Synthesis and biocidal activity of organophosphates derived from benzothiazole

Article abstract of DOI:10.1080/10426500802111579

The synthesis, biocidal activity, and spectroscopic data of a new series of S-phosphorylated/thiophosphorylated derivatives of 2-(2'-mercaptophenyl) benzothiazole are reported in this study. Derivatives were prepared by reacting 2-(2'-mercaptophenyl) benz

Full text of DOI:10.1080/10426500802111579

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Phosphorus, Sulfur, and Silicon
and the Related Elements
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Synthesis and Biocidal Activity
of Organophosphates Derived
from Benzothiazole
Priyanka Jhajharia a , Mahesh Kumar Samota a ,
Kusum Soni a & Gita Seth a
a Department of Chemistry , University of
Rajasthan , Jaipur, India
Published online: 04 Feb 2009.
To cite this article: Priyanka Jhajharia , Mahesh Kumar Samota , Kusum Soni &
Gita Seth (2009) Synthesis and Biocidal Activity of Organophosphates Derived from
Benzothiazole, Phosphorus, Sulfur, and Silicon and the Related Elements, 184:2,
315-321, DOI: 10.1080/10426500802111579
To link to this article: http://dx.doi.org/10.1080/10426500802111579
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Phosphorus, Sulfur, and Silicon, 184:315–321, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802111579
Synthesis and Biocidal Activity of Organophosphates
Derived from Benzothiazole
Priyanka Jhajharia, Mahesh Kumar Samota, Kusum Soni,
and Gita Seth
Department of Chemistry, University of Rajasthan, Jaipur, India
The synthesis, biocidal activity, and spectroscopic data of a new series of S-
phosphorylated/thiophosphorylated derivatives of 2-(2ꢀ-mercaptophenyl) benzoth-
iazole are reported in this study. Derivatives were prepared by reacting 2-(2ꢀ-
mercaptophenyl) benzothiazole with phosphorus oxychloride/phosphorus thiochlo-
ride in different molar ratios [1:1, 2:1, 3:1]. All of the derivatives were found to be
antifungal agents with less toxicity than the standard Dithane M-45.
Keywords Fungicidal activity; S-phosphorylated/thiophosphorylated derivatives of 2-
(2ꢀ-mercaptophenyl) benzothiazole
INTRODUCTION
Heterocyclic compounds are an important group of ligands in
organophosphorus chemistry and find a critical role in various
fields.1–3 Organophosphates are biodegradable, short-lived chemical
compounds, and their mode of action involves inhibition of acetyl-
cholinesterase (AChE).4 Organophosphorus compounds have found
numerous applications in insecticides, fungicides, herbicides, and
pesticides.5–11 These compounds find considerable use as asymmet-
ric hydrogenating catalysts, medicines, and flame retardants.12–15
2-Mercaptobenzoxazole has been found to possess various pharmaco-
logical and biological activities.16 Taking this into consideration, we
have synthesized the phosphorylated/thiophosphorylated derivatives
of 2-(2ꢀ-mercaptophenyl) benzothiazole.
Received 10 January 2008; accepted 8 April 2008.
We are thankful to the Head of the Department of Chemistry, University of Rajasthan,
Jaipur, India, for providing necessary facilities. Priyanka Jhajharia is grateful to Uni-
versity Grants Commission, New Delhi, India, for the financial support in the form of
Junior Research Fellow wide grant No. 10-2(5)/2006(i)-E.U. II.
Address correspondence to Gita Seth, Department of Chemistry, University of Ra-
jasthan, Jaipur-302 004, India. E-mail: gita seth@yahoo.co.in
315

