Synthesis of N-benzylidenebenzylamine from benzylamine under the action of iron-containing catalysts in ccl4

Article abstract of DOI:10.1134/S1070428012080052

A direct synthesis of N-benzylidenebenzylamine from benzylamine in the presence of iron-containing catalysts was performed with the 92-96% yield. The reaction proceeds in tetrachloromethane at 80-85°C over 8 h. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070428012080052

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 8, pp. 1059−1061. © Pleiades Publishing, Ltd., 2012.
Original English Text © R.I. Khusnutdinov, A.R. Baygusina, R.I. Aminov, 2012, published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48, No. 8, pp. 1063−1065.
Synthesis of N-Benzylidenebenzylamine from Benzylamine
under the Action of Iron-Containing Catalysts in CCl4
R. I. Khusnutdinov, A. R. Baygusina, and R. I. Aminov
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences,
Ufa, 450075 Russia
e-mail: ink@anrb.ru
Received January 25, 2012
Abstract—Adirect synthesis of N-benzylidenebenzylamine from benzylamine in the presence of iron-containing
catalysts was performed with the 92–96% yield. The reaction proceeds in tetrachloromethane at 80–85оС over 8 h.
DOI: 10.1134/S1070428012080052
heating at 80–85°С in the presence of iron-containing
catalysts [FeCl3·6H2O, FeCl3, FeCl2·4H2O, Fe(C2H5)2,
Fe(acac)3, Fe(OAc)2, Fe2(CO)9] in tetrachloromethane
within 8 h is converted into N-benzylidenebenzylamine
(I) in 92–96% yield.
N-Benzylidenebenzylamine (I) takes an important
place in Schiff bases series for it is widely used in analytic
and synthetic chemistry. N-Benzylidenebenzylamine (I)
is used as indicator in titrimetric determination of organo-
lithium compounds [1–3], in the synthesis of a number of
heterocycles, in particular, substituted piperidin-2-ones
possessing a wide range of physiologic action [4].
[Fe], CCl4
PhCH2NH2
PhCH NCH2Ph
80_85oC, 8 h
I
The classic preparation procedure of compound I con-
sists in the reaction of benzaldehyde with benzylamine.
The yield depends on many factors: the nature of the
solvent, temperature, the order of reagents mixing, and
the presence of a catalyst [5–11].
The high yield of compound I was obtained only
at a large excess of CCl4 ([PhCH2NH2]:[Fe]:[CCl4] =
100:1:200).Apparently CCl4 not only acts as a solvent but
it is directly involved into the reaction.According to GLC
analysis in the course of the reaction CCl4 is consumed
converting into chloroform. The essential influence of
air oxygen on the yield of compound I was observed. In
the reaction carried out in a sealed ampule in an argon
atmosphere the yield of imine I equals 24%, and in an
open system it grows to 81%. Beside chloroform in the
reaction mixture ammonium ions (49.1 mg/ml) and HCl
(59.9 mg/ml) were detected. The most notable fact is
the appearance in the reaction mixture of active chlorine
(1.89 mg/ml). The reason of this fact was found in the
literature [22]: The reaction of CCl4 with butylamine in
the presence of the catalyst Cu(OAc)2 proceeded through
the formation in situ of N-chlorobutylamine (III) with the
subsequent formation of N-butylidenebutylamine (IV).
In some studies N-benzylidenebenzylamine (I) was
prepared by oxidation of dibenzylamine (II) with oxygen
in the presence of compounds of copper, of metal gold
deposited on titanium dioxide, of 5% of Au on Al2O3, of
tropylium complexes, of gold acetate [12–18]. Besides
compound I was obtained by oxidizing dibenzylamine
(II) with a singlet oxygen generated from the triplet oxy-
gen in the presence of porphyrin photosensitizers [19].
N-Benzylidenebenzylamine (I) can be obtained by the
oxidation of benzylamine with t-BuOOH [20] or O2 in
the presence of diverse catalysts [15, 16, 18, 21].
We report here on a direct synthesis of N-benzylidene-
benzylamine (I) from benzylamine. Benzylamine at
C4H9NH2
C4H9NHCl
III
C4H9NH2 + CCl4
C4H9N CHC3H7
_CHCl3
IV
1059

