminum Hydride.-To a micro side arm phthalate column) and the over-all mole percentages calculated using Eastmen's correction for molecular weights.20 flask equipped with a water cooled reflux condenser which, in A sample of pure I1 was prepared by vapor chromatography. t u r n , was connected t o a Dry Ice t r a p was added a suspension of 1.08 g. (0.0286 mole) of lithium aluminum hydride in 5 Molecular weights of unknown compounds present in low ml. of d r y T H F . After this mixture had been heated t o concentrations were estimated b y their retention times with reflux temperature, 1.00 g. (0.00477 mole) of V was added relation t o known substances. slowly from a hypodermic syringe mounted in t h e side arm Anal. Calcd. for CEH7Cl (11): C, 58.54; H, 6.88. Found: C , 58.51; H , 7.11. Calcd. for CsHBClc (VI): C , of the flask. After addition of t h e chloride, t h e resulting mixture was held at reflux temperature for 2.5 hr. and allowed 28.61; H , 3.84. Found: C,28.68; H , 3.94. t o cool overnight. T h e mixture was then again heated t o Reaction B, Two Sunlamps.-The reaction with two 275 reflux temperature and t h e system swept with helium for 2 w. sunlamps placed approximately 1 cm. from the spiral8 hr. t o yield 1.10 g . of liquid in the cold t r a p . T h e two major was similar t o the above reaction, with the exception t h a t the components of this mixture (excluding T H F ) were separated Dry Ice condenser was replaced b y a spiral condenser cooled by means of vapor chromatography (didecyl phthalate b y a n ice-brine mixture. The amount of spiropentane chlo- column) a n d identified as 2-methylbutane (3OyOyield) and rinated was 18.8 g. (93y0 pure by vapor chromatography), 2-methyl-1-butene ( 45y0 yield) by comparison of t h e inand a 1: 10 ratio of chlorine t o hydrocarbon was maintained frared spectra with those of known compounds.21 throughout the reaction. T h e reaction was stopped at t h e Isomerization of Dichloride Mixture with Zinc Chloride end of 7 hr. when the boiler temperature reached 100'. and Isolation of I-Chloro-1-chloromethylcyclobutane(VI) .Spiropentane and spiropentyl chloride were removed b y A dichloride fraction containing 86.2% 111, 10.2% I V , 2.2% fractionation at atmospheric pressure though a 26-cm. spin- VI and 1.5% of a n unidentified substance was allowed to ning band column. T h e residue was analyzed b y vapor s t a n d in the presence of anhydrous zinc chloride for 100 hr. chromatography a t 154" (didecyl phthalate column) and From 0.576 g. of the mixture and 0.11 g. of zinc chloride was t h e products identified b y comparison of retention times recovered, by distillation, 0.512 g. (89% recovery) of diwith those of the products from the previous reaction. chloride mixture which was analyzed by gas chromatography Reaction A, Two Sunlamps and One Heat Lamp.-The on a didecyl phthalate column. T h e product contained procedure was like t h a t in the above reactions but with two 7.34y0 111, 31.8% IV and 58.6y0 T I . From a similar reacsunlamps about 1 and 2 cm. from the coil and a 250 w. heat tion mixture, a high concentration of VI, b.p. 46-49' (11.3 lamp about 5 c m . from t h e coil. T h e lamps were covered nim.), was obtained by fractional distillation through a 26with aluminum foil t o maximize their efficiency. A Dry cm. spinning-band column. Kearly pure \'I was then isoIce condenser was used. Spiropentane amounting t o 123 g. lated, contaminated with only traces of I11 and IV, by gas (appros. SSy, pure) was chlorinated for 16.5 hr. at a 1 : 10 Chromatography. ratio of chlorine t o hydrocarbon. The pot temperature was Anal. Calcd. for CbH8C12: C , 43.19; H, 5.80. Found: 100' at the end of this time. Gas chromatographic analysis C , 43.50; H, 5.74. (didecyl phthalate column) of the crude reaction mixture Treatment of Dichloride Mixture with Potassium Hygave the d a t a s h o w in Table I. This procedure was the 1.