316
P. Jhajharia et al.
SCHEME 1
RESULTS AND DISCUSSION
The S-phosphorylated benzothiazole derivatives have been synthesized
by the reaction of 2-(2ꢀ-mercaptophenyl)benzothiazole with phospho-
rous oxychloride/phosphorous thiochloride (1:1, 2:1, and 3:1 molar ra-
tio) in the presence of a stoichiometric amount of triethylamine in THF.
(C13H8NS2)P(O)Cl2 (1), (C13H8NS2)P(S)Cl2 (2), (C13H8NS2)2P(O)Cl(3),
(C13H8NS2)2P(S)Cl (4), (C13H8NS2)3P(O) (5), and (C13H8NS2)3P(S) (6)
were synthesized as exhibited in Scheme 1. The physical and analytical
data of the compounds are given in Table I.
IR Spectra
In the 2-(2ꢀ-mercaptophenyl)benzothiazole ligand, an absorption band
is found at 2550 cm–1, which is characteristic of the -SH group. Bands
due to ν(S-H) at 2550 cm−1 were absent in all the reported phospho-
rylated and thiophosphorylated benzothiazole derivatives due to the
deprotonation of the -SH group, resulting in the formation of P-S-C
bonds. In the phosphorylated and thiophosphorylated derivatives of 2-
(2ꢀ-mercaptophenyl)benzothiazole, characteristic stretching vibrations
of ν(P=S), ν(P=O) and ν(P-S-C)17–18 are found in a range of 654–685,
1240–1255, and 530–575 cm−1, which further confirms the formation
of S-phosphorylated/thiophosphorylated benzothiazole. The results of
the IR spectra are summarized in Table II.
1H NMR Spectra
The 1H NMR spectrum of 2-(2ꢀ-mercaptophenyl) benzothiazole
shows a SH proton signal at ∼3.60 ppm. In the phosphory-
lated/thiophosphorylated derivatives of substituted benzothiazole, the
signal for the -SH proton is absent due to the removal of H by Cl of
POCl3/PSCl3. The signals for the aromatic protons were found in the
expected range of 6.4–7.4 ppm.19

317

318
P. Jhajharia et al.
TABLE II Assignment of Main IR Bands (cm−1) of Phosphorylated
and Thiophosphorylated Derivatives of 2-(2ꢀ-Mercaptophenyl)
benzothiazole
IR Bands (cm−1
)
Compound
ν(P
S
C)
ν(P O)
ν(P S)
ν(P Cl)
(1)
(2)
(C13H8NS2)P(O)Cl2
575
1255
—
584 (asym)
540 (sym)
554 (asym)
500 (sym)
490
480
—
—
(C13H8NS2)P(S)Cl2
555
—
685
(3)
(4)
(5)
(6)
(C13H8NS2)2P(O)Cl
(C13H8NS2)2P(S)Cl
(C13H8NS2)3P(O)
(C13H8NS2)3P(S)
565
536
560
530
1248
—
1240
—
—
660
—
654
31P NMR Spectra
The phosphorylated and thiophosphorylated benzothiazole derivatives
were characterized by the 31P NMR signals obtained in the range of
58.4–68.3 ppm.20 The results of the NMR spectra are summarized in
Table III.
Antifungal Activity
The products have been screened for fungicidal properties against two
fungi, namely Aspergillus niger and Fusarium oxysporium at concen-
trations 50, 100, and 200 ppm. Radial growth method was used to
check an activity against fungi. The results of fungicidal screening
of the phosphorylated/thiophosphorylated derivatives with standard
Dithane M-45 are furnished in Table IV.
All the derivatives exhibited high toxicity towards both the fungi
even at low concentrations. The inference drawn from the table reveals
TABLE III 1H NMR and 31P NMR Spectral Data of Phosphorylated
and Thiophosporylated Derivatives of 2-(2ꢀ-Mercaptophenyl)
benzothiazole
Compounds
31P NMR (δ ppm)
1H NMR (δ ppm)
(1)
(2)
(3)
(4)
(5)
(6)
(C13H8NS2)P(O)Cl2
(C13H8NS2)P(S)Cl2
(C13H8NS2)2P(O)Cl
(C13H8NS2)2P(S)Cl
(C13H8NS2)3P(O)
(C13H8NS2)3P(S)
58.4
61.7
62.5
64.5
65.2
68.3
6.88–7.2 (m, 8H, Ar-H)
6.4–7.0 (m, 8H, Ar-H)
7.0–7.2 (m, 16H, Ar-H)
6.6–6.9 (m, 24H, Ar-H)
7.0–7.4 (m, 24H, Ar-H)
6.8–7.2(m, 24H, Ar-H)

