HYDROGEN CHLORIDE WITH -ALIPHATIC ALLEKES
Dec. 20, 19GO
4.311 g.) from this distillation gave a positive permanganate test for unsaturation. Vapor chromatographic analysis,of this residue (didecyl phthalate column) indicated two major components (VIII and I X ) formed in 32.5 and 6.7% yield, respectively. Two minor components were also observed, but these were formed in only about 3Yc total yield and were therefore not investigated further. By means of vapor chromatography, components VIII and I X were isolated for infrared and n.m.r. analyses in purities of 98.4 and 94.170, respectively (determined by vapor chromatography of VI11 in ether and I X in carbon tetrachloride solution). In both cases, the only contaminant observed was the other isomer. Bn analytical sample of VI11 was obtained by refractionation of an ether solution of 98.47, pure material by vapor chromatography. Anal. Calcd. for CsHsO: C, 71.39; H, 9.59. Found: C, 71.00; H, 10.04. 3-Methylenecylobutyl 3,S-Dinitrobenzoate.--X solution of approximately 70 mg. of 3-methylenecyclobutanol ( V I I I ) in a mixture of carbon tetrachloride and ether, which contained 49 mg. of acetic acid as an impurity, was combined with 0.394 g. of 3,5-dinitrobenzo>l chloride and 1 ml. of pyridine and the resulting mixture heated under reflux for 55 min. The dark brown mixture was then cooled and poured into ice-water. The aqueous mixture was filtered and the precipitate and filtrate extracted separately with ether. The ether extracts were combined and washed first with saturated
[CONTRIBUTIONFROM
THE
6397
sodium bicarbonate solution and then with water. Evaporation of the ether solution t o dryness 5 ielded a red oil which deposited 76 mg. of pink crystals, m.p. 100-103.5° (softened 9 4 O ) , upon addition of petroleum ether. Ahanalytical sample (white crystals, m.p. 102-105°) was obtained by chromatography on Florisil, recrystallization from benzenepetroleum ether and sublimation under reduced pressure. The infrared spectrum of the material so obtained was identical in every respect with the spectrum of the crude product. A n d . Calcd. for C1zHloN2Os: C, 51.80; H , 3.62. Found: C, 51.99; H, 3.74. Nuclear Magnetic Resonance Spectra.-The n.m.r. spectra were measured with a Varian high resolution spectrometer (model V-4300B with super stabilizer). The spectra of I11 and IV were measured a t 40 mc. with externnl methylene chloride as standard. Compound I11 was examined as a carbon tetrachloride solution containing 235 mg./ml. and IV as a deuterium oxide solution containing 200 mg./ml. The signal of the methylene chloride standard was taken to be a t -0.65 p.p.m. from water. The spectra of the other substances were measured a t 60 mc. with tetramethylsilane as an internal standard using the following solutions: V, 104 mg./ml. in carbon disulfide-phenol; VII, 164 mg./ml. in carbon disulfide-phenol; VIII, 216 mg./ml. in carbon tetrachloride; I X , approx. 60 mg./nil. in carbon tetrachloride. The signal of the tetramethylsilane standard was taken t o be a t 4.78 p.p.m. from water.
DEPARTMENT O F CHEMISTRY, UNIVERSITY
OF
CALIFORNIA, LOS AXCELES 24, CALIF.]
The Addition of Hydrogen Chloride to Aliphatic Allenic Hydrocarbons1 BY THOJIAS L.
JACOBS AND
ROBERT N.
