Preparation of N-alkyl-substituted 3,5-dinitroanilines by amination of 1,3,5-trinitrobenzene

Article abstract of DOI:10.3184/030823408X293198

Highly efficient amination of 1,3,5-trinitrobenzene by a number of simple aliphatic amines to form the corresponding N-alkyl-substituted 3,5-dinitroanilines has been achieved.

Full text of DOI:10.3184/030823408X293198

70 RESEARCH PAPER
FEBRUARY, 70–71
JOURNAL OF CHEMICAL RESEARCH 2008
Preparation of N-alkyl-substituted 3,5-dinitroanilines by amination of
1,3,5-trinitrobenzene
Chao Qian, Jinqiang Liu and Xinzhi Chen*
College of Materials Science and Chemical Engineering, Zhejiang University, Hangzhou 310027, P. R. China
Highly efficient amination of 1,3,5-trinitrobenzene by a number of simple aliphatic amines to form the corresponding
N-alkyl-substituted 3,5-dinitroanilines has been achieved.
Keywords: amination, 1,3,5-trinitrobenzene, N-alkyl-substituted 3,5-dinitroanilines
N-Alkyl-substituted
3,5-dinitroanilines
are
valuable
We report here the synthesis of N-alkyl-substituted 3,5-
dinitroanilines using 1,3,5-trinitrobenzene and lower aliphatic
amines under mild reaction conditions and with water as
solvent (see Scheme 1). This method not only shows gives
N-alkyl-substituted 3,5-dinitroanilines with high conversions
and chemoselectivities, but also eliminates the formation
of overalkylation products.
Table 1 illustrates the generality of this amination
procedure in the trinitrobenzene system. Note that the
second and third aromatic nitro groups are unaffected under
these conditions.
From a series of experiments we found that eight equivalents
of amine were required for completion of the reaction.
An increase in the amount of amine did reduce the time
required. Experiments show that a catalyst was unnecessary.
In an effort to elucidate the mechanism, amination
of nitrobenzene was attampted by reacting with amine
2a. We found that only starting material was recovered.
We conclude that the activity of the nitro group on the aromatic
ring increased because of the electron-withdrawing effect of
the other two nitro groups. Furthermore, the activity of the
remaining nitro groups decreased because of the electron-
industrial intermediates in the manufacture of dyes, plastics,
pharmaceuticals and agrochemicals. Traditionally, these
compounds are prepared in the liquid phase using mineral
acids as catalysts and alkyl halides or dimethyl sulfate as
alkylating agents.1-7 Though various new heterogeneous
catalysts and non-toxic alkylating agents, such as methanol8
and dimethyl carbonate,9,10 have been introduced, yields or
product selectivity are, with few exceptions, low and depend
on the nature of the catalysts and on the reaction conditions.
The major synthetic problem is competing over-alkylation,
which leads to mixtures of secondary and tertiary amines and
quaternary ammonium salts. The difficulty in preventing over-
alkylation is especially true when highly reactive electrophilic
compounds are used, such as methyl, ethyl, benzyl and allyl
alkylating agents. Besides the N-alkylation,11,12 other general
methods for the synthesis of secondary amines are amide
reduction13 and reductive amination.14 Although these methods
are quite reliable, there is also in these cases the necessity of
controlling the concomitant over-alkylations when the amine
is employed as the limiting substrate, which often reduces the
application of these methods.
R1
R2
R1
NO2
N
a R1=H, R2=Me;
NH
R2
R1=H, R22=Et;
b
c R1=H, R =n-Pr;
2
d R11=H, R2=n-Bu;
R =Me, R2=Me;
e
f
O2N
NO2
O2N
NO2
R1=Et, R2=Et.
1
3
Scheme 1
Table 1 Amination of 1,3,5-trinitrobenzene
Compound
1H NMR (d)
IR/cm-1/KBrdisks
M.p./°C/Lit.15
Yielda/%
3a
2.64(3H, d,J = 4.1 Hz), 6.89(1H, m, J = 4.1 Hz), 7.73(2H, s),
7.92(1H, s)
3366, 2928, 1623,
1587, 1338
156.5–157.4
(158)
88.2
91.2
3b
3c
3d
1.23(3H, t,J = 7.2 Hz), 3.38(2H, m), 7.74(2H, s), 7.92(1H, s),
7.98(1H, m, J = 3.7 Hz)
3376, 2986, 1626,
1520, 1336
184.9–185.6
(185–186)
0.95(3H, t,J = 7.3 Hz), 1.45(2H, m, J = 9.2 Hz), 3.32(2H, m,
J = 4.3 Hz), 6.42(1H, t, J = 4.2 Hz), 7.76(2H, s), 7.94(1H, s)
3383, 2984, 1626,
1514, 1330
130.1–130.5
(129–130)
87.6
84.3
0.90(3H, t,J = 7.1 Hz), 1.30(2H, m, J = 11.3 Hz), 1.41(2H, m,
J = 8.4 Hz), 3.32(2H, m, J = 7.5 Hz), 6.38(1H, m, J = 4.3 Hz),
7.77(2H, s), 7.95(1H, s)
3387, 2980, 1629,
1501, 1331
97.1–98.2
(99)
3e
3.15(6H, m), 7.72(2H, s), 8.21(1H, s)
3425, 2938, 1630,
1545, 1366
161.5–162.1
(164)
89.3
86.9
3f
1.18(6H, t, J = 7.2 Hz), 3.51(4H, m), 7.74(2H, s), 8.23(1H, s)
3444, 2941, 1643,
1587, 1351
111.1–111.9
(112)
aIsolated yield.
* Correspondent. E-mail: xzchen@zju.edu.cn
PAPER: 07/4950

JOURNAL OF CHEMICAL RESEARCH 2008 71
donating effect of the substituent amino group, so there were no
multiamino compounds observed.
We gratefully acknowledge the funding support of a grant
from the National Natural Science Foundation of China
(No. 20776127), the National Key Technology R&D Program
(No. 2007BA134B07), and the Opening Foundation of
Zhejiang Provincial Top Key Discipline (No. 56310101613).
In conclusion, a new method has been developed for the
synthesis of N-alkyl-substituted 3,5-dinitroanilines. The
materials are inexpensive and the yields are high. The method
described herein compares very favourably with known
methods and should be a valuable addition to amination
methodology.
Received 19 November 2007; accepted 28 January 2008
Paper 07/4950
doi: 10.3184/030823408X293198
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CAUTION: 1,3,5-trinitrobenzene is an explosive compound
and should be stored and handled using appropriate
precautions for the amounts involved.
General procedures for preparation of N-alkyl-3,5-dinitroanilines
3a–f.
8
9
1,3,5-Trinitrobenzene (6.4 g, 30 mmol) and amine (240 mmol) 2a–f
were taken up in 15 ml water in a 25 ml autoclave. The mixture was
heated at 180°C for 4 h after which time the starting material had been
consumed as evidenced by thin layer chromatographic (developing
solvent, EtOAc/hexanes = 3:1, V/V) analysis. The mixture was then
cooled, filtered and the solvent removed under reduced pressure to give
the crude product. Recrystallisation with ethanol:water = 3:1 (V/V)
afforded N-alkyl-3,5-dinitroanilines 3a–f. The yields obtained were
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