Intermolecular charge transfer facilitated synthesis and spectral characterization of Schiff bases of a weak nucleophile 2,3-diamino-1,4- naphthoquinone

Article abstract of DOI:10.1039/c2ra21372a

A new synthetic protocol for the formation of novel Schiff bases between a weak nucleophile, 2,3-diamino-1,4-naphthoquinone and aldehydes has been developed with addition of hexamethylbenzene (HMB). The driving force for the reaction is the intermolecular CT interaction between HMB and DANQ resulting in enhancement of nucleophilicity as evidenced from spectral and ab initio calculations. The structure of the compounds was confirmed by UV-vis, IR, ¹H NMR, ¹³C NMR and elemental analysis. The advantages of this procedure are mild reaction conditions, high yield of products, operational simplicity and easy work-up procedures.

Full text of DOI:10.1039/c2ra21372a

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Intermolecular charge transfer facilitated synthesis and
spectral characterization of Schiff bases of a weak
nucleophile 2,3-diamino-1,4-naphthoquinone3
Cite this: RSC Advances, 2013, 3,
1502
Angupillai Satheshkumar and Kuppanagounder P. Elango*
A new synthetic protocol for the formation of novel Schiff bases between a weak nucleophile, 2,3-
diamino-1,4-naphthoquinone and aldehydes has been developed with addition of hexamethylbenzene
(HMB). The driving force for the reaction is the intermolecular CT interaction between HMB and DANQ
resulting in enhancement of nucleophilicity as evidenced from spectral and ab initio calculations. The
structure of the compounds was confirmed by UV-vis, IR, 1H NMR, 13C NMR and elemental analysis. The
advantages of this procedure are mild reaction conditions, high yield of products, operational simplicity
and easy work-up procedures.
Received 6th July 2012,
Accepted 17th November 2012
DOI: 10.1039/c2ra21372a
www.rsc.org/advances
good yield, while those involving acid-sensitive carbonyl
compounds or weak nucleophilic amines can be troublesome,
Introduction
leading to decomposed starting materials or little or no yield.21
Under such circumstances the purification of the imine is also
very difficult. The main objective, therefore, of the present
endeavour is to make use of the phenomenon of charge
transfer complexation, by a foreign electron donor, in the
imine formation between a weak nucleophile, 2,3-diamino-1,4-
Ever since the discovery of imine formation in 1864 by Hugo
Schiff,1 this classical reaction has been a versatile tool in
organic synthesis. Imines have long been the focus of synthetic
chemistry due to their dynamic nature and broad spectrum of
applications such as build-up of complex molecular architec-
tures,2 interlocked molecules,3 in biological chemistry4 and
material areas.5 They are one of the synthetically important
scaffolds for the system of triheteroarylmethanes.6 The
nucleophilic addition of nitro alkanes to the CLN bond of
imines known as the aza-Henry reaction is a useful C–C bond
forming processes in organic synthesis.7 Likewise, imines are
employed in the synthesis of various compounds such as one-
step complex nitrogen heterocycles (poly-cyclic lactam pro-
ducts),8 piperidines9,10 and unusual amino acids.11 The
applications of imine compounds in other fields also are well
documented viz. metal ions and/or anions sensors,12 organic
semiconductors13 fluorescent and chromogenic probe drug
delivery systems15 and as most celebrated ligands in coordina-
tion chemistry.16
Major imine formation procedures involve the condensa-
tion of primary amines with carbonyl compounds under
conditions which remove water either chemically or physically
by using different catalyst and methods such as acetic acid as a
catalyst in ethanol,17 Lewis acid (TiCl4),18 molecular sieves,19
Dean–Stark apparatus,20 etc. Most of the reactions proceed in
naphthoquinone
(1)
(DANQ),
and
aldehydes.
Aminonaphthoquinones have a p-conjugated system, a strong
intramolecular charge-transfer chromophoric unit and are
thus of interest as candidates for non-linear optical materials.
