LEWISF.HATCH AXD KENNETH E.HARWELL
GOO2
dure for cis-dibenzoylethylene, in 42% yielf , recrystallized from ethanol-benzene mixture, m.p. 175.5 , colorless. Anal. Calcd. for Cz2H1602:C, 84.59; H , 5.17. Found: C, 84.59; H , 5.40. Reductions of the Unsaturated to the Saturated Diketones. 1,2-Diphenyl-4- (4 -xenyl) -2-butane-1,4-dione (XVII).-A solution of sodium hydrosulfite (0.9 g.) in 4 ml. of water was added to a refluxing solution of 0.5 g. of the unsaturated diketone XIV in 40 ml. of absolute ethanol. After continued refluxing for 45 min. the product was precipitated by adding wfter and crystallized from ethanol, yield SO%, m.p. 132.5 . Anal. Calcd. for C28H2202: C, 86.11; H, 5.6s. Found: C, 86.04; H, 6.01. Dehydration (as below) by acetic anhydride and sulfuric acid gave the furan XVI which was identified by misture melting point. 2,4-Diphenyl-l-(4-xenyl)-butane-l,I-diOne (VIIc) was obtained from IVc by the above procedure in 95% yield, recrystallized from acetic acid-xylene mixture, m . ~ 200'. . Anal. Calcd. for C28H2202: C, 86.11; H , 5.68. Found: C, 86.38; H, 5.92. This compound, VIIc, was obtained also by zinc-acetic acid reduction (refluxing for 2 min.). Furanization was effected by the procedure below. Dehydration of Saturated 1,4-Diketones. 2-Phenyl-5(4-xenyl)-furan (XIX) .-In a typical experiment a solution of 0.09 g. of XVIII in a few ml. of acetic anhydride was treated with 1 ml. of acetic anhydride containing 0.001 ml. of concd. sulfuric acid. Reaction was immediate. Hydrolysis with water gave 0.7 g. (85%); recrystallizations from ethanol containing some benzene brought the melting uoint to 164'. Anal. -Calcd. for C22H110: C, 89.16; H , 5.44. Found: C, 89.36; H, 5.69. This compound was made also by stannous chloride reduction of the cis unsaturated 1,4-diketone XX by the method described above for VIb. Sunlight inversionsfrom cis to trans. trans-l,2-Diphenyl4-(4-xenyl)-2-butene-1,4-dione(IVc).-After sunlight irraA
[CONTRIBUTION FROM
THE
DEPARTMENT OF CHEMISTRY
diation for 3 days of a solution of 5 g. of Vc (labile) in 70 ml. of acetone and evaporation, the products were dissolved in hot ethanol. From the fmt crystalline precipitate IVc (the stable isomer) was isolated and purified by recrystallization from ethanol, yield 1 g. (20%), m.p. 107-108". Anal. Calcd. for Ct8H2002: C, 86.59; H, 5.19. Found: C, 86.54; H , 5.23. Irans-l-Phenyl-4-( 4-xenyl)-2-butene-l,4-dione [ I-Benzoyl-2-(4-xenoyl)-ethylene] (XXI).lZo---A solution was prepared by exposure of the labile cis isomer XX in chloroform containing enough iodine t o maintain color, to strong sunlight for 6 hours. Crystallization of the yellow product from 1:2 benzene-ethanol mixture gave 80% yield, m.p. 158-159a. Anal. Calcd. for Cn?HleOa: C, 84.59; 11, 5.17. Found: C, 84.51; H , 5.17. Limited efforts to prepare this compound by the FriedelCrafts reaction on P-benzoylacrylyl chlorideL6verr not buccessful cis-l,4-Di-(4-xenyl)-2-butene-l,4-dione [ 1,2-Di-(4-xenoy1)-ethylene].1*o-A solution of the stable trans isomer" 111 chloroform was exposed to strong sunlight for 7 hours, colorless, crystallized from 3: 1 benzene-ethanol mixture m.p. 239-241'. Anal. Calcd. for C2~Hzo02:C, 86.57; € I , 3.19. Found. C, 86.22; H , 5.11. Acid-catalyzed inversions from trans to cis of IVa, b, c and XV were accomplished in 72-90% yields by refluxing for a short time solutions of the compounds in benzene containing a small amount of added concd. hydrochloric acid. The products (Va, b, c and XIV), isolated by washing with water, drying and evaporating, were purified and identified by mixture melting points with samples prepared directly from 111.
