4-Hydroxy-3-methoxy-benzaldehyde series aroyl hydrazones: Synthesis, thermostability and antimicrobial activities

Article abstract of DOI:10.1039/c4ra11747f

Efficient synthetic procedures for the preparation of aroyl hydrazones were developed by converting the corresponding ethyl ester into hydrazides, followed by a reaction with 4-hydroxy-3-methoxy-benzaldehyde. A series of aromatic hydrazides and aroyl hydrazones were characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR and thermogravimetric analysis. The thermal gravity analysis showed that the compounds 3a-3d were stable below 228.23, 227.65, 118.97 and 179.51 °C, respectively. The aromatic hydrazides and aroyl hydrazones showed antimicrobial activity towards Staplylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity experiments indicated that aroyl hydrazones had higher activity than the hydrazides. The presence of a hydroxyl group, as well as the number and position of the hydroxyl groups, were important and further enhance the antimicrobial activity. This journal is

Full text of DOI:10.1039/c4ra11747f

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4-Hydroxy-3-methoxy-benzaldehyde series aroyl
hydrazones: synthesis, thermostability and
antimicrobial activities
Cite this: RSC Adv., 2014, 4, 58895
a
a
b
b
*
*
Liang Wang, Da-Gang Guo, Yan-Yan Wang and Chang-Zheng Zheng
Efficient synthetic procedures for the preparation of aroyl hydrazones were developed by converting the
corresponding ethyl ester into hydrazides, followed by reaction with 4-hydroxy-3-methoxy-
a
benzaldehyde. A series of aromatic hydrazides and aroyl hydrazones were characterized by elemental
analysis, IR, 1H NMR, 13C NMR and thermogravimetric analysis. The thermal gravity analysis showed that
the compounds 3a–3d were stable below 228.23, 227.65, 118.97 and 179.51 ꢀC, respectively. The
aromatic hydrazides and aroyl hydrazones showed antimicrobial activity towards Staplylococcus aureus,
Escherichia coli and Pseudomonas aeruginosa. The antibacterial activity experiments indicated that aroyl
hydrazones had higher activity than the hydrazides. The presence of a hydroxyl group, as well as the
number and position of the hydroxyl groups, were important and further enhance the antimicrobial activity.
Received 3rd October 2014
Accepted 17th October 2014
DOI: 10.1039/c4ra11747f
www.rsc.org/advances
only intermediates but they are also very effective organic
compounds in their own right.
1. Introduction
Aroylhydrazones (>C]N–NH–CO–) are special group of
compounds due to their wide applications in chemistry and
biology and characterized by the presence two inter-linked
nitrogen atoms as Nsp2–Nsp3. Aroylhydrazones have been
attracting much attention from chemists in recent years
because of their biological activities, chemical and industrial
versatility, and strong tendency to chelate to transition
metals.14–16 However, the most valuable property of aroylhy-
drazones is their great physiological activity due to the presence
of the active pharmacophore and provides application in
medicinal and pharmaceutical elds with various biological
applications.17 Since it is well known that the hydrazone group
plays an important role for the antimicrobial activity. Aroylhy-
drazones are being synthesized in order to combat diseases with
minimal toxicity and maximal efficiency. These predictions has
provided therapeutic pathway to develop new effective biologi-
cally active hydrazones. A number of hydrazone derivatives have
been reported to exhibit notably antimicrobial, anticonvulsant,
antiinammatory, antitubercular and antitumoral activi-
ties.18–22 Careful literature survey for functional groups which
could be considered as pharmacophores for the antitubercular
activities revealed that the hydrazone moiety is common among
most of the antitubercular agents such as salinazid and vera-
zide.23,24 Therefore, the target compounds were rationalized so
as to comprise the hydrazone pharmacophores that are believed
to be responsible for the biological signicance of some rele-
vant chemotherapeutic agents. The substitution pattern of such
hydrazone derivatives was carefully selected so as to confer
different electronic environment to the molecules. Such
hydrazide–hydrazones compounds were designed in order to
During the past two decades, the frequency and types of life-
threatening infections has increased. A major associated
problem is that the incidence of drug-resistant isolated bacte-
rial strains in the community has become quite alarming. For
these reasons, the demand for new and better chemotherapic
compounds has increased, and nowadays the search for new
chemicals with antimicrobial activity has become an important
eld of research.1–4
Hydrazides are highly reactive base with reducing properties.
