ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2014, Vol. 88, No. 4, pp. 557–561. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © S.M. Pimenova, L.L. Pashchenko, E.A. Miroshnichenko, I.A. Nesterov, 2014, published in Zhurnal Fizicheskoi Khimii, 2014, Vol. 88, No. 4, pp. 564–568.
CHEMICAL THERMODYNAMICS
AND THERMOCHEMISTRY
Standard Enthalpies of Formation of 4ꢀMethylbiphenyl
and 4,4'ꢀDimethylbiphenyl
S. M. Pimenovaa, L. L. Pashchenkoa, E. A. Miroshnichenkob, and I. A. Nesterovc
a Department of Chemistry, Moscow State University, Moscow, 119991 Russia
b Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, 117977 Russia
c Samara State Technical University, Samara, 443100 Russia
eꢀmail: smpimenova@yandex.ru
Received April 17, 2013
Abstract—The energies of combustion of 4ꢀmethylbiphenyl and 4,4'ꢀdimethylbiphenyl in the crystal state
were measured in a precision calorimeter equipped with a selfꢀsealing bomb at 298.15 K. The enthalpies of
vaporization of these substances were measured in an isothermal heatꢀconducting Calvet microcalorimeter.
Standard enthalpies of formation were calculated for 4ꢀmethylbiphenyl and 4,4'ꢀdimethylbiphenyl in the
crystal, liquid, and gas states.
Keywords: calorimeter, bomb, enthalpies of combustion, enthalpies of formation, enthalpies of vaporization,
alkylbiphenyls.
DOI: 10.1134/S0036024414040207
INTRODUCTION
EXPERIMENTAL
The investigated substances were synthesized at the
Chair of Organic and Petrochemical Synthesis Techꢀ
nology, Samara State Technical University. The samꢀ
ple of 4ꢀMBP was prepared via the dehydrogenation of
4ꢀcyclohexyltoluene. The synthesis procedure was
described in detail in [6]. The sample was purified by
rectification under vacuum (рresidual = 0.8–1.0 kPa)
and subsequent fiveꢀfold recrystallization from ethaꢀ
nol. The purity of 4ꢀMBP was 99.67 wt % according to
data from GLC analysis, and 99.45 mol % according
to the depression of the melting point in measuring
heat capacity.
Twoꢀstep synthesis was used to prepare 4,4'ꢀdimeꢀ
thylbiphenyl. This included preparation of 4ꢀiodotolꢀ
uene and its Ullmann condensation [9]. 4ꢀIodotoluꢀ
ene was prepared by iodination of toluene using nitric
acid as the oxidizing agent for hydrogen iodide:
The data collected to date for the enthalpies of forꢀ
mation of alkylbiphenyls and a number of their funcꢀ
tional derivatives are insufficient and too contradicꢀ
tory for correctly predicting the enthalpies of formaꢀ
tion of these compounds, or for creating systems of
practical value in calculating the thermodynamic
properties of these substances [1, 2].
We recently measured the enthalpies of combustion
for 4ꢀtertꢀbutylꢀ and 4,4'ꢀdiꢀtertꢀbutylbiphenyls [3]
and 4,4'ꢀdinitrobiphenyl ether [4] and calculated the
enthalpies of their formation from the existing data. In
this work, the standard enthalpies of combustion
° °
ΔсНm) and formation (ΔfHm) were determined for 4ꢀ
(
methylbiphenyl (4ꢀMBP) and 4,4'ꢀdimethylbiphenyl
(4,4'ꢀDMBP), and the enthalpies of vaporization of
g
°
these substances (ΔliqHm) were measured via calorimꢀ
+I2
CH3
CH3
I
–HI
etry. In the literature, the results from thermochemical
studies of the investigated compounds can be found in
[2, 5] (Table 1). In both works, the enthalpies of comꢀ
bustion were determined for 4ꢀMBP and 4,4'ꢀDMBP;
4ꢀIodotoluene was isolated from the washed and
dried organic layer by distillation with Vigreux column
under atmospheric pressure, followed by recrystallizaꢀ
tion from ethanol.
°
in [5], the error in measuring ΔfHm for these subꢀ
stances was high: 7.1–7.5 kJ/mol. The enthalpies of
sublimation were measured for both substances in [2–
8]. The enthalpy of vaporization for 4ꢀMBP was meaꢀ
sured in [6]. In this work, we determine the enthalpy of
vaporization of 4ꢀMBP and the energies of combusꢀ
tion of 4ꢀMBP and 4,4'ꢀDMBP in order to refine the
existing literature data.
Our 4,4'ꢀDMBP was synthesized by condensing
4ꢀiodotoluene according to the recommendations in [9]:
CH3
I
CH3
CH3
–I2
4,4'ꢀDMBP was isolated by fractionating the reacꢀ
tion mixture with Vigreux column under vacuum
557