Hence, in the present study, it is used as a precursor for the
synthesis of Schiff bases.
Result and discussion
14
Attempts have been made by us to synthesize imines of the
weak nucleophile DANQ with different aldehydes under
different conventional conditions and the results obtained
are collected in Table 1. The overall reaction is depicted in
Scheme 1. The results indicated that all these efforts resulted
in either no or very poor yields.
It is presumed that the observed poor/no yields may be due
to the very weak nucleophilic nature of the amine. Also it is
due to the existence of intramolecular charge transfer
transition, from amine to quinone, within the DANQ
molecule.22 The electronic spectrum of DANQ exhibits the
characteristic intramolecular CT band at 516 nm (Fig. 1) which
is highly solvent dependent23 (Fig. 2). Both specific and non-
specific solute–solvent interactions were found to influence
the absorption maximum. The absorption maximum was
Department of Chemistry, Gandhigram Rural Institute (Deemed University),
Gandhigram, 624 302, India. E-mail: drkpelango@rediffmail.com;
Fax: +91 451 2454466
Electronic Supplementary Information (ESI) available: Synthesis & the UV-vis
3
spectra , Scott plot, Stern–Volmer plot, 1H and 13C NMR spectra of the products
and molecular orbital structure for HMB and DANQ.
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Table 1 Reaction conditions and amounts of imine formed between 1 and
representative aldehydes (2a–2c)a
Reagent
Reactant
apparatus Solvent Time (h) Temp. (uC) Yield (%)
A
B
C
D
Ethanol 12
78
40
40
32
—
—
20
DCM
DCM
12
12
Toluene 12
110
A
B
C
D
Ethanol 12
78
40
40
15
—
—
10
DCM
DCM
12
12
Toluene 12
110
A
B
C
D
Ethanol 12
78
40
40
13
—
—
5
DCM
DCM
12
12
Toluene 12
110
a
Fig. 1 Electronic absorbance spectra of SANQ, DANQ and DCNQ in ethanol at
A-Glacial acetic acid; B-TiCl4; C-Molecular sieves (4Å); D-Dean–Stark
apparatus; DCM-dichloromethane
298 K.
found to largely depend on the polarity of the medium and
observed to increase with an increase in polarity of the
intramolecular CT transition, the nitrogen atom of the amine
moiety would attain sufficient electron density and conse-
quently can form the imine with aldehydes quite easily. To
achieve this, a foreign electron donor, hexamethylbenzene
(HMB), has been added to the reaction mixture before the
addition of the aldehyde.
medium (see ESI ). Further, from Fig. 1, it is evident that there
3
is no such intramolecular CT transition in the case of 2,3-
dichloronaphthaquinone (DCNQ) while it is present in the
imine formed with salicylaldehyde, (2E)-2-(2-hydroxybenzyli-
deneamino)-3-aminonaphthalene-1,4-dione
(SANQ).
The selection of HMB is based on the fact that it is inert
towards either of the reactants, a relatively good electron
donor known to form intermolecular CT complexes with
DANQ and it is easily removable from the reaction mixture
after completion of the reaction, simply by n-hexane washing.
In line with our expectations this strategy has been found to
work exceedingly well. In order to investigate whether the
Furthermore, on adding increasing amounts of p-toluenesul-
fonic acid to an ethanolic solution of DANQ, the absorbance of
the intramolecular CT band decreased indicating a progressive
unavailability of the lone pair of electrons on the nitrogen
atom of the amino group for the CT transition, as a result of
protonation (Fig. 3). It is conceived that if, by some means, one
could either remove or relatively decrease the intensity of the
Fig. 2 Electronic spectra of DANQ in various solvents viz. a) carbon tetrachloride,
b) chloroform, c) ethylacetate, d) THF, e) tert-butyl alcohol, f) acetone, g)
ethanol, h) methanol, i) dimethylformamide, j) dimethylsulphoxide at 298 K.
Scheme 1 Condensation of 2,3-diaminonaphthoquinone with aldehydes.