They have been used as a synthetic intermediate to produce
several different types of drugs and in the treatment of various
chronic illnesses.5 Hydrazides used in medicine include the
anti-tuberculosis drug isoniazid and the antihypertensive and
peripheral vasodilator drug hydralsane, whose hydrochloride is
an effective drug for emergency reduction of blood pressure in
hypertensive crisis.6–8 Similarly, the hydralazine derivatives have
been widely applied in the treatment of tuberculosis and mental
disorder. Also, they can be used as antimicrobial, antihyper-
tensive, antimalarial and antitumoral agents.9–13
Hydrazones containing an azometine –NHN]CH– proton
are synthesized by heating the appropriate substituted hydra-
zides with aldehydes and ketones in solvents like ethanol,
methanol, tetrahydrofuran. Hydrazides and hydrazones are not
aState Key Laboratory for Mechanical Behavior of Materials, School of Materials
Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China. E-mail:
guodagang@mail.xjtu.edu.cn
bSchool of Environmental and Chemical Engineering, Xi'an Polytechnic University,
Xi'an 710048, China. E-mail: wanglcody@163.com
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investigate the effect of such structural variation on the anti- for the synthesis of the compounds (2a–2d, 3a–3d) with high
bacterial activities.
yield.
Wave numbers of the selected vibration of IR spectra of the
In view of these observations, herein we report the synthesis,
characterization and antimicrobial activity of series of aromatic compounds are listed in Experimental section. The IR spectrum
hydrazides and aroyl hydrazones with different position and of the compounds (3a–3d) are compared with the compounds
number of the hydroxyl groups in their molecules as trial to (2a–2d) to determine the binding mode of the aromatic hydra-
develop a novel antimicrobial. The antibacterial activity of the zides to aroyl hydrazones during the condensation. The IR
compounds to Staplylococcus aureus, Escherichia coli and Pseu- spectra of the compounds were found to be very similar to each
domonas aeruginosa were measured. Their structure and activity other. The IR spectra of the aromatic hydrazides displaying a
relationship were also examined. In addition, aroyl hydrazones sharp band around 1400 cmꢁ1 were assigned to C–N stretching.
thermal behaviors are studied by TG–DTG. The thermal analysis However, in the aroyl hydrazones, this band was changed to
exhibit either mass loss or gain due to decomposition, oxida- higher (4–18 cmꢁ1) wavenumbers indicating the participation
tion, or loss of volatiles.
of nitrogen and carbon formed a double bond (imine nitrogen).
As a general remark, a broad band in the range of 3395 cmꢁ1
free v(OH) stretching frequencies was observed in the spectra of
aromatic hydrazides (2b–2d). In the same way, in the spectrum
of the corresponding aroyl hydrazones, this band was in the
range of 3481 cmꢁ1 free v(OH) stretching frequencies. Terminal
methyl stretching vibrations were found in the range of 2996–
2838 cmꢁ1. The spectra of all the compounds showed shis for
m(C]O) at 1602–1684 cmꢁ1. Moreover, new band in the aroyl
hydrazones at 1201–1284 cmꢁ1 was attributed to the m(C–O)
vibrations.
NMR spectra of compounds were recorded in DMSO
(CD3OD) taking using TMS as an internal standard. 1H NMR
and 13C NMR spectra for the compounds are given in Experi-
mental, respectively. It is known that symmetric C and H atoms
in the compounds have the same chemical shi because of the
same chemical environment of the atoms. Chemical shi values
of compounds (2a–2d, 3a–3d) is in reasonable agreement with
2. Results and discussion
2.1. Chemistry
The aromatic hydrazides were obtained from the condensation
of aromatic ethyl ester with hydrazine hydrate. And the aroyl
hydrazones were obtained from the condensation of hydrazide
with 4-hydroxy-3-methoxybenzaldehyde (Scheme 1). The inves-
tigation showed that the aroyl hydrazones were obtained in
molar ratio 1 : 1 hydrazide–aldehyde ratio. At room tempera-
ture, aromatic hydrazides and aroyl hydrazones were very
stable. These compounds were characterised by elemental
analysis and other spectroscopic techniques. The compounds
are soluble in methanol, ethanol, DMF and acetonitrile.