.
(16) R. E. Lutz, THISJOURNAL, 62,3423 (1930). (17) H.G.Oddy, ibid., 46, 2160 (1923).
CIIARLOTTESVILLE, V I R G I X I A
AND THE
TEXAS J
DEFEXSERESEARCH LABORATORY, TffE
~ N I V E R S r T YO F
Allylic Chlorides. XX. Preparation and Properties of the 1 -Bromo-3-chloro-l -propenesl BY LEWISF. HATCHAND KENNETHE. HARWBLL RECEIVED JULY 13, 1953 The following compounds have been prepared and characterized: cis- and trans-l,3-dibromopropene, cis- and trans-3bromo-2-propen-1-01 and cis- and trans-1-bromo-3-chloro-1-propene.The bromochloropropenes isomerized a t room temperature in the presence of light but did not isomerize in the dark a t 0'. The relative reactivities of the allylic chlorides were determined with potassium iodide and with sodium ethoxide. The behavior of these geometrical isomers toward these reagents was similar to that of the 1,3-dichloropropenes.
Recent work with several pairs of geometrical isomers of the type CHCl=CYCH2CI has shown that the rate of reaction of the allylic chlorine atom with potassium iodide is greater when the vinyl chlorine atom and the chloromethyl group are in the cis position in respect to one another.2 This relationship between reactivity and configuration has been suggested as a means of assigning structure to compounds of this type. The present study of the 1-bromo-3-chloro-1-propeneswas undertaken to determine if the same relationship held when the vinyl halogen atom was bromine. These isomers would also further the study of the influence of size and electron attracting power of atoms in this (1) For number XIX of this series see L. F. Hatch and G. E. JourTHISJOURNAL, 76, 3712 (1953). (2) L. F. Hatch and D. W. McDonald, ibid., 74, 2911 (1952).
neay,
position on the reactivity of the allylic chlorine atom. The 1-bromo-3-chloro-1-propenes were prepared from 1-bromo-1-propene by treatment with Nbromosuccinimide to obtain 1,3-dibrornopropene which was then hydrolyzed to 3-bromo-?-propen1-01. The bromoakohol was converted to 1bromo-3-chloro-1-propene by concentrated hydrochloric acid. The 1-bromo-1-propene used was a mixture containing 70% cis- and 30% trans-1-bromo-1-propene. The 1-bromo-1-propenes isomerize to an equilibrium mixture a t room temperature after simple distillation. This isomerization has been noted previously, and it is suggested that most work reported in the literature to have been with either (3) G. Chavanne, Comfit. r e d , 118. 1698 (1914).
Dec. ij, 1953
PREPARATION AND PROPERTIES OF 1-BROMO-3-CHLORO-1-PROPENES
6003
the cis or trans isomer may have been with a mixture of the two isomers. Treatment of this mixture of isomers with Nbromosuccinimide gave a mixture of cis- (61%) and trans-l,3-dibromopropene (39y0). The two isomers of l13-dibromopropene did not isomerize during distillation or on standing in the light a t room temperature. l13-Dibromopropenehas been reported by Lespieau4 who prepared it in a 20% yield by dehydration of sym-dibromohydrin and by Stitzs who treated acrolein with phosphorus pentaO20 ' bromide. Lespieau thought that he had one isomer but probably had both isomers; Stitz made no effort to separate the two isomers. In the present work pure cis-1,3-dibrornopropene was prepared by distillation and pure trans-1,3Fig. 1.-Dehydrobromination of 3-bromo-2-propen-1-01 dibromopropene was obtained by recrystallization 50" with 10% aqueous NaOH: 0, a-(cis)-isomer; 0 , a t from diethyl ether a t -70" a t which temperature the cis isomer is a liquid. The structure of the two 8-(trans)-isomer. isomers was assigned on the basis of their physical acetone and sodium ethoxide in ethanol two sources properties and infrared spectra. of error, isomerization and reaction of the vinyl A mixture of the 1,3-dibromopropenes was hy- bromine atom, were given special consideration. drolyzed to a mixture of the 3-bromo-2-propen-1-01s The error due to isomerization is believed to be which was separated by distillation. The 3- small in the reaction with potassium iodide at 20" bromo-2-propen-1-01s did not isomerize during in the dark, because under these conditions these distillation nor at room temperature in the light. isomers