Facile route for green synthesis of N-benzylideneaniline over bimetallic reduced graphene oxide: chemical reactivity of 2,3,4-substituted derivatives of aniline

Article abstract of DOI:10.1007/s11164-019-03772-w

Mn–Co-decorated reduced graphene oxide (Mn–Co–rGO) was prepared by modified condensation method and characterized through XRD, SEM, EDX, FTIR and BET surface area analysis. The prepared sample was explored for its activity in the synthesis of N-benzylideneaniline (N-BA) using benzyl alcohol and PhNH₂ as precursors. The catalyst has been used efficiently with high activity and selectivity for oxidation of benzyl alcohol to benzaldehyde in the presence of molecular oxygen, which further react with aniline to produced N-BA with sustainable catalytic activity up to five cycles. Furthermore, the effect of the nature and position of the substituent on aniline on the chemical reactivity of the nucleophile was studied theoretically using density functional calculations.

Full text of DOI:10.1007/s11164-019-03772-w

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03772-w
Facile route for green synthesis of N‑benzylideneaniline
over bimetallic reduced graphene oxide: chemical
reactivity of 2,3,4‑substituted derivatives of aniline
Razia Aman · Saima Sadiq · Muhammad Ali · Muhammad Sadiq1 ·
1
1,2
1,2
1
3
1,4
1
Jehan Gul · Khalid Saeed · Adnan Ali Khan · Sagheer Hussain Shah
Received: 14 August 2018 / Accepted: 12 February 2019
©
Springer Nature B.V. 2019
Abstract
Mn–Co-decorated reduced graphene oxide (Mn–Co–rGO) was prepared by modi-
fed condensation method and characterized through XRD, SEM, EDX, FTIR and
BET surꢀace area analysis. The prepared sample was explored ꢀor its activity in the
synthesis oꢀ N-benzylideneaniline (N-BA) using benzyl alcohol and PhNH as pre-
2
cursors. The catalyst has been used eꢁciently with high activity and selectivity ꢀor
oxidation oꢀ benzyl alcohol to benzaldehyde in the presence oꢀ molecular oxygen,
which ꢀurther react with aniline to produced N-BA with sustainable catalytic activity
up to fve cycles. Furthermore, the eꢂect oꢀ the nature and position oꢀ the substitu-
ent on aniline on the chemical reactivity oꢀ the nucleophile was studied theoretically
using density ꢀunctional calculations.
Keywords Benzyl alcohol · Mn–Co–rGO · Benzaldehyde · Aniline ·
N-benzylideneaniline
Electronic supplementary material The online version oꢀ this article (https://doi.org/10.1007/s1116
4
-019-03772-w) contains supplementary material, which is available to authorized users.
*
Muhammad Sadiq
sadiq@uom.edu.pk; mohammad_sadiq26@yahoo.com
1
2
3
4
Department oꢀ Chemistry, University oꢀ Malakand, Chakdara, Khyber Pakhtunkhwa, Pakistan
School oꢀ Applied Chemical Engineering, Kyungpook National University, Daegu, South Korea
Department oꢀ Chemistry, Bacha Khan University, Charsadda, Khyber Pakhtunkhwa, Pakistan
Center ꢀor Computational Materials Science, University oꢀ Malakand, Chakdara,
Khyber Pakhtunkhwa, Pakistan
Vol.:(012
1
3456789)
3