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Table 2 Reaction conditions and amount of imine formed between 1 and (2a–
2j) aldehydes in ethanol
Nucleophile
Aldehyde
Temp. (uC)
Yield (%)
RT
94
7
23
RTa
80a
, 2a
, 2b
50
50
50
92
91
89
, 2c,
, 2d
Fig. 3 Electronic spectra of DANQ with the addition of pTSA of various
concentrations in acetonitrile at 298 K.
50
50
90
93
added donor HMB has completely overcome or decreased the
intensity of the intramolecular CT phenomenon, the interac-
tion between the HMB and DANQ has spectroscopically and
theoretically been studied. Incremental addition of HMB to
DANQ, decreased the intensity of the intramolecular CT band
, 2e
(Fig. S1 ) indicating the interaction of HMB with DANQ. To
3
investigate whether the medium or the aldehyde can act as a
donor in the formation of intermolecular CT complex with
DANQ, representative reactions were also carried out in
toluene (Table 1) and in benzene (Table 2). The results
indicated that toluene or benzene behaves simply as a medium
rather than as an electron donor to the extent to overcome the
intramolecular CT interaction. Likewise, an additional equiva-
lent of salicylaldehyde (as a representative case) added to the
reaction mixture doesn’t alter the percentage yield confirming
the non-participation of the aldehyde in the intermolecular CT
interaction.
After optimizing the reaction conditions, a variety of
aldehydes were also been employed under similar conditions
to evaluate the utility of this reaction. The results are shown in
Table 2. The aromatic aldehydes carrying both electron
withdrawing and electron releasing substituents were also
converted to their corresponding imines in good yields. It is
noteworthy that the reactions of substituted aldehydes
proceeded with the expected good yield and also no undesir-
able side reactions were observed.
, 2f
50
90
12
70a
, 2g
, 2h
RT
96
12
16
RTa
80a
RT
50
91
83
, 2i
, 2j
UV-Vis absorption spectroscopic study
a
In benzene;
The interaction between DANQ and HMB was studied using
UV-vis spectral technique. The formation constant (K) and
molar extinction coefficient (e) of the 1 : 1 CT complex formed
between HMB and DANQ in ethanol, were determined
spectrophotometrically using the Scott equation as reported
earlier.24 The values of K and e determined (K = 2180 mol L-1;
the formed CT complex is of strong type.25,28 Fluorescence
spectral technique has also been employed to investigate the
interaction between HMB and DANQ (Fig. 4).
log e = 3.32) from the linear Scott plot (Fig. S2 ) suggested that
3
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Fig. 5 Molecular orbitals of hexamethylbenzene (HMB) and 2,3-diamino-
naphthoquinone (DANQ).
(28.0870 eV) and the LUMO of DANQ (0.4446 eV) is 8.5316 eV
which corresponds to the energy required for the formation of
p–p* intermolecular CT complex which is relatively less when
compared to that required for the intramolecular CT transi-
tion. Thus, the intermolecular CT transition p*(eg)rp(eg),
between HMB and DANQ, can occur more easily. Also as these
two MOs which are involved in intermolecular CT complex
formation possess identical symmetries their overlap is
favored to a larger extent. However, this CT transition could
not completely overcome the intramolecular CT transition
between the amine moiety and quinone, as the energy
differences between them are narrow. Thus the intermolecular
CT transition is the driving force which makes the amine
moiety relatively electron rich and consequently allows
formation of the imines with aldehydes.
Fig. 4 Fluorescence spectra for the HMB–DANQ system in chloroform at fixed
concentration of [D] = {2.375 6 1023 M (curve D)} and variable concentrations
of [A] 6 1025 = {3.125 (curve a), 6.25 (curve b), 9.375 (curve c), 12.5 (curve d),
15.625 (curve e), 18.75 (curve f)} M at 298 K.
