Russian Journal of Organic Chemistry, Vol. 37, No. 6, 2001, pp. 889 890. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 6, 2001,
pp. 935 936.
Original Russian Text Copyright 2001 by Mochalov, Fedotov, Gazzaeva, Archegov, Trofimova, Zefirov.
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Uncommonly Easy Nitrodealkylation in Nitration
of para-Substituted Benzylcyclopropanes
S. S. Mochalov, A. N. Fedotov, R. A. Gazzaeva, B. P. Archegov,
E. V. Trofimova, and N. S. Zefirov
Lomonosov Moscow State University, Moscow, 119899 Russia
Received December 27, 2000
The nitrodealkylation, electrophilic substitution of
an alkyl group at the aromatic ring with a nitro
group, frequently accompanies the nitration of para-
or ortho-dialkylbenzenes.
is directed only to the position occupied by the
cyclopropylmethyl substituent (ipso- -complex A, see
the scheme). The known high stability of the methyl-
cyclopropyl-cation concurrently eliminated from the
ipso-position obviously is just the driving force of the
process taking predominantly the path (a).
This process is usually a side reaction, and
conversion of dialkylbenzenes into the corresponding
para- or ortho-alkylnitrobenzenes does not exceed
10 17%. Most often the nitrodealkylation occurs at
nitration of dialkylbenzenes containing isopropyl
[1 3] or tert-butyl [3, 4] groups. As to replacement
with the nitro group of methyl or ethyl, it was
observed only once in nitration of para-methyl- and
para-ethylphenylcyclopropanes [3]. We found that a
cyclopropylmethyl substituent in the para-substituted
benzylcyclopropanes was readily replaced with nitro
group at nitrating these substrates with nitric acid in
the acetic anhydride at 50 C.
It is not improbable that ipso- -complexes of the
B type also may arise in the course of the reaction.
However, firstly, their formation is considerably
hampered by sterical [2, 4] and electronic [5] reasons,
and secondly, the elimination from these ipso- -
complexes of X substituents presumably cannot
successfully compete with the leaving ability of
nitronium cation.
To 50 ml of freshly distilled Ac2O at 50 C was
3
added dropwise 13 ml of HNO3 (d 1.5 g cm ) and at
the same temperature was added 17.4 g (0.1 mol) of
hydrocarbon (I). The reaction mixture was stirred for
1 h at 50 C, then poured into 0.5 liter of water, the
reaction products were extracted into ether, the
extract was washed with water, 2 N solution of
sodium carbonate, again with water, and dried on
MgSO4. On evaporation of the solvent the residue
was subjected to column chromatography on Al2O3,
II grade of activity, eluent ethyl ether petroleum
ether, 1: 3. We obtained 14.5 g (88%) of p-nitroiso-
20
propylbenzene (IV), bp 128 C/12 mm Hg, nD
1.5380 [6].
Similarly from 18.8 g of p-tert-butylbenzylcyclo-
propane (II) we obtained 16.4 g (92%0 of p-tert-
butylnitrobenzene (V), bp 142 143 C / 17 mm Hg,
n2D0 1.5340 [7], and from 16.6 g of p-chlorobenzyl-
cyclopropane (III) we obtained 12.3 g (78%) of
p-nitrochlorobenzene (VI), mp 84 85 C [8].
X = i-Pr (I, IV), t-Bu (II, V), Cl (III, VI).
The high yield of nitrodealkylation products shows
that the ipso-attack of the electrophile during nitration
1070-4280/01/3706-0889$25.00 2001 MAIK Nauka/Interperiodica
Mochalov
