4316
HERMAN PINESAND VICTGRMARK
Table I1 shows that the influence of the CF3 group on the dissociating groups of the amino acids is in each case, where data are available, of about the same magnitude as in monofunctional compounds of equal distance between groups. The pK for the hydroxyl group of 4,4,4-trifluorothreonine, 12.7, may be compared with pK = 12.3 for 2,2,2-trifluoroethan01.~ Comparison of 6,6,6-trifluoronorleucine(;bK12.16, pKz 9.46) with ornithine (2,5-diaminopentanoic acid, pK1 1.81, fiKz 8.65)) and 2-amino-4,4,4-trifluorobutyric (pK1 1.60, pK? 8.17) with 2,3-di-
[CONTRIBUTION FROM THE IPATIEFF
Vol. ’78
aminopropionic acid (pKl 1.33, p K 2 6.80) gives some measure of the relative effect of the strong dipole1g CF3 and the charged group, +NH3. A similar comparison is available in w-CF3and w - +NH3 aliphatic carboxylic acids. As would be expected, the effect of the charged group is considerably the greater. especially when close to the dissociating group. (19) J. D. Roberts, R. L . Webb and E. A . McElhill, THISJ O U R N A L , 1 4 , 408 (1950); J. J. Conradiand N. C. I,;, i b i d . , l 5 , 1785 (1453).
TALLAHASSEE, FLORIDA
AND CATALYTIC LABORATORY, DEPARTMENT O F CHEMISTRY, XORTHWESTERN UNIVERSITY]
HIGHPRESSURE
Carbanions Additions in the Reaction of Aromatic Hydrocarbons with Monoolefins’a,b BY HERXAN PINESAND VICTOR MARK^ RECEIVED MARCH14, 1956 hlkylaromatic hydrocarbons which contain a benzylic hydrogen atom react with monosubstituted ethylenes, such as propylene, 1-butene and 1-octene in the presence of alkali, and an organoalkali compound prepared in situ a t about 250320” to form 1: 1 adducts. Propylene reacts with toluene, ethylbenzene, isopropylbenzene and diphenylmethane yielding isobutylbenzene, 2-phenyl-3-methylbutane, 2-phenyl-2,3-dimethylbutaneand l,l-diphenyl-2-methylpropane,respectively. 1-Butene and 1-octene with toluene give 2-benzylbutane and 2-benzyloctane. Under similar conditions toluene and isobutylene react t o give neopentylbenzene. Benzene reacts with ethylene t o form small amounts of ethylbenzene, sec-butylbenzene and biphenyl. t-Butylbenzene on reaction with ethylene under similar conditions forms 0-,m- and p-t-butylethylbenzene. The reaction of benzene with isobutylene yields t-butylbenzene, isobutylbenzene and biphenyl. T h e experimental results, which are interpreted by a carbanion chain mechanism, indicate that the mode of addition of carbanions to unsymmetrical olefins is determined entirely by polar rather than by steric factors. The mode of addition reveals that the primary alkylcarbanions are more stable and more easily formed than the secondary and tertiary ones. Several aspects of the carbanions and of their reaction mechanism are discussed.
There are only a few reports in the literature in which organoalkali compounds were added to monoolefins. Ziegler and Gellert3 described the reaction of primary alkyllithium compounds with ethylene under pressure to yield a series of adducts. The reaction failed, however, with other olefins. Bartlett and co-workers4 reported the addition of isopropyllithium and t-butyllithium to ethylene a t atmospheric pressure and low temperature. When propylene was substituted for ethylene only a small amount of an unidentified polymeric material was obtained. The reaction of several alkylaromatic hydrocarbons, which have a t least one benzylic hydrogen, with ethylene in the presence of sodium and a “promoter” recently has been described.j There are also a few patents in which similar reactions are claimed to take place in the presence of sodium6or organosodium compounds.7 The purpose of the present study was to investi(1) (a) Paper V of t h e series of Base Catalyzed Reactions. For I V see H. Pines and H . E. Eschinazi, T H x s J O U R N A L , 78. 1178 (1956). (b) Taken in p a r t from a dissertation submitted b y Victor M a r k t o t h e graduate school in partial fulfillment of t h e requirements for t h e P h . D . degree, October, 19;s. ( c ) Presented in p a r t befoie t h e Division of Organic Chemistry, American Chemical Society Meeting, March 29April 7, 1955. (2) Predoctoral Fellow, Universal Oil Products Co. 1953-54; E. I. du P o n t de Nemours and Co., 1954-1955. (3) IC. Ziegler and H. G. Gcllert, Ann., 561, 195 (1950). (4) P . D. Bartlett, S. Friedman and hf. Stiles, THISJ O U R I E A L , 76, 1771 (1953). (5) H. Pines, J. A. Vesely and V. S . Ipatieff, ibid., 11, 555 (1955). (a) G. M. Whitman, U. S . P a t e n t , 2,448,641 (1948); C . A . , 43, 1057 (19-19). (7) R . I.. Little, Jr., U. S . P a t e n t , 2,i48,803 (1951); ( / I . , 4 6 , 8531 (195 1).
