Synthesis, structures, and fungitoxicity of novel organophosphorus compounds

Article abstract of DOI:10.1080/10426507.2012.681408

A series of biologically active organophosphorus compounds have been synthesized by the reactions of O,O-diethylchlorophosphate with Schiff bases derived from 5-(phenyl/substituted phenyl)-2-hydrazino-1,3,4-oxadiazole and salicylaldehyde/2-hydroxyacetophenone. The compounds have been characterized on the basis of analyses and spectral (IR, ¹H, ¹³C NMR) data. Fungicidal activities of these derivatives against Colletotrichum falcatum, Fusarium oxysporum, and Curvularia pallescence have been evaluated. All compounds showed moderate to significant antifungal activity.

Full text of DOI:10.1080/10426507.2012.681408

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Synthesis, Structures, and Fungitoxicity
of Novel Organophosphorus Compounds
Venkatesh K. Pandey a , Kalpana Chaturvedi b , Ruchi Chandra a , Om
P. Pandey a & Soumitra K. Sengupta a
a Department of Chemistry, DDU Gorakhpur University, Gorakhpur,
273009, India
b Department of Chemistry, Agra College, Agra, 282002, India
Accepted author version posted online: 13 Apr 2012.Published
online: 06 Aug 2012.
To cite this article: Venkatesh K. Pandey , Kalpana Chaturvedi , Ruchi Chandra , Om P. Pandey &
Soumitra K. Sengupta (2012) Synthesis, Structures, and Fungitoxicity of Novel Organophosphorus
Compounds, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:11, 1401-1408, DOI:
10.1080/10426507.2012.681408
To link to this article: http://dx.doi.org/10.1080/10426507.2012.681408
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Phosphorus, Sulfur, and Silicon, 187:1401–1408, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.681408
SYNTHESIS, STRUCTURES, AND FUNGITOXICITY
OF NOVEL ORGANOPHOSPHORUS COMPOUNDS
Venkatesh K. Pandey,1 Kalpana Chaturvedi,2 Ruchi Chandra,1
Om P. Pandey,1 and Soumitra K. Sengupta1
1Department of Chemistry, DDU Gorakhpur University, Gorakhpur 273009, India
2Department of Chemistry, Agra College, Agra 282002, India
GRAPHICAL ABSTRACT
Abstract A series of biologically active organophosphorus compounds have been
synthesized by the reactions of O,O-diethylchlorophosphate with Schiff bases derived
from 5-(phenyl/substituted phenyl)-2-hydrazino-1,3,4-oxadiazole and salicylaldehyde/2-
hydroxyacetophenone. The compounds have been characterized on the basis of analyses
and spectral (IR, 1H, 13C NMR) data. Fungicidal activities of these derivatives against
Colletotrichum falcatum, Fusarium oxysporum, and Curvularia pallescence have been
evaluated. All compounds showed moderate to significant antifungal activity.
Keywords Organophosphorus derivatives; IR; NMR; fungicidal properties
INTRODUCTION
One of the most important groups of pesticides is the organophosphorus compounds.1
Their pesticidal value is rated high especially because they have wide spectrum of action
on plant pests, are readily metabolized, and have little residual toxicity. A few recent stud-
ies2–5 from our laboratory have shown that on the basis of suitable logic organic molecules,
incorporating phosphorus may be designed such that they may be less dangerous in use
without losing their value as effective pesticides. One of the useful properties of phosphorus
compounds is their relatively low stability and rapid metabolic breakdown in plants, ani-
mals, organisms, soil, and in other components of the environment, with the formation of
products that are safe for human beings and domestic animals.6 Another important feature
of these compounds is the high selectivity of their action. The discovery of the mechanism
Received 12 February 2012; accepted 28 March 2012.
We are grateful to the University Grants Commission, New Delhi, for financial support. R.C. also thanks
Department of Science and Technology, New Delhi, for the award of Women Scientist.
Address correspondence to Soumitra K. Sengupta, Department of Department, DDU Gorakhpur University,
Gorakhpur 273009, India. E-mail: sengupta@hotmail.co.uk
1401