JOHNSON
RECEIVED AUGUST17, 1960 The addition of hydrogen chloride to allene and 1,2-butadiene a t -78" involves attack a t a terminal methylene group of the allenic system. Allene requires a catalyst such as bismuth trichloride and yields a mixture of 2-chloropropene and 2,2dichloropropane. Slight rearrangement t o propyne occurs during the addition. 1,2-Butadiene yields a mixture of transand cis-2-chloro-2-butene in the ratio 87/13; 2-butyne is also formed but does not add hydrogen chloride under the conditions. The orientation of addition of hydrogen chloride to the allenic system is reversed when one end of the system is disubstituted; attack occurs a t the middle carbon. At - 78" 3-methyl-1,2-butadiene gives a mixture of 3-chloro-3-methyl-lbutene and l-chloro-3-methyl-2-butene in the ratio 64/36; rearrangement t o isoprene also occurs. It was shown that these allylic chlorides do not rearrange under the conditions employed. Hydrogen chloride adds t o isoprene more rapidly under the same conditions t o give the same products but the ratio is 83/17. This shows that not all of the addition t o the allem occurs through isoprene and that the classical carbonium ion, which should be the same from both hydrocarbons, cannot be the intermediate in both instances. I n these hydrogen chloride additions other possible addition products were absent; they could have been detected if present t o the extent of 0.17,. The principal product of the addition of 2,4-dinitrobenzenewhich represents the opposite orientation to that sulfenyl chloride t o allene is 2-(2,4-dinitrobenzenethio)-3-chloro-l-propene observed with hydrogen chloride. This reagent gives mixtures with 1,2-butadiene and 3-methyl-1,2-butadiene; pure addition products were not isolated.
The ionic addition of unsymmetrical reagents HA to allenic systems has not been studied extensively and some uncertainty remains about even the orientation in such reactions. Hydration of allene itself in the presence of sulfuric acid was shown to yield acetone in the first definitive paper on this compound2 and aliphatic monosubstituted allenes IICH=C=CH? yield methyl This orientation for the addition of reagents HA as H and A appears to be general for these classes of allenes. Other examples include the addition of (1) Taken from a dissertation submitted by Robert N. Johnson in partial fulfillment of the requirements f o r t h e Ph.D. degree, Univer. sity of California. Los Angeles, February, 1960. N o s t of this work was carried o u t under a contract with the Office of Ordnance Research, U. S. Army. Reproduction in whole or in part is permitted for purposes of t h e U S. Government. (2) G. Gustavson and N. Demjanoff, J . pra41. Chem., [21 88, 201 (1888). (3) hl. Bouis. Airrz chiin. ( P u r i s ) , [lo] 9 , 402 (1928). ( 4 ) W , H. Carothers and G. J Berchet. THISJ O U R N A L , 56, 1628
(1933). ( 5 ) G 1 . Hetinion aud J. J. Sheehan, i h i d . , 71, I Q 6 l (1940).
hydrogen fluoride to allene to yield 2,2-difluoropropane6 and of methyl alcohol to 1,2-hexadiene in the presence of boron trifluoride and mercuric oxide to yield the dimethyl ketal of 2 - h e ~ a n o n e . ~ None of these reactions establishes which double bond is attacked first. The reaction of 1,2-hexadiene with dry hydrogen chloride in the presence of bismuth trichloride gives a mixture of 2-chloro-2-hexene and 2,2-dichlorohexane.6 This establishes that reaction can occur first a t the terminal double bond, but attack a t the secondary carbon is not excluded because the dichloride may have arisen mainly from 2-chloro-lhexene which could react with hydrogen chloride more rapidly than its isomer. A single example of the addition of hydrogen chloride to a tertiary allene has been reported7; (6) P. R. Austin, TJ. S. Patent 2,588,529, Feb. 12, 1952; C . A . , 46, 3799 (1952). (7) I. W. Kondakov, J . Riiss. Phys.-Thenr. S o r , 21, 86 (1889): C h e w . Z c n l r . , 6 1 , I. 311 (1890)
6398
THOMAS L. JACOBS
AND
3-methyl-1,2-butadiene was said to give 3-chloro3-methyl-1-butene. The assignment of the tertiary structure to the product seems doubtful because this chloride is completely isomerized to the more stable allylic isomer l-chloro-3-methyl-2-butene under milder conditions than were employed for the addition? However, it seems certain that this reaction did yield an allylic chloride and that the orientation in the ionic addition to an allene of the structure R2C==C=CH2 is different from that observed with monosubstituted allenes. Several additions of hydrogen bromide to allenes have been reported, but these are less useful to establish orientations because in no instance has i t been proved that ionic rather than radical addition was occurring. Early work in Favorskil's laboratory9 on the addition of hypochlorous acid to allene and to 3methyl-1,2-butadiene established that mixtures were produced. From the former were obtained 3-chloro-1-hydroxy-2-propanoneas the principal product (50%) , and 2-chloro-2-propen-1-01 (10%) and 1,3-dichloro-2-propanone(15%) as minor products. 