Fly-ash-supported synthesis of 2-mercaptobenzothiazole derivatives under microwave irradiation

Article abstract of DOI:10.1080/00397910601055073

Microwave-assisted, solvent-free alkylation and acylation of 2-mercaptobenzothiazole has been attempted using silica gel, alumina, and a new solid support, fly ash. Fly ash, a waste generated at thermal power stations, could be used as solid support just as efficiently as commercial supports. The additional features of methodology include a much faster reaction, easy workup, higher yields, higher purity of the products, and an ecofriendly approach. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910601055073

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Fly‐Ash‐Supported Synthesis of
2‐Mercaptobenzothiazole Derivatives under
Microwave Irradiation
Hemant P. Narkhede a , Uttam B. More a , Dipak S. Dalal a , Nilesh S. Pawar a
, Dhananjay H. More a & Pramod P. Mahulikar a
a School of Chemical Sciences, North Maharashtra University , Jalgaon, India
Published online: 06 Mar 2007.
To cite this article: Hemant P. Narkhede , Uttam B. More , Dipak S. Dalal , Nilesh S. Pawar , Dhananjay H.
More & Pramod P. Mahulikar (2007) Fly‐Ash‐Supported Synthesis of 2‐Mercaptobenzothiazole Derivatives under
Microwave Irradiation, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 37:4, 573-577, DOI: 10.1080/00397910601055073
To link to this article: http://dx.doi.org/10.1080/00397910601055073
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Synthetic Communicationsw, 37: 573–577, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601055073
Fly-Ash-Supported Synthesis
of 2-Mercaptobenzothiazole Derivatives
under Microwave Irradiation
Hemant P. Narkhede, Uttam B. More, Dipak S. Dalal,
Nilesh S. Pawar, Dhananjay H. More,
and Pramod P. Mahulikar
School of Chemical Sciences, North Maharashtra University,
Jalgaon, India
Abstract: Microwave-assisted, solvent-free alkylation and acylation of 2-mercapto-
benzothiazole has been attempted using silica gel, alumina, and a new solid support,
fly ash. Fly ash, a waste generated at thermal power stations, could be used as solid
support just as efficiently as commercial supports. The additional features of method-
ology include a much faster reaction, easy workup, higher yields, higher purity of the
products, and an ecofriendly approach.
Keywords: dry media, fly ash, 2-mercaptobenzothiazole (MBT), microwave
irradiation, solid support
INTRODUCTION
Green chemistry involves the design and redesign of chemical synthesis[1] and
chemical products to prevent pollution and thereby solve environmental
problems. It is the use of chemical principles and methodologies for source
Received in India July 11, 2006
This paper is dedicated to Prof. R. B. Mane, Department of Chemistry, Shivaji
University.
This work was presented at the National Conference on Recent Trends in Synthetic
Organic Chemistry, North Maharashtra University, Jalgaon, India, December 16–17, 2005.
Address correspondence to Pramod P. Mahulikar, School of Chemical Sciences,
North Maharashtra University, Jalgaon 425001 M.S., India. E-mail: mahulikarpp@
rediffmail.com
573

574
H. P. Narkhede et al.
reduction that is the most desirable form of pollution prevention. It incorporates
pollution-prevention practices in the manufacture of chemicals and promotes
industrial ecology. It is a new way of looking at chemicals and their manufactur-
ing processes to minimize any negative environmental effects. Microwave (MW)
chemistry is one current approach in green chemistry. It is a boon in disguise for
environmentally conscious chemists. The MW energy is utilized in rapid
chemical transformations and also in solid state[2,3] without the use of water or
organic solvent. MW-mediated reactions[4] occur more rapidly, safely, and in
an environmentally friendly manner with high yields. Such reactions reduce
the amount of waste products and increase the pure required products.
Fly ash is a waste generated at thermal power stations by the burning of
coal.[5] The composition of fly ash varies from one thermal power station to an
other. An average composition of fly ash is SiO2 (62–68%), Al2O3 (17–29%),
Fe2O3 (3–7%), MgO (0.5–3.5%) and others (MnO2, CaO, P2O5, TiO2, SO3,
Na2O, K2O) (0.002–2.50%).
The disposal of fly ash is a major problem throughout the world. It is now
utilized in large quantities under three categories: a) Low-value-added
utilization (as a fill material for land or mines, embankments, and backfills; soil
amendment for agriculture; subgrade stabilization and road pavements), b)
medium-value-added utilization (bricks, cement, concrete, lightweight aggre-
gates, and other building construction materials); and c) high-value-added utiliz-
ation (mineral recovery, ceramics, cenospheres, and metal-matrix composites).
The major components of fly ash are SiO2 and Al2O3; thus, it could be used as
solid supports just as silica gel and alumina are used in organic synthesis.
2-Mercaptobenzothiazole (MBT) and its derivatives have been used to
protect copper and copper alloys against corrosion. MBT is an important vul-
canization catalyst in the rubber industry. It also plays a role in analysis as a
reagent for cadmium as well as for the determination of copper, lead, bismuth,
silver, mercury, thallium, gold, platinum, and iridium.[6] MBT derivatives
were reported to possess antifungal and antibacterial activities and were
also found to be useful in the leather industry.[7–9]
However, a literature survey has revealed that the synthesis of derivatives
of MBT[8–12] requires reflux conditions and longer reaction times. In continu-
ation of our work for the synthesis of biologically active compounds,[14–18] we
report herein a simple, rapid, efficient, and environmentally friendly method
for the synthesis of MBT derivatives (Scheme 1). The present work
includes solid-state alkylation and acylation of MBT using commercially
available silica gel, alumina, and fly ash as a new solid support. MBT was
adsorbed on silica gel, alumina and fly ash using aqueous sodium carbonate
and irradiated an Erlenmeyer flask with a funnel as a loose top cap with
various alkyl and acid halides to give the desired products. Importantly, fly
ash was found to be a better solid support for organic reactions in dry
media just as efficient as commercial ones such as silica gel and alumina.
The synthesized compounds were characterized by their physical constants
in comparison with literature data. [9–14]