Synthesis and Biocidal Activity of Organophosphates
319
TABLE IV Fungitoxic Screening Data of Organophosphorus
Derivatives of 2-(2ꢀ-Mercaptophenyl)benzothiazole
Percent mycelial inhibition
Aspergillus niger
compounds (ppm)
Fusarium oxysporium
compounds (ppm)
Compound
50
100
200
50
100
200
(1)
(2)
(3)
(4)
(5)
(6)
(C13H8NS2)P(O)Cl2
(C13H8NS2)P(S)Cl2
(C13H8NS2)2P(O)Cl
(C13H8NS2)2P(S)Cl
(C13H8NS2)3P(O)
(C13H8NS2)3P(S)
Dithane M-45
22.1
31.4
30.2
38.6
78.3
81.4
87.0
43.3
58.9
59.1
62.3
85.6
89.3
92.0
70.6
74.3
78.2
86.9
92.4
94.0
100.0
25.3
38.1
39.3
45.1
73.1
84.1
76.0
52.4
58.7
55.3
63.2
83.2
92.4
94.0
68.4
74.6
76.4
82.3
88.1
96.2
100.0
that the activity of derivatives increases with an increase in concentra-
tion. Derivatives having a P S bond resulted in higher toxicity than
derivatives having P O bond, with the same substituents attached to
the phosphorus. (C13H8NS2)3P(S) was found to be most toxic. Although
the toxicity of all the newly synthesized derivatives was quite high, it
was less than the standard Dithane M-45. The results show that the
phosphorylated and thiophosphorylated derivatives are more effective
fungicidal inhibitors than their parent benzothiazole counterparts, and
it also reveals that the results are comparable to standard fungicide
Dithane M-45. It is evident from the literature that organophosphorus
compounds are less harmful as they get easily hydrolyzed in aqueous
media and also on oxidation, organophosphorus fungicides result in less
toxic products. Moreover, organophosphates are biodegradable, short-
lived chemical compounds, so they do not get concentrated as they move
up the food chain.
EXPERIMENTAL
Solvents were distilled and dried by standard procedures before use.
Melting points were determined by the capillary method and are un-
corrected. NMR data were recorded on FT NMR spectrometer JEOL
FX-90Q using CDCl3 as solvent. IR spectra were recorded on a Shi-
madzu 8400 S FT-IR spectrometer as KBr discs. 31P NMR spectra were
recorded on a JEOL AL 300 MHz FTNMR spectrometer. The ligand
2-(2ꢀ-mercaptophenyl)benzothiazole was synthesized according to the
reported method.21

320
P. Jhajharia et al.
Synthesis of (C13H8NS2)P(O)Cl2/(C13H8NS2)P(S)Cl2
In the fast stirring solution of 2-(2ꢀ-mercaptophenyl)benzothiazole
(0.001 mol) in dry THF (30 mL) and Et3N (0.001 mol) in dry THF
(20 mL), a solution of POCl3/PSCl3 (0.001 mol) in dry THF was added
dropwise at 0◦C. The reaction was brought to room temperature, and
stirring was continued for 20–22 hours. Then it was cooled, and the
adduct (Et3N.HCl) that formed during the reaction was filtered through
a closed sintered funnel. The filtrate was then concentrated and
recrystallized.
Synthesis of (C13H8NS2)2P(O)Cl/(C13H8NS2)2P(S)Cl
In the fast stirring solution of 2-(2ꢀ-mercaptophenyl)benzothiazole
(0.002 mol) in dry THF (30 mL) and Et3N (0.002 mol) in dry THF
(20 mL), the solution of POCl3/PSCl3 (0.001 mol) in dry THF (30 mL)
was added dropwise at 0◦C. Then a reaction was carried out in a manner
similar as described above.
Synthesis of (C13H8NS2)3P(O)/(C13H8NS2)3P(S)
In the fast stirring solution of 2-(2ꢀ-mercaptophenyl)benzothiazole
(0.003 mol) in dry THF (30 mL) and Et3N (0.003 mol) in dry THF
(20 mL), a solution of POCl3/PSCl3 (0.001 mol) in dry THF (30 mL) was
added dropwise at 0◦C. Then a reaction was carried out in a manner
similar as described above.
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