R. Aman et al.
Introduction
The condensation oꢀ amines with carbonyl compounds is an important and useꢀul
organic transꢀormation, as the resultant imines (also called Schiꢂ bases or azome-
thines) are used as components in cycloaddition reactions [1–3], and have poten-
tial ꢀor therapeutic applications such as lipoxygenase inhibitors, anti-inꢃamma-
tory agents [4] and anti-cancer agents [5–7]. Thereꢀore, the eꢁcient and diverse
synthesis oꢀ imines is a hot research topic.
Traditionally, imines have been obtained by the condensation oꢀ carbonyl com-
pounds with amines [8, 9]. Several new methods have been developed ꢀor the syn-
thesis oꢀ imines during the recent years [10–15]. Among the new methodologies,
the oxidative coupling oꢀ alcohols with amines represents the most simple and
straightꢀorward way oꢀ obtaining imines. The preparation oꢀ imines ꢀrom alcohols
is also advantageous as alcohols are much greener than carbonyl compounds in
many aspects [16–21], and heterogeneous catalysts [22–29] have been reported
ꢀ
or the synthesis oꢀ imines ꢀrom alcohols.
Nonetheless, stability and economic ꢀeasibility keep the doors open ꢀor the
pursuit oꢀ ideal catalyst ꢀor the large-scale production oꢀ Schiꢂ bases [30, 31].
Several studies have been reported on the use oꢀ Mn as a catalyst ꢀor the synthe-
sis oꢀ imines by the oxidative coupling oꢀ alcohols and amines [32–37]. Cobalt
has also been reported as a catalyst ꢀor the preparation oꢀ imines ꢀrom alcohol
and amine [38]. Similarly, Cui et al. [39] reported Au and Pd/ZrO ꢀor one-pot
2
synthesis oꢀ imine through the oxidation oꢀ benzyl alcohol (7 h) and nucleophilic
addition oꢀ aniline with benzaldehyde (1 h). However, the economic aspect oꢀ
the prevailing processes provokes researchers to minimize the cost oꢀ the catalyst
and duration oꢀ the reaction. Thereꢀore, Yamaguchi et al. [40] reported Ru/Al O
2
3
ꢀ
or the synthesis oꢀ imine ꢀrom primary and secondary alcohols with good cata-
lytic activity and selectivity. Also, Yuan et al. [30] eꢁciently used Ru O /GO ꢀor
2
2
selective synthesis oꢀ imine through oxidation oꢀ amines. However, the ruthenium
is a rare earth metal and has high cost oꢀ $250/troy ounce; thereꢀore, the catalyst
used ꢀor the imination reaction needs ꢀurther investigation ꢀor a cheap and easily
available catalyst ꢀor industrial-scale production.
Density ꢀunctional theory (DFT) provides excellent explanation oꢀ chemical
reactivity oꢀ molecules as the chemical reactivity oꢀ a molecule is controlled by
its electronic properties, kinetics and thermodynamic stability [41–50]. Thereꢀore,
Spirtovic et al. [51] studied the structural and electronic properties using standard
Spartan 10 soꢀtware (B3LYP/6-31 G*) and predicted the chemical reactivity oꢀ
4
-hydroxycoumarin and its 3-substituted derivatives, 4-hydroxy-3-iminomethyl-
coumarin and 3-acetyl-4-hydroxy-coumarin. On the basis oꢀ HOMO–LUMO
energy gap, it was predicted that 4-hydroxy-3-iminomethyl-coumarin, among the
other two compounds, has good chemical reactivity, which provokes us to study
the eꢂect oꢀ substituted derivatives oꢀ aniline on the imination reaction oꢀ PhNH
2
and benzaldehyde [51–56].
In this paper, we report Mn–Co supported on graphene as a new heterogeneous
catalyst ꢀor the tandem one-pot synthesis oꢀ imines ꢀrom alcohols. Moreover, we
1
3

Facile route for green synthesis of N-benzylideneaniline…
also explored the chemical reactivity oꢀ 2,3,4-substituted derivatives oꢀ aniline
experimentally as well as theoretically.
Experimental
In this investigation, chemicals and reagents were used without any ꢀurther treat-
ment. Benzyl alcohol, n-heptane, acetonitrile, ethanol, aniline and its 2,3,4-substi-
tuted derivatives and benzaldehyde were purchased ꢀrom Merck, Sigma Aldrich,
Scharlau and BDH, respectively.
Synthesis of reduced graphene oxide
Hummer’s method with modifcation was used ꢀor the synthesis oꢀ graphene oxide
(
GO). Brieꢃy, 2.0 g oꢀ graphite powder and 1.0 g oꢀ sodium nitrate were reacted
with 46 mL oꢀ concentrated H SO in a round-bottom ꢃask oꢀ 500 mL. The mixture
2
4
was stirred overnight at 35 °C. Potassium permanganate (6 g) was spiked gradually
into the reaction mixture at 40 °C and was kept stirring ꢀor an additional 30 min.
The obtained suspensions were diluted with 200 mL oꢀ water, gradually in 30 min.
The GO was ꢀormed by the addition oꢀ 10 mL H O (30%). The GO was reduced by
2
2
chemical method using hydrazine and then separated by centriꢀugation and washed
with 30% HCl and distilled water.
Immobilization of Mn–Co on reduced graphene oxide
The already-prepared reduced GO (rGO) was dispersed in 50 mL oꢀ ethanol and
5
mL each oꢀ 0.1 M Co(OAc) and 0.5 M Mn(OAc) aqueous solutions. Then the
2 2
mixture was sonicated ꢀor 30 min. The mixture was then diluted with 10 mL oꢀ
water and 2 mL oꢀ NH OH at 25 °C. The obtained mixture was reacted overnight
4
at 80 °C. Mn–Co/rGO was obtained by centriꢀugation and cleaned with water and
n-hexane. The immobilized Mn–Co/rGO was then dried at 100 °C overnight.
Characterization of the catalyst
Scanning electron microscopy (SEM), X-ray diꢂractometry (XRD), BET surꢀace
area analysis and Fourier transꢀorm inꢀrared (FT-IR) spectroscopy were used to
characterize the catalyst. SEM and EDX were carried out using a scanning electron
microscope (JSM 5910, JEOL, Japan). XRD analysis was carried using an X-ray
diꢂractometer (Rigaku D/Max-II, Cu tube, Japan), BET surꢀace analysis was per-
ꢀ
ormed using a Quantachrome NOVA 2000 and FT-IR spectra were recorded by a
spectrometer (Prestige 21, Shimadzu, Japan).
1
3