gate the reaction of alkylaromatic hydrocarbons containing a benzylic hydrogen with simple monoolefins other than ethylene, in the presence of sodium and a substance capable of forming an organosodium compound. Another objective of the present experiments was to determine whether benzene and t-butylbenzene under similar conditions would react with olefins. Results Propylene and Aromatic Hydrocarbons.-The experimental condition used and the results obtained are summarized in Tables I and 11. The “promoters” employed were anthracene, o-chlorotoluene and dimethylmercury. The yield of isobutylbenzene produced from the reaction of toluene with propylene, amounting to about 10 to 23 mole per cent., was based on the propylene charge and not on the propylene reacted.* Ethylbenzene, isopropylbenzene and diphenylmethane yielded on reaction with propylene, respectively, 2-phenyl-3-methylbutane (3-methyl-2butyl)-benzene, 2-phenyl-2,3-dimethylbutane(23dimethyl-2-butyl)-benzene and 1,l-diphenyl-2methylpropane. The yield of the latter amounted to alY0. The adducts obtained from the interaction of one mole of aromatic hydrocarbons with one mole of propylene were comparable in purity, according to infrared spectra, with the respective (8) A 4 % yield of isobutylbenzene based on propylene charged, was previously found b y treating 1 mole of toluene with 0.8 mole of propylene in t h e presence of 0.27 g. atom of sodium and 0.014 mole of di-fbutyl peroxide a t 200°. Unpublished work b y H. Pines and J. A. Vesely from t h e IJniversal Oil Prtiducts C w , Riverside, Ill.
Sept. 5 , 1956
CARBANIONS IN REACTION OF AROMATIC HYDROCARRONS WITH M O N O ~ L E F I N S431 7 TABLE I REACTION OF TOLUENE WITH PROPYLENE One mole of toluene and one mole of propylene" were used in each experimentb
Experiment
2
1
Chain initiator precursor, g. (mole)
+Anthracene+ +0.9(0.005)4 1.0(0: 043) 5.0(0.215) 29 1 292 297 306 90 135 20 19.5
Sodium g. (atom) Temp. of pressure drop, OC. Highest temp., "C. Highest pressure, atm. Duration, hours Product obtained 8-Methyl-x-pentene, g. (mole) Isobutylbenzene, g. (mole) Bottoms and/or holdup, g.
5.3(0.063) 29,4(0.22) 4.0
6 . 2 (0.074) 13.0(0.097)
2.4
3
4
Dimethylmercury 2.5(0.0114) 1.0(0.043) 291 304 86 27
o-Chlorotoluene 8.0(0.063) 4.6(0.2) 290 300 82 15
2,5(0.03) 13(0.097) 2.5
1.7(0.02) ZZ(0.165) 3.3
Gaseous product recovered, mole Hydrogen 0.012 0.0085 ,0164 .023 Methane Ethane .0025 .0054 Propylene .350 .Ol Propane ,163 .33 a Composition, mole per cent. : propylene 96, propane 3, ethane 1. * The reaction was made in a 250-ml. capacity MagneDash autoclave.