isomerize very slowly. Although the Lespieau4 reported the preparation of this bromo- temperature (50") was favorable for isomerization alcohol but did not give any physical properties. during the sodium ethoxide reaction, the solvent The two isomers were characterized as to geometri- used was ethanol which is an inhibitor for cis-trans cal configuration by their physical properties, isomerization. If there had been a significant infrared spectra and their ease of dehydrohalogena- amount of isomerization during this reaction, there tion. would have been a drift in the rate constants toward Each isomer of 3-bromo-2-propen-1-01 was de- a common value with increasing time, and no drift hydrobrominated using 10% solution of sodium was observed. hydroxide. Figure 1 gives a graphic representation The possibility of reaction with the vinyl bromine of the data obtained. The lower boiling isomer atom was checked using a mixture of the l-bromo-lwas 5.7 times more readily dehydrobrominated propenes. There was no reaction with potassium than the higher boiling isomer. Assuming that iodide, but the l-bromo-l-propenes reacted with trans elimination takes place more readily than sodium ethoxide to the extent of 4% in six hours. cis elimination6 the dehydrobromination data in- Under the same conditions cis-l-bromo-3-chloro-1dicate that the lower boiling isomer has the cis propene reacted to the extent of 65%, while the configuration. trans was 58% reacted. A partial correction was The previously unreported l-bromo-3-chloro-l- made for the reaction of the vinyl bromine atom. propenes were prepared from a mixture of the The errors that exist in the quantitative aspects corresponding bromoalcohols by treatment with of the rate data do not greatly affect the conclusions concentrated hydrochloric acid. The 1-bromo- which were drawn primarily from the qualitative 3-chloro-l-propenes isomerize fairly rapidly in the relationships between the rate values. light at 40"; the trans isomer also isomerizes quite Table I gives the data obtained in these rate rapidly in the dark, but the cis isomer isomerizes studies. The l-bromo-3-chloro-l-propenes have only slowly under these conditions. Both isomers relative reactivities potassium iodide which ' in the dark, and are consistent with with retain their configuration a t 0 of similar compounds those they can be separated and purified by low temperaand agree with previous generalizations both as to ture distillation. Configuration was assigned to of configuration and as to the size of the influence the two isomers on the basis of their physical cis isomer of l-bromo-3the atom or group.* The properties, infrared spectra and their relative reactivity toward potassium iodide in acetone and chloro-l-propene has the greater reactivity (20) sodium ethoxide in ethanol. The presence of the and is more reactive than either cis-crotyl chloride chlorine atom in the allylic position was established (8.35) or cis-1,3-dichloropropene (8.58). The trans by treatment of the l-bromo-3-chloro-l-propenes isomers of these compounds all have about the with lithium aluminum hydride to give the equilib- same relative reactivities. The difference in reactivity (20 and 1.2) between the two isomers of rium mixture of the l-bromo-l-propenes.' In the rate studies of the reaction between 1- l-bromo-3-chloro-l-propeneis greater than is bromo-3-chloro-l-propene and potassium iodide in common for compounds of this type. This is a further indication of the lack of isomerization (4) M. R. Lespieau, Ann. chim. fihys., I71 11, 232 (1897). during reaction. ( 5 ) F.Stitz, Osferv. Chsm. Z., 48, 186 (1947). The -relative reactivities of cis- and truns-l(6) L. F. Hatch and P. S. Hudson, THIS JOURNAL, 7Z, 2505 (1950). bromo-3-chloro-1-propene with sodium ethoxide (7) L. F. Hatch and R. H. Perry, ibid., 71, 3262 (1949).
F
TABLE I SEVERAL HALOOLEFINS REACTIOSWITH POTASSIUM IODIDE IN ACETONEAT 20" ri7-l -~Rrnmo-3-chloro-l -propene (9570'1 'Time, hr . 13 22.; n 412 n .;IF, n m t o.860 Reacted, % ;;.7 5X 3X 68 74 k , h r . mole 1. 9.7 9.7 8.9 $1 0 8 .t i 9.2 f 0 1 Av. k Extrpd. k" 9.9 R ~ Ireactivity" . 20 I
