ALKYLATION OF BENZENE WITH l=HEXENE USING ALUMINUM CHLORIDEN ITROALKAN E CATALYSTS H . S. N. S E T T Y ' A N D
H. W . P R E N G L E , J R .
Chemical Engineering Department, 1;lzrerszt~of Houston. Houston. Tex
A rate and mechanism study of the alkylation of benzene with 1 -hexene in homogeneous liquid phase using aluminum chloride-nitroalkane, AIC13 :NOzR, catalyst complexes is presented. Data were obtained at 85" F. and atmospheric pressure, catalyst mole fractions of 2.5 to 25 X and benzene-hexene ratio of 10. The fact that the catalyst complexes possessed no isomerization activity was established. Four catalyst complexes-AIC13: NOzCHs, AIC13: N O Z C ~ HAIC13: ~ , N02CSHi-1, and AIC13: NO~C3H7-2-were used and their activities as alkylation catalysts compared. A consecutive simultaneous mechanism is used; the rate equation was not formally integrable. The rate constants were evaluated on the basis of a method of composite kinetic parameters. The experimental evidence and the rate constants consistently indicated that the alkylation of benzene proceeds by a nucleophilic substitution mechanism.
variety of hydrocarbon reactions-alkylation, isomerization, polymerization, etc.-which are catalyzed by acid-type catalysts have been explained as occurring by way of carbonium ions as follows:
A
WIDE
ilddition of a carbonium ion to an unsaturated molecule via a pair of pi electrons to yield a carbonium ion of higher molecular weight. Decomposition of carbonium ion to another ion-e.g., a smaller carbonium ion or a proton-and an unsaturated compound. Isomerization of a carbonium ion via migration of hydrogen, alkyl, or aryl, together with a pair of electrons. T h e final carbonium ion is converted to the reaction product by elimination of a proton o r other cation o r by abstraction of a hydride ion or other anion from another molecule. T h e same theory is generally accepted for the Friedel-Crafts reaction primarily because the reaction is enhanced by strong electrophilic catalysts a n d easily ionized alkyl halides. Rearrangements characteristic of carbonium ions are common during alkylation, and require the presence of promoters like HC1 or H 2 0 . This ionization mechanism, however! does not permit a prediction as to which of the possible products will be major and which minor o r completely absent. nor does it adequately explain differences obtained with different catalysts. Also: the definite dependence of the alkylation rate constant on the structure of the aromatic cannot be explained on the ionization mechanism alone. At present, a number of other considerations have led to the hypothesis that the alkylation of benzene, particularly in the presence of aluminum chloride, occurs not only by a n electrophilic mechanism but also by a nucleophilic displacement mechanism. .4ttempts to obtain kinetic and stereochemical evidence as to the participation of the nucleophilic displacement mechanism have so far been unsuccessful because the
Present address, Red Barn Chemicals. Inc., Shreveport. La 300
IBEC FUNDAMENTALS
investigations either involved a heterogeneous system or used unsatisfactory analytical methols. This paper deals bvith the studies of alkylation of benzene with I-hexene using A1C13:N O l R catalysts described by Schmerling (5), and seeks some insight into the reaction mechanism. Experimental
Materials. Phillips Petroleum Co. technical grade (95 mole % purity) 1-hexene and reagent grade 2-hexene and J. T. Baker Chemical Co. reagent grade benzene (99.957, purity) were used. Fisher Scientific Co. anhydrous grade aluminum chloride and reagent grade nitromethane bvere used without further purification. Sitroethane. 1-nitropropane, and 2-nitropropane (hlatheson Coleman 8r Bell Co.) were purified as directed by Bell and Higginson ( I ) . Very pure (99.0%) 1-: 2-: and 3-phenylhexanes \vere supplied by the Continental Oil Co. for use as chromatographic standards. Eastman Organic Chemical Co. m-bis(m-phenoxyphenoxy)benzene was used. 2,2 '-Oxydipropionitrile and dimethylsulfolane were obtained from the \V. H. Curtin Co. Runs. T h e alkylation experiments (Table I ) xvere conducted in a stainless steel reactor of 2000-ml. capacity. equipped with thermowell. cooling coil, motor-driven stirrer. inlet and outlet valves: and a sample probe. T h e reactor was charged with benzene and hexene! cooled to reaction temperature, and kept stirred. '4 small floiv of dry nitrogen gas was maintained through the reactor to prevent moisture from entering. T h e catalyst was introduced through the sample probe by means of a hypodermic syringe. Samples were Lvithdrawn at definite intervals, and products were isolated from the reaction mixture by washing with Lvater and aqueous sodium h>.droxide. and dried over Drierite. T h e isomerization runs were conducted in serum bottles immersed in a constant temperature bath. T h e results of the special isomerization runs are presented in Table 11.
