Interconversion equilibria between tert-butylbenzenes and tert-butyltoluenes

Article abstract of DOI:10.1134/S0965544108030043

The equilibrium of six positional isomerization reactions in the systems of sterically unhindered tert-butylbenzenes (TBB) and tert-butyltoluenes (TBT) was experimentally studied in the liquid phase over a wide temperature range. The thermodynamic charact

Full text of DOI:10.1134/S0965544108030043

ISSN 0965-5441, Petroleum Chemistry, 2008, Vol. 48, No. 3, pp. 193–200. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © I.A. Nesterov, T.N. Nesterova, N.N. Vodenkova, P.V. Naumkin, N.M. Repkin, 2008, published in Neftekhimiya, 2008, Vol. 48, No. 3, pp. 194–201.
Interconversion Equilibria between tert-Butylbenzenes
and tert-Butyltoluenes
I. A. Nesterov, T. N. Nesterova, N. N. Vodenkova, P. V. Naumkin, and N. M. Repkin
Samara State Technical University, ul. Molodogvardeiskaya 244, Samara, 443100 Russia
e-mail: xiao3xiong@gmail.com
Received August 17, 2007
Abstract—The equilibrium of six positional isomerization reactions in the systems of sterically unhindered
tert-butylbenzenes (TBB) and tert-butyltoluenes (TBT) was experimentally studied in the liquid phase over a
wide temperature range. The thermodynamic characteristics of the reactions were obtained, their interpretation
was given, and the enthalpy of interaction of the (1-TB)–(3-TB) type between the substituents in alkylbenzene
molecules was determined on the basis of the experimental and literature data.
DOI: 10.1134/S0965544108030043
Alkylbenzenes (ABs) are the main feedstock for thermodynamics of the process is a factor that deter-
manufacturing a wide range of products of organic syn- mines the choice of alkylation conditions.
thesis. In this context, the attention given to the alkyla-
To develop general approaches to the prediction of
tion of aromatic compounds as a basic process for the
the chemical equilibrium in systems of this type, we
preparation of alkylbenzenes is quite understandable.
have performed a detailed analysis of the entire array of
The alkylation of aromatic compounds is one of few
the relevant data collected to date. Whenever needed, a
processes that proceed at chemical equilibrium. More-
target-oriented experiment is useful. The results of the
over, its running under the equilibrium conditions is
study of the equilibrium of the positional isomerization
optimal in many cases. For example, this concerns the
and transalkylation of tert-butylbenzenes (TBB) and
manufacturing of isopropylbenzene or ethylbenzene in
tert-butyltoluenes (TBT), which are of interest not only
the presence of a catalytic complex based on aluminum
from the practical point of view, but also as a successful
chloride [1]. At the same time, the process has consid-
theoretical model, are presented in this paper.
erable advantages that have not been realized in many
respects. For example, it is believed that the alkylation
of benzenes with higher linear alkenes will yield a mix-
ture of secondary alkylbenzenes and the alkylation with
branched alkenes will give tertiary ABs or a mixture of
secondary and tertiaryABs. However, catalytic systems
that can mediate the process against the Markovnikov
rule to yield primary alkylbenzenes with a high selec-
tivity have been found [2, 3]. The mechanism of those
mentioned is under debate. We suppose that not only
the operation of specific alkylation mechanisms, but
also the prevention of the isomerization of all types are
important for the accomplishment of such processes.
The reasons for the experimental fact of the substan-
tial prevalence of secondary ABs over their tertiary iso-
mers upon the alkylation of benzene and its derivatives
with branched alkylating agents in the presence of
Lewis acids also remain unclear [4–6].
Molecules of TBB and TBT may be regarded as bal-
anced symmetrical tops, whose centers of gravity occur
on their rotational axes. The tops possess a large
enough mass, so that the behavior inherent in TBB and
TBT can be attributed to related structures as well. The
substituents in TBB and TBT molecules are sufficiently
bulky to make it possible to substantially vary the
degree of hindrance of the aromatic ring by changing
their amount. This possibility is important for testing
the procedures for the prediction of the equilibrium of
AB transformations.
tert-Butyl substituents exhibit a sufficiently high
kinetic mobility in electrophilic substitution reactions,
a property that predetermines in many respects the reli-
ability of the obtained equilibrium data and the indus-
trial importance of such transformations. Despite the
fact that the basic quantitative information on the chem-
ical equilibrium in the systems under consideration
refers to the liquid phase, we consider in this work the
equilibrium of gas-phase reactions as well, taking into
account the growing interest in the issue [7–10].