3-Methyl-l,2-butadiene gave l-chloro-3methyl-3-hydroxy-2-butanone (38%) and 2,2-dichloro-3-methylbutane-1,3-diol (7.5%) ; some evidence was presented that 2-chloro-3-methyl-land 1,3buten-3-01) 2-chloro-3-methyl-2-buten-1-01 dichloro-3-methyl-2-butanone were present in the mixture. Although further work is needed in this difficult system, these results indicate that the orientation of the major product with allene is the reverse of that observed with HA reagents, but is the same as for the tertiary allene. The work described in the present paper was undertaken to establish the orientation of the addition of hydrogen chloride to a series of allenes varying in the extent of alkyl substitution on one of the carbons. Allene, 1,2-butadiene and 3-methyl1,2-butadiene were studied a t - 78' without solvent, and a clean reversal of orientation between the di- and tri-substituted allenes was established. With allene and 1,Bbutadiene the hydrogen of hydrogen chloride adds to the terminal methylene group, and if we assume the conventional picture of addition of the reagent to olefins, this means initial attack a t the terminal position. With 3-methyll,Z-butadiene, attack is on the central carbon of the allenic system. Alkyl substitution increases the rate of addition as with simple olefins. It was also found that rearrangement of the allenic system occurs during the addition reactions; allene gives propyne, 1,2-butadiene gives 2-butyne and 3methy1-lj2-butadiene gives isoprene. Bismuth trichloride or other catalysts are required with allene, but with the others without catalyst a t -78' the rates of rearrangement are comparable with the rates of addition. The results are summarized in Table I. Formation of these rearrangement products made i t necessary to examine the behavior of each in the addition reaction under the same conditions. Hydrogen chloride does not add to propyne at - 78' in the absence of a catalyst nor does rearrangement (8) A. J. UltCe, J . Chcm. Soc., 530 (1948). (9) F. Smirnoff. J . Russ. PhyJ.-Chcm. Soc., 96, 854 (1903); 86, 1184 (1904); Chcm. Zenfr., 76, I. 576 (1904); 76, I. 344 (1905).
ROBERTN. JOHNSON
VOl. 82
to allene occur, but in the presence of bismuth trichloride slow addition occurs to give the same products that are formed from allene. Slight rearrangement of propyne to allene was also observed. It was reported many years agolo that these addition products were formed when propyne was allowed to stand in solution in excess cold hydrochloric acid for a long time. The addition of hydrogen chloride to 1- and 8-butyne has not been reported previously, When 1-butyne was treated a t -78' with hydrogen chloride in the absence of solvents or catalysts no reaction could be detected by gas chromatography after six days and the starting material was recovered unchanged. 2Butyne adds hydrogen chloride much more slowly than 1,2-butadiene; slight rearrangement to the allene also occurs (Table I). Thus the allene and 1,2-butadiene addition products reported in Table I do not arise by addition to the corresponding acetylenes. Isoprene was found to add hydrogen chloride more rapidly than 3-methyl-lP2-butadiene to give the same products, but in different proportions (Table I). Isoprene recovered when the addition reaction was not carried to completion contained no 3-methyl-l,P-butadiene, but this is not surprising because the equilibrium between these two hydrocarbons would be expected to lie far on the isoprene side. Although the experimental precision necessary for analysis of the complex addition of hydrogen chloride to dimethylallene was not attained, and a system containing no solvent is not ideal for the precise study that is needed, i t is possible to learn a good deal qualitatively about the reaction from the data on hand. The reactions may be formulated as Dimethplallene ( D )
I ktD L+
r+
kpD
tert-chloride (CH3)2CClCH=CHz
3.
prim-chloride
(CH3)&=CHCH&1
If one assumes that the addition reactions for both D and I and the rearrangement are the same order in hydrogen chloride and first order in hydrocarbon, one may write -dD/dt kD(D)(HCl). k D = k r -I- k t D -I- d l / d t = kl(I)(HCl)" - kR(D)(HCl)" kI = ktr
+
kpD kpl
This can be rearranged and integrated in terms of rate constant ratios: k r / k D = a = fraction of dimethylallene that rearranges to isoprene ; k I / k D = b = specific rate for reaction of isoprene relative to dimethylallene. This gives
(10) E. Reboul, Comfit. rend., 74, 669 (1872).