Analytical. T h e gas liquid chromatographic analytical procedure used for hexene isomers is the one developed by Knight ( 3 ) . Tw.0 columns. 2:2 '-oxydipropionitrile and dimethylsulfolane. were used. T h e experimental conditions were : 40Cc 2,2 '-0x1-dipropionitrile (207, in case of dimethyl-
Table I.
Summary of Data"
Alkylation of benzene with 1 -hexene a t 8.5' F. (Benzene/olefin ratio of 10 : 20)
Catalyst M o l e Fraction
Time, 'Win.
Total Fractional Conversion
3 4 1
0.00026 0 00041 0 00070 0 00096 0 00100 0 00102 0.00140 o on174 0 00204 0 00253
117.95 115.00 32.85 61.20 66.45 75.00 36.83 39.25 27 83 24.58
0.7248 0,8271 0.5566 0.8722 0.9061 0.9487 n. 8404 . . 0 9114 0 8317 0 8354
11 13 18 17 12 19 14
0.00073 0.00085 0.00087 0 00110 0 00127 0 00213 0 00244
64.67 75.50 141.13 116.88 63.83 45.82 28.37
0.5755 0.6820 0.9007 0.9170 0.7786 0 8150 0.6505
22 20 23 21 25 24
0 0 0 0 0 0
00083 00099 00117 00123 00144 00180
250.17 163.15 226.53 165.38 139.32 197.72
0.7132 0.5997 0.8051 0.6931 0.67'79 0.9030
26 27 28 29 30 31
0 0 0 0 0 0
00087 00121 00168 00214 00245 00257
229.12 274.28 198.20 234.75 236.67 125.90
0.4677 0.6874 0.6785 0.8114 0.8694 0.6413
Catalyst
Run
AlC13:S 0 2 C H 3
7 10 6 8b 5 9 2
4
R,(')
Res(')
111
a23
112
113
507 503 506 429 510 468 522 405 465 478
152 125 105 121 87 137 56 144 46 47
495 495 504 474 48 1 467 466 41 5 465 476
103 97 94 97 93 109 76 97 81 39
75 71 69 71 68 80 56 71 59 28
28 26 25 26 25 29 21 26 22 10
49 7
97
96 91 94 96 86 91 34
71 66 69 70 63 67 25
26 24 25 26 23 25 9
222
104
226 225 216 223 249 222 232
102 96 55 53 41
226 222 21 3 223 226 221 224
70 65 67 66 66 74
94 93 149 68 77 85
70 65 67 65 65 70
94 93 113 93 95 93
69 68 82 68 70 68
25 25 30 25 26 25
65.8
100
35 38 37 37 38 36
120 124
35 38 37 36 37 36
97 99 115 96 100 90
71 73 84 70 73 66
26 27 31 26 27 24
35.8
105
79
93
55 100 39
For product distribution data ( 6 , 7 ) .
96.8
Alkylation w i t h 2-hexene.
sulfolane) on C-22 firebrick; 50-foot '/(-inch copper tubing;
Proposed Mechanism
25' C . ; helium flow. 30 cc. per minute a t 10-p.s.i. inlet pressure. 'The aromatics and the phenylalkanes were analyzed on a 10-foot column ("a-inch copper tubing) filled with 15% rn-bis(rn-phenoxvphenoxy)benzene deposited on C-22 firebrick. T h e experimental conditions ivere: 174' C . ; helium flow. 80 cc. per minute a t 30-p.s.i. inlet pressure. Further details of analysis are given elsewhere ( 6 ) .
Experimental evidenceStability of the phenylhexanes (Table 11) in presence of the aluminum chloride-nitroalkane catalyst complexes in benzene solution under the alky-lation conditions Absence of olefin isomers in the reaction aliquots and the VOL.
3
NO. 4
NOVEMBER
1964
301
Table II. Experiment Isomerization under alkylation conditions 1. 1-Phenylhexane
Results of Mechanistic Investigation Catalyst
Remarks
1-Phenylhexane recoxred
unchanged 2.