From the above consideration, it is evident that the
potentialities of the alkylation are still far from being
revealed and they cannot be ascertained without a thor-
ough theoretical analysis of the process. In this paper,
we considered one of the aspects of such an analysis,
namely, chemical equilibrium in systems composed of
The equilibrium of the reactions presented below
sterically unhindered alkylbenzenes, for which the and in Table 1 are considered.
193

194
NESTEROV et al.
Table 1. Results of the study of the interconversion equilibrium between alkylbenzenes
T, K
Kx
n*
m
ts
pin/pfin
Kp
T, K
Kx
n*
m
ts
pin/pfin
Kp
1,4-Di-tert-butylbenzene
1,3-Di-tert-butylbenzene (1)
0.483
373
10.0e
41
18
6
4
1.8
1.3
2.12
2.01
4.7
1.1a
2.28
403 10.5e
5.2
298
273
293
333
373
279
303
1.11b,c 36
1.14b,c 36
1.25b,c 50
1.32b,c 28
1.02d
1.08d
3
3
5
3
3
1
0.01
0.03
0.03
0.05
0.01
0.02
0.455
0.477
0.531
0.590
0.461
0.490
2.44
2.40
2.35
2.24
2.22
2.20
423
353
373
403
423
8.6e
7.2f
7.2f
8.1f
9.9f
21
14
10
23
27
19
4
2
1
3
3
2
1.1
4.0
0.7
1.3
1.1
1.9
1.97
2.22
2.12
2.01
1.97
1.94
4.4
3.2
3.4
4.0
5.0
5.2
22
7
453 10.1f
tert-Butylbenzene + 1,3,5-tri-tert-butylbenzene
2 × 1,3-Di-tert-butylbenzene (3)
323
1.12d
25
4
0.01
0.517
2.16
343
363
308
338
343
358
373
403
423
353
373
403
423
1.14d
1.16d
1.06e
1.12e
1.10e
1.13e
1.17e
1.20e
1.22e
1.31f
1.25f
1.33f
1.36f
54
21
28
25
6
8
5
4
4
1
1
7
5
4
2
2
2
3
0.04
0.05
0.05
0.02
0.06
0.11
0.04
0.08
0.03
0.26
0.20
0.18
0.11
0.546
0.575
0.496
0.538
0.546
0.568
0.590
0.633
0.660
0.561
0.590
0.633
0.660
2.08
2.02
2.14
2.08
2.01
1.99
1.98
1.90
1.85
2.35
2.13
2.10
2.05
273
293
333
373
2.61b,c 36
2.94b,c 36
3.47b,c 50
3.48b,c 29
4-tert-Butyltoluene
1.778h
2
2
2
2
0.02
0.02
0.36
0.20
0.504
0.541
0.631
0.631
0.552
0.572
0.626
0.626
3-tert-Butyltoluene (4)
5
298
283
303
279
303
323
343
363
0.841
0.828
0.845
0.824
0.845
0.861
0.874
0.886
2.36
57
23
45
16
23
23
27
1.984g 29
1.964g 24
2.094d 20
3
3
3
1
4
8
5
0.04
0.03
0.02
0.01
0.04
0.18
0.21
2.40
2.32
2.54
2.38
2.33
2.62
2.69
2.011d
7
2.005d 25
2.290d 48
2.382d 40
Toluene + 3,5-di-tert-butyltoluene
3-tert-Butyltoluene (5)
453
1.34f
21
2
0.04
0.696
1.93
Benzene + 1,3-di-tert-butylbenzene
tert-Butylbenzene (2)
281
6.34d
31
6
0.53
2.09
3.03
273 12.93b,c 36
293 12.32b,c 35
333 10.43b,c 50
3
3
5
3
0.45
0.49
0.63
0.20
3.00
2.73
2.35
2.12
4.31
4.51
4.44
4.38
303
323
343
363
5.17d
5.82d
6.21d
5.74e
33
30
43
41
4
5
7
5
0.66
1.04
0.64
0.73
1.98
1.92
1.88
1.85
2.60
3.03
3.30
3.10
373
9.29b,c 30
TBB + 3,5-di-TBT
3-tert-Butyltoluene
281
8.35d
48
6
0.96
2.88
2.90
+ 1,3-Di-tert-butylbenzene (6)
293
303
323
343
363
308
338
8.48d
7.2d
9.0d
8.13d
8.2d
9.1e
3
36
30
49
41
26
23
1
4
5
8
5
4
4
0.50
1.1
2.73
2.62
2.43
2.28
2.17
2.57
2.32
3.11
2.74
3.72
3.56
3.79
3.5
281
303
323
343
363
363
2.12d
2.07d
2.10d
2.16d
2.14d
2.14d
45
28
24
49
41
41
6
4
4
8
5
5
0.07
0.16
0.10
0.09
0.11
0.11
0.99
1.01
1.03
1.05
1.07
1.07
2.14
2.05
2.04
2.05
1.99
1.99
1.8
0.84
1.6
1.1
9.8e
1.2
4.2