Dec. 20, 1960
HYDROGEN CHLORIDE WITH ALIPHATIC ALLENES
6399
TABLE I ADDITIONOF HYDROGEN CHLORIDE TO ALLENE, 1,2-BUTADIENE, 3-METHYL-1,2-BUTADIENE AND Hydrocarbon taken
Equiv.,
HC1
Time,
hr.
Ream.,
%"
Alleneb
1.0 1.5
216 336
1.22
216
22 31
Propyne
CHiCECH 3 3 CHz=C=C€I*
2.7
1.2-Butadiene
Product distribution, yo
r
e
CHaCCl=CHz 60 33 CHaCCl=CHt 2
ISOPRENE AT -78' Ratio a d d n . prods.
Mono/di CHaCC12CHs 62/38 37 34/66 64 CH~CCIPCH~ Trace
CH3CECCHs
2-Butyne 3-Methyl-1,2-butadiene
1.8 1.5 1.8 2.1 1 to 2
43 144 144 142 144
CHsCCI=CHCHa trans cis 40.0 53.5 6.5 38.5 53.5 8.0 8.8 38.9 52.3 39.8 52.1 8.1 Trace of tran~-CH3CCl=CH2~ CHa Allylic chlorides
20 20 24 59
I
0.5 .5 .5 .5 .7 .75 1.12 1.32
1.5 1.5 1.0 1.5 2.0 1.5 1.63 1.76
32.5 42.8 43.7 48.6 49.1 (65) 87.5 100
CH*=CCH=CH* 4.53 4.84 4.70 4.59 3.08
..
2.5
tert. 17.7 24.7 25.8 27.3 29.9 41.0 54.4 62.0
pri. 10.3 13.3 13.2 16.7 16.1 24.0 30.6 38.0
D/Ia 93.7/6.3 92.2/7.8 92.3/7.7 91.8/8.2 94.3/5.7
. .. . . . .
83.1/16.9
.... ...
trans/cis 89/11 87/13 86/14 87/13
tert./pri. 63/37 65/35 66/34 62/38 65/35 63/37 64/36 62/38
(CH&CClCH=CHZ ( CH3)2C=CHCH2Cl % of diadduct 83 17 .. 41 0.5 1.5 85 15 43 .5 1.0 84 16 .. 47 1.5 .5 76 24 41 100 1.3 2.33 18 14 82 1.0 20 90 1 80 20 2.75 98 1.12 Values for % reaction represent yields of addition products plus yields of rearrangement products as determined by analyOne gram of bismuth trichloride was added to 14.0 g. of allene as a catalyst. sis of the recovered hydrocarbon mixt. The propyne used contained 0.0370 allene initially, and the propyne recovered after reaction contained 0.7% allene. The recovered 2-butyne contained 0.5% of 1,a-butadiene indicating slight rearrangement during the reaction. e U/I = % ' 3-methyl-1,2-butadiene/yoisopropene in recovered hydrocarbons. Isoprene
..
