Thermal transformations of 4-tert-butylbiphenyl

Article abstract of DOI:10.1134/S0965544110020118

The thermal stability of 4-tert-butylbiphenyl was studied in the range of 703-763 K. The competition of the cracking and isomerization reactions of alkyl substituents on the aromatic ring of the reactant and its products has been revealed. The kinetic characteristics of the complex of transformations occurring in the system have been determined. Recommendations are provided regarding the conditions for the determination of the critical parameters of 4-tert-butylbiphenyl and for the processing and use of compounds with a tert-butyl moiety in the molecule.

Full text of DOI:10.1134/S0965544110020118

ISSN 0965ꢀ5441, Petroleum Chemistry, 2010, Vol. 50, No. 2, pp. 149–153. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © N.M. Repkin, T.N. Nesterova, I.A. Nesterov, E.V. Golovin, 2010, published in Neftekhimiya, 2010, Vol. 50, No. 2, pp. 143–147.
Thermal Transformations of 4ꢀtertꢀButylbiphenyl
N. M. Repkin, T. N. Nesterova, I. A. Nesterov, and E. V. Golovin
Samara State Technical University
eꢀmail: megaregion@gmail.com
Received July 9, 2009
Abstract—The thermal stability of 4ꢀtertꢀbutylbiphenyl was studied in the range of 703–763 K. The compeꢀ
tition of the cracking and isomerization reactions of alkyl substituents on the aromatic ring of the reactant
and its products has been revealed. The kinetic characteristics of the complex of transformations occurring in
the system have been determined. Recommendations are provided regarding the conditions for the determiꢀ
nation of the critical parameters of 4ꢀtertꢀbutylbiphenyl and for the processing and use of compounds with a
tertꢀbutyl moiety in the molecule.
DOI: 10.1134/S0965544110020118
Alkylbiphenyls (ABPs) are organic compounds There are only data on the pyrolysis and hydrogenolyꢀ
with a good present and a brilliant future. They are sis of biphenyl and dimethylbiphenyls [5].
currently used as raw materials for the manufacture of
liquid crystal materials and will be used in the field of
4ꢀtertꢀButylbiphenyl (4ꢀTBBP) was chosen as one
of the models for studying the thermal stability of
nanotechnologies in the future. The application of
ABPs, since it has an interesting structure suitable for
ABPs as feedstock for synthesizing liquid crystal mateꢀ
the determination of the stability threshold for steriꢀ
rials is complemented by their potential use as organic
cally unstrained compounds of this class.
semiconductors, lightꢀemitting materials, and drug
components. Herewith, a combination of semiconꢀ
ducting and lightꢀemitting properties with the ability
of biphenyl derivatives to selfꢀassemble into monomoꢀ
EXPERIMENTAL
4ꢀtertꢀButylbiphenyl was synthesized by the
authors according to the procedure described in [6].
The concentration of the base compound in the prodꢀ
uct used in the study was 99.96 wt % according to the
data of gas–liquid chromatography.
lecular layers is of great interest. This combination
makes it possible to construct electronic devices of a
new type: the fabrication of nanoconductors with
biphenyl fragments in a molecule [1, 2]. For example,
4,4'ꢀsubstituted biphenyls qualify as molecular transisꢀ
tors [3]. The phenomenon of the polymorphism of
biphenyl derivatives is considered to be a source of
information on the intramolecular interactions in
crystals, the physical properties (boiling point, solubilꢀ
ity, viscosity, thermal conductivity) of substances, and
the effect of the environment on the molecular strucꢀ
ture [4].
The thermal stability was studied via the stepwise
thermostating of the sample placed in a sealed pressurꢀ
ized glass capillary. The temperature range in the study
was (703–763)
1 K with a step size of 5 K and was
limited by the degree of 4ꢀTBBP conversion and the
mechanical strength of the capillary. The contact time
was varied from 5 to 80 min and was limited by the
duration of the sample thermostating and the extent of
the occurring transformations.