Initially, the two-step reaction was carried out with different
solvent under reux. In our observations, ethanol was sufficient
Scheme 1 Synthesis of compounds (2a–2d, 3a–3d).
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literature data for the similar compounds.25,26 In NMR spectra,
aromatic proton peaks were observed at about 6.78–7.96 ppm,
and aromatic carbon peaks were shown at 108.54–160.72 ppm.
The chemical shi of the NH group of the compounds in DMSO-
d6 is in the range of 8.25–9.77 ppm. Difference of chemical shi
might be attributed to the formation of intermolecular inter-
actions with polar solvent DMSO. The 13C NMR of aromatic
hydrazide and aroyl hydrazone, conrmed the appearance of
carbonyl in the high eld region. The other carbon atoms of the
phenyl moieties all appeared at the expected chemical shis.
2.2. Thermogravimetric analysis
Thermogravimetric analysis was carried out to examine the
thermal stability of 3a–3d. The crushed single crystal sample
was heated up to 1000 ꢀC in N2 at a heating rate of 10 ꢀC minꢁ1
.
Fig. 2 Thermal analysis curves (TG and DTG) of 3b.
Fig. 3 Thermal analysis curves (TG and DTG) of 3c.
Fig. 4 Thermal analysis curves (TG and DTG) of 3d.
The stages of decomposition, temperature range as well as the
weight loss percentages of aroyl hydrazones are shown in Fig. 1–4.
The experimental weight loss values are in good agreement with
the calculated values.
The TG curves for 3a showed that it is stable up to 228.23 ꢀC
without any weight loss, which means the compound could
retain structural integrity to 228.23 ꢀC. It can be seen from
Fig. 1, 3a undergoes one major stage of weight loss during
ꢀ
228.23–369.26 C, and the endothermic peak is in the temper-
ature of 324.40 ꢀC at the heating rate of 10 ꢀC minꢁ1. The value
of the weight loss at this stage is 53.37% (calcd 54.44%), and the
lost group is shown in Fig. 5. In Fig. 2, two stages of weight loss
ꢀ
of 3b can be clearly discerned under the heating rate of 10 C
minꢁ1. The rst step starts from 227.65 ꢀC and ends at 345.54 ꢀC
with the sum loss of 33.06% (calcd 32.52%). The second stage
occurred at 394.08–526.38 ꢀC with the mass loss of 25.62%
(calcd 24.47%), which is shown in Fig. 5. The endothermic peak
are in the temperature of 275.42 ꢀC and 470.50 ꢀC, respectively.
In the TG and DTG curves of 3c, as described in Fig. 3, four mass
loss stages are obserꢀved. The rst two step starts from 86.17 ꢀC
and ends at 165.63 C with the sum loss of 0.80% and 4.69%
which should be assigned to the water in the sample. The third
ꢀ
ꢀ
step starts from 169.29 C and ends at 224.78 C with the sum
loss of 25.02% (calcd 24.47%), and the endothermic peak is in
the temperature of 196.48 ꢀC. The fourth step starts from
ꢀ
ꢀ
227.64 C and remains level at 334.22 C. In this temperature
region, the sum of weight loss is 31.86% (calcd 32.52%) and the
decomposition process is represented in Fig. 5. The TG curves
Fig. 1 Thermal analysis curves (TG and DTG) of 3a.
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Fig.
5 Illustration of main thermal decomposition processes for
3a–3d under nitrogen.
for 3d showed that it is stable up to 179.51 ꢀC without any
Fig. 6 Antimicrobial activities of compounds against bacteria. Values
weight loss, which means the compound could retain structural
are average of three independent measurements for each compound.
ꢀ
integritꢀy to 179.51 C (Fig. 4). The one major stage starts from
ꢀ
179.51 C and ends at 318.03 C with the sum loss of 62.28%
(calcd 61.32%) and the endothermic pꢀeak is in the temperature
bacterial strains. 2a have poor activity against microorganism.
The compounds (2b–2d, 3a–3d) exhibited a remarkable anti-
bacterial activity against all organisms. Aroyl hydrazones(3a–3d)
inhibitory activity are stronger than aromatic hydrazides(2a–2d).
