An expeditious synthetic approach towards the synthesis of Bis-Schiff bases (aldazines) using ultrasound

Article abstract of DOI:10.1016/j.ultsonch.2013.12.011

Aldazines (Bis-Schiff bases) 1-24 were synthesized using aromatic aldehydes (heterocyclic and benzaldehydes) and hydrazine hydrate under reflux using conventional heating and/or via ultrasound irradiation using BiCl₃ as catalyst. Ultrasonication conditions with cat. BiCl₃ proved to be an effective, environmentally friendly synthetic procedure. This methodology is robust in the presence of electron donating and electron withdrawing groups affording desired products with high yields (>95%) in just a couple of minutes vs. hours using conventional heating.

Full text of DOI:10.1016/j.ultsonch.2013.12.011

Ultrasonics Sonochemistry 21 (2014) 1200–1205
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
An expeditious synthetic approach towards the synthesis of Bis-Schiff
bases (aldazines) using ultrasound
Khalid M. Khan a, , Waqas Jamil a,e, Nida Ambreen a, Muhammad Taha a,b, Shahnaz Perveen c,
⇑
Guillermo A. Morales d
a H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi 75270, Pakistan
b Research Institute of Natural Products for Drug Discovery (RiND), Faculty of Pharmacy, Universiti Teknologi MARA (UiTM), Puncak Alam Campus, 42300 Bandar Puncak Alam,
Selangor Darul Ehsan, Malaysia
c PCSIR Laboratories Complex, Karachi, Shahrah-e-Dr. Salimuzzaman Siddiqui, Karachi 75280, Pakistan
d Morales Consulting LLC, 11474 Perkins Street, Carmel, IN 46032, USA
e Institute of Advance Research Studies in Chemical Sciences, University of Sindh Jamshoro, Hyderabad 76080, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
Aldazines (Bis-Schiff bases) 1–24 were synthesized using aromatic aldehydes (heterocyclic and benzalde-
hydes) and hydrazine hydrate under reflux using conventional heating and/or via ultrasound irradiation
using BiCl3 as catalyst. Ultrasonication conditions with cat. BiCl3 proved to be an effective, environmen-
tally friendly synthetic procedure. This methodology is robust in the presence of electron donating and
electron withdrawing groups affording desired products with high yields (>95%) in just a couple of min-
utes vs. hours using conventional heating.
Received 22 February 2012
Received in revised form 22 October 2013
Accepted 11 December 2013
Available online 21 December 2013
Keywords:
Ó 2013 Elsevier B.V. All rights reserved.
Aldazines (Bis-Schiff bases)
Ultrasonication
Rapid
High yielding method
1. Introduction
important tool in the field of synthetic organic chemistry. The
use of ultrasound irradiation to drive and expedite chemical
Schiff bases are an important class of compounds in organic
chemistry exhibiting in many cases biological and pharmacological
activities [1–5]. Several Schiff bases, some containing different het-
erocyclic moieties, have been reported to exhibit anticancer [6],
antibacterial [7], antifungal [8,9], herbicidal [10], cytotoxic [11],
anticonvulsant [12], and antiproliferative [13] activities. Com-
plexes also containing Schiff bases have also been found to posses
antibacterial [14–20], antifungal [21,22], anticancer [23,24], and
herbicidal effects [25]. Aldazines or Bis-Schiff bases have received
great attention because of their analytical applications, particularly
as good spectrophotometric [26] and flourimetric agents [27,28].
Although several synthetic methods for the synthesis of Schiff
and Bis-Schiff bases have been reported [29–38], many of them suf-
fer of several disadvantages such as low yields, prolonged reaction
times, harsh reaction conditions, and requiring excess amounts of
catalysts. Therefore, there is a need to identify new, efficient, eco-
nomical synthetic methods for this class of compounds.
transformations has made and continues to make a great impact
in organic synthesis, a fact well documented in the literature
[39,40].