All of the above is sufficient to pay close attention
to studying the properties of ABPs with structurally
different substituents. Knowledge of the kinetics of the
thermal transformations of alkylbiphenyls will allow
for reasonably choosing the technology of their isolaꢀ
tion and processing and the prediction of the operating
conditions for their products and wares with similar
structural fragments in the molecule providing for the
preservation of their quality. This knowledge will proꢀ
vide for the reliability of the information on the critical
properties of biphenyl derivatives, which are the key
parameters in the calculations of the properties of subꢀ
stances based on the principle of corresponding states.
Immediately before the experiment, a glass capilꢀ
lary (of 13ꢀ to 23ꢀmm length and 0.85ꢀ to 1.56ꢀmm
diameter) was filled to 40–60% of its volume with the
powdered test substance and was sealed on a hydrogen
microburner. The ampoule with the sample was introꢀ
duced into the tube placed into the isothermal zone of
the oven. The temperature was measured using a referꢀ
ence platinum resistance thermometer (PTSꢀ10)
(
R0 ~ 10
Ω
) calibrated according to the International
Thermodynamic Scale (ITSꢀ90). The temperature
was recorded using a multichannel precision temperaꢀ
An analysis of published data revealed a lack of data ture meter (MIT 8.10) with a measurement error of
on the thermal stability of substances of this class. 0.03 K.
149

150
REPKIN et al.
It was found by means of special experiments that 4ꢀMethylbiphenyl (4ꢀMeBP) was identified using the
the time taken for thermostating the ampoule after its pure compound synthesized by the authors and its
placement into the oven did not exceed one minute. mass spectrum. In addition, the presence of ABPs in
The substance in the capillary withdrawn from the the reaction mass (except 4ꢀMeBP) was confirmed by
oven was in the gaseous state. After the experiment, the retention times of the corresponding components
the ampoule with the sample was instantaneously of the mixture of the isomers obtained by the alkylaꢀ
quenched. Quenching was carried out in two modes, tion of biphenyl with propyl and
either in a test tube precooled in a freezing chamber at the presence of AlBr3
nꢀbutyl bromides in
.
⎯
10°С (the capillary was not destroyed) or in a test
Based on the possible thermal decomposition
mechanism of 4ꢀTBBP and the product buildup
curves, the following transformations occurring in the
system were distinguished for the kinetic analysis of
the process:
tube filled with cold water (the capillary was someꢀ
times destroyed). The reaction mass composition was
independent of the quenching procedure.
Analysis of the reaction products was performed
using the method of gas–liquid chromatography
(GLC) on a Kristall 2000 M instrument with a flame–
k
1
4ꢀTBBP
4ꢀnꢀBBP
(1, –1)
k
–1
ionization detector and a fused silica column 50 m
×
k
2
4ꢀTBBP
4ꢀisoꢀPBP + 0.5С2Н4
(2)
(3)
0.25 mm with the wallꢀbonded SEꢀ30 stationary phase
under the following conditions: the carrier gas was
helium, the outlet pressure was 1.5 atm, the evaporator
temperature was 523 K, the detector temperature was
473 K, and the column temperature was 443 K. The
composition was calculated using the internal normalꢀ
ization or internal standard technique (at temperaꢀ
tures of 718 K and 748–763 K). In both cases, the
results of the qualitative and quantitative determinaꢀ
k
3
4ꢀTBBP
BP + isoС4Н8
k
4
4ꢀnꢀBBP
4ꢀEBP + С2Н4
(4)
k
5
4ꢀisoꢀPBP
4ꢀnꢀPBP
(5, −5)
k
–5
k
6
4ꢀ
n
ꢀPBP
4ꢀMeBP + С2Н4
BP + 0.5С2Н4
BP + С2Н4
(6)
(7)
k
7
4ꢀMeBP
4ꢀEBP
tion of the eluate composition were identical. nꢀOctaꢀ
decane (of 97.7 wt % purity according to GLC data)
was used as an internal standard. All of the compoꢀ
nents eluted under the GLC conditions were identiꢀ
fied.