* n is the number of determinations of equilibrium constants; m is the number of series of experiments; the confidence intervals characterize a diver-
a
b
gence between serial values of equilibrium constants at m > 1 and represent the error of primary experiment in a series at m = 1. [11]; [12];
c
d
f
e
[13]; the benzene + TBB + toluene + tert-butyltoluenes system, this work; the benzene + TBB + biphenyl+ tert-butylbiphenyls system, this
g
work; the benzene + TBB + phenol + tert-butylphenols system, this work; the benzene + TBB + toluene + tert-butyltoluenes + 97% cyclohex-
ane system, this work; and the system reported in [14].
h
PETROLEUM CHEMISTRY Vol. 48 No. 3 2008

INTERCONVERSION EQUILIBRIA
195
(1)
(2)
+
+
2
(3)
(4)
+
(5)
2
(6)
+
+
The published data for TBB refer to the liquid-phase with the use of the effect of protective groups, in which
transformations at 298 K in CS2 solvent (5–500-fold the technological procedure of deprotecting is realized
dilution) for reaction (1) [11], at 273–373 K without in an optimum manner under the conditions of achieve-
solvent for reactions (1)–(3) [12, 13], and at 298 K for ment of equilibrium by the system as a whole or, at
reaction (4) [14]. The temperature range was extended least, its significant fraction. The results are also impor-
to 453 K by running an additional experiment, and the tant for the processes of the simultaneous production of
range of equilibrium concentrations for all of the com- advanced alkylaromatic compounds of various classes.
ponents was increased to 5–70 mol % from 20–60 mol %
for benzene [12, 13], to 10–70 mol % instead of
EXPERIMENTAL
35−60 mol % for tert-butylbenzene [12, 13], to 1–35 mol %
from 2–15 mol % for 1,3-di-TBB and 1,4-di-TBB [12,
13], and to 0.05–20 mol % from 0.05–1 mol % for
1,3,5-tri-TBB [12, 13].
The equilibrium of transformations of TBB and
TBT was studied in the liquid phase in the presence of
a catalyst complex based on aluminum chloride
Proceeding from the demands of practice, the prop- (2−10 wt %). The temperature was maintained constant
erties of a medium in which the chemical transforma- with a heat-transfer medium boiling in the reactor
tions occurred were varied. The equilibrium of the posi- jacket: at 329 K with acetone, 373 K with water, and
tional isomerization in the aromatic ring was studied in 405 K with chlorobenzene. The experiment was per-
the medium of related compounds (benzene, toluene, formed at these temperatures in a reactor equipped with
and alkylbenzenes) or in combination with components a stirrer. A change in the boiling point of the heat-trans-
of another nature (cyclohexane, biphenyl, tert-butylbi- fer media caused by the difference in atmospheric pres-
phenyls, phenol, and tert-butylphenols). The results sure did not exceed 0.9 K. Vigorous stirring was
obtained are important for the application of processes stopped 3 min before sampling for the sharp separation
PETROLEUM CHEMISTRY Vol. 48 No. 3 2008

196
NESTEROV et al.
