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NAUMKIN et al.
xylene (analytical grade) with tertiary amyl chloride or
Time counting started from the point of attaining
isoamyl bromide (at least 98 wt % according to GLC the required temperature in the reactor. The resulting
data) over AlCl3 or AlBr3, respectively, as a catalyst.
reaction mixture was held at the prescribed temperaꢀ
ture with continuous stirring. In all experiments, the
time of holding the system at equilibrium was at least
twice as long as the time taken to reach the equilibꢀ
rium. The reaction mixture/catalyst complex volume
ratio by the end of the experimental run was not less
than 5 : 1.
Five minutes before sampling, stirring was stopped;
the samples were taken from the organic layer and were
immediately treated with water to decompose the catꢀ
alyst complex. Special experiments have shown that
the composition of the reaction mixtures does not
change upon the withdrawal and treatment of the samꢀ
ples.
The equilibrium was studied either in the absence
of an extrinsic solvent or in a cyclohexane medium
(the reactants to cyclohexane ratio was 1 : 80) to
ensure the high selectivity of the process. The results of
the study allowed for the conclusion that this dilution
and the nature of the solvent do not affect the values of
the equilibrium constants for the given reactions.
The synthesis was carried out in a glass reactor
equipped with a stirrer, a reflux condenser, and a jacket
in which a heatꢀtransfer fluid circulated. The temperꢀ
ature in the reactor jacket was maintained accurate to
within
1 K. Prior to alkylation, the reactants were
cooled to 273 K to preclude the carryover of the alkyꢀ
lating agent. To obtain the reaction mixture of the
required composition, alkylation was run at different
substrate : reagent : catalyst ratios. The alkylating
agent was introduced into the system in portions.
Depending on the purpose of the process, it was conꢀ
ducted in different modes.
In order to completely exclude the possibility of
positional isomerization in both the aliphatic chain
and aromatic ring, alkylation was conducted in a
homogeneous system. This condition was provided for
by maintaining a certain excess concentration of the
halogenoalkane. Chemical transformations occurred
throughout the entire volume in this case.
When the process was aimed at reaching a severe
isomeric conversion of a given type or attaining equiꢀ
librium in the system on the whole, alkylation and the
subsequent isomerization were run in a heterogeneous
system with vigorous stirring. In this case, one phase
was a mixture of hydrocarbons with the dissolved catꢀ
alyst and the other was a catalyst complex (similar to
other processes involving Lewis acids). Chemical
transformations occur largely at the interface in this
case. The prevalence of the secondary over the tertiary
structures during the progress of the system in question
toward equilibrium becomes evident already at the
step of the synthesis of the reactants.
It should be emphasized that the amount of
byproducts depended not only on the alkyl/aryl ratio,
but also on the temperature of the process, the amount
of the catalyst, the contact time, and the presence or
absence of the solvent. In this context, the experimenꢀ
tal conditions in each case were selected in such a
manner as to provide for the selectivity of the process
in general of at least 90%.
It is noteworthy that the ratio of the isomer concenꢀ
trations characterizing the equilibrium constant
remained unchanged at a constant temperature even
when the degree of irreversible conversion of 1,2ꢀ
diMPB and 1,1ꢀdiMPB into neopentylbenzene
reached 95%.
All structural isomers involved in the transformaꢀ
tions subjected to investigation were identified mass
spectrometrically.
The analysis was performed by the GLC method on
a Kristall 2000 M chromatograph with a flame ionizaꢀ
The isomerization equilibria of pentylbenzenes,
pentyltoluenes, and pentylꢀoꢀxylenes were studied in
tion detector using a 50 m 0.25ꢀmm fusedꢀsilica capꢀ
×
illary column with the grafted SEꢀ30 stationary phase
under the following conditions: helium as the carrier
gas; an inlet pressure of 2.3 atm; and column oven,
evaporator, and detector temperatures of 383, 623,
and 573 K, respectively. Gas chromatographic–mass
spectrometric determinations were performed at the
Organic Chemistry Department, Samara State Techꢀ
nical University on a Finnigan Trace DSQ instrument
using the NIST 2002, Xcalibur 1.31.Sp 5 database.
The mass spectra measured in this work for 1,1ꢀ
diMPB, 1,2ꢀdiMPB, and 2,2ꢀdiMPB were consistent
with those given in the NIST database [14].
the liquid phase in the presence of a catalyst complex
based on aluminum bromide (2–10 wt %). The temꢀ
perature range examined for pentylbenzenes was 280–
363 K. At 343 K, the equilibrium was studied for all
three systems represented by pentylbenzenes, pentylꢀ
toluenes, and pentylꢀoꢀxylenes.
The investigation procedure was as follows. The
study of the equilibrium was preceded by alkylation,
which was run at 273–298 K. After the completion of
the alkylation, heating to the required investigational
temperature was switched on.
The alkylating agent/aromatic substrate molar
Published data on the mass spectra of pentyltoluꢀ
ratio was varied over the range of (0.7–1) : 1. A higher enes and pentylxylenes are unavailable. Based on the
excess of the alkylating agent facilitated the formation principles of the electronꢀionization fragmentation of
of a greater amount of polysubstituted alkylaromatics, ions [15] and the mass spectra recorded in this work
byproducts, and tars and resulted in catalyst deactivaꢀ (Tables 1, 2), we identified the structural isomers in the
tion.
reaction mixture as shown in the figure.
PETROLEUM CHEMISTRY Vol. 50
No. 2
2010