KHUSNUTDINOV et al.
1060
tion (1) of the formation of N-chloro-benzylamine (V).
The proof that the reaction proceeds by this route is
the appearance in the reaction mixture of chloroform,
butylnitrile, and HCl.
Therefore the sum of the data obtained permits a con-
clusion that the formation of compound I most probable
occurs through N-chlorobenzylamine (V).
Taking into consideration the composition of the
reaction mixture containing compound I, chloroform,
benzonitrile (<1%), HCl, ammonium ions and active
chlorine it is presumable that a sequence of reactions
(1−4) occurs, and the key process is the conversion (1)
of benzylamine in N-chlorobenzylamine (V).
EXPERIMENTAL
1Н and 13С NMR spectra were registered on a spec-
trometer Bruker Avance-400 (400.13 and 100.62 MHz
respectively) in CDCl3, the chemical shifts are reported
with respect to TMS. Mass spectra were obtained on an
instrument Shimadzu GCMS-QP2010Plus (capillary
column SPB-5 30 m × 0.25 mm, carrier gas helium,
ramp from 40 to 300°C, heating rate 8deg/min, vaporizer
temperature 280°C, temperature of the ion source 200°C,
ionizing energy 70 eV). GLC analysis was carried out on
a chromatograph Shimadzu GC-9A, GC-2014 [column
2 m × 3 mm, stationary phase silicone SE-30 (5%) on
Chromaton N-AW-HMDS, ramp from ramp from 50 to
270°С, heating rate 8 deg/min, carrier gas helium (flow
rate 47 ml/min)]. The gas phase was analyzed on a GC-
MS instrument Thermo Finnigan MAT 95 XP.
[Fe]
PhCH2NHCl + CHCl3
PhCH2NH2 + CCl4
(1)
V
(2)
PhCH2NHCl
PhCH NH + HCl
V
VI
PhCH NCH2Ph + NH3
PhCH NH + PhCH2NH2
I
VI
(3)
(4)
NH3 + HCl
NH4Cl
Taking into account the increase in the yield of com-
pound I in the presence of oxygen, the participation of
the catalyst and the formation of ammonia (in the form
+
of NH4 ), the reaction mechanism through the stage (5)
Elemental analysis of samples was carried out on an
analyzer Karlo Erba 1106.
of dibenzylamine (II) formation cannot be excluded. In
the final stage (6) dibenzylamine (II) is converted into
imine I by oxidation with oxygen or by dehydrogenation.
Both reactions are catalyzed by FeCl3·6H2O, the former is
accompanied with water release, the latter with gaseous
hydrogen formation.
As initial reagents were used commercial benzylamine
and tetrachloromethane after preliminary distilla-
tion. Iron-containing catalysts [FeCl3·6H2O, FeCl3,
FeCl2·4H2O, Fe(C2H5)2, Fe(acac)3, Fe(OAc)2, Fe2(CO)9]
were commercial reagents.
[Fe]
(5)
(PhCH2)2NH + NH3
PhCH2NH2
N-Benzylidenebenzylamine (I). Amixture of 1 mmol
of FeCl3·6H2O, 100 mmol of benzylamine, 200 mmol of
CCl4 was heated at 80–85°С while stirring over 8 h. On
the completion of the reaction the reaction mixture was
cooled, neutralized with 10% aqueous Na2CO3 at stirring
for 0.5–1 h, the organic substances were extracted into
chloroform, the extract was dried and filtered. The solvent
was distilled off, N-benzylidenebenzylamine (I) was dis-
tilled in a vacuum. Yield 96%. Oily fluid, bp 124–125°C
(2 mm Hg) {200–202°C (30 mm Hg) [23], 125–127°C
(0.1 mm Hg) [24]}. 1H NMR spectrum (CDCl3) δ, ppm:
4.86 s (2H, PhСH2N), 6.86–8.20 m (10Harom), 8.43 s (1H,
N=CHPh). 13С NMR spectrum, δ, ppm: 65.05 (PhСH2N),
126.79, 127.98, 128.28, 128.49, 128.60, 130.76, 136.17,
139.29, 162.00 (N=CHPh). Mass spectrum, m/z (Irel, %):
195.25 [M]+ (35), 194 (33), 165 (5), 152 (3), 117 (15), 91
(100), 65 (20), 51 (5). Found, %: C 86.10; H 6.73; N 7.17.
II
O2
_H2O
[Fe]
(PhCH2)2NH
II
PhCH NCH2Ph
(6)
_H2
I
Trying to find facts confirming these reactions we
analyzed the reaction mixture for the presence of water
and the gas phase for the content of hydrogen. The wa-
ter concentration was measured by Fischer titration and
that of hydrogen, by GC-MS method on a spectrometer
Thermo Finnigan MAT 95 XP. Water was found in trace
quantity, and the hydrogen peak corresponded to its
background content in air.
Taking into account the absence of oxygen-containing
compounds in the reaction mixture it is presumable that
the part of О2 consists in the initiation of the radical reac-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 8 2012

SYNTHESIS OF N-BENZYLIDENEBENZYLAMINE FROM BENZYLAMINE
1061
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11. Law, M.C., Cheung, T.W., Wong, K.-Y., and Chan, T.H.,
J. Org. Chem., 2007, vol. 72, p. 923.
C14H13N. Calculated, %: C 86.11; H 6.71; N 7.18.
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The study was carried out under the financial sup-
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