The series of hydrazides antibacterial activity from strong to
weak order: 2d, 2c, 2b, 2a. The series of aroyl hydrazones anti-
bacterial activity from strong to weak order: 3d, 3c, 3b, 3a. The
correlations between functional groups and antibacterial
activities show that 3d has the highest activity against micro-
organisms. Reason of this phenomena can be explained due to
presence delocalization of p electrons over the whole aromatic
ring and also its activity may be arise from the hydroxyl group
which may play an important role in the antimicrobial activity.
The electronic delocalization supposed within the aromatic ring
system may increase the lipophilic character of the compounds.
Test results show that the presence of hydroxyl group, as well as
the number and position of hydroxyl groups, are important and
further enhance the antimicrobial activity. The more hydroxyl
of 250.53 C at the heating rate of 10 C minꢁ1. The decompo-
ꢀ
sition process is represented in Fig. 5. The nal residue was
probably 4-hydroxy-3-methoxy-phenyl fragments.
2.3. Antibacterial activity
The antibacterial activities of the tested compounds were
examined with Staplylococcus aureus, Escherichia coli and Pseu-
domonas aeruginosa. The antibacterial screening of the
compound was evaluated at the concentration of 5 ꢂ 105–5 ꢂ
106 cfu mLꢁ1, and the inhibition zones were measured in mm.
The activity of the aromatic hydrazides and aroyl hydrazones
against the used organisms are depicted in Table 1. As shown in
Table 1, the synthesized compounds showed different antibac-
terial activities. The mean values of three independent
measurements for each compound were shown in Fig. 6. On the
basis of the data obtained for diameter of inhibition zone, it was
found that all of the compounds were active on three types of
Table 1 Antibacterial activities of the compounds as zone diameter (mm)a
Organism
sample
S. aureus (ATCC 25923)
E. coli (ATCC 25922)
P. aeruginosa (ATCC 27853)
1
2
3
1
2
3
1
2
3
N,N-Dimethylformamide
6.00
7.32
8.05
8.27
10.58
9.22
10.55
10.77
12.22
6.00
7.36
8.13
8.35
11.06
9.25
10.62
10.74
12.15
6.00
7.43
8.18
8.34
11.06
9.36
10.52
10.60
12.05
6.00
7.26
8.30
8.58
11.34
9.05
10.24
10.71
12.44
6.00
7.28
8.42
8.61
11.34
9.16
10.37
10.83
12.42
6.00
7.44
8.41
8.63
11.45
9.11
10.37
10.82
12.29
6.00
7.06
8.34
8.67
11.14
9.18
10.39
10.58
12.31
6.00
7.12
8.26
8.74
11.15
9.22
10.48
10.65
12.45
6.00
7.13
8.21
8.81
11.22
9.24
10.46
10.68
12.41
2a
2b
2c
2d
3a
3b
3c
3d
a
Note: more than 7 mm in diameter with antibacterial activities.
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group, the higher of the antimicrobial activity. Comparing with p-PhH), 7.11 (dd, J ¼ 2, 8.4 Hz, 2H, o-ArH), 6.85 (d, J ¼ 8 Hz, 1H,
2b (3b), 2c (3c) have less space steric hindrance. Counterpoint to m-ArH), 4.91 (s, 1H, ArOH), 3.97 (s, 3H, CH3), 3.33 (s, 1H,
introduce hydroxyl compounds in less space steric hindrance, CH]N). 13C NMR (400 MHz, d4-methanol): 170.15 (C]O),
so that the antibacterial activity was improved.
154.75 (C]N), 149.30, 145.22, 133.54, 131.89, 128.62, 127.37,
124.28, 122.76, 116.81, 116.05 (aromatic carbons), 56.32 (OCH3).
