March 20, 1964 [CONTRIBUTIOK No. 85
1065
ISOPROPYLATION AND 1-BUTYLATION OF HALOBENZENES FROM THE
EXPLORATORY RESEARCHLABORATORY, Dow CHEMICAL OF CANADA, LTD.,SARNIA,ONTARIO,CAN.]
Aromatic Substitution. XIX.' Friedel-Crafts Isopropylation and &Butylation of Halobenzenes BY GEORGEA. OLAH,SYLVIA H. FLOOD, A N D MARYANNE E. MOFFATT RECEIVEDSEPTEMBER 28, 1962 T h e isopropylation and t-butylation of halobenzenes with alkyl halides and olefins were studied under the conditions previously described for benzene and the methylbenzenes. Relative reactivities compared with benzene and isomer distributions were determined in competitive experiments using gas chromatography.
Jntroduction In previous papers of this series',* the Friedel-Crafts isopropylation and t-butylation of benzene and methylbenzenes were investigated with alkyl bromides and olefins. This work has now been extended to the k o propylation and t-butylation of halobenzenes. Results and Discussion Competitive X1C13~CH3NO2, FeCl3CH3?rT02, and SnC14 catalyzed isopropylation and t-butylation of benzene and halobenzenes with isopropyl bromide, t-butyl bromide, propylene, and isobutylene were carried out in nitromethane solution a t 25'. Product compositions were analyzed by gas-liquid chromatography using Golay type capillary columns. Under the experimental conditions employed, identical with those used in previous work in connection with alkylation of benzene and methylbenzenes, no di- or higher alkylation of halobenzenes was observed. Using as catalyst in competitive experiments with benzene sometimes substantial amounts (up to 25% of monoalkylate) of di-t-butylbenzene was formed, probably a t least partly by disproportionation of t-butylbenzene. Relative rate data therefore have to be corrected, taking into account the amount of dialkylation of benzene. Using stannic chloride as catalyst the amount of dialkylation is small enough (generally less than 3%) to be neglected. From the areas of individual peaks in the gas chromatograms mole 76figures were calculated for each product after first determining the individual response data. The observed reactivities of the halobenzenes relative to that of benzene, together with the isomer distributions of the monoalkylated products, are summarized in Tables I-VI. (All data reported represent, as in previous work, the average of a t least three parallel experiments.) TABLE I .lIC13.CH3IiO2 C A T A L Y Z E D I S O P R O P Y L A T I O N O F BENZENEA X D HALOBESZEXES R'VITH I S O P R O P Y L BROMIDE I N NITROMETHANE SOLUTIOK AT 25" -Isomer distribuiion, 70---
TABLE I11 ;\IC13.CH3S02CATALYZED ISOPROPVLATION OF BESZENEASD HALOBEKZEXES XYITH PROPYLENE IS SITROMETHASE SOLUTIOS AT 25' Aromatic
Benzene FiuoroChloroBromo-
kAr Ykbenzene
1.00 0.23 ,11
-Isomer ortho
41.3 53.9 55.4
.07
distribution, 5 7mela para
2 1 5 1 8.6
56.4 41.0 36.0
TABLE IV A1CI8.CH3n'O2CATALYZED ~-BUTYLATIOK OF BENZENE ASD HALOBENZENES WITH &BUTYLBROMIDE IX XITROMETHANE AT 25' Aromatic
k A r : kbenzene
Benzene FluoroChloroBromo-
0.16 .03 .02
-Isomer ortho
distribution, 57--meta pava
1.00 3.6
0.1 5.5 3.0
96 3 94.5 97.0
TABLE V SnCla CATALYZED t-BUTYLATIOS O F BENZENE A N D HALOBESZENES WITH t-BUTYL BROMIDE I N XITROMETHANE AT 25" Aromatic
Benzene FluoroChloroBromo-
kAr:kbenzene
-Isomer orlho
distribution, 7cmeta para
1.0
0 12
3.6
07 .02
I
0.1
96 3
5.0
95.0 100.0
TABLE T'I AICI3.CH3XO2CATALYZED I-BUTYLATIOS OF BESZEXEASD HALOBENZENES W I T H ISOBUTYLENE I K Aromatic
kAr : kbennene
Benzene FluoroChloroBromo-
1 00 0 19 06 03
--Isomer orlho
1 8
S I T R O M E T H A S E AT
25"
distribution meta
%--
0 1 5 5
98.1 94 5 100 0
para