R. Aman et al.
Catalytic test
Catalyst (0.1 g oꢀ Mn–Co/rGO) and 10 mL oꢀ the prepared solution [1 M benzyl alco-
hol (BzOH) in acetonitrile/ethanol/heptane] were loaded in a three-necked reactor
enꢀolded in heating tape connected to a Digi-Sense with a temperature controller (Cole
Parmer, USA) and connected with a reꢃux condenser. The reaction mixture was stirred
(
250–1500 rpm) at 298–328 K ꢀor 45–270 min under the continuous ꢃow oꢀ oxygen
(
40 mL/min). Then, 2 mL oꢀ 1 M aniline (PhNH ) was added to the reactor under the
2
ꢃow oꢀ N to obtain the required product in 1 h as shown in Scheme 1. The product
2
was analyzed with an UV–visible spectrophotometer, gas chromatography (GC), high-
perꢀormance liquid chromatography (HPLC) and proton nuclear magnetic resonance
1
(
H NMR).
N‑benzylideneaniline
1
H NMR (400 MHz; CDCl ): 8.40 (s, 1H), 7.40–7.60 (m, 5H), 7.20–7.30 (m, 5H).
3
Quantum‑chemical calculations
All the calculations were perꢀormed using Gaussian 09 soꢀtware. The geometries oꢀ
all the molecules were optimized using the B3LYP density ꢀunctional in combination
with a 6–311++G(d, p) basis set. Harmonic vibration analysis was perꢀormed ꢀor all
the optimized geometries at standard temperature and pressure (STP) using the same
model chemistry to determine the nature oꢀ the minima located on the potential energy
surꢀace (PES), and to compute thermochemistry. The highest occupied molecular
orbital–lowest unoccupied molecular orbital (HOMO–LUMO) energy gap was used to
fnd the ionization potential and electron aꢁnity.
Energy gap, ΔE = HOMO − LUMO
Ionization Potential (IP) = −HOMO
Electron affinity (EA) = −LUMO
(1)
(2)
(3)
The hardness (η) and soꢀtness (σ) oꢀ the molecules are given by Eqs. (4) and (5),
respectively [51].
E
LUMO
− EHOMO
IP − EA
ꢀ
=
=
(4)
2
2
Scheme 1 Catalytic synthesis oꢀ N-BA in one-pot synthesis starting ꢀrom BzOH using optimized reac-
tion conditions
1
3

Facile route for green synthesis of N-benzylideneaniline…
The soꢀtness is the inverse oꢀ the hardness (Eq. 5).
1
ꢀ
=
(5)
ꢁ
LUMO + HOMO
ꢀ
=
(6)
2
where μ is the escaping tendency oꢀ an electron ꢀrom an equilibrium system, while ω
is the electrophilic index character given by the ꢀollowing equation:
2
ꢁ
ꢀ
=
(7)
2
ꢂ
Results and discussion
Characterization of catalysts
The images oꢀ Mn–Co/rGO (SEM) show a smooth morphology and also reveal the
dispersion and presence oꢀ Mn and Co on the surꢀace oꢀ rGO support as shown in
Fig. 1a. EDX spectra shows that there is 44.1% carbon, 22.7% oxygen, 14.1% man-
ganese and 19.1% cobalt as shown in Fig. 2b. From these results, it is also clear
that on the surꢀace oꢀ rGO, the cobalt and manganese nanoparticles are present in
large quantities. In EDX spectrum, the high percentage oꢀ oxygen indicates that
Fig. 1 a SEM image oꢀ Mn–Co/rGO with magnifcation 60,000 with a line oꢀ 0.2 µm, b EDX spectrum
and weight % elemental composition oꢀ Mn–Co/rGO, c XRD spectra oꢀ rGO, d XRD spectra oꢀ Mn–Co/
rGO
1
3