3.2.3. Procedure for the synthesis of 2-hydroxybenzhy-
drazide (2b). Ethyl 2-hydroxybenzoate (1b) (6.6 g, 40 mmol) was
dissolved in anhydrous ethanol (30 mL) at room temperature
3. Experimental section
3.1. Materials and physical measurements
ꢀ
and heated at 95 C. Hydrazine hydrate (2.4 g, 48 mmol) was
All starting materials and solvents used in this work were of
analytical grade and used as purchased from Sinopharm
Chemical Reagent Co. Ltd without further purication. Melting
points were determined in open capillaries on a Mel-Temp
apparatus and are uncorrected. Elemental analyses (C, H, N)
were performed using a Vario EL elemental analyzer. FT-IR
spectrum was measured as KBr pellets on a Nicolet Nexus FT-
IR spectrometer in the 4000–400 cmꢁ1 region. The 1H NMR
and 13C NMR spectra were recorded in DMSO-d6 on a Bruker-
400 spectrometer (400 MHz). All the chemical shis are repor-
ted in d (ppm) using TMS as an internal standard. Thermogra-
vimetric analyses (TGA) were carried out on a Perkin-Elmer
Pyris-1, thermogravimetric analyzer operating at a heating rate
added into the mixture. Aer being reuxing for 9 h, the
mixture was cooled to room temperature. Then the crystals were
precipitated and collected by ltration. Finally, the product was
recrystallized from ethanol and dried under reduced pressure to
give compound of 2b. Yield: (4.9 g, 81%). M.p.: 147–150 ꢀC.
Anal. calcd (%) for C7H8N2O2: C, 55.25; H, 5.30; N, 18.42. Found
(%): C, 55.19; H, 5.28; N, 18.44. Selected IR (KBr pellet, cmꢁ1):
n(O–H) 3318; n(N–H) 3269, 3135; n(C–H) 3011, 2835; n(C]O)
1648; n(C–N) 1417. 1H NMR (400 MHz, DMSO-d6): d 7.81 (dd, J ¼
1.6, 8.0 Hz, 1H, NH), 7.38 (td, J ¼ 8.4, 1.6 Hz, 1H, p-ArH), 6.91–
6.84 (m, 3H, ArH), 4.65 (s, 1H, Ph-OH), 3.35 (s, 2H, NH2). 13C
NMR (400 MHz, DMSO-d6): 165.34 (C]O), 156.14 (ArC), 133.33
(ArC), 128.67 (ArC), 121.29 (ArC), 120.77 (ArC), 115.28 (ArC).
3.2.4. Procedure for the synthesis of 4-hydroxy-3-
methoxybenzaldehyde-2-hydroxybenzoyl hydrazone (3b). 2b
(3.0 g, 20 mmol) was dissolved in anhydrous ethanol (10 mL) at
room temperature and heated at 95 ꢀC. 4-Hydroxy-3-
ꢁ1
ꢀ
of 10 C min in a ow of dry oxygen-free nitrogen at 20 mL
minꢁ1
.
3.2. Synthesis
3.2.1. Procedure for the synthesis of benzoylhydrazine (2a). methoxybenzaldehyde (3.0 g, 20 mmol) was added into the
Ethyl benzoate (1a) (6.0 g, 40 mmol) was dissolved in anhydrous mixture. Aer being reuxing for 6 h, the mixture was cooled to
ethanol (30 mL) at room temperature and heated at 95 ꢀC. room temperature. Then the crystals were precipitated and
Hydrazine hydrate (2.4 g, 48 mmol) was added into the mixture. collected by ltration. Finally, the product was recrystallized
Aer being reuxing for 9 h, the mixture was cooled to room from ethanol and dried under reduced pressure to give
temperature. Then the crystals were precipitated and collected compound of 3b. Yield: (4.5 g, 79%). M.p.: >228 ꢀC. Anal. calcd
by ltration. Finally, the product was recrystallized from (%) for C15H14N2O4: C, 62.93; H, 4.93; N, 9.79. Found (%): C,
ethanol and dried under reduced pressure to give compound of 62.89; H, 4.96; N, 9.83. Selected IR (KBr pellet, cmꢁ1): n(O–H)
2a. Yield: (4.3 g, 78%). M.p.: 112.5 ꢀC. Anal. calcd (%) for 3481; n(N–H) 3259; n(C–H) 3066, 2940; n(C]O) 1635; n(C–N)
C7H8N2O: C, 61.75; H, 5.92; N, 20.58. Found (%): C, 61.83; H, 1422; n(C–O) 1276. 1H NMR (400 MHz, DMSO-d6): d 8.35 (s, 1H,
5.87; N, 20.44. Selected IR (KBr pellet, cmꢁ1): n(N–H) 3300, 3212; NH), 7.89 (dd, J ¼ 1.2, 7.6 Hz, 1H, o-ArH), 7.46–7.42 (m, 2H,
n(C–H) 3018, 2874; n(C]O) 1659; n(C–N) 1402. 1H NMR (400 ArOH), 7.33 (d, J ¼ 1.6 Hz, 1H, p-PhH), 7.12 (dd, J ¼ 1.6, 8 Hz,
MHz, DMSO-d6): d 9.77 (s, 1H, NH), 7.83–7.81 (m, 2H, o-PhH), 2H, o-ArH), 6.96 (t, J ¼ 8.8 Hz, 1H, m-PhH), 6.86 (d, J ¼ 8.4 Hz,
7.53–7.43 (m, 3H, PhH), 3.35 (s, 2H, NH2). 13C NMR (400 MHz, 1H, m-ArH), 3.84 (s, 3H, CH3), 3.34 (s, 1H, CH]N). 13C NMR
DMSO-d6): 167.22 (C]O), 133.15 (ArC), 131.94 (ArC), 128.26 (400 MHz, DMSO-d6): 171.36 (C]O), 153.68 (C]N), 156.19,
(ArC), 127.36 (ArC).