The accuracy of the gas-liquid chromatographic method was found to be better than + 5 relative per Benzene 1.00 cent, based on analyses of mixtures of known composi0 23 41.8 Fluoro1 9 56.3 tions. Investigation of the concentration variation of 49.8 Chloro10 7.9 42 3 benzene and halobenzenes in competitive experiments, 51.4 Bromo.08 11.3 37.3 as described in previous work, showed that the relative ratios remained practically unchanged, if first-order TABLE I1 dependence on the aromatic substrates is accepted. FeCI3.CH3h'02 CATALYZED ISOPROPYLATIOS OF BENZENEAND Thus the method of competitive rate determination HALOBENZENES WITH ISOPROPYL BROMIDE IN SITROMETHANE can be applied to the present systems. SOLUTION AT 25' I t is not possible to state with certainty whether the -Isomer distribution, 70observed isomer distributions (and relative rates) were Aromatic k.kr: k b e n e e n e ortho mefa para obtained under entirely nonisomerizing conditions, Benzene 1.00 from the present experimental results. The amount of 40.8 Fluoro0.28 2.8 56.4 m-isomers is higher than the benzylation3 or nitration4 Chloro13 51.4 8.1 40.5 of halobenzenes. I t is, however, suggested, on the Bromo11 51.8 11.6 36.6 basis of our experimental data, that even if isomerization cannot entirely be excluded, it cannot be signifiAromatic
k.kr: kbenzene
o r h
meta
para
J . A m . Chem. S O ~ 86, . , I060 (1964). (2) G. A. Olah, S.H. Flood, S.J . * K u h n , M. E. Moffatt, and N. A. Overvhuck, part X V I , ibid.,86, 1 0 4 F (1964). (1) P a r t X V I I I .
(3) G. A. Olah, S. J. K u h n , and S. H. Flood, ibid., 84, 1695 (1962) ( 4 ) G. A. Olah. S. J. K u h n , and S. H. Flood, ibid..83, 1831 (1961)
GEORGE A.
1 OMj
O L A H , SYLVIA
H. FLOOD, AND
LfARYANNE
E.
~~OFFATT
Vol. 8lj
cant. A1Cl3,CH3N02 was replaced in a number of experiments with milder catalysts as FeCI3 or SnC14, without effecting any significant changes in the isomer distributions. As example, Tables I1 and V show relative reactivities and isomer distributions obtained in competitive isopropylation of benzene and halobenzenes replacing .k1C13 with FeC13,, and t-butylations using SnC14 as catalyst, but keeplng reaction conditions otherwise identical, in nitromethane solution. comparison of these results with those using AlCl3. C H 3 N 0 2 as catalyst indicate very little difference, suggesting strongly t h a t AlC13 CH3h'02probably does not cause significant isomerization. The only cases in which isomerization seems to have affected the isomer distributions is that of the bromocumenes (bromo-tbutylbenzenes) and to a lesser degree, the chlorocumenes. The relatively large amount of m-isomer formed in the AlC13and FeC13catalyzed isopropylations of bromobenzene with isopropyl bromide (11.3 and l l . S % , respectively) and in similar reactions of chlorobenzene (7.9 and 8.1yo)are probably due to partial isomerization, as the related isopropylations with propylene show decreased amounts of m-isomers (5.1 and 8.6%). The aluminum chloride catalyzed isomerization of halocumenes and halo-t-butylbenzenes results in equilibrium mixtures containing the m-isomer in excess of A comparison of the relative reactivities of benzene and halobenzenes in isopropylation and t-butylation shows that t-butylation produces higher substrate selectivity than isopropylation, both giving, however, preferential ortho-para directions (high positional selectivity), as is the case with isopropylation and tbutylation of methylbenzenes. The observed relative reactivities of halobenzenes in the case of isopropylations show good agreement with relative stabilities of complexes of halobenzenes with a-acids and also with previously established reactivities in nitration with N02+BF4-" and benzylations with benzyl ~ h l o r i d e . ~Less correlation is observed in the case of t-butylations.