2-Phenylhexane
3.
3-Phenylhexane No isomerization detected
4. 1-Hexene 5.
2-Hexene
6.
Alkylation of benzene with 2-hexene under alkylation conditions (Runs 8 and 31)
AlCl3: h'02CH3 .AlClj: NOpC3H;-2
Same mixtures of 2- and 3-phenylhexanes obtained
high ratio of 2-phenylhexane to 3-phenylhexane. indicating that the alkvlatioa is favored over isomerization T h e same product mixture, obtained irrespective of the nature of the olefin Complete absence of any abnormal products, indicating no side reaction led us to propose a consecutive simultaneous mechanism as follows
+ S O z R 2 AlC13:N02R CH3-CHg-CHz-CHp-CH=CHz + AlC13 :NOzR t A1C13
4CH3-CH2-CH2-CHz-CH-CH 666 f
66
6 4-
(1) ki -1
9
i (-1 AlC13: NOzR 686
+
66 f
6
+
CH3-CH2-CHz-CHz-CH-CHe
i (-1
+ C gH
(2)
+
(3)
e 3-phenylhexane + AlC13:NO*R k-a
(4)
ka
I' =
a'sx + C-l?CC?
Equation 10 is handled in a manner similar to that proposed by Lineweaver and Burke ( 4 ) and Dalziel (2). A plot of the composite kinetic parameters. I' us. X . has been presented (7). and was found to be a straight line \\ith a small intercept incicating that the rate constants, kL1, k-?. and LJ, are small. T h e intercept. C-12CCY@lr was evaluated and a first approximation of klyA-ycs obtained: r " 1
are negligible. the following
+
also, a first approximation of
which can be written symbolically:
ke3yA*~B can
(9
C+S&S
(10)
@I
where the definitions of the terms are obvious by comparison iiith Equation 9. and
As E + 1: and since LY and equation can be derived :
:NOlR
2-phenylhexane k-z
or
6
AlC13: NOZR k2
~ J isomerization o detected
[*&%(E*
be obtained :
- E)dt
ki
A A*
+ CS=
k -I
+B
k3
2
k-a
A*
(6)
k2
+ CS De + CS Di
(7)
T h e reverse rate constants are included a t this point. because it is desired to ascertain their magnitude by the mathematical trea tinen t. Analysis of Data
For the mechanism proposed the rate equations can be written, and follow a procedure presented b) Setty, Barona, and Prengle (7). A material balance and definition of pertinent terms are given in Table I1 (7). As t + m , f * 1, t* * f , the appropriate differential equation becomes
302
I&EC
FUNDAMENTALS
T h e final values. equation
kt and
kY3,
are obtained by curve-fitting the
starting with the first approximate values. k1c1) and k23(l', obtained above. Finally. constants k 2 and 6 3 are obtained.
63
= kY3
k?
=
(1 -
kY3
-
;:)
k3
(17)
T h e values of k l anti R e 3 as Xes,> + 0. kl(O' and k23'O' are obtained by plotting k l and k?3 1's. X,,, and extrapolating to X c s o = 0 as shown in Figure 1. The values of k P . k ~ 3 ( " , k:. k ~ 3 62. , 63. k l ( O ' >and k 2 3 ( 0 'are summarized in Table I. T h e intermediate complex, A * , can be calculated [as outlined in ( 7 ) ] using the value of ???E. and a typical profile is presented in Figure 2.
I
6001
LEAST
SQUARES
kl 400
m
I50
5
15
IO
XCSO" Figure 1.
20
25
104
Rate constants for AIC13: N02CHa catalyzed
O u r alkylation results are in good agreement \vith this theory. .\lC13: NO?C4HYcatalyst ~vould be expected t o be completely unsuitable as a n alkylation catalyst. A1CI3:NO.C:H3 is highly acidic: and AIC13: NO2C3H;-2 is least acidic. If the combination of aluminurti chloride and nitroalkane is capable of producing free protons. a free carbonium ion is possible in reaction step 2. If this is true, reaction step 2 should be rate-controlling. but the alkylation NO,(:H, and .41Cl3:NO?C?Hjcatalysts show ntrolling reaction is 3 and 4 afid riot 2. indicating that carbonium ions are impossible with these catalysts. LVhen carbonium ions are not possible in strongly acidic combinations like ;\IC O?CH:, and .I\ICia:SO$~Hj. their and .\lC;la : existence in combinations like .\IC13 : NO.C:~E~I;-~ SOrC3H;-2 is very remote: but in these latter tivo catalysts reaction 2 is rate-controlling. Also, the alkylation proceeds ivirhout being promoted by- {cater. Conclusions
'l'he olefin-catalyst complex, according to inductive effect theory, consists of three electrophilic carbon atoms susceptible to nucleophilic attack ( S S ? ' ) by the benzene molecule? producing 2- and 3-phenylhexanes.