The association constant, Kf , for the HMB–DANQ interac-
tion has been computed using emission data method
described by Ward (Fig. S4 ).26,28 The value of Kf obtained
3
for the HMB–DANQ system is found to be 3.09 6 105 mol L21
indicating
a strong interaction between the constituent
partners. The standard Gibbs energy change DGo was
calculated from Kf using the relation DGo = 22.303 RT log10
Kf. The DGo value for the system was found to be 231 kJ
mol21, indicating spontaneous interaction between the reac-
tion partners.
The energies of the HOMO and the LUMO MOs of the
imines (3a–j) were also computed by the same method and are
collected in Table S1 . It is evident from the results that the
3
energy required for intramolecular CT transition to occur in
the imines is relatively lower than that required in DANQ. As a
result of this, the intramolecular CT transition in 3a–j can
occur easily when compared to that in DANQ. Though the
energy required to form intermolecular CT complex between
the imines and HMB is comparable with that for DANQ–HMB
CT complex, it could not overcome the easy intramolecular CT
transition prevailing in the imines. Consequently it prevents
the formation of dimeric imines by reacting with another
aldehyde molecule. This observation is well supported by the
magnitude of the formation constants for these two CT
complexes determined by using fluorescence data.
Further, the positive deviation observed in the Stern–Volmer
plot (Fig. S3 ) at higher concentrations of DANQ may be due to
3
the simultaneous presence of dynamic and static quenching
mechanisms in the interaction between HMB and DANQ.27,28
Furthermore, the interaction between HMB and representa-
tive imines (3g and 3i) has also been studied by fluorescence
methods and the formation constant Kf calculated are 3.61 6
102 and 14.11 mol L21 for 3g and 3i, respectively. This
indicated that the intermolecular charge transfer transition
between HMB and imines are relatively weaker than that of
HMB–DANQ and which may not be strong enough to derive
the formation of imine dimer.
Mechanism of the reaction
The plausible mechanism of the imine formation by the weak
nucleophile, DANQ, is depicted in Scheme 2. The added
foreign donor HMB initially forms an intermolecular CT
complex with DANQ. Such a complexation relatively reduced
the intensity of intramolecular CT transition between the
amine moiety and quinone in the DANQ molecule. This
intermolecular CT complexation made the N-atom of the
quinone relatively electron rich and consequently assisted the
imine formation of the weak nucleophile DANQ with different
aldehydes. The reaction conditions and observed yield of the
imine formed between DANQ and different aldehydes are
Theoretical calculation
Ab initio computations were performed (method: RHF/6-311G),
without considering the solvent effects for HMB and DANQ
molecules. The molecular orbitals (MOs) thus computed are
shown in Fig. 5. In the case of DANQ molecule, the energy
corresponding to the HOMO and LUMO are 28.8653 and
0.4446 eV, respectively. The energy gap between these two
MOs29 is 9.3099 eV which corresponds to the energy needed
for the intramolecular CT transition to occur within the
molecule. While the energy gap between the HOMO of HMB
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(2 g, 0.0106 mol) in 10 mL of ethanol, HMB (1.897 g, 0.0116 mol)
was added and the reaction mixture was stirred at RT for 15 min.
Afterwards 2-hydroxybenzaldehyde (2a) (2.595 g, 0.0212 mol) was
slowly added into the reaction mixture. The reaction mixture was
stirred at RT for 1 h and the reaction was monitored by TLC
(Thin Layer Chromatography). Once the reaction has been
completed 20 mL of n-hexane was poured into the crude reaction
mixture and stirred for 5 min. Finally the reaction mixture was
filtered through filter paper under vacuum and washed with 20
mL of n-hexane to get the pure product as a dark brown solid
(1.49 g) ; Yield = 94%.
1H NMR (DMSO-d6, 300 MHz) d 12.11 (s, 1H), 9.14 (s, 1H),
7.98 (t, J = 9 Hz, 2H), 7.81 (t, J = 9 Hz, 1H), 7.73 (m, 2H), 7.39 (t,
J = 9 Hz, 1H), 7.10 (s, 2H), 6.96 (t, J = 6 Hz, 2H).