R. Aman et al.
Fig. 2 Optimization oꢀ reaction parameters: a eꢂect oꢀ time and temperature on BzOH to BzH; b time
profle oꢀ nucleophilic addition oꢀ PhNH and BzH; c solvent eꢂect on step a and step b; d comparison
2
oꢀ catalyzed and uncatalyzed nucleophilic addition and eꢂect oꢀ 2,3,4-substituted derivatives oꢀ aniline
graphene has OH and COOH groups, while the BET surꢀace area oꢀ Mn–Co/rGO
2
was 273 m /g, which is in good agreement with the results reported elsewhere [30].
XRD spectra oꢀ manganese and cobalt nanoparticles supported on rGO are shown in
Fig. 1c, d. The large peaks reꢀer to the presence oꢀ crystal-phase rGO with 2θ values
oꢀ 25.8° [56]. Small peaks at 2θ values oꢀ 41°, 54° and 76° represent cobalt, while
other peaks at 2θ values oꢀ 31.7° and 38.9° [57] reꢃect the presence oꢀ manganese
which is very close to the reported literature [56–60].
Catalyst screening
All the reactions were carried out in a selꢀ-designed, Pyrex, three-necked batch reac-
tor. The reactor was loaded with 10 mL oꢀ benzyl alcohol (ꢀrom 500 mL oꢀ 1 M solu-
tion), 0.1 g oꢀ catalyst (Mn–Co/rGO), oxygen at 40 mL/min, pressure oꢀ 760 Torr, ꢀor
4
5–270 min, with stirring at 1250 rpm and temperature at 298–328 K, while nucleo-
phile addition oꢀ PhNH with BzH was completed in 1 h in N atmosphere at 328 K.
2
2
The reaction was investigated ꢀor diꢂerent reaction duration and it was ꢀound that the
step a rate oꢀ oxidation oꢀ BzOH to BzH increases with increase in reaction time and
the maximum BzH was achieved at 180 min, while the same trend was observed in
the nucleophilic addition ꢀollowed by elimination (step b) oꢀ PhNH and BzH to N-BA
2
(
1 h) as presented in (Fig. 2a, b). It was ꢀound that step b mainly depends on the reac-
tion duration oꢀ step a. The most probable reason is the availability oꢀ BzH ꢀrom the
oxidation oꢀ benzyl alcohol ꢀor ꢀurther nucleophilic addition oꢀ PhNH . Similarly, the
2
1
3

Facile route for green synthesis of N-benzylideneaniline…
activation energy oꢀ the reaction was calculated through Arrhenius’ equation (Eq. 8) ꢀor
both steps oꢀ oxidation oꢀ BzOH to BzH and nucleophilic addition in one-pot synthesis.
Ea
ln %conv = ln A −
(8)
RT
It was observed that the activation energy ꢀor step a and step b was 58.9 and 57.7 kJ/
mole, respectively, which clarifes the absence oꢀ the mass transꢀer eꢂect in both steps,
as shown in Figure S1. This is also supported by the agitation eꢂect on the % conver-
sion oꢀ BzH and N-BA, respectively, as presented in Figure S2 which shows there is no
eꢂect oꢀ agitation above 1000 rpm on the % conversion in both steps. The kinetic con-
trol reactions were ꢀavorable according to the needs oꢀ industry and green chemistry.
The reaction was carried out in one pot and in two steps in step a; benzyl alcohol oxida-
tion to benzaldehyde. Meanwhile, in step b, the benzaldehyde ꢀormed combined with
PhNH to ꢀorm N-BA. The reaction was considered as a consecutive reaction as shown
2
in Figure S3, where the K is the rate constant oꢀ oxidation oꢀ benzyl alcohol to benza-
1
ldehyde, while K is the rate constant oꢀ nucleophilic addition oꢀ PhNH with benzal-
2
2
dehyde. In the reaction, it was observed that K <<K ; thereꢀore, the rate-determining
1
2
step is the oxidation oꢀ benzyl alcohol in step a. Since the concentration oꢀ benzyl alco-
hol was linearly decreased with the increase oꢀ reaction duration, the most probable
reaction proceeds with the frst order. The thermodynamic study oꢀ the reaction shows
that the oxidation oꢀ benzyl alcohol to benzaldehyde in step a and the nucleophilic
addition oꢀ PhNH and benzaldehyde to N-BA in step b both are spontaneous reactions
2
3
with negative Gibb’s ꢀree energy. The Gibb’s ꢀree energy (− 5.5×10 ) ꢀor oxidation
oꢀ BzOH to BzH and Gibb’ ꢀree energy oꢀ nucleophilic addition oꢀ PhNH and BzH
2
3
(
− 4.2×10 ) show good agreement with theoretically calculated values. Solvent also
has a pronounced eꢂect on the oxidation oꢀ BzOH to BzH and nucleophilic addition oꢀ
PhNH and BzH. The most ꢀavorable solvent ꢀor these reactions was ethanol in terms
2
oꢀ conversion and selectivity as shown in Fig. 2c. Cui et al. [39] have also reported the
eꢂect oꢀ diꢂerent solvents such as methanol, ethanol, toluene and DMF on the % con-
version and % selectivity oꢀ benzyl alcohol oxidation to benzaldehyde using Au–Pd/
ZrO , and predicted that ethanol was the best solvent among the others, as shown in
2
Table 1; this is consistent with our results. Similarly, toluene was also reported as a
solvent ꢀor the synthesis oꢀ N-BA while using MnCo O -500 nanorods as catalyst, with
2
4
9
0.9% yield in 15 h, as shown in Table 1. The blank reaction was also investigated in
the absences oꢀ catalyst under optimized reaction conditions. Oxidation oꢀ BzOH to
BzH was not observed without catalyst under the same set oꢀ parameters, although the
nucleophilic addition oꢀ PhNH with BzH occurred with negligible yield in 1 h, while
2
it was comparatively high in 7 h. But catalyzed nucleophilic addition oꢀ PhNH with
2
BzH was 76.5% in 1 h, which is very high in comparison to uncatalyzed reaction under
optimized reaction conditions as shown in Fig. 2d.
Recyclability of the catalyst
The catalyst was separated ꢀrom the reaction mixture on the completion oꢀ experi-
mental run, washed with ethanol and heated at 100 °C ꢀor 3 h. The used catalyst was
1
3