In past few decades bismuth compounds have been used as cat-
alyst in organic synthesis. Their low cost, high stability and ease of
handling make them both attractive and useful catalysts for syn-
thetic applications. Among them bismuth(III) trichloride (BiCl3)
has been reported to be an efficient catalyst for many widely used
organic transformations, such as intramolecular hetero-Diels–Alder
reactions [41], selective hydroarylation of styrenes [42], C-alkyl-
ation of pyrroles [43], regioselective ring opening of epoxides
[44], and quinoline synthesis [45].
Although several Schiff bases have been synthesized via sonica-
tion irradiation using catalysts, to the best of our knowledge no
study has been reported on the synthesis of Bis-Schiff bases with
the assistance of ultrasound irradiation using BiCl3 as catalyst.
We herein wish to report a newly developed method for the
quick and high-yielding synthesis of aldazines (Bis-Schiff bases)
using ultrasound irradiation in the presence of catalytic amounts
of bismuth(III) trichloride. A comparison of this novel ultra-
sound-based synthetic approach with conventional synthetic
methods demonstrates that our new methodology is robust and
The chemical application of ultrasound irradiation, also referred
to as sonochemistry, has become a leading methodology and
⇑
Corresponding author. Tel.: +92 2134824910; fax: +92 2134819018.
E-mail addresses: hassaan2@super.net.pk, khalid.khan@iccs.edu (K.M. Khan).
1350-4177/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2013.12.011

K.M. Khan et al. / Ultrasonics Sonochemistry 21 (2014) 1200–1205
1201
compatible with electron donating and electron withdrawing
groups affording desired products with high yields (>95%) in just
a couple of minutes vs. hours when using conventional heating.
was formed within 2 min. This solid was filtered, collected, and
washed with water and proved to be desired pure product with
95% yield conversion. Only when necessary the final product had
to be purified via recrystallization from ethanol (Scheme 1). The
identity and structure of the Bis-Schiff bases (1–24) were con-
firmed by 1H NMR, mass spectrum, and elemental analyses.
The conventional heating method was found to be time con-
suming suffering of low yields when compared to our ultrasonica-
tion-based method (Table 1). The role of BiCl3 in our
ultrasonication-based method was found to accelerate the reaction
further. This was confirmed by carrying out a reaction in the ab-
sence of BiCl3 finding that, although the reaction took place, it took
longer (10–15 min) vs. the 1–2 min when in the presence of BiCl3.
We confirmed the robustness of our BiCl3-catalyzed ultrasoni-
cation-based method using heterocyclic aldehydes obtaining de-
sired Bis-Schiff bases 14 and 15 in excellent yields. We also
assessed that our method is compatible with a broad range of elec-
tron donating and electron withdrawing groups present in the
benzaldehyde moiety. Moreover, the final crude products were iso-
lated in many cases highly pure, and only when necessary they
were recrystallized from ethanol.
2. Result and discussion
2.1. Chemistry
Bis-Schiff bases 1–24 were synthesized by sonication as well as
conventional heating methods (Table 1).
In the conventional heating study, benzaldehyde was dissolved
in absolute ethanol followed by the addition of 2–3 drops of conc.
hydrochloric acid, and hydrazine hydrate. The reaction mixture
was heated to reflux for 2–4 h, the solvent evaporated, and the
resulting residue washed with and recrystallized from ethanol to
afford desired product with 70–80% yield. When the same reaction
was repeated using BiCl3 as a catalyst instead of hydrochloric acid
no significant yield improvement and time shortening were
observed. However, when the same reaction was carried out in
the presence of ultrasound irradiation at room temperature
(instead of conventional heating) it was found that a precipitate
3. Experimental details
Table 1
Comparison of conventional (Convn.) vs. ultrasonication (US) method.
