ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 9, p. 1821. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © A.P. Zaraiskii, 2008, published in Zhurnal Obshchei Khimii, 2008, Vol. 78, No. 9, p. 1582.
LETTERS
TO THE EDITOR
Phase-Transfer Catalysis in Electrophilic Substitution Reactions:
X.1 A Phase-Transfer Catalyst for an Elementary Nitration Act
A. P. Zaraiskii
Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine,
ul. R. Luksemburg 70, Donetsk, 83114 Ukraine
e-mail: azar@skif.net
Received November 23, 2007
DOI: 10.1134/S1070363208090296
The role of phase-transfer catalysts in heterogenous
reaction systems is usually restricted to a transfer of
one reactant or of its active form or of particles
activating reaction to the reaction phase. In the
elementary act of the whole transformation, the phase-
transfer agent does not play any role if this is not
specially intended for it, as, for example, in the certain
cases of phase-transfer metal complex catalysis [2].
However, the involvement of phase-transfer catalyst in
an elementary act can be revealed in cases where the
catalytic and noncatalytic reactions differ not only by
their kinetics.
−, −, 57.0, 0.374, 0.920, 36, 11, 60/40; (2) I, 7.45, 57.0,
0.502, 0.267, 6.6, 9, 40/60; (3) II, 1.71, 57.0, 0.266,
0.165, 2, 99, 40/60. (4) II, 0.46, 54.0, 0.197, 0.804, 3,
80, 41/59; and (5) II, 2.2, 27.7, 0.50, 0.11, 6, 6.4, 41/59.
Comparative calculation of the partial rates from
these data shows the following. The rates of biphenyl
substitution in different ortho positions in the nonca-
talytic reaction is 75% of those in different para
positions. In the catalytic experiments, the ortho posi-
tions are 3 times less reactive than the para positions.
Thus, the resulting data show that the “catalytic
matrix” contributes to the elementary nitration act that
defines orientation, and the catalyst functions not only
as a carrier for the reacting species to the organic
phase. In other words, probably, supramolecular
interactions of the electrophile (N2O4H+ [4]) carrier
and the participants of the elementary act defining
orientation reveal themselves through steric hind-
rances. Such explanation seems the most acceptable,
since there are no reasons to suggest that the difference
in the mechanisms of the catalytic and noncatalytic
processes is significant in any other respect.
We obtained data on ortho/para orientation of the
nitro group the noncatalytic and catalytic phase-transfer
nitration of biphenyl in the benzene–aqueous nitric acid
system (2:1, v/v). The reaction was initiated with so-
dium nitrite and as catalysts we used (C6F5)4B−·NMe4+
(I) and (C6F5)4B−·Na+ (II). We had to increase the
concentration of nitric acid used in the experiments as
compared to that used in previous studies of this
reaction, since the noncatalytic nitration did not lead to
detectable amounts of nitro compounds: Biphenyl is
the least reactive compound among the polycyclic
arenes studied [3]. Analysis of the products was
carried out GLC using reference compounds [3].
REFERENCES
1. Zaraiskii, A.P., Kachurin, O.I., Velichko, L.I., and
Zaraiskaya, N.A., Zh. Org. Khim., 2003, vol. 39, no. 11,
p. 1646.
2. Gol’dberg, Yu.Sh., Izbrannye glavy mezhfaznogo kata-
liza (Selected Chapters of Phase-Transfer Catalysis), Riga:
Zinatne, 1989.
3. Kachurin, O.I., Velichko, L.I., and Zaraiskii, A.P., Zh.
Org. Khim., 1995, vol. 31, no. 5, p. 705.
4. Kachurin, O.I., Velichko, L.I., and Matvienko, N.M.,
Ukr. Khim. Zh., 1993, vol. 59, no. 6, p. 642.
We have performed five experiments; listed below
are the experiment number, the catalyst and its
concentration as calculated for the organic phase, mM;
HNO3 concentration, %; initial concentrations of
biphenyl in the organic phase and of NaNO2 in the acid
phase, M; reaction time, h; biphenyl conversion, %;
and ortho/para ratio in the resulting nitrobiphenyls: (1)
* For communication IX, see [1].
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