3.2.2. Procedure for the synthesis of 4-hydroxy-3- 116.88, 116.04, 115.83 (aromatic carbons), 56.38 (OCH3).
methoxybenzaldehyde benzoyl hydrazone (3a). 2a (2.7 g, 20
3.2.5. Procedure for the synthesis of 4-hydroxybenzhy-
mmol) was dissolved in anhydrous ethanol (10 mL) at room drazide (2c). Ethyl 4-hydroxybenzoate (1c) (6.6 g, 40 mmol) was
149.31, 145.12, 133.33, 128.07, 124.85, 122.72, 121.21, 120.67,
temperature
and
heated
at 95
ꢀC.
4-Hydroxy-3- dissolved in anhydrous ethanol (30 mL) at room temperature
ꢀ
methoxybenzaldehyde (3.0 g, 20 mmol) was added into the and heated at 95 C. Hydrazine hydrate (2.4 g, 48 mmol) was
mixture. Aer being reuxing for 6 h, the mixture was cooled to added into the mixture. Aer being reuxing for 9 h, the
room temperature. Then the crystals were precipitated and mixture was cooled to room temperature. Then the crystals were
collected by ltration. Finally, the product was recrystallized precipitated and collected by ltration. Finally, the product was
from ethanol and dried under reduced pressure to give recrystallized from ethanol and dried under reduced pressure to
compound of 3a. Yield: (4.1 g, 76%). M.p.: >228 ꢀC. Anal. calcd give compound of 2c. Yield: (4.4 g, 73%). M.p.: 264–266 ꢀC. Anal.
(%) for C15H14N2O3: C, 66.65; H, 5.22; N, 10.37. Found (%): C, calcd (%) for C7H8N2O2: C, 55.25; H, 5.30; N, 18.42. Found (%):
66.61; H, 5.19; N, 10.44. Selected IR (KBr pellet, cmꢁ1): n(O–H) C, 55.28; H, 5.36; N, 18.38. Selected IR (KBr pellet, cmꢁ1): n(O–H)
3301; n(N–H) 3212; n(C–H) 3038, 2838; n(C]O) 1643; n(C–N) 3325; n(N–H) 3282, 3199; n(C–H) 3011, 2885; n(C]O) 1684; n(C–N)
1
1
1420; n(C–O) 1284. H NMR (400 MHz, CD3OD): d 8.25 (s, 1H, 1411. H NMR (400 MHz, DMSO-d6): d 9.49 (s, 1H, NH), 7.82–
NH), 7.96–7.94 (m, 2H, o-PhH), 7.64–7.46 (m, 3H, m-PhH, 7.68 (m, 2H, o-ArH), 6.85 (d, J ¼ 8.4 Hz, 1H, m-ArH), 6.78 (d, J ¼
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8.8 Hz, 1H, m-ArH), 4.39 (s, 1H, Ph-OH), 3.78 (s, 2H, NH2). 13C NMR (400 MHz, DMSO-d6): 170.27 (C]O), 155.23 (C]N),
NMR (400 MHz, DMSO-d6): 167.26 (C]O), 160.72 (ArC), 128.25 149.39, 146.09, 145.02, 135.12, 128.92, 124.83, 122.77, 116.82,
(ArC), 126.13 (ArC), 115.87 (ArC).