Table 2. Results of approximation of experimental p–T data
Coefficients of the equation
lnp(bar) = A + B(K/T) + Cln(T/K) + D(T/K) (1)*
Compound
Tb, K
pn–pf, Pa
A
B
C
103 × D
Benzene
353.228
383.858
442.298
509.460
497.198
510.510
527.306
4611–4 898000 107.1498
–7311.2018
–7587.328
–9007.005
–10632.19
–10996.60
–10626.39
–16225.20
–15.7402
16.735
14.151
8.292
3.163
9.604
4.160
24.243
Toluene
0.7–4183000
70–199 984
15–103880
7–104 290
99.43573
96.34263
87.31393
114.1650
91.11864
218.2980
–14.29995
–13.07128
–10.91615
–15.59200
–11.61340
–31.95677
tert-Butylbenzene
3,5-di-TBT
1,3-di-TBB
1,4-di-TBB
1,3,5-tri-TBB
379–118 231
76–103580
of the catalyst complex. The samples were taken from tion. The retention times of the compounds and their
the upper hydrocarbon layer. The equilibrium at 353, areas were determined with an ITs-26 integrator.
423, and 453 K was studied in sealed glass ampules
The conditions of the analysis on a Kristall 2000 M
preliminarily filled with the reactant mixture and the
chromatograph with a flame ionization detector and a
catalyst complex. The ampules were placed in a ther-
mostat ( 0.5 K) and periodically shaken.
splitter were as follows: a 50 m × 0.25 mm fused-silica
capillary column with the grafted OV-101 stationary
phase; a carrier gas (helium) flow rate of 2 ml/min; a
The samples withdrawn from the reactor and the
split ratio of 1 : 40; and evaporator, detector, and col-
contents of the ampules were immediately treated with
umn temperatures of 623, 573, and 373 K, respectively.
water to decompose the catalyst complex. The duration
The calibration factors for all of the compounds were
of the experiment from the time of the equilibration of
accepted equal to unity according to [15].
a system to the last sampling was as follows for the sys-
The chemicals used were synthesized via the alkyla-
tion of benzene, toluene, and tert-butylbenzene with
isobutylene or tert-butyl chloride. The individual sub-
stances were isolated using a combination of vacuum
rectification and recrystallization. All tert-butylben-
zenes and tert-butyltoluenes used had an amount of the
base substance of at least 98 wt %.
tems consisting of benzene and TBB or TBB and tert-
butylbiphenyls: 23–154 h at 273 K, 2–20 h at 293 K,
1−10 h at 308, 333 and 338 K; 0.25–7 h at 373 K; and
0.05–0.5 h at 403 and 423 K; benzene, TBB, phenol,
and tert-butylphenols: 16–530 h at 353 K; 16–355 h at
373, 2–74 h at 403 K, 1–31 h at 423, and 0.5–5 h at
453 K; and benzene, TBB, toluene, TBT (and cyclohex-
ane): 0.8–18 h at 279–303 K, and 0.1–9 h above 303 K.
RESULTS AND DISCUSSION
The total equilibrium concentration of benzene and
tert-butylbenzenes varied from 10 up to 70 wt % in
their mixture with biphenyls and from 20 up to 50 wt %
in a mixture with phenols; the total equilibrium concen-
tration of benzene, tert-butylbenzenes, toluene, and
tert-butyltoluenes in a mixture with cyclohexane
changed from 2 up to 80 wt %.
The obtained experimental results and published
data are collated in Table 1. The average values of equi-
librium constants Kx were calculated as the ratio of
molar fractions of the components of the studied reac-
tions.
The gas-phase equilibrium constants Kp (Table 1)
were calculated in the Raoult’s law approximation for a
liquid–gas system represented by related components.