where Do and Io are initial concentrations of dimethylallene and isoprene, respectively. From the constant ratios of tert- to pri- allylic chlorides in the runs starting from pure D (64/36) and pure I (83/17), the limiting values of a in terms of the fraction, k,D/(k,D ktD), of the D undergoing addition which gives primary chloride are the following: direct addition to D gives only primary chloride, kpD/(kpD f ktD) = 1, U = 0.77; D gives no rearrangement to isoprene, k,D/(k,D ktD) = 0.36, a = 0. However some rearrangement of D to I occurs because I can be isolated from runs starting from pure D. Observation of the maximum concentration of isoprene in such runs permits calculation of kl/kD in terms of the limits of a. At maximum I
+
+
-
dI/dt = K,(D)(HCl)" RI(I)(HCl)" = 0 kr(D) = h ( I )
The determination is very inaccurate because the concentration of I remains almost constant near the maximum as D changes over a wide range. From Table I the percentage of I varies only from 4.53 to 4.84 between 32.5% and 48.6% reaction, where D changes from 67.5y0 to 51.4%. At I = 4.84%, D = 57.2% and k, = 0.0846k1 or k1 = 11.8kr. Where a = 0.77 (addition t o D gives only
primary chloride), k1 = 9.lkD; as a decreases, kI/kD becomes smaller. If the maximum I concentration has already been reached by 32.5% reaction and this concentration is taken as the average of the four readings between 32.5% and 48.6% reaction, I = 4.67 and D = 67.5. Then kr = 14.5kr and a t a = 0.77, kr = 1 l . l k ~ . Competitive runs can be used to check these figures. Table I1 records the results of four such runs. Values for b between a = 0.77 and a = 0 were calculated using the integrated rate expression. The agreement between the runs is only fair, but i t is possible to deduce a reasonable lower limit for a of around 0.62 because a t b = 9, as low as the competitive runs will permit, the calculation from the maximum concentration of isoprene in the pure D runs makes a = 0.62 to 0.76. The range of b = kl/kD based on a = 0.62 to 0.77 is 9.4 to 15.4. In runs 2 and 4 the calculated and observed ratios of 3-chloro-3-methyl-1-butene to 1-chloro-3-methyl2-butene are in good agreement; run 1 is less satisfactory. Tentative conclusions about the addition of hydrogen chloride to dimethylallene a t -78' without solvent may be summarized as: (1) isoprene adds hydrogen chloride 9 to 15 times faster than di-
THOMAS L. JACOBS
6400
COMPETITIVE
ROBERT N.
TABLE I1 ADDITIONSOF HYDROGEN CHLORIDE TO ISOPRENE Ream.,
Run
AND
%
Doll0 b
D/I
,--Range
c
a =
0.77
Vol. 82
JOHNSON
-78""
AND 3-METHYL-1,2-BUTADIENE AT OF bd7-lerl-chloride/pri.-
0.62
0
Obsd.
Calcd.
77/23 81.6/18.4 49.4/50.6 17.0 58.0/42.0 15.4 15.2 14.5 12.0 11.8 10.7 80/20 80.5/19.5 51.2/48.8 36.4 73.O/27.0 3 51.8/48.2 44.5 82.0/18.0 15.2 14.9 13.3 4 50.0/50.0 46.3 78.0/22.0 9.7 9.4 8.1 80/20 79.7/20.3 Contact time in runs 1 and 3 was 60 min., in 2 and 4 it was 90 min.; 0.5 equiv. of hydrogen chloride used. * Initial n = k,/kn; ratio of 3-methyl-l,2-butadienet o isoprene. c Ratio of D t o I in hydrocarbon fraction recovered from run. b = ki/kD. 1 2
methylallene; (2) rearrangement of the allene to isoprene is 1.5 to 3 times faster than direct addition; (3) direct addition of hydrogen chloride to the allene gives a t least two-thirds and possibly exclusively l-chloro-3-methyl-2-butene corresponding to initial attack a t the central carbon of the allenyl system and addition to the terminal double bond. The clean orientation observed in these addition reactions is one of their striking features. With each of the allenes it was shown by examining the behavior in the gas chromatographic apparatus of known samples of the other possible addition products that these could have been detected if present to the extent of 0.1% in the addition runs. In each instance no traces of these alternative products could be found. The possibility of an allylic rearrangement of the chlorides produced in these addition reactions is of critical importance for these conclusions and is serious because hydrogen chloride is known to catalyze such a rearrangement.8 Blank runs were carried through with known mixtures of these allylic isomers and hydrogen chloride using the procedure for workup and analysis as in the addition reactions. No rearrangement was observed nor was isoprene detected as a product. When appreciable amounts of diadduct are formed, the ratios of the allylic isomers vary as might be expected. No attempt was made to determine whether the diadduct was 1,3-dichloro-3methylbutane (the compound expected from primary chloride"), 2,3-dichloro-2-methylbutane (the expected but as yet undemonstrated product from tertiary chloride), or a mixture of these. The diadduct gave a single peak on a gas chromatogram, but examination of authentic dichlorides would be necessary to establish that this represented a single isomer. It is also possible that the higher concentrations of hydrogen chloride cause allylic rearrangement. At first sight it may appear surprising that addition does not always start by attack of a proton on the central carbon atom of the allenic system to give an allylic carbonium ion >C=CH-;