t 15 U
and "A
IO
- - 00 0 2
0 5
- - 0001
A*
00 0
20
80 100 TIME IN MINS.
40
120
60
+ S 0 . R 4A1C13:N02R CH3CH?-CH?-CH2-CH=C€~~ + hlC:l,: N02R k
.\1C13
666
+
L
Joooo
(-1
AICls: NOzR
140
Product distribution
---f
+
6
C€13CH?-CH?-CH?-CH-CH?
H
Figure 2.
66
T
(22) kl
a
(23)
p
8 + Hx CH3CH2-CH2-CH2-CH-CH2
SS8+
SS+
I
Discussion
(-)
AIC13: N 0 2 R
I'he primary and secondary nitroalkanes with a-hydrogen atom are knowm to act as pseudoacids a n d catalyze condensation reactions of the aldol type :
H
H
H
H
1
1
1
+ H---C--N02
C,H5-!=0
Q
CH3(CH2)3-CH-CH3
+ AICI3:
NO2R
2-Phenylhexane
(244
1 --f
C2H5-C-C-N02
1
I
H
OH
(18)
1
H
H
aH
p
*
a m + %a+ a h , C H 3 C H 2 - CH2-CH2-CH--
CH2
Sitroalkanes also catalyze the dehydration of acetaldehyde hvdrate :
J,
(-1
AIC13: NO2 R
+
CH&H(OH)2
+ HB S CH3CHOH(OH2) + B-* C H 3 C H 0 + H 2 0 + HB
(19)
Rate-controlling
3-Phenylhexane
T h e tertiary nitroalkanes. which lack a-hydrogen. d o not show any acidic properrirs. According to the BrGnsted concept of acids and bases, nitromethane. nitroethane, 1-nitropropane. and 2-nitropropane with 3: 2, 2, and 1 detachable protons, respectively, should fall into the following order of acidity: SOaCH3
>
NOgCaHj
>
~ 0 2 c 3 H j - l > NOnC3H;-2
(20)
Since aluminum chloride is a Lewis acid, it merely brings out the acidity of these nitroalkanes ; hence, the nitroalkane-based aluminum chloride catalysts should possess the following order of acidity: .41C13: S 0 2 C H 3
> 41CIs :NOZC?H, > A11C13:SOICFHj-1 > .MCls NOrC 3H;-2
+ AICl+
CH3(CH2),-CH-CH2-CH3
NOBR
(24b)
T h e fact that 2-hexene leads to the same product mixture can be explained as follo\vs : .
+ AICl3 : N 0 2 R
CH~-CH~-CH~-CHTCH-CH~
/@7
Fast -+
CHS-CH~-CH~-CH-CH-C-H
IA
AlC13:&02R( -) Fast
-+CH
666t
a-CH
2-CH
66+
6+
z-CH2-CH-CH2
1
(2 1)
(-1
AIC13: NOaR VOL. 3
NO. 4
NOVEMBER 1 9 6 4
303
E
Consequently the 2-hexene reacts in the same way as in step 23. T h e formation of olefin-catalyst complex in a rate-controlling step does not necessarily imply carbonium ions. Benzene is a strong nucleophile (as inclicated by the constancy of k?3 values. irrespective of the nature of the catalyst complex).