As the reaction mass composition inevitably
became increasingly complex with an increase in the
temperature and contact time, the required set of
chemical procedures and mass spectrometric analysis
carried out on a Finnigan Trace DSQ instrument with
the NIST 2002, Xcalibur 1.31.Sp5 base at the Organic
Chemistry Department, Samara State Technical Uniꢀ
versity, was also used for identifying the reaction mass
components.
k
8
(8)
k
9
4ꢀisoꢀPBP
BP + С3Н6
BP + С3Н6
(9)
k
10
4ꢀnꢀPBP
(10)
(11)
(12)
(13)
(14)
(15)
(16)
k
11
4ꢀnꢀPBP
BP + isoꢀС4Н8
k
12
4ꢀ
4ꢀEBP
4ꢀisoꢀPBP
n
ꢀPBP
4ꢀsecꢀPBP + 0.5С2Н4
4ꢀMeBP + 0.5С2Н4
k
13
k
14
4ꢀEBP + 0.5С2Н4
4ꢀEBP + 0.5С2Н4
4ꢀMeBP + С3Н6
k
15
4ꢀ
nꢀPBP
k
16
4ꢀ
nꢀBBP
RESULTS AND DISCUSSION
The calculation algorithm was as follows.
the product buildup curves were described by the
As a result of the work, it was found that not only
the reactions of the decomposition of the initial comꢀ
pound and the products formed during the thermal
treatment of 4ꢀTBBP, but also the structural isomerꢀ
ization of butylꢀ and propylbiphenyls occur. The reacꢀ
tion mass under the most severe experimental condiꢀ
•
2
polynomial Cexp
at = 763 K are presented in Table 1.
The rate constant of each reaction was determined
=
a
τ
+
b
τ
+ c, where the coefficients
T
under the condition that the sum of the ABP concenꢀ
trations obtained after processing using the method of
internal normalization was 100%.
tions included 4ꢀTBBP, 4ꢀ
4ꢀ ꢀpropylꢀ, 4ꢀethylꢀ, 4ꢀmethylbiphenyls, and bare
biphenyl.
The mass chromatograms of biphenyl (BP), 4ꢀethꢀ
ylbiphenyl (4ꢀEBP), and 4ꢀisoꢀpropylbiphenyl (4ꢀiso
nꢀbutylꢀ, 4ꢀisoꢀpropylꢀ,
n
•
In the case of reaction (3), the rate constant was
calculated using the integral method for the firstꢀorder
2
ꢀ
model ([Cexp
–
Ccalc
]
min, where Ccalc =
PBP) obtained in this study agreed with those of the
AIST database [7].
eln(C ) – k τ ). The values of k3 found were assumed to be
constant and were not involved in the subsequent
operations.
0
3
The identification of 4ꢀ
PBP) and 4ꢀ ꢀbutylbiphenyl (4ꢀ
formed on the basis of the results of electronꢀimpact
ion fragmentation [8] and the obtained mass spectra. allowed for the obtainment of equations describing the
n
ꢀpropylbiphenyl (4ꢀ
nꢀ
n
nꢀBBP) was perꢀ
•
The differentiation of the function of Cexp
=
f(τ)
PETROLEUM CHEMISTRY Vol. 50
No. 2
2010

THERMAL TRANSFORMATIONS OF 4ꢀtertꢀBUTYLBIPHENYL
151
2
Table 1. Values for the coefficients of the equation Cexp
=
a
τ
+
the Arrhenius equation were calculated for reactions
(1)–(6), (12), and (13). Their values are presented in
Table 3.
+
b + c for the conversion of the reaction mass components at
τ
763 K
Component
BP
Coefficient
b
Correlaꢀ
tion coeffiꢀ
cient
It turned out to be quite surprising that the isomerꢀ
ization of the alkyl substituents takes place along with
their degradation at elevated temperatures, with the
isomerization rates being comparable to those of the
decomposition of molecules, which is especially proꢀ
nounced in the case of transformations of 4ꢀTBBP.
a
c
,
R
0
0.0013
10–6 0.0020
10–6 0.0007 –0.1842
10–7 0.0046 –0.0239
10–7 0.0022
10–6 0.0117
0.0899
0.1252
0.99
0.99
0.99
1.00
0.99
0.93
1.00
4ꢀMeBP
4ꢀEBP
2
1
×
×
×
×
×
On the basis of the obtained kinetic characteristics,
the concentrations of the reaction mixture compoꢀ
nents were calculated and compared to the experiꢀ
mental data. The deviation of the experimental values
of concentrations from the calculated values is in the
range of 0.01–3.00 wt %, which points to the adeꢀ
quacy of the calculation according to the chosen
model.