~the best one for svnthesis of chlorosnirooentane . ~ .(11 ~ __,, . isolated ..~. droxide and Isolation of 1,l-Bis-( chloromethy1)-cyclopropane (III).-To a micro reaction flask equipped with reflux conyield being 58 g . (b.p. 95-96")'(32%). denser and calcium chloride tube was added 6.4 g . of a mixReaction D , Total Darkness.-The apparatus for the dark reaction was identical with t h a t used fdr reaction C. The ture containing approximately equimolar amounts of 111 and IV. Powdered potassium hydroxide (11.0 6.) was then glass spiral of the chlorination apparatus8 was heated b y means of a resistance wire heater to 116' (the approximate added and the resulting mixture heated at steam-bath temperature for 7 hours. -4fter cooling overnight, the mixturc temperature measured for reaction C ) . The weight of spiropentane used wits 16.3 g. (96.5% pure b y vapor chroma- was diluted ~ i t hdiethyl ether and the excess potassium tography), a n d the chlorine t o hydrocarbon ratio was main- hydroxide removed by filtration. Ether was removed by distillation through a Holzman column, and the residue was tained at 1:20 throughout t h e 6 hr. reaction time. At t h e then fractiondted through a 26-cm. spinning band column t o end of this time, the boiler temperature was 65". Thermomyield a total of 1.8 g . of colorless liquid, b.p. 48-51' (12.1 eter and flowmeter readings were taken with the aid of a mm.). Vapor chromatography of a center fraction (dismall penlight covered with several layers of red crepe paper. The reaction mixture was crudely fractionated in total dark- decylphthalate column) showed 111 t o be 9l.7Y0 pure, I i r being the only impurity. Infrared, n.m.r. and carbonness yielding 5.1 g . of low boiling material and 17.5 g. of hydrogen a n d y e s were obtained on this material. high boiling residue. An infrared spectrum of the low boiling material was identical with t h a t of a known sample of spiroAnal. Calcd. for CjH&12: C , 43.19; H , 5.80. Found: pentane. The over-all composition of t h e reaction mixture C, 43.35; H, 5.86. was determined by vapor chromatographic analyses of both Isolation of 4-Chloro-2-chloromethyl-I-butene (IV).-A4 low and high boiling materials (156", didecyl phthalate sample of dichloride mixture, b.p. 68" (31 mm.), containing column) and comparison of retention times with those of I 80% I V was obtained b y fractional distillation through the through VI isolated from previous reactims. modified Podbielniak column. This sample was then distilReduction of Spiropentyl Chloride (II).-In a micro 3- led in part through a 26-cm. spinning-band column. T h e necked flask equipped with dropping funnel, stirrer and Dry residue found t o be about 90y0 I V (gas chromatography), Ice t r a p was placed a suspension of 0.24 g. (0.034 g. a t o m ) and waswas further purified by gas chromatography (didecyl of finely cut lithium wire in 4.5 ml. of tetrahydrofuran ~
~~~~
~~~~~
(19) J , Cason and H. Rapoport, "Laboratory Text in Organic Chemistry," Prentice-Hall, Inc., Xew York, S . Y., 1950, p. 237. (20) R. H. Eastman, THISJOURNAL, '79, 4243 (1957).
(21) American Petroleum Institute, Research Project 44 a t National Bureau of Standards, "Infrared Absorption Spectrograms," Vol. I, Iios. 196,241.