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V. K. PANDEY ET AL.
of action6,7 of organophosphorus compounds makes it possible to develop the fundamental
principles of the direct synthesis of new substances and to establish the cause of their
selective action on an organism. Organophosphorus compounds containing P O C and
P S C bonds show exciting pesticidal properties.8 Studies on organophosphorus deriva-
tives could constitute a new and promising field of application in the national economy. The
present study was therefore undertaken to evaluate the antifungal efficacy of some newly
synthesized organophosphorus compounds against various important fungal pathogens of
sugarcane.
RESULTS AND DISCUSSION
Reactions of O,O-diethylchlorophosphate with Schiff bases derived from 5-(phenyl/
substituted phenyl)-2-hydrazine-1,3,4-oxadiazole and salicylaldehyde/2-hydroxyacetop-
henone have been carried out in methanol in the presence of pyridine and a variety of
organophosphorus derivatives have been isolated according to Scheme 1.
X
X
X
Reflux
Reflux
CONHNH2
COOH
COOCH3
conc.H2SO4
CH3OH
CH3OH/NH2NH2.H2O
Reflux
CS2/KOH/CH3OH
N
N
N
N
R
C
N
N
X
NHN
OH
SH
Reflux
X
O
X
Reflux
O
NHNH2
O
NH2NH2.H2O
R
OH
O
P
O
C2H5O
C2H5O
Ethanol
Pyridine
Cl
N
N
O
R
X
NHN
C
O
P OC2H5
OC2H5
O
X=H, R=H (I); X=H, R=CH3 (II); X=2-Cl, R=H (III); X=2-Cl, R=CH3 (IV); X=4-Cl,
R=H (V); X=4-Cl, R=CH3 (VI); X=4-NO2, R=H (VII); X=4-NO2, R=CH3 (VIII)
Scheme 1 Synthetic route of O,O-diethylchlorophosphate derivatives containing Schiff bases derived from 5-
(phenyl/substituted phenyl)-2-hydrazino-1,3,4-oxadiazole and salicylaldehyde/2-hydroxy acetophenone.
The methods used for the preparation and isolation of these compounds gave ma-
terials of good purity as supported by their analyses and thin layer chromatography. The
elemental analyses and physical properties of the organophosphorus derivatives are given in
Table 1. The organophosphorus derivatives are found to be soluble in dimethylformamide,
tetrahydrofuran, and dimethylsulfoxide.
Infrared Spectra
The infrared spectral bands of the ligands and their corresponding complexes are
given in Table 2. A comparison of characteristic infrared absorption bands of Schiff bases
with those of the corresponding organophosphorus derivatives gives information regarding
the structures of the compounds. The infrared spectra of the Schiff bases show bands at ca.

1403

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PROPERTIES OF ORGANOPHOSPHORUS COMPOUNDS
1405
1620–1610 and 1580–1565 cm−1 that may be assigned7–9 to ν(C N; azomethine group)
and ν(C N; ring), respectively. All these bands are present almost at the same position in
their corresponding organophosphorus derivatives indicating the non-involvement of these
groups in the bond formation. All Schiff bases and their corresponding organophosphorus
derivatives show band at ca. 3150 cm−1 assignable10 to ν(N H). The ν(C O C) bands
in the Schiff bases occur at ca. 1350 cm−1 (asymmetric) and at ca. 1280 cm−1(symmetric),
which remain unaltered in the spectra of the complexes indicating11–13 the non-coordination
of oxygen atom of the oxadiazole ring. The infrared spectra of these Schiff bases show
strong band at ca. 3400 cm-1 due to ν(O H). However, this band disappears in the spectra
of their corresponding complexes indicating14 the coordination of the phenolic oxygen to
phosphorus. The ν(P O C) band appears4,5 at ca. 1025 cm−1. In addition, all phosphate
derivatives show bands at ca.1260 cm−1 due to ν(P O).15–17
Proton Magnetic Resonance Spectra
The proton magnetic resonance spectra of the derivatives have been recorded in
dimethyl sulfoxide (DMSO)-d6 (Table 3). The line intensities were determined by plani-
metric integration. The Schiff bases and their corresponding organophosphorus derivatives
show signal at ca. δ ∼7.20 due to NH proton. The signals (multiplet) due to aromatic
ring protons appear in region ca. δ 7.40–7.65. The signals due to ethoxy group appear
at ca. δ 2.10–2.28 (triplet, CH3) and at ca. δ 3.18–3.40 (quartet, CH2) in the spectra of
all organophosphorus derivatives. The spectra of all Schiff bases show a signal at ca. δ
10.50, which disappear in their corresponding organophosphorus derivatives indicating the
deprotonation of phenolic proton and formation of bond between oxygen and phosphorus.
The signal, because of the methyl group, appears at ca. δ 1.98 (singlet, CH3). A signal,
because of the azomethine proton ( CH N ), appears at ca. δ 8.12–8.22 in the spectra
of Schiff bases and their corresponding organophosphorus derivatives.
13C Magnetic Resonance Spectra
The 13C NMR spectral data of organophosphorus compounds are given in Table 3.
For O,O-diethyl group, two signals appear at ca. δ 58.1–59.2 (CH2) and δ 14.1–15.0 (CH3).
For oxadiazole ring carbons, two signals appear at ca. 160–166 ppm, while for imine carbon
a signal appears at ca. δ 154.7–155.6. For phenyl ring, a number of signals appear.
1
Representative H and 13C NMR spectra for compounds I and V are shown in the
Supplementary Materials (Figures S2–S5; posted online only).
Antifungal Activity
Sugarcane, a major source of sugar and important cash crop, is extensively grown
worldwide. Diseases are one of the major constraints in the profitable cultivation of sugar-
cane. About 100 diseases of sugarcane caused by virus, fungi, bacteria, phytoplasma, and
nematodes have been reported from different parts of the world. Among fungal diseases,
red rot by Colletotrichum falcatum, wilt caused by Fusarium monliforme and Fusarium
oxysporum, and leaf spots caused by Curvularia lunata and Curvularia pallescence are the
main diseases responsible for loss in sugarcane production.6
The organophosphorus derivatives containing Schiff bases of 5-(phenyl/substituted
phenyl)-2-hydrazino-1,3,4-oxadiazole show promising results inhibiting the mycelia