The saturated vapor pressures for the majority of the
compounds were calculated by Eq. (1) (Table 2) with
the coefficients (Table 2) calculated by the least-
squares technique with the use of orthogonal functions
and recommendations [16, 17] on the basis of the fol-
The analysis has been carried out by the GLC
method on Chrom-5 or Kristall 2000 M instruments
with the Khromatek–Analitik program complex. The
analysis conditions on the Chrom-5 chromatograph
with a flame ionization detector and a stream splitter
were as follows: a 50 m × 0.25 mm fused-silica capil-
lary column with the grafted SE-30 stationary phase,
helium as the carrier gas, an inlet pressure of 1.5 atm; lowing array of experimental data in the ranges 4654–
an evaporator temperature of 623 K, and a detector tem- 86417 [18], 6397–103997 [19], 385940–4898000
perature of 523 K; the column temperature depended [20], and 4611–4888000 Pa [21] for benzene;
on the composition of the mixture and was adjusted to 0.7−4183000 [21] and 1.1–166405 Pa [22] for toluene;
ensure the complete resolution of all components. The 70−520 Pa [23] and 1333–199984 Pa [24] for tert-
accuracy of the maintenance of the temperature in the butylbenzene; 15–127 [23], 17–436 (our experiment by
thermostat of columns was 0.2 K. The stability of the the transfer method), and 1318–103880 Pa (our ebul-
pressure was maintained with the use of double reduc- liometric data) for 3,5-di-TBT; 7–197 [23] and 8889–
PETROLEUM CHEMISTRY Vol. 48 No. 3 2008

INTERCONVERSION EQUILIBRIA
197
Table 3. Results of the approximation of experimental equilibrium constants
Coefficients
of the equation
Coefficients
∆rH0m
(l, Tav),
∆rS0m
(l, Tav),
of the equation
∆rH0m
(g, Tav),
∆rS0m
(g, Tav),
Reaction Tav,
ln(Kx) = a × 103T–1 + b
ln(Kp) = a × 103T–1 + b
no.
K
kJ/mol
J/(mol K)
kJ/mol
J/(mol K)
a
B
A
b
1(b, c)
1(d)
320 –0.1828 0.7685
331 –0.1544 0.5834
368 –0.1841 0.6537
408 –0.2013 0.7645
346 –0.1520 0.6015
346
1.52 0.15 6.39 0.49
1.28 0.18 4.85 0.55
1.53 0.20 5.43 0.55
1.67 0.91 6.36 2.24
1.26 0.16 5.00 0.45
0.0816
0.1119
0.1418
0.1468
0.1480
0.5986 –0.68 0.16
0.4106 –0.93 0.20
0.3033 –1.18 0.20
0.3575 –1.22 0.90
0.3215 –1.23 0.15
–1.23 0.07*
4.98 0.51
3.41 0.62
2.52 0.55
2.97 2.24
2.67 0.44
3.11*
1(e)
1(f)
1(a-f)
1(a-f)
2(b-f)
3(b, c)
346
0.1364 1.8554 –1.13 0.71 15.4 2.1
–0.1757
–0.1412
–0.1076
1.9264
1.0269
1.2441
1.46 0.68
1.17 0.26
0.89 0.56
0.11 0.10*
1.1 1.2
16.0 2.0
8.54 0.84
10.3 1.8
7.01*
320 –0.3054 2.1067
2.54 0.59 17.5 1.9
1.62 0.56 11.3 1.8
4(d, g,h) 312 –0.1947 1.3634
4(d, g, h) 312
5(d)
6(d)
323
0.0186 1.7065
–0.2 1.2
14.2 3.8
–0.1343
0.0702
1.5196
12.6 3.6
4.16 0.58
323 –0.0252 0.8292
0.21 0.23 6.89 0.71
0.4998 –0.58 0.19
* The entropy change is calculated by the method of statistical thermodynamics; the enthalpy is the average value of ∆rH0m (g, T ) calcu-
i
lated for all K values (Table 1) with the use of calculated ∆ S0 (g, T ).
p
i
r
m
104 290 Pa [25] for 1,3-di-TBB; 379–1647 (our exper- obtained by the joint processing of all of the data
iment by the transfer method), 380–30596 [22], and (Table 3) is comparable to that of the modern calori-
2220–118231 Pa [25] for 1,4-di-TBB; and 204–241 metric experiment. This is a particularly important con-
(our experiment by the transfer method), 76–18825 clusion because it allows the use of the obtained results
[22], and 11607–103580 Pa [25] for 1,3,5-tri-TBB.
for the thermodynamic analysis of the processes carried
out in various media.