R. Aman et al.
1
3

Facile route for green synthesis of N-benzylideneaniline…
recycled ꢀor fve experimental runs consecutively under the optimal reaction condi-
tions. In each run, the catalyst retained its catalytic activity and selectivity which
revealed the extended liꢀe span oꢀ the catalyst.
Chemical reactivity of 2,3,4‑substituted derivatives of aniline
Under the optimized set oꢀ reaction parameters (stirring 1250 rpm, temperature
3
28 K, time 180 min, ꢃow oꢀ oxygen 40 mL/min), the imination reaction was car-
ried out under ꢃow oꢀ N ; methyl-substituted aniline at diꢂerent positions reacted
2
with benzaldehyde to synthesize imine. It was observed that the % yield show ꢃuc-
tuation with the nature and position oꢀ substituent on aniline. It is quite clear ꢀrom
the order given in Figure S4 that the aniline, which has a methyl group at ortho and
para positions, has almost equal reactivity, which is more reactive than meta-substi-
tuted aniline toward electrophilic substitution oꢀ benzaldehyde. This is because the
methyl group is electron-donating and it activates the aniline towards electrophilic
substitution iꢀ it is attached at ortho and para positions as shown in Fig. 2d, Figure
S4 and Table S1 (entries 2, 3 and 4). Similarly, Naeimi et al. [63] have reported the
retarding eꢂect oꢀ 3- and 4-substituted methyl derivatives oꢀ aniline on the % yield
oꢀ N-BA while using P O /SiO at room temperature. But the results are contradic-
2
5
2
tory to our reported results, because we have observed the % yield oꢀ NBA increases
with methyl substitution on aniline.
Similarly, structures in Figure S5 show that unsubstituted aniline is more reactive
than nitro-substituted anilines. Para-nitroaniline is least reactive among nitroanilines
as presented in Fig. 2d, Figure S5 and Table S1 (entries 5, 6 and 7). Here, the results
reported by Naeimi and coworkers [63] are in good agreement with our observa-
tion, in that 3- and 4-nitro-substituted anilines have a retarding eꢂect on the % yield
oꢀ the imination reaction. Aniline substituted with a methoxy group has an order
oꢀ chemical reactivity, as shown in Figure S6, toward nucleophilic addition oꢀ ben-
zaldehyde; p-methoxy aniline and o-methoxy aniline have almost similar reactivity
which has greater reactivity than m-methoxy aniline represented in Fig. 2d, Figure
S6 and Table S1 (entries 8, 9 and 10), which in turn is more reactive than unsub-
stituted aniline. The reactivity order oꢀ substituted aniline is –OCH >CH >NO
3
3
2
towards the electrophile because oꢀ the electron-donating and electron-withdrawing
eꢂects. –OCH as well as CH are electron-donating which activates the ring ꢀor
3
3
electrophilic substitution, while the NO group is electron-withdrawing and deacti-
2
vates the benzene ring ꢀor electrophilic substitution.
Structural and electronic properties
The optimized geometries and their coordinates are presented in Fig. 3 and Table S2,
respectively. The stabilities oꢀ the structures substituted with methyl, nitro and meth-
oxy groups at various positions were compared, using the total energies in Table S2.
The energy values in Table S2 suggest that ꢀor methyl substituted structures, the
stability ꢀollows the order p-methyl>o-methyl>m-methyl, ꢀor nitro substituted
m-nitro>o-nitro>p-nitro, and ꢀor methoxy p-methoxy>o-methoxy>m-methoxy.
1
3