1406

PROPERTIES OF ORGANOPHOSPHORUS COMPOUNDS
1407
growth of all the test fungi. Best result was obtained with O,O-diethylphosphate derivative
containing 2-(1{(5-(4-chlorophenyl)-[1,3,4] oxadiazole-2-yl]-hydrazono}-ethyl]-phenol
(VI). This compound showed activity upto 77.8% against C. falcatum, 71.2% against
F. oxysporum, and 69.8% against C. Pallescence at 1000 ppm concentration. Other
derivatives also showed antifungal activity against all test fungi from 37.8% to 70.2% at
1000 ppm concentration. A graphical representation of the results is presented in Table S1
and Figure S1 (Supplementary Materials; posted online only).
EXPERIMENTAL
The reaction of O,O-diethylchlorophosphate was carried out under anhydrous condi-
tions. Special precautions were taken to exclude moisture from the apparatus and chemicals
as the starting materials (O,O-diethylchlorophosphate) and reactions were susceptible to
hydrolysis. Glass apparatus with interchangeable joints were used throughout the work.
All the organic solvents used were of analytical reagent grade. The solvents were purified
and dried using the method described in the literature.2 O,O-diethylchlorophosphate was
prepared by adding a solution of pyridine, absolute ethanol, and benzene dropwise to an
◦
ice-cooled solution of phosphorus oxychloride in benzene at temperature below 20 C.3
After 3 h of stirring, the pyridine hydrochloride was filtered off. The product, after distil-
lation, was obtained as colorless liquid (bp 60–63 ◦C/2.5 mm Hg). The details of analysis
and physical measurements were the same as reported earlier.2
For antifungal activity, all the compounds were tested against all test fungi by the food
poison technique4 at three concentrations (10, 100, and 1000 ppm). For this, the desired
amount of chemical was dissolved in 0.5 mL of solvent and mixed with the culture medium
on the basis of the volume of medium in each Petri plate (80 mm diameter). Oatmeal agar
medium was used for all test fungi. In controls, the same amount of medium containing the
requisite amount of solvent was poured in place of test chemicals. A mycelia disk (5 mm
diameter) obtained from the periphery of two-week old cultures was taken and transferred
to the center of each Petri plate. Plates were incubated for seven days at 28 2 ◦C. Each
treatment was repeated three times, and the inhibition was recorded relative to percent
mycelia inhibition calculated using, the formula:
[(dc − dt)/dc] × 100
where dc is the average diameter of the mycelia colony of the control and dt is the average
diameter of the mycelia colony of the treatment.
Reactions of O,O-diethylchlorophosphate with Schiff bases: O,O-diethylchloro-
phosphate (0.01 mol) was added to a solution of the appropriate Schiff base (0.01 mol)
in methanol (25 mL) in the presence of pyridine (5 mL), and reaction mixture was re-
fluxed for ca. 21–26 h. The precipitate, thus obtained, was filtered off. The compound was
recrystallized from methanol.
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