4ꢀIPBP
4ꢀnꢀPBP
4ꢀnꢀBBP
4ꢀTBBP
–7
4
0.4892
2.0350
–4
0
–0.0219 97.9770
product buildup rates as a function of time
rexp '( ).
The product buildup rates were determined in
terms of the selected transformations occurring in the
system, with all of the rate constants except k3 being
It should also be noted that the macrovalues of the
kinetic parameters intended primarily for the estimaꢀ
tion of the thermal stability of ABPs under different
conditions are highly significant alongside the microvꢀ
alues. For this purpose, the calculations were based
exclusively on the 4ꢀTBBP concentration.
(
=
f
τ
)
•
included in the treatment (k3
(rcalc
=
f
(ki,
τ
), i = 1, 2,
4–16)
•
.
The decomposition rate constants were calculated
using the linear least squares method in terms of the
firstꢀorder model (under the condition of the constant
volume) of the decomposition processes according to
The minimization of the sum of the squared
deviations of the calculated values of the rates from the
2
experimental values (
[rexp
–
rcalc
]
min) was used
to estimate the rate constants of the occurring transꢀ
formations (Table 2). As a result of the optimization,
reactions (–1), (–5), (7–11), and (14–16) were
excluded from the system as negligible.
The obtained results show that reactions (4)–(6),
(12), and (13) dominate in the system. Reactions (2)
and (3) have the lowest rates, indicating the prevalence
C0
the equation lnꢀꢀꢀꢀ
=
kτ. As a result, it was found that
C
C0
the function lnꢀꢀꢀꢀ
C
=
f
(
τ
)
is linear, emanating from the
origin, a fact that is the main criterion for the adeꢀ
quacy of the choice of the kinetic model.
of the isomerization of the reactant 4ꢀTBBP into 4ꢀ
nꢀ
BBP over its decomposition to 4ꢀisoꢀPBP and BP.
The results of the calculation of the rate parameters
Using the calculated rate constants, the parameters of for 4ꢀTBBP are presented in Tables 4 and 5.
Table 2. Values of reaction rate constants
T
, K
k1
,
s–1
k2
,
s–1
k3
,
s–1
k4
,
s–1
10–5
10–5 8.61
10–5
10–5
10–5
k5
,
s–1
k6
,
s–1
k12
,
s–1
k13
,
s–1
703
708
713
718
723
728
733
738
743
748
753
758
763
9.41
5.30
1.46
1.76
2.39
3.54
8.03
1.33
8.43
9.61
1.22
1.81
2.09
×
10–6 1.25
10–6 1.78
10–5 2.53
10–5 3.58
10–5 5.04
10–5 7.05
10–5 9.83
10–4 1.36
10–5 1.88
10–5 2.59
10–4 3.55
10–4 4.84
10–4 6.57
×
10–6 3.94
10–6 7.24
10–6 6.75
10–6 7.75
10–6 1.15
10–6 1.49
10–6 3.06
10–5 6.95
10–5 5.08
10–5 5.08
10–5 6.38
10–5 9.50
10–5 1.34
×
10–7 1.76
10–7 2.46
10–7 3.43
10–7 4.76
10–6 6.58
10–6 9.05
10–6 1.24
10–6 1.69
10–6 2.29
10–6 3.10
10–6 4.18
10–6 5.61
10–5 7.50
×
1.37
10–5 1.89
×
10–4 2.94
10–4 4.10
10–4 5.69
10–4 7.88
10–4 1.08
10–4 1.49
10–4 2.03
10–3 2.76
10–3 3.73
10–3 5.03
10–3 6.76
10–3 9.04
10–3 1.20
×
×
×
×
×
×
×
×
×
×
×
×
×
10–5 1.53
10–5 2.11
10–5 2.89
10–5 3.96
10–4 5.39
10–4 7.30
10–4 9.86
10–4 1.33
10–4 1.78
10–4 2.37
10–4 3.15
10–4 4.17
10–3 5.50
×
×
×
×
×
×
×
×
×
×
×
×
×
10–4
10–4
10–4
10–4
10–4
10–4
10–4
10–3
10–3
10–3
10–3
10–3
10–3
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
×
2.59
3.55
4.83
10–5
6.56
10–4 3.77
10–4 2.68
10–4 6.10
10–4
10–4 3.05
10–4 9.46
10–4 9.94
×
×
×
10–4 8.86
10–4 1.19
10–4 1.60
2.13
10–4 2.84
10–4 3.76
10–4 4.97
×
×
×
PETROLEUM CHEMISTRY Vol. 50
No. 2
2010

152
REPKIN et al.