13C NMR (DMSO-d6, 75 MHz) d 181.3, 176.2, 159.8, 142,
134.7, 132.9, 132.4, 131.6, 130.0, 125.9, 125.3, 122.4, 120.5,
119.1, 116.4.
Scheme 2 Mechanism of intermolecular CT assisted condensation reaction
between DANQ and aldehydes.
FT-IR (KBr, cm21) 3430 (OH), 1671, 1604 (CLO), 1577
(HCLN–).
Elemental analysis: Anal. Calcd. for C17H12N2O3: C, 69.86; H,
4.14; N, 9.58. Found: C, 69.31; H, 4.20; N, 10.10.
given in Table 2. Further, when the reaction was carried out in
the presence of HMB in ethanol at 40 uC it was considerably
reduced to less than an hour for all the chosen aldehydes.
Also, as expected, after completion of the reaction, HMB can
be completely and easily removed from the reaction mixture
simply by washing with n-hexane in which the imines are
insoluble.
2-((Thiophene-2-yl)methyleneamino)-3-aminonaphthalene-1,4-
dione (3b). The procedure followed for the synthesis was the
same as that of 3a; (2b) thiophene-2-carbaldehyde (2.383 g,
0.0212 mol) was used instead of 2a and the reaction
temperature was changed to 40 uC instead of RT. The final
product (3b) was a dark brown solid (1.38 g); Yield = 92%.
1H NMR (DMSO-d6, 300 MHz) d 9.44 (s, 1H), 7.96 (t, J = 9 Hz,
2H), 7.82 (t, J = 6 Hz, 2H), 7.71 (m, 2H), 7.22 (t, J = 3 Hz, 6 Hz,
1H), 6.93 (s, 2H).
Conclusion
To conclude, the intermolecular CT complex formed between
HMB and the weak nucleophile DANQ, assisted the imine
formation of the later with different aldehydes. The proposed
intermolecular charge transfer assisted synthetic protocol
works well for the synthesis of Schiff bases of a weak
nucleophile DANQ with variety of aldehydes and is suitable
for scale up purposes.
13C NMR (DMSO-d6, 75 MHz) d 181.2, 177.2, 155.4, 144.1,
143.6, 134.7, 132.6, 132.5, 132.3, 130.9, 130.1, 128.2, 125.9,
125.2, 121.9.
FT-IR (KBr, cm21) 1666, 1603 (CLO), 1573 (HCLN–).
Elemental analysis: Anal. Calcd. for C15H10N2O2S: C, 63.81;
H, 3.57; N, 9.92. Found: C, 64.01; H, 3.52; N, 9.90.
Experimental Section
2-((Furan-2-yl)methyleneamino)-3-aminonaphthalene-1,4-dione
(3c). The procedure followed for the synthesis was the same as
that of 3a; (2c) furan-2-carbaldehyde (2.042 g, 0.0212 mol) was
used instead of 2b. The final product (3c) was a dark red solid
(1.287 g); Yield = 91%
General. Commercially available high purity solvents and
reagents were used as received. Thin layer chromatography
was performed with fluorescent silica coated aluminum
sheets. The electronic absorption spectra of the products were
recorded on a double beam spectrophotometer (Jasco, Japan
V-630) using 1 cm matched quartz cells. The fluorescence
spectra were obtained on a spectrofluorimeter (JASCO 6200,
Japan). The excitation wavelength was 270 nm and the
emission was monitored at 307 nm. The excitation, emission
slit width (5 nm) and the scan rate (250 nm) was kept constant
for all of the experiments. FT-IR spectra were obtained as KBr
pellets (JASCO FT-IR 460 Plus, Japan). Reaction products were
characterized by nuclear magnetic resonance spectroscopy
1H NMR (DMSO-d6, 300 MHz) d 9.25 (s, 1H), 7.99 (m, 3H),
7.82 (t, J = 9 Hz, 1H), 7.71 (t, J = 9 Hz, 1H), 7.31 (d, J = 6 Hz, 1H),
7.09 (s, 2H), 6.72 (m, 1H).