2372
DOUGLAS E. APPLEQUISTAND ALANH. PETERSOX
phthalate column) t o give 99y0 1 V containing 0.4y0 I11 and 0.6% of a n unknown low boiling material which was easily removed by fractionation a t reduced pressure through a semi-micro Vigreux column. Infrared, carbon-hydrogen and n.m.r. analyses were obtained on the material thus obtained. -4nal. Calcd. for CSHsC12: C , 43.10; H,5.80. Found: C, 43.39; H, 5.86. Preparation of Trichloroacetyl Peroxide .-TrichloroacetS-1 peroxide was prepared in low yield by the method of Zimiiierinan2*and used without recrystallization. Liquid-phase Chlorination of Spiropentane. Reaction E, NO Initiator.-To a small ampule with a constriction at t h e top t o facilitate sealing was added 0.41 g . (0.00603 mole) of s ~ i r o p e n t a n eof 99.4% purito. The resulting liquid was coolcd t o Dry Ice temperature, and 29.6 nil. (0.0014 mole) of gaseous chlorine was then slowly added by means of a gas buret through a capillary tube extending below the surface of the liquid. The addition of chlorine was made in total darkness. After addition was complete, the ampule was quickly sealed with a n oxygen torch and allowed t o stand a t room temperature in total darkness for 24 hr. ;It the end of this time, the ampule was broken and the reaction mixture poured into a saturated solution of sodiiiin bisulfite a t 0'. .lftcr remaining in contact with the bisulfite solution for 10 inin. t o destroy all unreacted chlorine, the mixture was reinoved from the dark and tlie organic layer separated, dried and distilled. T h e mixture was analyzed by vapor chromatography a t 156" (didecyl phthalate column), employing Eastinan's correction for molecular weights.20 The molecular weights of unknown compounds, which were present in small amounts in all three liquid phase reactions, were estimated by their retention times with relation t o known compounds. Major products were identified by comparison of retentioii tinies with those of known samples of I , I1 and 111. A n infrared spectrum of t h e reaction mixture was identical with t h a t of a knowii sample of spiropentane except for a weak absorption a t 1265 cni.-' which m a y be attributed to t h e preseuee of 111. Reaction F, Initiation by Peroxide .-The same apparatus :in13 procedure was used as was discussed for the uninitated c : ~ . The spiropentane used rras of 97.570 purity and amounted t o 0.58 g. (0.0129 mole). The impurities viere :ill present in less than 0.4yG,except l,l-dimeth!-lcyclopropane which was present in a concentration of 1.2Yo (deterniined by vapor chromatography).' -1fter the ampule containing spirol)cntane had been cooled t o Dry Ice temperature, approxiinatel? 10 mg. of trichloroacetyl peroside was added. T h e peroxide could not he weighed due t o its rapid, and sometimes violent decomposition at or near room temperature. Chlorine (6%nil ,, 0.0025 mole) was then added, a s before, in total darkness. .After sealing, the ampule was completely submerged i i i a beaker of water at room temperature and allowed t o st:ind in total darkness for 4 hr. -4ny excess chlorine was again decomposed with bisulfite and the clrganic layer separated, dried and distilled. T h e reaction ( 2 2 ) C . Zinimerrnan, U. S . P a t e n t 2,580,373 (1931); lilili8a (1'352).