116.04, 108.55 (aromatic carbons), 56.21 (OCH3).
3.2.6. Procedure for the synthesis of 4-hydroxy-3-
methoxybenzaldehyde-4-hydroxybenzoyl hydrazone (3c). 2c
(3.0 g, 20 mmol) was dissolved in anhydrous ethanol (10 mL) at
room temperature and heated at 95 ꢀC. 4-Hydroxy-3-
methoxybenzaldehyde (3.0 g, 20 mmol) was added into the
mixture. Aer being reuxing for 6 h, the mixture was cooled to
room temperature. Then the crystals were precipitated and
collected by ltration. Finally, the product was recrystallized
from ethanol and dried under reduced pressure to give
compound of 3c. Yield: (3.9 g, 68%). M.p.: >119 ꢀC. Anal. calcd
(%) for C15H14N2O4: C, 62.93; H, 4.93; N, 9.79. Found (%): C,
62.96; H, 4.92; N, 9.81. Selected IR (KBr pellet, cmꢁ1): n(O–H)
3481; n(N–H) 3262; n(C–H) 3084, 2939; n(C]O) 1623; n(C–N)
1425; n(C–O) 1241. 1H NMR (400 MHz, DMSO-d6): d 8.58 (s, 1H,
NH), 7.80–7.39 (m, 4H, o-ArH), 7.25 (dd, J ¼ 2, 8.4 Hz, 2H,
ArOH), 6.97 (d, J ¼ 8 Hz, 2H, m-ArH), 6.88 (d, J ¼ 8 Hz, 1H,
m-ArH), 3.84 (s, 3H, CH3), 3.36 (s, 1H, CH]N). 13C NMR (400
MHz, DMSO-d6): 168.42 (C]O), 154.59 (C]N), 160.07, 149.33,
145.28, 128.74, 126.16, 124.68, 122.73, 116.82, 116.09, 115.86
(aromatic carbons), 56.29 (OCH3).
3.3. Temperature programmed combustion
The experiments were performed in a Perkin-Elmer Pyris-1
thermogravimetric analyzer with the sample mass loss
percentage and mass loss rate (TG–DTG signal) as functions of
time or temperature recorded continuously under the temper-
ature programmed combustion. During the experiments, the
temperature increased from 25 to 1000 ꢀC at a linear heating
rate of 10 ꢀC minꢁ1. At the same time, the chamber blowing gas,
N2 (99.99% purity), was xed at 20 mL minꢁ1. When data
derived from TG–DTG curves were analyzed, they would be dealt
with taking the original sample mass into consideration to
eliminate the effect of mass different on the process. The
detailed TG–DTG curves and educed data are shown in corre-
sponding section which validates the stability of the experi-
mental system.
3.4. Preparation of microbial cultures
Microorganisms were provided from the culture collection of
the Biotechnology Laboratory of the affiliated hospital of Xi'an
Medical University, China. Staplylococcus aureus ATCC 25923,
Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC
27853 were used as the test organisms in this study. Bacterial
strains were inoculated into Nutrient Broth (Difco) and incu-
bated at 30 ꢃ 0.1 ꢀC for 24 h. In order to test the antimicrobial
effects of aromatic compounds, 15 mL of Mueller-Hinton agar
(Merck) for bacteria, and YPD Agar (Merck) were placed in Petri
dishes which were then inoculated with strains of bacteria by
taking 100 mL from cell culture media. Test compounds and 15
mL of YPD Agar (Merck) were placed in Petri dishes which were
then inoculate temperature for a while, and then holes were
made on top with a sterile stick. It was le to solidify at room
entities stated aboveꢀ were then added to these holes. Petri
dishes were le at 4 C for 2 h. Then, bacterial cultures were
incubated at 34 ꢃ 0.1 ꢀC for 24 h, and yeast cultures were
3.2.7. Procedure for the synthesis of 3,4,5-trihydroxy-
benzhydrazide (2d). Ethyl 3,4,5-trihydroxybenzoate (1d) (7.9 g,
40 mmol) was dissolved in anhydrous ethanol (30 mL) at room
ꢀ
temperature and heated at 95 C. Hydrazine hydrate (2.4 g, 48
mmol) was added into the mixture. Aer being reuxing for 9 h,
the mixture was cooled to room temperature. Then the crystals
were precipitated and collected by ltration. Finally, the
product was recrystallized from ethanol and dried under
reduced pressure to give compound of 2d. Yield: (5.2 g, 70%).