Table 3. Parameters of the Arrhenius equations of the reacꢀ
tions occurring in the system
the number of experimental data points for the deterꢀ
mination of the constant at the chosen temperature. In
the case of calculating the Arrhenius parameters, the
Reaction no.
k
0, s–1
Е, kJ/mol
reproducibility variance s02 was determined as the
3.8
2.4
3.0
2.4
1
2
1014.5
1016.0
1013.0
1016.0
109.6
1016.0
1016.0
1016.0
264 53
295 33
261 42
279 33
184 106
267 33
276 33
266 33
average value of the adequacy variance for the deterꢀ
m
mination of the constants (s02
=
(sk2)i/mi , where
3
∑
i = 1
4
7.5
m
= 13 is the amount of experimental data points).
5
Verification of the variance homogeneity hypothesis
was performed using the Fisher distribution for a conꢀ
2.4
2.4
2.4
6
12
13
fidence level of P = 0.05. If the condition of Fexp < Ftabl
is not observed, the degree of freedom in the case of
treatment according to the Arrhenius equation was
calculated as f2
is the sum of the degrees of freedom in the calculation
= m –2. If this condition is fulfilled, it
Table 4. Rate constants of the transformations of 4ꢀTBBP
of the constants and kinetic parameters f'2
= f2 +
Confidence interval
Temperaꢀ
ture, K
m
k
, s–1
R
of the correlation
coefficient
(f1)i . The confidence ranges were calculated as the
∑
i = 1
703 1 (1.09 0.10)
708 1 (1.09 0.08)
713 1 (1.90 0.22)
718 1 (3.02 0.58)
723 1 (2.96 0.21)
728 1 (4.45 0.49)
733 1 (5.51 0.30)
738 1 (8.20 0.86)
743 1 (1.33 0.10)
748 1 (3.20 0.39)
753 1 (2.72 0.41)
758 1 (4.15 0.34)
763 1 (4.92 0.60)
×
×
×
×
×
×
×
×
×
×
×
×
×
10–5 0.99
10–5 0.94
10–5 0.97
10–5 0.80
10–5 1.00
10–5 0.94
10–5 0.99
10–5 0.98
10–4 0.99
10–4 0.88
10–4 0.90
10–4 0.98
10–4 0.93
0.94–1.00
0.81–0.98
0.88–0.99
0.56–0.91
0.98–1.00
0.83–0.98
0.98–1.00
0.90–0.99
0.97–1.00
0.72–0.95
0.64–0.97
0.92–0.99
0.76–0.98
product of the rootꢀmeanꢀsquare deviation of the calꢀ
culated value by the ꢀtest.
The obtained macrokinetic information can be
used to estimate the behavior of TBBP under applicaꢀ
tion or for the determination of their properties.
t
Herewith, three trends of the application are conꢀ
sidered: (I) under the conditions of longꢀterm service
and processing at relatively low temperatures (to 423 K);
(II) in the case of running an industrial process, e.g.,
under their separation by fractional distillation in the
temperature range from 423 to 573 K; and (III) during
the determination of the critical temperatures of the
compounds of interest.
The results of the performed kinetic analysis (on
the assumption of the possibility of the extrapolation
of experimental data) are as follows: 4ꢀTBBP barely
degrades (less than 1%) over the period of time that
significantly exceeds 100 years or within 5.5 years
under conditions (I) or (II), respectively.
Table 5. Parameters of the Arrhenius equation
It is estimated that the critical temperature of the
test compound is on the order of 830 K. However, the
residence time of 4ꢀTBBP in the zone of critical temꢀ
peratures (conversion of less than 1%) must not be
longer than 400 ms.