R. Aman et al.
Ortho-methyl
Meta-methyl
Para-methyl
Ortho-nitro
Meta-nitro
Para-nitro
Ortho-methoxy
Meta-Methoxy
Para-methoxy
Fig. 3 Geometries optimized by using B3LYP/6-311++G(d, p) level oꢀ theory
Frontier molecular orbitals analysis and energy gap
The HOMO and LUMO ꢀor all the molecules in a ground state, as obtained using
the same level oꢀ theory as used ꢀor geometry optimization, are depicted in Fig. 4.
Electron aꢁnity (EA) and ionization potential (IP) were calculated using Koop-
man’s theorem according to which EA=−E
and IP=−E
.
LUMO
HOMO
HOMO–LUMO energy gap has an important role in determining the reac-
tivity oꢀ a molecule [41, 42]. The smaller the HOMO–LUMO gap, the
more reactive the molecule is. It can be seen ꢀrom Table 2 that the smallest
HOMO–LUMO gaps ꢀor methyl-, nitro- and methoxy-substituted structures are
shown by ortho-substituted, meta-substituted and para-substituted, respectively,
1
3

Facile route for green synthesis of N-benzylideneaniline…
Fig. 4 HOMO and LUMO ꢀor methyl-substituted aniline computed at a B3LYP/6-311++G(d, p) theory
level
and, accordingly, these represent the most reactive species among their counter-
parts. The ΔΕ in Table 2 suggest that ꢀor methyl-substituted structures, the energy
gap ꢀollows the order m-methyl>o-methy>p-methyl (Fig. 4), ꢀor nitro-substi-
tuted o-nitro>p-nitro>m-nitro (Fig. 5), and ꢀor methoxy substitution, m-meth-
oxy>o-methoxy>p-methoxy (Fig. 6).
Table 2 HOMO and LUMO energies (a.u.), IP and EA (eV), energy gap ΔΕ (eV), hardness ƞ (eV), soꢀt-
ness σ (eV− ) computed with B3LYP/6-311++G(d, p)
1
Complex
E (Hartree) −HOMO
a.u.)
−LUMO (a.u.) IP (eV) EA (eV) Energy gap
(eV)
ƞ (eV)
(
o-Methyl
m-Methyl
p-Methyl
o-Nitro
m-Nitro
p-Nitro
o-Methoxy −671.4474 −0.21198
m-Methoxy −671.4494 −0.22564
p-Methoxy −671.4427 −0.21518
−596.2209 −0.22770
−596.2211 −0.22555
−596.2193 −0.22294
−761.4587 −0.24595
−761.4450 −0.24979
−761.4544 −0.25539
−0.07428
−0.07082
−0.06977
−0.09241
−0.10716
−0.10694
−0.06769
−0.06976
−0.07260
−6.196 −2.021 4.174
−6.137 −1.927 4.210
−6.066 −1.898 4.167
−6.693 −2.515 4.178
−6.797 −2.916 3.881
−6.949 −2.909 4.039
−5.768 −1.842 4.039
−6.139 −1.898 4.242
−5.855 −1.975 3.879
2.0875
2.105
2.084
2.089
1.9405
2.02
1.963
2.1205
1.9400
1
3

R. Aman et al.
Fig. 5 HOMO and LUMO ꢀor nitro-substituted aniline computed at a B3LYP/6-311++G(d, p) theory
level
Hardness and softness
Hard and soꢀt character oꢀ molecules are considered by small and large energy
gaps, respectively. The hard and soꢀt character oꢀ molecules in Table 2 sug-
gest that ꢀor methyl-substituted structures, the hardness ꢀollows the order
m-methyl>o-methyl>p-methyl, ꢀor nitro-substituted o-nitro>p-nitro>m-nitro, and
ꢀ
or methoxy-substituted m-methoxy>o-methoxy>p-methoxy, while the soꢀtness
has reverse order ꢀor all molecules. The larger value oꢀ hardness shows the stability
and less reactivity oꢀ the molecule [51, 60, 64].
Conclusion
The Mn–Co/rGO catalyst was used ꢀor the selective oxidation oꢀ benzyl alcohol to
benzaldehyde ꢀollowed by nucleophilic addition oꢀ aniline with benzaldehyde under
mild reaction conditions eꢁciently. The good catalytic activity ꢀor the oxidation oꢀ
benzyl alcohol and imination reaction was achieved with optimal reaction parameters
(
e.g. stirring 1250 rpm, temperature 328 K, time 180 min, ꢃow oꢀ oxygen at 40 mL/
min), while the imination reaction was carried out in N atmosphere with the same
2
ꢃow rate (40 mL/min). Both experimental and quantum-chemical calculations ꢀor
1
3