total fractional conversion of olefin fractional conversion of olefin to 2-phenylhexane $ 2 = fractional conversion of olefin to 3-phenylhexane E* = total fractional conversion of olefin to complex 6 = time derivative of
Nomenclature
literature Cited (1) Bell, R. P.: Higginson, \C. C. E., Proc. Roy. Soc. A197, 141
A , A * , B , C? CS, D1: D2,S
=
reactant and product species
ai = activity of species i k l , k.: k3: k-,, k p l : kp3 = specific reaction rate constants k23 = (kr k3) nA, = initial number of moles of olefin n, = total number of moles in reactor at any time t V = volume of reaction mixture Xes,, = initial mole fraction of catalyst
+
GREEKSYMBOLS LY = initial benzene-olefin ratio yt = activity coefficient of 1' = initial catalyst-olefin ratio
E1
= =
SUPERSCRIPTS ( l ) , (0) = first approximation, and extrapolated value to xcs = 0
(1949). (2) Dalziel, K., Acta Chem. Scand. 11, h-0. l o ? 1706 (1957). (3) Knight, E. S.. Anal. Chem. 30, 9 (1958). (4) LineweaLer, H.: Burke: D.. J . ,4m. Chem. Soc. 56, 658 (1934). (5) Schmerling. L.. Znd. Eng. Chcm. 40, 207Z (3948). (6) Setty, H. S. S . , "Kinetics of Homogeneous Liquid Phase Reactions. Alkylation of Benzene w i t h Hexene-l Using AICI,: N 0 2 R Catalvsts." Ph.D. dissertation, University of Houston, Houston, Tex., 19\13. (7) Setty, H . S. N.: Barona! N., Prengle, H. IC.,Jr., IND. ENG. CHEM.FUXDAMESTALS 3, 294 (1964). RECEIVED for review August 23, 1963 ACCEPTED August 28: 1964
ION EXCHANGE RESIN CATALYSIS OF SUCROSE INVERSION IN FIXED BEDS ELDON W .
R E E D ' A N D JOSHUA S. DRANOFF?
Department of Chemical Enpneering. Columb~a C;izLerst/), .Vezt l h r k , .V. 1'
The kinetics of continuous sucrose inversion catalyzed by fixed beds of acid form ion exchange resin was studied. A reactor 1 inch in diameter was used and solution flow rate and catalyst particle size were varied to cover a modified Reynolds number range of 0.014 to 4.8. Reaction terr.perature was varied from 50" to 75" C. The reaction was clearly first-order over this range and showed an activation energy of 15,950 cal. per gram mole. The data indicate that the observed rate of reaction is strongly influenced by diffusion within the resin particles and that external (film) mass transfer is not significant for the range of conditions explored.
HE inversion of sucrose in acid solutions has been well Tstudied in the past. I n fact. the measurement of the rate of this reaction in 1859 by \Vilhelmy ( 7 7 ) was the first kinetic study reported in the chemical literature. T h e heterogeneous catalysis of this reaction by suitable acid catalysts has also been investigated, especially since the advent of statle synthetic ion exchange resins. T h e latter are particularly convenient for such reactions because of the ease of separating catalyst from reaction products without chemical purification steps. With but one recent exception, however, previous stu' ies of ion exchange-catalyzed sucrose inversion in aqueous solutions have been carried out using batch-stirred reactors. T h e most complete work of this type was reported by Bodamer and Kunin ( 7 ) , who found that the reaction remained apparently first-order, as in the homogeneous catalyzed case. that the rate was strongly influenced by pore ciffusion. and that the reaction had a n activation energy of from 18:300 to 25:000 cal. per
1
2
304
Present address, Mobil Oil Co., Paulsboro, N.J . Present address. North\\eestern University, Evanston. I11 I&EC FUNDAMENTALS
gram mole, depending on the resins used as catalyst. Bodamer and Kunin also measured the activation energy for the honiogeneous reaction and found it to range between 28.000 and 30>000cal. per gram mole. Later studies of the reaction have been reported by Hsieh and Su (5). Govindon and Bofna ( 2 ) , and Taufel and Grunert (70). T h e latter showed that the effects of separate homogeneous and heterogeneous catalysii could be linearly combined to describe the behavior of a reactor in which both acted simultaneously. They also reported activation energies in the same general range reported earlier by Bodamer and Kunin. The only paper dealing Lvith fixed bed catalpis of this reaction was published recently by Saito et ai. (9). They reported the kinetics of several liquid phase reactions catalyzed by ion exchange resins (Dowex i o ) . I n particular. their data for sucrose inversion sho\v deviation from first-order kinetics with increasing ?pace velocities. This suggests an effect of external diffuiion or mass transfer on the observed reaction rates which Lvould make scale-up from stirred reactor data difficult. .4s a result of these data it was decided to carrv out further