The vapor pressures and acentric factors for 3-TBT
and 4-TBT were calculated by the Ambrose–Walton
method [26] with the critical temperatures calculated
on the basis of the Randic molecular connectivity indi-
ces according to the method described in [27], and with
the critical pressures calculated by the Lydersen
method [28]. The experimental values of Kx and calcu-
lated Kp for the test reactions were approximated by lin-
ear equations; the coefficients to these equations are
presented in Table 3, in which the values of the enthalpy
and entropy of the reactions calculated on the basis of
these factors are also given.
As applied to the benzene + TBB system, the use of
the obtained thermodynamic characteristics is illus-
trated in Figs. 2 and 3, in which the equilibrium compo-
sitions of the reaction mixtures depending on the initial
tert-butyl/aromatic rings ratio are presented. The maxi-
mum equilibrium concentration of tert-butylbenzene in
the liquid phase almost does not depend on the temper-
ature (53 and 52 mol % at 273 and 453 K, respectively)
and decreases to 45 mol % upon passing to the gaseous
state at 453 K.
The maximum total equilibrium concentration of di-
TBB in the liquid phase also weakly depends on the
temperature (61 and 64 mol % at 273 and 453 K,
respectively) at a varying ratio of isomers in the group;
the concentration of 1,3-di-TBB increases with an
increase in temperature (Fig. 2). The transition to the
gaseous state also reduces the maximum total equilib-
rium concentration of di–TBB (50 mol % at 453 K) and
substantially changes the ratio of isomers in favor of
1,3-di-TBB.
The results obtained lead to the conclusion that the
properties of the medium (mixture of benzene and alky-
lbenzenes, benzene + tert-butylbenzenes + phenol +
tert-butylphenols, cyclohexane + benzene + toluene +
TBB + TBT, and carbon disulfide + TBB) have no sig-
nificant effect on the thermodynamic characteristics of
the reactions over a wide range of composition not only for
the positional isomerization in the aromatic ring, but also for
the transalkylation reactions of the considered types. The
conclusion is based on the observation that the level of the
The results presented in Table 3 also allow us to
somehow elucidate the question of the level of the
enthalpy of the intramolecular interaction of substitu-
measurement error for ∆rH0m (l, íav) and ∆rS0m (l, íav)
PETROLEUM CHEMISTRY Vol. 48 No. 3 2008

198
NESTEROV et al.
Mole fraction
Mole fraction
1.0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
1
2
3
4
5
6
7
1
2
3
4
5
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
ííTB/Ar, mol/mol
íTB/Ar, mol/mol
Fig. 1. Equilibrium in the benzene–tert-butylbenzenes sys-
tem (liquid) at 273 and 453 K: (1) benzene; (2) TBB;
(3) 1,3-di-TBB, 273 K; (4) 1,4-di-TBB, 273 K; (5) 1,3,5-tri-
TBB; (6) 1,3-di-TBB, 453 K; and (7) 1,4-di-TBB, 453 K.
Fig. 2. Equilibrium in the benzene–tert-butylbenzenes sys-
tem (gas) at 453 K: (1) benzene, (2) TBB, (3) 1,3-di-TBB,
(4) 1,4-di-TBB, and (5) 1,3,5-tri-TBB.
The values of ∆f H0m (g, 298 K) determined with the
ents (of the tert-butyl–tert-butyl and methyl–tert-butyl
types) at their noncontiguous arrangement in alkylben-
zene molecules. The effects in question are relatively
small, having a magnitude comparable to the error of
modern calorimetric experiments, but they are signifi-
cant for the prediction of the chemical equilibrium. The
validity of the estimation of such enthalpies may be
increased with the use of information obtained from
different sources. Owing to its high sensitivity to the
parameters of the process, the method of investigation
of chemical equilibrium is a deserving supplement to
calorimetry. The analysis presented below is an exam-
ple of the use of the method.