m-Fluoro-t-butylbenzene was prepared from m-t-bu tylaniline (obtained through reduction of m-nitro-t-butylbenzctle~~ by t h e Schiemann reaction, b . p . 170-172'. .Anal. Calcd. for C l f , ~ I , : j F : C, 78.95; H , 8 . 5 5 ; F, 12.5. F o u n d : C , 79.18; H , 8.42; F, 12.4. p-Fluoro-t-butylbenzene was prepared from p-t-butylalliline according t o t h e preparation of the m-isomer, b.p. 17;j-l75O. ilnel. Found for C I O H I ~ FC: , 78.91; H , 8.49; F,12.6. Competitive isopropylation a n d t-butylation of halobenzenes and benzene were carried o u t in t h e following way: .IIuminun1 chloride (ferric chloride, stannic chloride), 0.05 mole, was dissolved in 50 g. of nitromethane. To this solution was added 0 . 2 5 mole each of benzene a n d halobenzene. T h e stirred reactivii mixture, protected from atmospheric moisture, was then placed in a reaction flask (equipped with thermometer, reflux condenser, and dropping funnel or gas inlet t u b e ) in a constant temperature bath 125 =k 0.1') and a solution of 0.05 mole of alkyl bromide (isopropyl or t-butyl) dissolved in 30 g . of nitromethane was added dropwise. T h e addition generally was completed in 10 min. a n d t h e reaction mixture was thereafter stirred for another 10 min. I n t h e alkylation with olefins (propylene and isobutylene j 0.05 mole of the gaseous olefin was introduced into the stirred nitromethane solution of t h e substrates and catalyst a t the same temperature. A t t h e end of t h e reactions t h e mixtures were washed once with water, then three times with 5c; sodium hydroxide solution t o remove not only t h e by-product acid, b u t also nitromethane, followed by another water washing. T h e organic layer was separated, dried with calcium chloride, a n d analyzed by gas-liquid chromatography. As t h e separation of t-butylbenzene from o-t-butylfluorobenzene by gas-liquid c h r o n ~ a t o g raphy was not complete, t h e benzene :fluorobenzene reactivity ratio could not directly be determined from t-butylation of benzene and fluorobenzene. In this case competitive butylations of chlorobenzene and fluorobenzene, a s well as broniobenzene and fluorobenzene, were carried o u t a n d t h e fluorobenzene-benzene reactivity rate determined from these d a t a , taking in account t h e chlorobenzene-benzene reactivities, determined in direct cornpetitive butylations. Analyses.--All analyses of isopropylations a n d t-butylations were carried out by gas-liquid chromatograph). c>n a PerkinElmer Model 154-D vapor fractometer equipped with Golay type capillary column (150 f t . j coated with polypropylene glycol arid using a hydrogen flame ionization detector. Peak areas were obtained b y t h e use of a n electronic printing integrator. T h e geiierally used column conditions were: H e carrier gas pressure 40 p.s.i.g,., with characteristic retention times a n d temperatures given in Table 1-11,
Experimental
CHARACTERISTIC RETENTION TIMESO F HALOALKVLRESZESES ON C A P I L L A RCY o ~ r ~ x
T h e halobenzenes, alkyl halides, olefins, a s well a s t h e aluminum chloride, ferric chloride, a n d stannic chloride used were comniercially available chemicals of highest purity, purified if necessary by standard methods. T h e isomeric halocumenes a n d halo-t-butylbenzenes, all previousl?. reported with t h e exception of u- and nz-fluorocumene a n d m-fluoro-t-butylbenzene, were available in this laboratory, prepared by known methods. T h e y were purified a n d analyzed by gas-liquid chrornatography arid infrared spectroscopy. o-Fluorocumene was prepared from o-isopropylaniline (available tlirough reduction of u-nitrocumene") by t h e Schiemann reaction.' T h e intermediate o-isopropylphenyldiazonium tetrafluoriiborate LVBS obtained from t h e aniline with XO+BF4-, according t o Wannagat and Hohlstein.* o-FCsHdCH(CHa)* had b.p. 118-150' (distillation a t atmospheric pressure results in some decomposition and the cornpound is therefore better distilled under vacuum). .-1nei. Calcd. for C ~ H I I F :c , 78.30; H, 7.94; F, 13.76. Found C , 78.48; H , 8.02; F , 13.5. ni-Fluorocumene was prepared from m-isopropylaniline accordAnal. ing t o the preparation of the o-isomer, b.p. 151-152'. Fouiid for C Y H I I F C : , 78.45; H , 7.95; F, 13.6. -~
._____
G A . Olah a n d M W. hieyer, unpuhlished results, t o be reported elsewhere (til C7 A . Olah S J K u h n , and S . H Flood, J . Am. C h e m . Soc., 83, 4571 (1961). ( 7 ) .4 Roe, "Organic I