Confidence interval
of the correlation
coefficient
Comꢀ
pound
E,
k
0, s–1
R
kJ/mol
2.3
4ꢀTBBP 1017.7
306 32 0.99
0.96–1.00
At present, attempts are being made to improve the
methods for determining the critical temperatures.
There are suggestions regarding the reduction of the
experimental time to several minutes and even milliꢀ
seconds [9].
We consider it expedient to pay attention to yet
another circumstance. In the literature, an approach
for the prediction of the thermal degradation temperꢀ
ature on the basis of the bond dissociation energy
alone is quite frequently used. In particular, Steele and
In the cases when the composition of the reaction
masses was determined using the internal standard
method, namely at 718 and 748–763 K, the relationꢀ
2
ships
C
=
aτ
+
bτ + c were derived to describe the conꢀ
centrations of the uneluted components on the conꢀ
tact time; the coefficients for these equations are preꢀ
sented in Table 6.
In the calculation of the rate constants, the number
of degrees of freedom in the case of the determination
Ediss
Chiriko recommend the equation
T = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ [10] for
of the adequacy variance s2 was f1
=
n
–1, where
n
is
64.7R
PETROLEUM CHEMISTRY Vol. 50
No. 2
2010

THERMAL TRANSFORMATIONS OF 4ꢀtertꢀBUTYLBIPHENYL
153
2
Table 6. Coefficients of equation
ed components
C
=
a
τ
+
b
τ
+
c
for unelutꢀ
TBBP at 703–763 K have been calculated. It has been
found that competing reactions are the isomerization
of alkyl substituents and the dissociation of bonds. The
degradation of the tertꢀbutyl substituent prevails over
its detachment from the biphenyl molecule. Areas of
the practical application of the experimental data are
shown.
Coefficient
Temperaꢀ
ture
R
a
b
c
718
748
753
758
763
–2
–3
–5
–3
–7
×
×
×
×
×
10–6 0.0075
10–6 0.0103
10–6 0.0200
10–6 0.0191
10–6 0.0284
–0.0988
0.8753
0.93
0.92
0.94
0.91
0.94
–0.8075
3.4634
ACKNOWLEDGMENTS
The work was supported by the Ministry of Educaꢀ
tion and Science of the Russian Federation under the
program “Development of the Scientific Potential of
the Higher School in 2006–2008” RNP.2.1.1.1198.
1.6397
this purpose. This relationship has been obtained on
the basis of data on the monomolecular decomposiꢀ
tion of alkanes, but it is extended to compounds of
other classes. Since transformations occurring during
the thermal treatment of organic compounds are comꢀ
plex in character, it is quite likely that wrong concluꢀ
sions will be drawn if such an approach is used.
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2, 143 (2008).
Thus, in accordance with the recommendation in
[10] and the С6Н5С(СН3)2–СН3 bond dissociation
2
, 435
energy of 303.3
8,4 kJ/mol [11], we conclude that
4, 59
the degradation of the tertꢀbutyl substituent in the
4ꢀTBBP molecule must start already at 560 K. That is,
substances that contain such moieties in their strucꢀ
ture cannot be used in the formulas of compositions
designed for longꢀterm service/operation at elevated
temperatures. However, the experimental data
obtained in this work disproves this conclusion. TBBP
preserves its stability at 560 K for at least 10 years.
Thus, its structural analogues can be considered as
promising components of mixtures for the above purꢀ
poses.
5. B. R. Cook, B. B. Wilkinson, C. C. Culross, et al.,
Energy Fuels, No. 11, 61 (1997).
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(BINOM. Laboratoriya znanii, Moscow, 2003) [in
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CONCLUSIONS
A. Nguyen, J. Chem. Eng. Data 47 (4), 689 (2002).
As the result of the study, the rate constants and
Arrhenius parameters for the transformations of 4ꢀ
11. Comprehensive Handbook of Chemical Bond Energies
Ed. By YuꢀR. Luo (CRC 2007) p. 1688.
PETROLEUM CHEMISTRY Vol. 50
No. 2
2010