use of calorimetry for eight tert-butylbenzenes are
available (Table 4), although the values for six of these
are presented only in one paper. For two compounds
(tert-butylbenzene and 3-tert-butyltoluene), the mea-
surements were made by two groups of authors. In this
case, the divergence in the estimates is 1.8 kJ/mol for
tert-butylbenzene and 3.6 kJ/mol for 3-butyltoluene,
thus complicating the interpretation of the results. The
values of ∆f H0m (g, 298 K) for 1,3-di-TBB and 1,4-di-
TBB (Table 4) assume either the absence of significant
effects of the interaction of the noncontiguous substitu-
ents in TBB molecules or the equality of the effects. At
the same time, the results of the investigation of chem-
Table 4. Experimental and calculated values of the enthalpies of formation of tert-alkylbenzenes
∆f H0m (g, 298 K), exp.,
∆f H0m (g, 298 K), calc.,
Compound
Source
kJ/mol
kJ/mol
tert-Butylbenzene
–22.6 1.3
–24.4 0.8
29
23
30
23
30
23
23
23
23
23
–23.3
–23.3
tert-Butylbenzene
3-tert-Butyltoluene
–54
–57.6 1.0
–57
2
–56.0
3-tert-Butyltoluene
–56.0
4-tert-Butyltoluene
2
–56.0
1,3-Di-methyl-5-tert-butylbenzene
1,3-Di-tert-butylbenzene
1,4-Di-tert-butylbenzene
3,5-Di-tert-butyl-toluene
1,3,5-Tri-tert-butylbenzene
–89.9 0.9
–129.2 0.8
–129.2 0.6
–164.0 1.0
–238.8 1.4
–88.9
–130.5
–129.5
–163.3
–238.8
PETROLEUM CHEMISTRY Vol. 48 No. 3 2008

INTERCONVERSION EQUILIBRIA
199
ical equilibrium (Tables 1 and 3) indicate not only a sig- substituents in molecules when the level of the effects
nificant difference in ∆f H0m (g, 298 K) between these
is low for being evaluated by means of other methods
may also be of interest. The further study of the equilib-
isomers, but also the reproduction of the value of at
rium data accompanied by the detailed analysis of the
least one of the effects (meta-tert-butyl–tert-butyl)—
see reactions (1)–(3) and (5) as an example.
The result of processing (in the simple additivity
approximation) the experimental data (Tables 3 and 4)
supplemented with reliable ∆f H0m (g, 298 K) values of
entropy term of the equilibrium constant will provide a
new insight into the intramolecular processes and their
relations to the macroscopic characteristics of sub-
stances.
82.9 0.5, 50.2 0.4, and 17.3 0.8 kJ/mol [29] for
benzene, toluene and 1,3-dimethylbenzene, respec-
tively, turned out to be interesting. The processing of
the calorimetric data alone resulted in a value of
−106.1 1.8 kJ/mol for the increment due to hydrogen
atom replacement on the aromatic ring and in enthalp-
ies of –1.1 1.8 and –0.4 3.4 kJ/mol for the meta-tert-
butyl–tert-butyl and meta-methyl–tert-butyl interaction
of substituents, respectively. The magnitude of error of
the calorimetric experiment makes such effects insig-
nificant.
However, the processing of the equilibrium data
alone with the same substitution increment yields
−1.1 0.3 kJ/mol for meta-tert-butyl–tert-butyl inter-
action, a significant value (Table 3), and +0.5 1.2 kJ/mol
for the meta-methyl–tert-butyl interaction, which is
insignificant (Table 3).
The combined processing of the data presented in
Tables 3 and 4 and the enthalpies of formation of ben-
zene, toluene, and 1,3-di-methylbenzene resulted in the
following values: –106.2 1.8 kJ/mol for the increment
of the hydrogen atom replacement with the tert-butyl
substituent on the aromatic ring, and –1.1 0.4 kJ/mol
for the heat of the meta-tert-butyl–tert-butyl interaction
between the substituents in the 1,3-di-TBB, 3,5-di-TBT
and 1,3,5-tri-TBB molecules. The results of the predic-
tion of the enthalpies of formation of tert-butylben-
zenes with these values are presented in Table 4.
ACKNOWLEDGMENTS
This work was supported by the Ministry of Education
and Science of the Russian Federation under the program
the “Development of the scientific potential of higher
schools (2006–2008)” (project no. RNP.2.1.1.1198).
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