C. /I.,
Vol. s2
mixture was analyzed by vapor chromatography in a manner identical t o t h a t described for the reaction E, retention times being compared with those of known samples of I , 11, 111, IITa n d V. After removal of excess spiropentane, a crude distillation of the reaction mixture yielded three fractions. The infrared spectrum of fraction 1 clearly showed tlie presence of 11. Similarly, infrared analysis of fraction 2 indicated a mixture of I11 and IV. Compound V was further identified by comparison of t h e vapor chromatographic retention time of this component in fraction 3 with a known sample a t 190" (silicone oil column). Reaction G , Initiation by Light.-The s c u m apparatus and generul procedure was used as was employed in the two previous liquid phase chlorinations. Chlorine (57.7 ml., 0.0023 mole) \vas added t o 0.795 g. (0.0117 mole) of spiropentane of the same purity a s t h a t used for the peroxideinitiated reaction. The addition nf chlorine and the sealing of the ampule were, :is before, carried out in darkness. After submerging the seded ampule iii a beaker of water at rooin temperature, the contents of t h e beaker were irradiated with a 275 w. sunlamp for 1.5 hr. starting at a distance of 12 f t . and moving to 6 f t . a t the end of 45 min. Since no noticeable r e x t i o n occurred with t h e lain]) a t these distances, the reactioii mixture was irradiated at 3 ft. for a tutal o f 3.5 lir. After 1 hr. :it this distance, thereaction mixture was almost colorless. =\t t h e end of tlie 5 h r . reaction time, the colorless reaction mixture was treated with bisulfite, separated, dried and distilled a s before. A4nalysisa n d identification of products by comparison of vapor chromatographic retention times 1.i-ith authentic samples A t 156" n'as carried out as iti the two previous reactions. Since the concentration of spiropentyl chloride n w too lvir t:) permit isolation b>-distillation, the presence of I1 was further proved by comparison of its rcrilcntion time with t h a t of a known sample at 132" (didecyl phthalate colurnu). Infrared analysis of the above reaction mixture, after reinov:il of exceb5 spiropentane, cleLirl1- showed the presence of 111 and suggested the presence of IV. Final idcnlificatiuii of 1. in thc above concentrated reaction mixture \ v : ~ s accomplished by comparison of its retention time u ith t h a t of an authcntic sdmple at 190" (silicone oil column). Nuclear Magnetic Resonance Spectra.-Thc ii .ni.r. spectra were inerisured in carbon tetrachloride solution with :t I7arian high resolution spectrometer (iiiodcl V-430013 with super stabilizcrj using inethylene chloride as :in external standard. Tlie 40 inc. spectra were measured in c:Lrbon tetrachloride solutions a t the follon-iiigcrmcentrations for the various substances: I , 296 ing./inl.; 11, 370 mg./ml; 111, 281 rng./ml.; I\-, 260 mg.!ml.; L7, 212 ing./iiil.; and V I , 260 ing. /nil. The signd of t h e methylene chloride external standard was assumed t o be at -0.65 p.p.ni. from mater. The 60 nic. spectrum of 111 was iiieasured on t h e neat liquid, but the chemical shifts assigned iii the discussion arc those measured on the above 10 mc. spectrum in carbon tetrachloride. JVherc peaks were obscured by overlap at the lwq-er frequency, it was assurned that relative shifts w r e the same iii t h e tmu cxscs.
46, P
URBASA,ILL -
[COSTRTRUTIOS PROM
THE S O Y E S
CHEMICAL LABORATORY,
U N I V E R S I T Y OF I L L I S O I S ]
The Stereochemistry of the Hunsdiecker Reaction on a Cyclopropane Ring1 BY DOUGLAS E. APPLEQUISTA?JD
ALAN
H.
PETERSON
RECEIVED SEPrEMBER 21, 1959 'Tlie Iirciiniiiztive ciecarbrmylation (Hunsdiecker reaction) of silver 2-inethylc~clopropallecarbosS.late in carbon tctracliloridc a t room tcmpcrature has been found t o give the same mixture of cis- arid trans-2-methylcyclopropyl bromides froiii cithcr the ris or lvans silver salt. I t is concluded t h a t the cyclopropyl free radical is either planar about the 1-position or iiiverts i t a configuration very rapidly, and is thus qualitatively like an unstrained alkyl free radical.
either planar in configuration about the trivalent
carbon or subject to rapid inversion if they are non-planar, very little attention has been given to the effect of hybridization changes on the stereo-
' : ) Taken from t h e P h . D thesis o f Alan H. Petersun, University of Illinok 1960. ( 2 ) (a) G. Herzberg aiid .I.S h o u s m i t l i , C U J L ./. . P i i y ~ . ,34, 523 (195ti); (b) AI. Karplus, J . Chem. Pizvs., SO, 13 (1959).
. Sewinan's "Steric Effects i n Organic m s , Inc.. N e w York, N . Y . , l%X,P . 140; (b) C. Walling, "Free Radicals in Solution," Juhn Wiley and Sons. Inc.. S e w York, .'IP Y., 1967, p. 502.
Altliough extensive physical2 and chemical3 data have revealed that ordinary free alkyl radicals are