13C NMR (DMSO-d6, 75 MHz) d 181.3, 177.3, 153.3, 149.4,
146.0, 144.3, 134.7, 132.6, 132.3, 130.1, 125.8, 125.2, 121.7,
115.2, 112.6.
FT-IR (KBr, cm21) 1668, 1600 (CLO), 1573 (HCLN–).
Elemental analysis: Anal. Calcd. for C15H10N2O3: C, 67.67; H,
3.79; N, 10.52. Found: C, 67.39; H, 3.55; N, 10.44.
1
1
(Bruker, H NMR 300 MHz, 13C NMR 75 MHz). The H NMR
spectra data is expressed in the form: Chemical shift in units
of ppm (normalized integration, multiplicity, the value of J in
Hz).
2-(4-Hydroxy-3-methoxybenzylideneamino)-3-aminonaphtha-
lene-1,4-dione (3d). The procedure followed for the synthesis
was the same as that of 3a; (2d) 4-hydroxy-3-methoxybenzalde-
hyde (3.235 g, 0.0212 mol) was used instead of 2b. The final
product (3d) was a brown solid (1.5243 g); Yield = 89%.
Synthesis of compounds 3a–j. (2E)-2-(2-Hydroxybenzylideneamino)-
3-aminonaphthalene-1,4-dione (3a). To a stirred solution of DANQ
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1H NMR (DMSO-d6, 300 MHz) d 9.80 (s, 1H), 9.15 (s, 1H),
8.08 (d, J = 6 Hz, 1H), 7.95 (m, 2H), 7.82 (m, 2H), 7.69 (s, 1H),
7.43 (d, J = 6 Hz, 1H), 6.99 (s, 2H), 3.88 (s, 3H).
13C NMR (DMSO-d6, 75 MHz) d 181.4, 176.9, 164.5, 158.5,
155.2, 133.4, 132.9, 132.4, 132.3, 131.5, 129.0, 125.9, 125.3,
120.4, 119.1, 58.6
1H NMR (DMSO-d6, 300 MHz) d 9.57 (s, 1H), 8.70 (d, J = 6 Hz,
2H), 8.00 (m, 4H), 7.85 (m, 1H), 7.73 (m, 3H).
13C NMR (DMSO-d6, 75 MHz) d 181.4, 177.1, 158.09, 150.11,
146.1, 144.0, 135.0, 132.8, 132.3, 130.0, 125.9, 125.4, 122.0,
120.1.
FT-IR (KBr, cm21) 1667, 1610 (CLO), 1560 (HCLN–).
Elemental analysis: Anal. Calcd. for C16H11N3O2: C, 69.31; H,
4.00; N, 15.15. Found: C, 69.43; H, 4.20; N, 15.31.
FT-IR (KBr, cm21) 3320 (OH), 1661, 1603 (CLO), 1566
(HCLN–).
Elemental analysis: Anal. Calcd. for C18H14N2O4: C, 67.07; H,
4.38; N, 8.69. Found: C, 67.21; H, 4.29; N, 8.56.
2-Amino-3-(pyridin-2-ylmethyleneamino)naphthalene-1,4-dione
(3i)30. The procedure followed for the synthesis was the same
as that of 3a; (2i) picolinaldehyde (2.272 g, 0.0212 mol) was
used instead of 2b. The final product (3i) was a dark brown
solid (1.34 g); Yield = 91%.
2-(4-Chlorobenzylideneamino)-3-aminonaphthalene-1,4-dione
(3e). The procedure followed for the synthesis was the same as
that of 3a; (2e) 4-chloro benzaldehyde (2.979 g, 0.0212 mol)
was used instead of 2b. The final product (3e) was a dark
brown solid (1.48 g); Yield = 90%.