NMR spectra were recorded on
a Bruker AM 300 MHz
instrument, Bruker Avance-300, France. A Carlo Erba Strumentazi-
on-Mod-1106, Italy was used for CHN analysis. Mass Spectra were
recorded on a Finnigan MAT-311A, Germany. Thin layer chromatog-
raphy (TLC) was carried out on pre-coated silica gel glass plates
(Kieselgel 60, 254, E. Merck, Germany). UV light (254 nm and
365 nm) and/or iodine was used to visualize/develop the TLC plates.
S. No.
Aldehyde
derivatives
Conventional Ultrasonication Yield % Yield
time (min)
time (min)
(Convn.) % (US)
1
2
2-Methoxy
benzaldehyde
4-Methoxy
benzaldehyde
4,5-Dimethoxy
benzaldehyde
3,4,5-Trimethoxy
benzaldehyde
2-Ethoxy
benzaldehyde
4-Ethoxy
benzaldehyde
2-Chloro
benzaldehyde
3-Chloro
benzaldehyde
4-Chloro
benzaldehyde
3,4-Dichloro
benzaldehyde
2,4-Dichloro
benzaldehyde
2-Fluoro
benzaldehyde
3-Fluoro
benzaldehyde
2-Furfural
3-Thiophene
aldehyde
2-Nitro
benzaldehyde
3-Nitro
60
1
68
75
75
66
82
76
80
68
78
76
66
67
78
>95
>95
>95
>95
>95
>95
>95
>95
>95
>95
>95
>95
>95
60
60
1
1
1
1
1
1
1
1
1
1
2
2
3
4
60
3.1. Ultrasonic process equipment
5
60
Ultrasonic mediated reactions were carried out in Clifton Ultra-
sonic Bath (2 x T2A, 300 W, DU-4) made by Nickel Electro Ltd,
Weston-S-Mare Somerset, England. All the experimental parame-
ters were performed with output power of 300 W.
6
60
7
60
8
60
3.2. General procedure for the synthesis of compounds
9
60
3.2.1. Conventional method
10
11
12
13
120
120
120
120
To a solution of benzaldehyde (1 mmol) in ethanol (10 mL) was
added conc. HCl (1–2 drops) and then hydrazine hydrate 55% (Sigma
Alrich) (1 mL). The reaction was stirred and refluxed for a specific
time (see Table 1). Upon reaction completion (TLC analysis) the sol-
vent was evaporated, the resulting residue washed with cold water,
and then re-crystallized from ethanol to afford desired product.
14
15
60
60
1
1
66
68
>95
>95
3.2.2. Ultrasonication method
16
17
120
120
2
2
78
80
>95
>95
A reaction flask containing benzaldehyde (1 mmol), hydrazine
hydrate 55% (Sigma Alrich) (1 mL) and catalytic (0.1 mol%)
amounts of BiCl3 was immersed in an ultrasonic bath containing
water at room temperature. The reaction mixture was exposed to
ultrasound irradiation for 1–2 min (reaction complete based on
TLC analysis). The resulting precipitate is filtered and washed with
water to afford pure desired product (yellow crystals). Only, when
necessary, final products were re-crystallized from ethanol.
benzaldehyde
2-Napthaldehyde
4-Methylthio
benzaldehyde
4-N,N-
Dimethylamino
benzaldehyde
Benzaldehyde
2-Hydroxy
18
19
60
60
2
1
66
75
>95
>95
20
60
1
77
>95
21
22
60
120
1
1
70
78
>95
>95
3.2.2.1. 2-Methoxybenzaldehyde-N-[-(2-methoxyphenyl)methylidene]
hydrazone (1). Yield: 97%; 1H NMR: (300 MHz, DMSO-d6): d 9.02 (s,
1H, –N@CH), 7.97, (dd, 1H, J6,4 = 1.5 J6,5 = 7.2 Hz, H-6), 7.58 (m, 2H,
H-5), 7.12, (d, 1H, J3,4 = 8.4 Hz, H-3), 7.05, (t, 2H, J4,(5,6) = 7.5 Hz,
H-4; EI MS: m/z (rel. abund.%), 268 (M+, 26), 237 (100), 150 (64),
benzaldehyde
2-Methyl
benzaldehyde
4-Methyl
23
24
60
60
1
1
76
68
>95
>95
benzaldehyde

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K.M. Khan et al. / Ultrasonics Sonochemistry 21 (2014) 1200–1205
1. HCl, reflux, 1-2 h
R
R
R-CHO
+
NH2NH2 H2O
.
