Facile one-pot synthesis of 2-arylbenzothiazoles catalyzed by H3PO4/TiO2-ZrO2(1/1) under solvent-free conditions

Article abstract of DOI:10.1080/00397911.2016.1159697

A highly efficient and simple protocol for the preparation of 2-arylbenzothiazoles through condensation of 2-aminothiophenol and different aldehydes in the presence of H₃PO₄/TiO₂-ZrO₂(1/1)-cetyl pyridinium bromi

Full text of DOI:10.1080/00397911.2016.1159697

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Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Facile One-pot Synthesis of 2-Arylbenzothiazoles
Catalyzed by H3PO4/TiO2-ZrO2 (1/1) Under Solvent-
free Conditions
Hossein Naeimi & Arash Heidarnezhad
To cite this article: Hossein Naeimi & Arash Heidarnezhad (2016): Facile One-pot Synthesis
of 2-Arylbenzothiazoles Catalyzed by H3PO4/TiO2-ZrO2 (1/1) Under Solvent-free Conditions,
Synthetic Communications, DOI: 10.1080/00397911.2016.1159697
To link to this article: http://dx.doi.org/10.1080/00397911.2016.1159697
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Date: 15 March 2016, At: 05:03

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Facile One-pot Synthesis of 2-Arylbenzothiazoles Catalyzed by H3PO4/TiO2-ZrO2
(1/1) under Solvent-free Conditions
Hossein Naeimi1, Arash Heidarnezhad1
1Department of Organic Chemistry, Faculty of Chemistry, University of Kashan, Kashan,
I.R., Iran
Corresponding author Hossein Naeimi Department of Organic Chemistry, Faculty of
Chemistry, University of Kashan, Kashan, 87317, I.R., Iran E-mail:
naeimi@kashanu.ac.ir
Abstract
A highly efficient and simple protocol for the preparation of 2-arylbenzothiazoles
through condensation of 2-aminothiophenol and different aldehydes in the presence of
H3PO4/TiO2-ZrO2 (1/1)-cetyl pyridinium bromide (CPB) is described. The reaction was
preceded under mild and solvent free conditions to afford 2-arylbenzothiazole
derivatives. In this method, the title compounds were obtained in high to excellent yields
and short reaction times. The structure of synthesized products was identified by IR, 1H
NMR, 13C NMR and Mass spectroscopy.
KEYWORDS: 2-Arylbenzothiazole, H3PO4/TiO2-ZrO2, 2-Aminothiophenol, Synthesis,
Aldehyde
INTRODUCTION
1

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Benzothiazole is a privileged bicyclic ring system. It contains a benzene ring fused to a
thiazole ring. The small and simple benzothiazole nucleus is present in compounds
involved in research aimed at evaluating new products that possess interesting biological
activities such as antitumor [1, 2] anticandidous [3] antiparkinsonism [4] antiflammatory and
antihistaminic. Benzothiazole have also shown significant effect against cancer. [5]
A
variety of methods for the synthesis of 2-arylbenzothiazoles have been developed. [6, 7]
The most general approaches for synthesis of 2-arylbenzothiazoles include the following;
(1) Oxidative cyclization of phenolic Schiff bases derived from the condensation of 2-
aminothiophenols and aldehydes using various oxidants such as Sc(OTf)3-molecular
oxygen [8] and pyridinium chlorochromate, [9] and (2) The condensation of 2-
aminothiophenols with carboxylic acids under microwave irradiation in the presence of a
Lewis acid. [10, 11]
Heterogeneous organic reactions have proven useful to chemists in the laboratory as well
as in the industrial context. These reactions are effected by the reagents immobilized on
the porous solid supports and have advantages over the conventional solution phase
reactions. [12, 13] The reactions on solid-supports under solvent-free conditions are
currently the subject of considerable attention for synthetic chemists to develop eco-
friendly techniques because these heterogeneous organic reactions have many
advantages, such as ease of handling, low corrosion, minimum execution time,
environmentally safe disposal and waste minimization by developing cleaner synthetic
routes. [14-21] Consequently, it is important to note that the combination of heterogeneous
2

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catalysis with the use of solvent-free conditions represent a suitable way toward the so-
called ideal synthesis.
During the past few years, different solid acid catalysts such as zeolites, [22] metal cation
exchanged clays [23] ion exchange resins, supported-heteropolyacids, [24] nano-sized
TPA/ZrO2 dispersed in SBA-15 channels, [25] TPA/ZrO2 dispersed in MCM-41 channels
[26] and mixed metal oxides have been used for organic reactions. Phosphate-based solid
acids have already been quite efficacious in several industrially important acid-
demanding reactions. [27, 28] In addition, phosphate seems to enhance catalytic properties,
to stabilize surface area and crystal phase, to improve the surface acidity and to make the
impregnated material porous. [29]
In this research, we hope to report an efficient one-pot synthesis of various substituted 2-
arylbenzothiazoles from the reaction of 2-aminothiophenol and different aldehydes in the
presence of catalytic amounts of H3PO4/TiO2-ZrO2 (1/1)-CPB under solvent free and
mild conditions.
RESULTS AND DISCUSSION
Catalyst Characterization
In order to evaluate the crystalline structure of the optimized catalyst, XRD pattern for
the calcined sample at 500 oC after loading of 30 wt% H3PO4 was shown in Figure 1. In
general, TiO2-ZrO2(1/1)-CPB shows an amorphous form, but after the loading of H3PO4,
the corresponding peaks of the crystalline TiO2 phase and crystalline ZrO2 phase are
3