TABLE I1 REACTION OF AROMATIC HYDROCARBONS WITH PROPYLENE Experiment
Propylene, g. (mole) Aromatic hydrocarbon, g. (moles) Chain initiator precursor, g. (moles) Sodium, g. (atom) Temp. of pressure drop " C . Highest temp., "C. Highest pressure, atm. Duration, hours Product obtained 2-Methyl-x-pentene Aromatic hydrocarbon"
5
42(1.0) Ethylbenzene 92( 0 . 8 7 ) Anthracene 0.9(0.005) 5.0(0.215) 282 29 1 153 10
6
7
38( 0.91) 42( 1 . 0 ) c1sopropylbenzene-t +120( 1.0)o-Chlorotoluene None S.O(O.063) ... 4.q0.2) h'one 270 280 302 95 238 13 14
None 3 . 7 ( 0 044) 2-Phenyl-32-Phenyl-2,3Xone methylbutane dimethylbutane g. (moles) 21.4(0.145) 12.1(0.075) Yield, Mole % 16.7 7.8 Bottoms and/or holdup, g. 5.0 3.4 0 a Product of the interaction of 1 mole of charged aromatic hydrocarbon with 1 mole of propylene.
aromatic hydrocarbons reported by the API Project 44.9 The reaction of propylene with aromatic hydrocarbons was in most of the experiments accompanied by dimerization of propylene to form 2 methyl-x-pentene. The organosodium compounds required for the above reactions were generated in situ by using as chain initiator precursors anthracene,5 o-chlorotoluene5 and d i m e t h y l m e r ~ u r y . ~ -No l ~ particular attempt was made in any of these or the following reactions to determine optimum reaction conditions. Isobutylene and Aromatic Hydrocarbons.-The reaction of toluene with isobutylene proceeded (9) Catalogue of Inirared Spectra, American Petroleum Institute Project 44. (IO) H. Gilman and H. A. Pacevitz, THWJ O U R N A L , 6 2 , 1;;s (1940).
8
27(0.64) Diphenylmethane lOg(0.64) o-Chlorotoluene 5.6(0.04) 3 . 0 ( 0 . 13) 250 270 42
7
1,l-Diphenyl-2methylpropane GB(0.314) 51 6.3
sluggishly. The temperature necessary to assure a reaction was considerably higher than in the experiments in which propylene was used. The pentylbenzenes obtained from the reaction consisted of neopentylbenzene and of 3-methylbutylbenzene, the latter resulting from a thermal, free radical, reaction. The presence of 2-benzylbutane (2-methylbutylbenzene) in the reaction product resulted from the catalytic reaction of toluene with n-butylene present as a contaminant in isobutylene. The carbanion reactions are not specific to sodium, and lithium and potassium1' gave similar results. The use of sodium hydride as a chain initiator also was demonstrated. The results are summarized in Table 111. I n the reaction products of isopropylbenzene (11) L. Schaap, unpublished results from this Laboratory.
4318
HERMAN PINES 4 N D
Vol. 78
I'ICTOR AI.%RK
TABLE 111 REACTIOS01; TOLUESE WITH ISOBUTYLESE Experiment
Isobutylene," g. (moles) Toluene, g. (moles) Chain initiator precursor, g. (mole) Alkali metal g. (atom) Temp. of pressure drop, "C. Highest temp., "C. Highest pressure, atm. Duration, hours
9
10
11
12
56( 1 . 0 )
56(1.0) 45(0.8) 9 2 ( l .0 ) 6910.75) +o-Chlorotoluene+8.0(0.063)+ Sodium Lithium 4. s ( 0 . 2 ) 1.4(0.2) 323 380 348 386 207 104 14.5 27
89(1 58) 135(1 47) Noiie
92(i.o) S aH 2.q0.1)
...
Sone
... 320 334 222 14
332 354 210 24
2 2(0 015) Traces o q n 003) 1 ,5
0 18.2(0.123)
Product obtained, g. (moles) I\-eopentylbenzene 9 4(0 063) 3-Methylbutylbenzene Present 2-Benzylbutane 2 o(n 0135) Bottoms and/or holdup 13 2 Composition: 99sc isobutylene, 17 butenes.