N
N
2. Sonication, cat. BiCl3
R.T., 1-2 min
24 examples
Method 1) Conventional heating; Method 2) Ultrasound irradiation
Compound No.
1
R
Compound No.
13
R
MeO
2
6
5
6
5
3
F
4
4
6
5
2
3
3
4
2
3
14
15
5
O
OMe
2
6
4
5
2
5
MeO
2
S
OMe
6
O2N
6
5
4
5
6
16
17
18
3
MeO
OMe
4
OMe
EtO
2
6
5
6
3
5
O2N
8
4
4
1
7
2
6
5
3
6
3
5
4
OEt
6
5
2
3
Cl
6
5
7
8
19
20
3
4
SMe
6
2
3
2
6
5
5
Cl
4
N(Me)2
2
3
6
5
2
3
6
9
21
22
23
24
5
4
Cl
2
HO
Me
6
5
6
5
10
11
12
Cl
3
4
Cl
Cl
F
6
5
6
5
3
3
4
Cl
4
6
5
2
3
6
3
5
Me
Scheme 1. Synthesis of Bis-Schiff bases (1–24).

K.M. Khan et al. / Ultrasonics Sonochemistry 21 (2014) 1200–1205
1203
119 (100), 91 (68), 77 (30). Anal. Calcd for C16H16N2O2, C = 71.62,
H = 6.02, N = 10.44. Found: C = 71.59, H = 6.01, N = 10.42.
3.2.2.10. 3-4-Dichlorobenzaldehyde-N-[-(3–4-dichlorophenyl)methyl-
idene]hydrazone (10). Yield: 97%; 1H NMR: (300 MHz, DMSO-d6): d
8.68(s, 2H, –N@CH), 8.09 (dd, 2H, J2,6 = 1.8 Hz, H-2), 7.90, (dd, 2H,
J6,2 = 2.1 Hz, J6,5 = 8.4 Hz, H-6), 7.70 (d, 2H, J5,6 = 8.4 Hz, H-5), EI
MS: m/z (rel. abund.%), 346 (M+, 9), 246 (6), 199 (60), 145 (53),
3.2.2.2. 4-Methoxybenzaldehyde-N-[-(4-methoxyphenyl)methylidene]
hydrazone (2). Yield 98%; 1H NMR: (300 MHz, DMSO-d6): d 8.57 (s,
1H, –N@CH), 7.83, (d, 2H, J6,5/2,3 = 8.7 Hz, H-6/2), 7.02 (d, 2H, J5,6/
3,2 = 8.7 Hz, H-3/5), 1.41(s, 6H, CH3); EI MS: m/z (rel. abund.%),
268 (M+, 87), 241 (15), 147 (100), 77 (20). Anal. Calcd for
123 (100). Anal. Calcd for
C14H8Cl4N2, C = 48.59, H = 2.33,
N = 8.10. Found: C = 48.58, H = 2.31, N = 8.08.
C
16H16N2O2, C = 71.62, H = 6.02, N = 10.44. Found: C = 71.58,
3.2.2.11. 2-4-Dichlorobenzaldehyde-N-[-(3–4-dichlorophenyl)methyl-
idene]hydrazone (11). Yield: 98%; 1H NMR: (300 MHz, DMSO-d6): d
8.97(s, 2H, –N@CH), 8.24 (d, 2H, J6,5 = 8.4 Hz, H-6), 7.54, (dd, 2H,
J5,3 = 2.1 Hz, J5,6 = 8.4 Hz, H-5), 7.66 (d, 2H, J3,5 = 2.1 Hz, H-3), EI
MS: m/z (rel. abund.%), 346 (M+, 3), 310 (19), 274 (21), 147 (15),
H = 6.02, N = 10.40.
