Anshu Jain

Microwave-assisted synthesis of nitrogen-containing heterocycles

Abstract In the recent years, microwave (MW) radiation is widely used as a source of heating in organic synthesis. Since the discovery of the MW heating approach, MW-assisted reaction has emerged as a new green-method in organic synthesis as it provides spectacular accelerations, higher yields under milder reaction conditions, and higher product purities, and it reduces pollution of the environment through the use of solvent-free reaction protocols. N-containing heterocycles hold a special place among pharmaceutically significant natural products and synthetic compounds needed for any developed human society. Therefore, organic chemists have been engaged in extensive efforts to produce these compounds following various greener techniques, primarily to circumvent growing environmental concerns. In this review, we discuss only the MW-assisted synthesis of N-containing heterocyclic compounds.

Rationally designed tri-armed imidazole–indole hybrids as naked eye receptors for fluoride ion sensing

ABSTRACT The present communication describes the design, synthesis, and characterization of unique tri-armed imidazole–indole hybrids RA-RE for naked eye detection of fluoride ion in 9:1 DMSO–water at concentration level of 1.5 ppm, which is recommended permissible limit of fluoride ion. Molecular structures of the receptors are so fabricated that both heterocyclic units, namely, indole and imidazole have been rationally used as chromophore and binding unit, respectively. Strategical introduction of nitro group(s) at the fifth position of indole ring remarkably enhances the binding ability of receptor RD making it highly selective toward fluoride ion (tetrabutylammonium salt) over other typical anionic species. The sensing event can be visualized by naked eyes swiftly with color change. This observation is well corroborated by a redshift of 80 nm in UV–visible spectroscopic studies. A peak at 16.1 ppm due to in 1H NMR titration validates the deprotonation of imidazolium N‒H by fluoride ion. GRAPHICAL ABSTRACT

Coumarin Based Receptor for Naked Eye Detection of Inorganic Fluoride Ion in Aqueous Media

Abstract In this communication, we wish to report the design, synthesis and real life applications of coumarin based “naked eye” artificial receptor for fluoride ion detection in aqueous media. Amongst easy-to-synthesize 1-(1-(substituted-2-oxo-2H-chromen-3-yl)-ethylidene)-thiosemicarbazide (receptors A-E), receptor B exhibited remarkable colour change from yellow to pink instantly upon addition of fluoride salt (sodium fluoride) 1×10-5 M (0.19 ppm), in aqueous media. Interestingly, receptor B also gave distinct and discernible colour changes perceivable even with naked eye at different fluoride ion (sodium salt) concentrations (viz., <1.5, 1.5–5 and >5 ppm) fluoride in water which allows a semi-quantitative data to be generated for fluoride contaminated drinking water. Preliminary investigation with everyday commodity items like toothpaste and mouthwash clearly show visual colour change, which may be helpful for detecting presence of fluoride in these items. This method is so simple that it has the potential for being developed as a tool for detecting different levels of fluoride in ground water, especially suitable for rural areas, where the literacy rate is low. The working pH range of receptor B was found to be 6.5–7.5. The binding constant of receptor for fluoride ion was found to be 1.38×105 M-1.