Facile route for green synthesis of N-benzylideneaniline…
Fig. 6 HOMO and LUMO ꢀor methoxy-substituted aniline computed at a B3LYP/6-311++G(d, p) the-
ory level
the chemical reactivity oꢀ 2,3,4-substituted derivatives oꢀ aniline with benzaldehyde
have good agreement. Para-methoxy-substituted aniline shows more nucleophilic
character among the studied substituted derivatives oꢀ aniline. The electrophilic
index (ꢀ) oꢀ substituted aniline has the order nitro-aniline (5.7 eV)>methyl-aniline
(
3.8 eV)>methoxy-aniline (3.7 eV), which clarifes that the methoxy-aniline has
more nucleophilic character and has more chemical reactivity towards the nucleo-
philic addition with BzH to yield N-BA. To sum up, the reaction is eco-ꢀriendly and
industrially ꢀavorable to replace the existing reaction ꢀor Shiꢂ base ꢀormation.
References
1
2
3
.
.
.
O. Tsuge, R. Kanemasa, Adv. Heterocycl. Chem. 45, 231 (1989)
M.F. Aly, M.I. Younes, S.A.O. Matwally, Tetrahedron 50, 3159 (1994)
V.V. Kuznetsov, A.R. Palma, A.E. Aliev, A.V. Varlamov, N.S. Prostakov, Zh. Org. Khim. 127, 1579
(
1991)
4
5
.
.
D.J. Hadjipavlou-litina, A.A. Geronikaki, Drug Des. Discov. 15, 199 (1996)
M. Cushman, D. Nagarathnam, A.K. Chakraborti, C.M. Lin, E.J. Hamel, Med. Chem. 34, 2579
(
1991)
6
.
M. Cushman, H.M. He, C.M. Lin, E.J. Hamel, Med. Chem. 36, 2817 (1993)
1
3

R. Aman et al.
7
.
P. Vicini, A. Geronikaki, M. Incerti, B. Busonera, G. Poni, C.A. Cabras, P.L. Colla, Bioorg. Med.
Chem. 11, 4785 (2003)
8
9
.
.
R.W. Layer, Chem. Rev. 63, 489 (1963)
J.P. Adams, J. Chem. Soc. Perkin Trans. 1, 125 (2000)
1
1
1
1
1
1
1
1
1
1
2
0. M. Largeron, A. Chiaroni, M.B. Fleury, Chem. Eur. J. 14, 996 (2008)
1. X. Lang, H. Ji, C. Chen, W. Ma, J. Zhao, C. Chen, Angew. Chem. Int. Ed. 50, 3934 (2008)
2. J.S.M. Samec, A.H. Ell, J.E. Backvall, Chem. Eur. J. 11, 2327 (2005)
3. H. Choi, M.P. Doyle, Chem. Commun. 7, 745 (2007)
4. G. Jiang, J. Chen, J.S. Huang, C.M. Che, Org. Lett. 11, 4568 (2009)
5. C.S. Yi, D.W. Lee, Organometallics 28, 947 (2009)
6. G.E. Dobereiner, R.H. Crabtree, Chem. Rev. 110, 681 (2010)
7. T.D. Nixon, M.K. Whittlesey, J.M.J. Williams, Dalton Trans. 5, 753 (2009)
8. G. Guillena, D.J. Ramon, M. Yus, Chem. Rev. 110, 1611 (2010)
9. B. Gnanaprakasam, J. Zhang, D. Milstein, Angew. Chem. Int. Ed. 49, 1468 (2010)
0. M.A. Esteruelas, N. Honczek, M. Oliván, E. Oñateand, M. Valencia, Organometallics 30, 2468
(
2011)
2
2
2
2
2
2
2
2
2
3
3
3
1. L. Jiang, L. Jin, H. Tian, X. Yuan, X. Yu, Q. Xu, Chem. Commun. 47, 10833 (2011)
2. L. Blackburn, R.J.K. Taylor, Org. Lett. 3, 1637 (2001)
3. S. Sithambaram, R. Kumar, Y.C. Son, S.L. Suib, J. Catal. 253, 269 (2008)
4. M.S. Kwon, S. Kim, S. Park, W. Bosco, R.K. Chidrala, J. Park, J. Org. Chem. 74, 2877 (2009)
5. H. Sun, F.Z. Su, J. Ni, Y. Cao, H.Y. He, K.N. Fan, Angew. Chem. Int. Ed. 48, 4390 (2009)
6. J.W. Kim, J. He, K. Yamaguchi, N. Mizuno, Chem. Lett. 38, 920 (2009)
7. R. Cano, D.J. Ramón, M. Yus, J. Org. Chem. 76, 5547 (2011)
8. Y. Shiraishi, M. Ikeda, D. Tsukamoto, S. Tanaka, T. Hiraia, Chem. Commun. 47, 4811 (2011)
9. S. Kegnæs, J. Mielby, U.V. Mentzel, C.H. Christensen, A. Riisager, Green Chem. 12, 1437 (2010)
0. Y. Guohao, J. Ind. Eng. Chem. Res. 46, 279 (2017)
1. W. Cui, Catal. Today 235, 152 (2014)
2. M. Arup, A. Nerush, G. Leitus, L.J.W. Shimon, Y.B. David, stein. J. Am. Chem. Soc. 138, 4298
(
2016)
3
3
3. S. Shanthakumar, R. Kumar, Y.C. Son, S.L. Suib, J. Catal. 253, 269 (2008)
4. E. Saravanakumar, J. Neumann, J.B. Sortais, K. Junge, C. Darcel, M. Beller, Nat. Commun. 7,
1
2641 (2016)
3
5. M. Matthias, M. Glatz, N. Gorgas, B. Stöger, E. Pittenauer, G. Allmaier, L.F. Veiros, K. Kirchner,
Eur. J. Chem. 22(35), 12316 (2016)
3
3
3
3
4
4
4
4
4
4
6. B. Chen, J. Li, W. Dai, L. Wang, S. Gao, Green Chem. 16, 3328 (2014)
7. X. Yu, C. Liu, L. Jiang, Q. Xu, Org. Lett. 13(23), 6184 (2011)
8. G. Zhang, S.K. Hanson, Org. Lett. 15(3), 650 (2013)
9. W. Cui, Q. Xiao, S. Sarina, W. Ao, M. Xie, H. Zhu, Z. Bao, Catal. Today 235, 152 (2014)
0. K. Yamaguchi, N. Mizuno, Angew. Chem. Int. Ed. 42(13), 1480 (2003)
1. A. Beyramabadi, A. Morsali, Int. J. Phys. Sci. 6(7), 1780 (2011)
2. P.K. Chattaraj, B. Maiti, J. Am. Chem. Soc. 125(9), 2705 (2003)
3. A.A.H. Kadhum, A.A. Al-Amiery, A.Y. Musa, A. Mohamad, Int. J. Mol. Sci. 12, 5747 (2011)
4. A.A.H. Kadhum, A.A. Al-Amiery, M. Shikara, A. Mohamad, Int. J. Phys. Sci. 6(29), 6692 (2011)
5. W. Koch, M.C. Holthausen, A Chemist’s Guide to Density Functional Theory (Wiley, Weinheim,
2
000)
4
4
4
6. S. Liu, J. Chem. Sci. 117(5), 477 (2005)
7. C.A. Mebi, J. Chem. Sci. 123(5), 727 (2011)
8. M. Monajjemi, M. Sayadian, K. Zare, A.R. Ilkhani, F. Mollaamin, Int. J. Phys. Sci. 6(16), 4063
(
2011)
4
5
5
9. R.G. Pearson, Chemical Hardness–Applications from Molecules to Solids (Wiley, Weinheim, 1997)
0. J.W. Peters, W.N. Lanzilotta, B.J. Lemon, L.C. Seeꢀeldt, Science 1998, 282 (1853)
1. S. Špirtović-Halilović, M. Salihović, E. Veljović, A. Osmanović, S. Triꢀunović, D. Završnik, Glas.
Hem. Technol. Bosne Herceg. 43, 57 (2014)
5
2. S. Špirtović-Halilović, M. Salihović, H. Džudžević-Čančar, S. Triꢀunović, S. Roca, D. Soꢀtić, D.
Završnik, J. Serb. Chem. Soc. 79(4), 435 (2014)
5
5
3. D. Završnik, F. Bašić, F. Bečić, E. Bečić, S. Jažić, Period. Biol. 105(2), 137 (2003)
4. D. Završnik, S. Špirtović-Halilović, D. Soꢀtić, Period. Biol. 113(1), 93 (2011)
1
3