3.2.2.3. 3,4-Dimethoxybenzaldehyde-N-[-(3,4-dimethoxyphenyl)meth
ylidene] hydrazone (3). Yield: 98%; 1H NMR: (300 MHz, DMSO-d6):
d 8.57 (s, 2H, –N@CH), 7.72 (d, 2H, J6,5 = 7.06 Hz, H-5), 7.60 (s, 2H,
H-2), 7.37 (dd, 2H, J6,5/6,2 = 7.5 Hz, H-6), 3.87 (s, 12H, OCH3), EI MS:
m/z (rel. abund.%), 328 (M+, 38), 297 (3), 191 (54), 151 (20) 79
(100), 77 (71). Anal. Calcd for C16H16N2O2, C = 71.62, H = 6.01,
N = 10.44. Found: C = 71.60, H = 6.00, N = 10.43.
123 (100). Anal. Calcd for
C14H8Cl4N2, C = 48.59, H = 2.33,
N = 8.10. Found: C = 48.56, H = 2.31, N = 8.06.
3.2.2.12. 3-Florobenzaldehyde-N-[-(3-florophenyl)methylidene]hydra-
zone (12). Yield: 97%; 1H NMR: (300 MHz, DMSO-d6): d 8.87 (s, 2H,
–N@CH), 8.16 (td, 2H, J4,5/4,2/4,6 = 7.8 H-4), 7.62, (dd, 2H, J2,4/
2,6 = 1.8 Hz, H-2), (dd, 2H, J5,6/5,4 = 7.5 Hz, H-5),7.27 (dd 2H, J6,5/
2,6 = 9.0 Hz, H-6) EI MS: m/z (rel. abund.%), 244 (M+, 42), 216 (18),
149 (100), 122 (50), 75 (61). Anal. Calcd for C14H10F2N2, C = 68.85,
H = 4.13, N = 11.47. Found: C = 68.82, H = 4.12, N = 11.46.
3.2.2.4. 3,4,5-Trimethoxybenzaldehyde-N-[-(3,4,5-trimethoxyphenyl)
methylidene] hydrazone (4). Yield: 98%; 1H NMR: (300 MHz,
DMSO-d6): d 8.57 (s, 2H, –N@CH), 7.72 (s, 2H, H-2), 7.60 (s, 2H,
H-6), (s, 18H, OCH3), EI MS: m/z (rel. abund.%), 388 (M+, 38), 257
(3), 191 (54), 151 (20) 79 (100), 77 (71). Anal. Calcd for
C
20H24N2O6, C = 61.84, H = 6.23, N = 7.21. Found: C = 61.80,
3.2.2.13. 2-Fluorobenzaldehyde-N-[-(2-fluorophenyl)methylidene] hy-
drazone (13). Yield: 88%; 1H NMR: (300 MHz, DMSO-d6): d 8.74 (s,
1H, –N@CH), 8.06 (dd, 2H, J3,4/3,5 = 8.7 Hz, H-3), 7.40 (m, 4H, H-4/5),
7.03 (t, 2H, J6,(5,7) = 7.50 Hz, H-6),; EI MS: m/z (rel. abund.%), 267
(M+, 7), 239 (100), 212 (9), 118 (76), 95 (71). Anal. Calcd for
H = 6.20, N = 7.21.
