Ganapati S. Shankarling

Environmentally benign and energy efficient methodology for condensation: an interesting facet to the classical Perkin reaction

We have reported use of biodegradable deep eutectic solvent (DES) based on choline chloride and urea, for the synthesis of cinnamic acid and its derivatives viaPerkin reaction. The reaction proceeds efficiently under mild condition without use of additional catalyst with better yields. Ease of recovery and reusability of solvent with consistent activity makes this method efficient and environmentally benign. This method is also energy efficient and easy to handle.

Ultrasound and deep eutectic solvent (DES): A novel blend of techniques for rapid and energy efficient synthesis of oxazoles

The present work deals with the synthesis of novel oxazole compounds by using effective combination of ultrasound (US) and deep eutectic solvent (DES). The reaction was also conducted by thermal method (NUS) and the comparative studies are provided. It was observed that applying ultrasound not only improved yields and reduced reaction times but also saved more than 85% energy as shown by energy consumption calculations. The advantages of using DES as reaction medium is highlighted from the fact that it is bio-degradable, non-toxic, recyclable and could be easily prepared using inexpensive raw materials. The recyclability for DES was studied wherein it was found that ultrasound has no negative effects on DES even up to four runs. In addition, the present work is the first report on the combinative use of DES and US in organic synthesis.

A novel colorimetric and fluorogenic chemosensor for selective detection of Cu2+ ions in mixed aqueous media

A novel and easy-to-synthesize chemosensor (L) was developed for the selective sensing of Cu2+ ions in mixed aqueous medium. Sensor L showed both colorimetric and spectral (UV-Vis and fluorescence) responses towards Cu2+, which was not affected in the presence of other surveyed metal ions (Na+, Mg2+, Al3+, K+, Ca2+, Fe2+, Co2+, Ni2+, Zn2+, Ba2+, Hg2+ and Pd2+). The 1 : 1 binding stoichiometry between Cu2+ and L was obtained using the Jobs plot and ESI-MS analysis. The binding constant (Ka) of 1.56 x 104 M−1 for L–Cu2+ complex was calculated from the Benesei–Hildebrand plot. Further, theoretical calculations were performed using the density functional theory (DFT) method to complement the experimental results.

Synthesis of chalcone (3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one): Advantage of sonochemical method over conventional method

In this work, an attempt was made to synthesize chalcone (3-(4-fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one) by condensation of 4-fluorobenzaldehyde with 1-(4-methoxyphenyl)ethanone under basic conditions by using both conventional (NUS) and sonochemical (US) methods. A simple condensation reaction of 4-fluorobenzaldehyde and 1-(4-methoxyphenyl)ethanone using potassium hydroxide as a base was carried out for the study. The synthesized chalcone derivative was characterized for FTIR, NMR, elemental analyses and studied for XRD, PSM, TGA and SEM properties to evaluate its performance obtained under ultrasonic energy. It was observed that complete conversion to chalcone occurred in 10 min by sonochemical method and in 4h by conventional method. Also it was found that crystallinity of the US synthesized chalcone was found to be increased by 63% than that of NUS synthesized chalcone. Finally, it has been observed that chalcone synthesis using sonochemical method is an energy efficient technique over conventional method (almost 90% of energy saving).

Deep eutectic solvents and glycerol: a simple, environmentally benign and efficient catalyst/reaction media for synthesis of N-aryl phthalimide derivatives

Abstract Deep eutectic solvents (DES) and glycerol have been successfully employed as efficient catalysts/reaction media in the synthesis of N-aryl phthalimide derivatives from phthalic anhydride and primary aromatic amines. The DES prepared from choline chloride and malonic acid proved to be an efficient catalyst whereas glycerol and the DES of choline chloride and urea played a dual role of catalyst and solvent. These mixtures are biodegradable, nontoxic, and cost-effective thereby providing a good industrial alternative to conventional methods. These methods gave products in moderate to high yields with good recyclability of catalyst/solvent at least up to five consecutive runs.

Comparative material study and synthesis of 4-(4-nitrophenyl)oxazol-2-amine via sonochemical and thermal method.