1H NMR (DMSO-d6, 300 MHz) d 9.52 (s, 1H), 8.68 (d, J = 6 Hz,
1H), 8.56 (d, J = 9 Hz, 1H), 7.98 (m, 2H), 7.87 (m, 2H), 7.73 (t, J
= 6 Hz, 9 Hz, 1H), 7.55 (s, 2H), 7.46 (t, J = 6 Hz, 1H).
13C NMR (DMSO-d6, 75 MHz) d 181.4, 177.1, 160.9, 155.7,
149.3, 145.6, 136.4, 134.9, 132.8, 132.2, 130.0, 126.0, 125.3,
124.9, 121.0, 120.4
1H NMR (DMSO-d6, 300 MHz) d 9.42 (s, 1H), 8.11 (d, J = 6 Hz,
2H), 7.98 (m, 2H), 7.83 (t, J = 9 Hz, 6 Hz, 2H), 7.75 (s, 2H), 7.56
(d, J = 6 Hz, 2H) .
13C NMR (DMSO-d6, 75 MHz) d 181.3, 177.2, 155.3, 145.8,
140.71, 134.6, 133.1, 132.9, 132.5, 132.4, 132.2, 130.4, 128.9,
125.7, 125.3, 124.5, 121.1.
FT-IR (KBr, cm21) 1669, 1600 (CLO), 1568 (HCLN–).
Elemental analysis: Anal. Calcd. for C16H11N3O2: C, 69.31; H,
4.00; N, 15.15. Found: C, 69.43; H, 4.17; N, 15.22.
FT-IR (KBr, cm21) 1669, 1610 (CLO), 1570 (HCLN–).
Elemental analysis: Anal. Calcd. for C17H11ClN2O2: C, 65.71;
H, 3.57; N, 9.02. Found: C, 65.41; H, 3.60; N, 9.17.
2-(2-Methylpropyllideneamino)-3-aminonaphthalene-1,4-dione
(3j). The procedure followed for the synthesis was the same as
that of 3a; (2j) isobutyraldehyde (1.532 g, 0.0212 mol) was used
instead of 2b. The final product (3j) was a highly viscous liquid
(1.06 g); Yield = 83%.
4-((3-Amino-1,4-dioxo-1,4-dihydronaphthalen-2-ylimino)-
methyl)benzonitrile (3f). The procedure followed for the
synthesis was the same as that of 3a; (2f) 4-formylbenzonitrile
(2.805 g, 0.0212 mol) was used instead of 2b. The final product
(3f) was a dark brown solid (1.4890 g); Yield = 93%.
1H NMR (DMSO-d6, 300 MHz) d 9.61 (s, 1H), 8.27 (d, J = 6 Hz,
2 H), 7.99 (m, 4H), 7.66 (d, J = 6 Hz, 2H), 7.45 (s, 2H).
13C NMR (DMSO-d6, 75 MHz) d 181.3, 177.0, 158.3, 145.9,
141.5, 134.9, 133.1, 132.8, 132.5, 132.3, 132.2, 130.0, 128.9,
125.9, 125.3, 124.5, 120.4, 118.7, 112.4.
1H NMR (DMSO-d6, 300 MHz) d 9.06 (s, 1H), 8.10 (m, 2H),
7.88 (m, 2H), 6.90 (s, 1H), 3.77 (s, 1H), 1.38 (d, J = 6.9 Hz, 3H),
1.12 (m, 3H).
13C NMR (DMSO-d6, 75 MHz) d 178.3, 176.2, 163.0, 151.8,
135.5, 133.3, 131.0, 130.7, 130.5, 126.8, 126.3, 126.1, 33.2, 25.4,
24.2.
FT-IR (KBr, cm21) 1672, 1600 (CLO), 1573 (HCLN–).
Elemental analysis: Anal. Calcd. for C18H11N3O2: C, 71.75; H,
3.684; N, 13.95. Found: C, 71.60; H, 3.58; N, 13.89.
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