3.2.2.5. 2-Ethoxybenzaldehyde-N-[-(2-ethoxyphenyl)methylidene] hy-
drazone (5). Yield: 98%; 1H NMR: (300 MHz, DMSO-d6): d 9.04 (s,
2H, –N@CH), 8.10 (dd, 2H, J6,4 = 3 Hz J6,5 = 9 Hz, H-6), 7.47 (m, 2H,
H-4),(d, 2H, J3,4 = 8.1 Hz, H-3),(t, 2H, J5,(4,6) = 7.5 Hz, H-5), 4.21 (q,
4H, –CH2), 1.47 (t, 6H, –CH3); EI MS: m/z (rel. abund.%), 298 (M+,
9),165 (60), 135 (20), 118 (25), 74 (54). Anal. Calcd for
C14H10F2N2, C = 68.85, H = 4.13, N = 11.47. Found: C = 68.82,
H = 4.11, N = 11.45.
3.2.2.14. 2-Furaldehyde-N-[-2-furylmethylidene]hydrazone
(14). Yield: 98%; 1H NMR: (300 MHz, DMSO-d6): d 8.47(s, 2H, –
N@CH), 7.79 (d, 2H, J2,3 = 3.0 Hz, H-2), 7.06 (d, 2H, J4,3 = 3.3 Hz, H-
4), 7.54 (dd, 2H, J3,2/3,4 = 3.6 Hz, H-3); EI MS: m/z (rel. abund.%),
188 (M+, 100),131 (37), 94 (40), 52 (50). Anal. Calcd for
C
18H20N2O2, C = 72.95, H = 6.80, N = 9.45. Found: C = 72.92,
H = 6.79, N = 9.43.
3.2.2.6. 4-Ethoxybenzaldehyde-N-[-(4-ethoxyphenyl)methylidene] hy-
drazone (6). Yield 98%; 1H NMR: (300 MHz, DMSO-d6): d 8.57 (s,
1H, –N@CH), 7.83, (d, 2H, J6,5/2,3 = 8.7 Hz, H-6/2), 7.02 (d, 2H, J5,6/
3,2 = 8.7 Hz, H-3/5), 4.16 (q, J = 7 Hz, 4H, OCH2), 1.41(t, 6H, CH3);
EI MS: m/z (rel. abund.%), 296 (M+, 87), 269 (15), 175 (100), 133
(90), 120 (56), 77 (20). Anal. Calcd for C18H20N2O2, C = 72.95,
H = 6.80, N = 9.45. Found: C = 72.92, H = 6.79, N = 9.43.
C10H8N2O2, C = 63.82, H = 4.28, N = 14.89. Found: C = 63.79
H = 4.26, N = 14.85.
3.2.2.15. 3-Thiophenecarbaldehyde-N-[-3-thienylmethylidene]hydra-
zone (15). Yield: 97%; 1H NMR: (300 MHz, DMSO-d6): d 8.67 (s,
2H, –N@CH), 8.10 (s, 2H, H = 2), 7.67 (d, 4H, J4,5 = 3.0 Hz, H-4),
7.54 (d, 4H, J5/4 = 3.6 Hz, H-5); EI MS: m/z (rel. abund.%), 219 (M+,
63),192 (40), 174 (35), 110 (100). Anal. Calcd for C10H8N2S2,
C = 54.52, H = 3.66, N = 12.72. Found: C = 54.50, H = 3.65, N = 12.69.
3.2.2.7. 2-Chlorobenzaldehyde-N-[2-chlorophenyl)methylidene] hydr-
azone (7). Yield: 78%; 1H NMR: (300 MHz, DMSO-d6): d 9.04 (s, 2H,
–N@CH), 8.24 (d, 2H, J3,4 = 7.8 Hz, H-3), 7.56 (m, 6H, H-4/5/6), EI
MS: m/z (rel. abund.%), 277 (M+, 5), 240 (46), 206 (47), 129 (18),
75 (100). Anal. Calcd for
N = 10.11. Found: C = 60.66, H = 3.64, N = 10.08.