Facile route for green synthesis of N-benzylideneaniline…
5
5
5. L. Stobinskia, B. Lesiaka, A. Malolepszyc, M. Mazurkiewiczc, B. Mierzwaa, J. Zemekd, P. Jiricek,
I. Bieloshapkad, J. Electron Spectrosc. Relat. Phenom. 195, 145 (2014)
6. S. Drewniak, R. Muzyka, A. Stolarczyk, T. Pustelny, M.K. Moranska, M. Setkiewicz, Sensors 16,
1
03 (2016)
5
5
5
6
6
6
6
6
7. T.N. Blanton, D. Majumda, Powder Diꢂr. 2, 68 (2013)
8. R. Miao, J. He, S. Sahoo, Z. Luo, W. Zhong, S.Y. Chen, C. Guild, ACS 7, 819 (2017)
9. A. Manceau, A.I. Gorshkov, V.A. Drits, Am. Miner. 77, 1144 (1992)
0. P.K. Chattaraj, B. Maiti, J. Am. Chem. Soc. 125(9), 2705 (2003)
1. X. Huang, L. Liu, H. Gao, W. Dong, M. Yang, G. Wang, Green Chem. 19, 769 (2017)
2. S. Michlik, R, Kempe. Chem. Eur. J. 16, 13193 (2010)
3. H. Naeimi, H. Sharghi, F. Salimi, K. Rabiei, Heteroat. Chem. 19, 43 (2008)
4. A.A.H. Kadhum, A.A. Al-Amiery, A.Y. Musa, A. Mohamad, Int. J. Mol. Sci. 12, 5747 (2011)
Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional aꢁliations.
1
3