2 7(0 018) 0 I ( 0 043) Present
0
25
TABLE Il' REACTIOX OF AROMATIC HYDROCARBONS WITH ISOBUTYLENE Experiment
13
14
15
Isobutylene, g. (mole) 20 q 0 . 3 7 ) 47(0 8 5 ) 50(0 89) Aromatic hydrocarbon +Isopropylbenzene+ Diphenylmethane g . (mole) ino(o 59) 103(0 86) 120(1 0 ) Chain initiator precursor o-Chlorotoluerie o-Chloroisopropylbenzene g. (mole) 5 B(0 04) s 2(0 0 5 ) 8 2(0 05) Alkali metal Sodium Potassium Sodium g. (atom) 3.0(0.13) 4 6(0 2 ) 3 . 9 ( 0 1) Temp. of pressure drop, "C. 280 Highest temp., "C. 293 292 317 Highest pressure, atm. 182 in3 110 Duration, hours 16 26 10 Product, g. 4 9"*b 2 5c 9.gd Bottoms and/or holdup, g. 10 4 3 2 6 0 a Corresponds t o a fraction of the boiling range between 192 and 231'; 2-phenyl-2,4-dimethylpentane was present in the fraction. * -4 lower boiling product was also obtained from which 3 g. (0 027 mole) of 2,4,4-trimethyl-x-pentene was isolated Corresponds to a fraction boiling between 211 and 219'; it contained 2-phenyl-2,4-dimethylpentane. Corresponds t o a fraction boiling between 270 and 294'; l,l-diphenyl-3-methylbutane was identified in this fraction
and diphenylmethane with isobutylene the presence of only the thermal adducts was detectable, Table IV. Toluene with I-Butene and I-0ctene.-The presence of 2-benzylbutane in the reaction product from toluene with isobutylene was attributed to n-butylenes present as impurities in isobutylene used. In order to confirm the validity of such an assumption an experiment was made in which 1butene and toluene were used as reactants. 2Benzylbutane was the only pentylbenzene formed (Table V). The reaction of 1-octene with toluene in the presence of sodium and anthracene as chain precursor yielded 2-benzyloctane as the adduct. The recovered octenes consisted predominantly of transoctenes, which shows that migration of the double bond took place. Toluene and Cyc1ohexene.-A reaction between these two hydrocarbons (one mole of each) was attempted under experimental conditions used for expt. 9. Only one gram of a product boiling between 21s and 252' was obtained. Infrared spectral analysis indicated the presence of only a small amount of benzylcyclohexane, contaminated
TABLE V REACTIOSOF T ~ L U E SVITH E BUTENE Experiment
Olefin g. (moles) Toluene, g. (mole) Anthracene, g. (mole) Sodium, g. (mole) Temp. of pres. drop, "C. Highest temp., " C . Highest pressure, atm. Duration, hours Product, g. (mole)
16
ASD
1-OCTENE 17
I-Butene 62(1.1) 92( 1. O )
I-Octene 39.5(0.35) 92(1. 0 ) 0.q n . 005) 0 . 9 ( 0 . 0 0 5 ) 5 . 0 ( 0 . 2 1 5 ) 4.0(0.1;1) 290 299 289 173 22 23 50 b
i q o . o g 5 ) 5 . i(0.02~5) Bottoms and/or holdup, g. 6.8 3.0 The presence of low boiling hydroa 2-Benzylbutane. carbons was not investigated. * 2-Benzyloctane. Recovered olefins were composed predominantly of transoctenes.
with an unsaturated hydrocarbon. Experiments along this line were therefore not pursued. Benzene and t-Butylbenzene with Olefins.-The reaction of benzene with ethylene and isobutylene and of t-butylbenzene with ethylene was investi-
Sept. 5 , 1956
CARBANIONS IN REACTION OF AROMATICHYDROCARBONS WITH MONOOLEFINS 4319 TABLE VI REACTIOSOF BESZEXEA'ND t-BUTYLBENZENE WITH OLEFINS 18
Experiment
Olefin g. (mole) Aromatic hydrocarbons g. (moles) Chain initiator precursor g. (mole) Sodium, g. (atoms) Temp. of pressure drop, " C . Highest temp., " C . Highest pressure, a t m . Duration, hours Product, g. (mole) Bottoms and/or holdup, g.
20
21
Isobutylene 56( 1.0) -+
Ethylene
19
+
Ethylene-
+-
14(0,5)
14(0.5)
14(0.5)
+
Benzene
110( 1.41) Bromobenzene
Anthracene
t -
15(0.095)
0.9(0.005)
4
7.0(0.06)
4.6(0,2)
5.0(0.215)