Synthesis of 2-Mercaptobenzothiazole Derivatives
575
Scheme 1. Reagent ratio: MBT, 10 mmol; RX, 10 mmol; XRX, 5 mmol; Na2CO3,
1.06 g; adsorbent (silica gel/alumina/fly ash), 1.5 g; H2O, 5 mL.
EXPERIMENTAL SECTION
All chemicals were of analytical grade, and dichloromethane was freshly
distilled before use. A microwave oven (model OM9918C, 2450 MHz,
900 W) was used to carry out the reactions. The fly ash was collected from
the thermal power plant in Deepnagar, Bhusawal, Dist. Jalgaon (M.S.),
India, and used as such for the reactions. Silica gel (60–120 mesh) and
alumina (60–120 mesh) were of synthetic grade (S. D. Fines Chem. Ltd).
The reactions were monitored by silica-gel thin-layer chromatography
(TLC) using petroleum ether–chloroform (8:2). Melting points and boiling
points are uncorrected.
General Procedure for Microwave-Assisted Synthesis of MBT
Derivatives (1a–p and 2a–f)
MBT (10 mmol) was dissolved in aqueous sodium carbonate solution (5 mL,
2 N). Then, adsorbent (1.5 g) was added to this solution and stirred well. The
mixture was evaporated in a microwave oven for complete removal of water.
Dry powder, alkyl halide, or acid chloride (10 mmol) or a,v-dibromoalkane or
diacid chloride (5 mmol) was added and irradiated in the microwave oven at
270 W at pulses of 30 s for 1–5 min. After completion of reaction (monitored
by TLC), the mixture was cooled and extracted with dichloromethane
(2 Â 25 mL). Then the extract was dried with anhydrous calcium chloride
and filtered to remove the solvent and afford the products 1a–p and 2a–f
(Scheme 1, Table 1).

576
H. P. Narkhede et al.
Table 1. MBT derivatives
Lit.[9–14] mp
(bp/mm)
(8C)
Solid support, yield (%)
Compound Silica gel Alumina Fly ash
Mp (bp/mm)
(8C)
1a
1b
1c
1d
1e
1f
81
80
79
78
79
78
76
75
77
82
84
86
84
85
83
82
84
80
85
84
83
83
84
82
81
80
81
78
79
77
78
85
88
89
85
84
83
84
85
83
89
86
85
86
83
81
81
80
80
77
78
76
78
83
85
87
85
85
82
83
85
82
86
85
85
84
48
26
48–49[11,13]
26[9,11]
(172/15)
(110–12/0.5)
240–242
(144–146/1)
(127–129/0.5) (125–128/0.5)[12]
(138–140/0.5) (139–140/0.5)[12]
(126–128/0.05) (126–128/0.05)[10]
40
178–179
130
(168–175/15)[12]
(110–115/0.5)[10,12]
240–242[14]
(145–146/1)[12]
1g
1h
1i
1j
39–40[13]
178–181[9]
129–131[9]
165–167[13]
141–142[13]
66–67[9]
1k
1l
1m
1n
1o
1p
2a
2b
2c
2d
2e
2f
166–167
142
66
89
89–90[9]
139–140
210
135
139–140[14]
210[14]
135[14]
164
145
164–165[13]
145[14]
120
119–121[13]
CONCLUSION
Fly ash, a waste generated at thermal power stations by burning of coal,
was used as a solid support as efficiently as the commercial supports
silica gel and alumina. S-Alkyl, S-acyl, and dimeric derivatives of MBT
have been synthesized in higher yields using fly ash as a new solid
support. The main features of this method are a much faster reaction,
easy workup, higher yields, high purity of the products, and an ecofriendly
approach. Fly ash has found to be an economic and viable alternative solid
support to carry out organic reactions. In the present work, the rate of
reactions and yield of products using fly ash as solid support were found
to be almost the same in comparison with silica gel and alumina
supports. Thus, the work has proved the viability of fly ash as a solid
support in organic synthesis. This work will again help to exploit more
applications of fly ash in synthetic organic chemistry. Furthermore, the
use of fly ash will definitely help to solve the disposal problem to certain
extent.

Synthesis of 2-Mercaptobenzothiazole Derivatives
ACKNOWLEDGMENT
577
Hemant P. Narkhede and Uttam B. More are thankful for awards of Teacher
Fellowships under the Faculty Improvement Programme and financial assist-
ance from the University Grants Commission, New Delhi.
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