The present paper deals with the synthesis of aminooxazole derivatives via thermal and ultrasonic methods using deep eutectic solvent as medium. It was observed that ultrasound-assisted method gave 90% yield in just 8min as against 3.5h required to get 69% yield by thermal method. One of the compounds 4-(4-nitrophenyl)-1,3-oxazol-2-amine synthesized by both methods were subjected to material characterization study via XRD, TGA and SEM analysis. It was observed that use of ultrasound not only increased the rate of reaction but also improved the quality of product obtained. The crystallinity of the product from ultrasound method was 21.12% whereas thermal method fetched only 8.33% crystallinity thereby improving crystallinity by almost 60%. In addition, sonochemical synthesis also saved more than 70% energy as depicted by energy calculations.

Extensive Reduction in Back Electron Transfer in Twisted Intramolecular Charge‐Transfer (TICT) Coumarin‐Dye‐Sensitized TiO2 Nanoparticles/Film: A Femtosecond Transient Absorption Study

We report the synthesis, characterization, and optical and electrochemical properties of two structurally similar coumarin dyes (C1 and C2). These dyes have been deployed as sensitizers in TiO2 nanoparticles and thin films, and the effect of molecular structure on interfacial electron-transfer dynamics has been studied. Steady-state optical absorption, emission, and time-resolved emission studies on both C1 and C2, varying the polarity of the solvent and the solution pH, suggest that both photoexcited dyes exist in a locally excited (LE) state in solvents of low polarity. In highly polar solvents, however, C1 exists in an intramolecular charge-transfer (ICT) state, whereas C2 exists in both ICT and twisted intramolecular charge-transfer (TICT) states, their populations depending on the degree of polarity of the solvent and the pH of the solution. We have employed femtosecond transient absorption spectroscopy to monitor the charge-transfer dynamics in C1- and C2-sensitized TiO2 nanoparticles and thin films. Electron injection has been confirmed by direct detection of electrons in the conduction band of TiO2 nanoparticles and of radical cations of the dyes in the visible and near-IR regions of the transient absorption spectra. Electron injection in both the C1/TiO2 and C2/TiO2 systems has been found to be pulse-width limited (<100 fs); however, back-electron-transfer (BET) dynamics has been found to be slower in the C2/TiO2 system than in the C1/TiO2 system. The involvement of TICT states in C2 is solely responsible for the higher electron injection yield as well as the slower BET process compared to those in the C1/TiO2 system. Further pH-dependent experiments on C1- and C2-sensitized TiO2 thin films have corroborated the participation of the TICT state in the slower BET process in the C2/TiO2 system.

Choline chloride based eutectic solvents: direct C-3 alkenylation/alkylation of indoles with 1,3-dicarbonyl compounds

C-3 alkenylation/alkylation of indoles depends on the position of the substituent on the indole used in the reaction. C-2 substituted indole results in the formation of C-3 alkenylated indole derivatives, whereas plain indole gives rise to the bis(indolyl)carbonyl derivative instead of the C-3 alkenylation product under the same set of reaction conditions. Deep eutectic mixtures are cost-effective, and bio-degradable.

Steric-Hindrance-Induced Regio- and Chemoselective Oxidation of Aromatic Amines

Unusual regio- and chemoselective oxidation of aromatic amines hindered with ortho substituents (except -NH2, -NHCH3, and -OH) to the corresponding nitro compounds is described by use of nonanebis(peroxoic acid). The mechanistic investigation for selective oxidation of amines ortho-substituted with -NH2 or -OH showed the involvement of H-bonding between the ortho hydrogen of the adjacent -XH group (where X = NH, NR, or O) and an oxygen atom from the diperoxy acid. Various mono- and diamines are oxidized into corresponding mononitro derivatives in high yield and purity without employing any protection strategies. The protocol was also found to successful on the gram scale.

Photophysical and thermal properties of novel solid state fluorescent benzoxazole based styryl dyes from a DFT study

Novel benzoxazole styryl dyes 6a–6e with donor(D)–π(pi)–acceptor(A) were synthesized and characterized. The spectral (absorption and emission) and thermogravimetric properties of the dyes were investigated. They were found to possess red-shifted absorption with a high molar extinction coefficient when compared to their reported analogues. The compounds exhibited enhanced fluorescence emission in the solid state (540–603 nm). They showed excellent thermal and photochemical stability. The effect of the benzoxazole moiety on the photophysical properties is explained by comparing with reported analogues and density functional theory (DFT) calculations. Thus investigations of photophysical properties provide an important foundation for the molecular design and development of novel optoelectronic materials for OLED and NLO applications.