C14H10Cl2N2, C = 60.67, H = 3.64,
3.2.2.16. 2-Nitrobenzaldehyde-N-[-(2-nitrophenyl)methylidene] hy-
drazone (16). Yield: 98%; 1H NMR: (300 MHz, DMSO-d6): d9.05
(s,1H, –N@CH), 8.30 (dd, 1H, J3,5 = 1.5 Hz, J3,4 7.5 Hz, H-3), 7.91
(td, 1H, J4,5/4,3 = 7.8 Hz, H-4), 7.83 (m, 2HH-5), 8.17 (dd, 1H,
J6,41.2 Hz, J6,5 = 7.8 Hz, H-6);; EI MS: m/z (rel. abund.%), 294 (M+,
6), 298 (68), 206 (22), 135 (100), 103 (40), 91 (100). Anal. Calcd
for C14H10N4O4, C = 56.38, H = 3.38, N = 18.78. Found: C = 56.36,
H = 3.36, N = 18.74.
3.2.2.8. 3-Chlorobenzaldehyde-N-[-(3-chlorophenyl)methylidene] hy-
drazone (8). Yield: 97%; 1H NMR: (300 MHz, DMSO-d6): d 8.67 (s,
2H, –N@CH), 7.95(br. s, 2H, H-2), 7.93, (dd, 2H, J6,5/6,4 = 8.1 Hz, H-
6), (m, 4H, H-4/5), EI MS: m/z (rel. abund.%), 277(M+, 18), 165
(83), 138 (24), 111(60), 75 (100). Anal. Calcd for C14H10Cl2N2,
C = 60.67, H = 3.64, N = 10.11. Found: C = 60.64, H = 3.63, N = 10.09.
3.2.2.17. 3-Nitrobenzaldehyde-N-[-(3-nitrophenyl)methylidene]
hydrazone (17). Yield: 97%; 1H NMR: (300 MHz, DMSO-d6): d 8.40
(s, 2H, –N@CH), 8.65 (dd. 2H, J2,4/2,6 = 1.8 Hz, H-2), 8.32, (m, 2H,
H-4), (m, 2H, H-5), (dd, 2H, J6,5/6,2 = 8.1 Hz, H-6), EI MS: m/z (rel.
abund.%), 298(M+, 24), 165(28), 118(58), 89(100). Anal. Calcd for
3.2.2.9. 4-Chlorobenzaldehyde-N-[-(4-chlorophenyl)methylidene] hy-
drazone (9). Yield: 97%; 1H NMR: (300 MHz, DMSO-d6): d 8.67 (s,
2H, –N@CH), 7.56 (d, 4H, J2,3/6,5 = 8.7 Hz, H-2/6), 7.94 (d, 4H, J3,2/
5,6 = 9 Hz, H-3/5), EI MS: m/z (rel. abund.%), 277 (M+, 6), 165 (56),
138 (21), 111 (58), 75 (100). Anal. Calcd for
C
14H10Cl2N2,
C14H10N4O4, C = 56.38, H = 3.38, N = 18.78. Found: C = 56.35,
C = 60.67, H = 3.64, N = 10.11. Found: C = 60.64, H = 3.63, N = 10.09.
H = 3.36, N = 18.75.

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K.M. Khan et al. / Ultrasonics Sonochemistry 21 (2014) 1200–1205
3.2.2.18. 2-Napthaldehyde-N-[-(2-napthyl)methylidene]hydrazone
(18). Yield: 98%; 1H NMR: (300 MHz, DMSO-d6): d 8.44 (s, 2H, –
N@CH), 8.11 (s, 2H, H-), 8.10 (m, 4H, H-5/8), 7.99 (m, 4H, H-6/7)
7.61 (m, 4H, H-3/4); EI MS: m/z (rel. abund.%), 308 (M+, 41), 281
(51), 181(61), 172 (44), 154 (28), 127 (100). Anal. Calcd for
Acknowledgements
This work was supported by the Higher Education Commission
(Pakistan) under National Research Program for Universities Pro-
ject no. 20-1910.
C22H16N2, C = 85.69, H = 5.23, N = 9.08. Found: C = 85.67, H = 5.2,
N = 9.07.
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