M.p.: 295–298 ꢀC. Anal. calcd (%) for C7H8N2O4: C, 45.65; H,
4.38; N, 15.22. Found (%): C, 45.59; H, 4.42; N, 15.17. Selected IR
(KBr pellet, cmꢁ1): n(O–H) 3431, 3395, 3339; n(N–H) 3282, 3248;
n(C–H) 3063, 2853; n(C]O) 1657; n(C–N) 1418. 1H NMR (400
MHz, DMSO-d6): d 8.32 (s, 1H, NH), 6.92, 6.78 (s, 2H, o-ArH),
4.20 (s, 3H, Ar-OH), 3.73 (s, 2H, NH2). 13C NMR (400 MHz,
DMSO-d6): 168.37 (C]O), 146.10 (ArC), 135.16 (ArC), 128.09
(ArC), 108.54 (ArC).
3.2.8. Procedure for the synthesis of 4-hydroxy-3-
methoxybenzaldehyde-3,4,5-trihydroxybenzhydrazone (3d). 2d
(3.7 g, 20 mmol) was dissolved in anhydrous ethanol (10 mL) at
room temperature and heated at 95 ꢀC. 4-Hydroxy-3-
methoxybenzaldehyde (3.0 g, 20 mmol) was added into the
mixture. Aer being reuxing for 6 h, the mixture was cooled to
room temperature. Then the crystals were precipitated and
ꢀ
incubated at 30 ꢃ 0.1 C for 72 h. And the end of incubation
time, the inhibition zones on the bacterial and yeast nutrient
media were measured as diameter zone, mm.27,28 All the tested
compounds were solubilized in DMF as a solvent. The antimi-
crobial activity results are the average data of three experiments.
4. Conclusions
collected by ltration. Finally, the product was recrystallized A series of aromatic hydrazides and aroyl hydrazones had been
from ethanol and dried under reduced pressure to give successfully prepared from readily available starting
compound of 3d. Yield: (4.1 g, 64%). M.p.: >180 ꢀC. Anal. calcd compounds with convenient procedure and screened for their
(%) for C15H14N2O6: C, 56.60; H, 4.43; N, 8.80. Found (%): C, antimicrobial application. It was found that both number and
56.58; H, 4.51; N, 8.82. Selected IR (KBr pellet, cmꢁ1): n(O–H) position of hydroxyl groups contained in the compounds dis-
3476, 3431, 3397; n(N–H) 3295; n(C–H) 3081, 2996; n(C]O) 1602; played remarkable difference in antimicrobial activity and
n(C–N) 1422; n(C–O) 1201. 1H NMR (400 MHz, DMSO-d6): d 8.58 particularly compared to the other compounds. The present
(s, 1H, NH), 7.46 (d, J ¼ 1.6 Hz, 1H, o-ArH), 7.25 (dd, J ¼ 1.6, 8.4 initial study implies that the aromatic hydrazides and aroyl
Hz, 4H, ArOH), 6.94 (s, 1H, o-ArH), 6.88 (d, J ¼ 8 Hz, 1H, m-ArH), hydrazones would be potential medicinal antimicrobial mate-
6.79 (s, 2H, o-ArH), 3.84 (s, 3H, CH3), 3.36 (s, 1H, CH]N). 13C rial. Keeping in view the above importance of the compounds,
58900 | RSC Adv., 2014, 4, 58895–58901
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we thought it worthwhile to construct the aromatic hydrazides 11 L. T. Yildirim and O. Atakol, Cryst. Res. Technol., 2002, 37,
and aroyl hydrazones and theirs coordination compounds with 1352–1359.
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Conflicts of interest
The author(s) conrms that this article content has no conicts
of interest.
15 P. V. Chalapathi, B. Prathima, S. Y. Rao, K. J. Reddy,
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Acknowledgements
This work was supported nancially by the Fundamental
Research Funds for the Central University, the National Natural
Science Foundation of China (no. 51072159; 51273159) and
Program for New Century Excellent Talents in Universities
(Chinese Ministry of Education, NCET-08-0444).
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