Development of hydrogelator-based gel-entrapped base catalysts (GEBCs) as heterogeneous basic catalysts for the synthesis of 3-acetylcoumarins

New gel entrapped base catalysts (GEBCs) have been prepared by entrapping some organic and inorganic bases into a solid aqueous gel matrix.

Synthesis of a dihydroquinoline based fluorescent cyanine for selective, naked eye, and turn off detection of Fe3+ions

A cyanine dye was synthesized by condensing 6-formylated 1,2,2,4-tetramethyl-1,2-dihydroquinoline (TMDQ) and 1,7-dimethyl-2-phenylimidazo[1,2-a]pyridin-1-ium iodide.

Unusual tandem sequence of oxa Diels–Alder reaction, retro Diels–Alder reaction, and oxa 6π-electrocyclic ring opening in the reaction of 6-amino-4-(4-methoxyphenyl)-2H-pyran-2-ones with benzaldehydes

The oxa Diels–Alder reaction of 6-amino-4-(4-methoxyphenyl)-2H-pyran-2-ones with benzaldehydes took an unusual path whereby an unexpected tandem sequence of three reactions yielded 3-(4-methoxyphenyl)-5-phenyl-1-(piperidin-1-yl/pyrrolidin-1-yl)penta-2,4-dien-1-ones.

Regiospecific inverse electron demand Diels–Alder reactions of 7-methylcoumarin-4-azadienes

Condensation of 7-methylcoumarin-4-carbaldehyde with different anilines affords 7-methylcoumarin-4-azadienes which on Diels–Alder reaction with dihydropyran gives coumarinyl substituted pyranoquinolines.

3-Methyl-benzo[1,2-c:5,4-c']dichromen-6(8H)-one

The title compound, C₂₁H₁₄O₃, crystallizes with eight independent mol­ecules (A–H) in the asymmetric unit which are arranged in four groups of two mol­ecules each (AB, CD, EF and GH). In each mol­ecule, the pyran-2-one ring is planar (r.m.s. deviations vary from 0.001 to 0.017 Å), while the pyran ring has a screw-boat conformation. In the crystal, mol­ecules stack in two columns, along the [10-1] direction, composed of mol­ecules C, B, E and G, and D, A, F and H. Mol­ecules A and F are linked via C—H⋯O hydrogen bonds. In addition, there are a number of C—H⋯π contacts present involving all of the mol­ecules. These inter­actions result in the formation of a three-dimensional network.

Synthesis of a dihydroquinoline based merocyanine as a ‘naked eye’ and ‘fluorogenic’ sensor for hydrazine hydrate in aqueous medium and hydrazine gas

1,2,2,4-Tetramethyldihydroquinoline (TMDQ) is formylated at the 6-position and the resulting quinoline aldehyde is condensed with 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one to obtain a merocyanine 6-pyrazolinyl TMDQ.

rac-4a,10b-cis,10b,5c-trans-5-(7-Methyl-2-oxo-2H-chromen-4-yl)-3,4,4a,5,6,10b-hexa-hydro-2H-pyrano[3,2-c]quinoline

In the racemic title compound, C₂₂H₂₁NO₃, the nitro­gen-containing ring of the pyran­oquinoline moiety adopts a slightly distorted half-chair conformation and the oxygen-containing ring adopts a slightly distorted chair conformation. The benzene rings make a dihedral angle of 84.97 (8)°. In the crystal, weak C—H⋯O inter­actions link the mol­ecules into chains extending along the a-axis direction.

Ultrasound-promoted synthesis of 1-amidoalkyl-2-naphthols via a three-component condensation of 2-naphthol, ureas/amides, and aldehydes, catalyzed by sulfamic acid under ambient conditions

A three-component one-pot condensation of 2-naphthol, ureas/amides and aldehydes catalyzed by sulfamic acid, under ultrasound irradiation and ambient conditions gives 1-amidoalkyl-2-naphthols in excellent yield and in short time.

Oxidation of alkylarenes using aqueous potassium permanganate under cavitation: comparison of acoustic and hydrodynamic techniques

Various alkylarenes were oxidized to the corresponding aryl carboxylic acids using aqueous potassium permanganate under heterogeneous condition in the presence of hydrodynamic cavitation and the results of the reaction have been compared with the acoustic cavitation in terms of their energy efficiency. The rate of reaction was determined for each reaction. In the oxidation of p-xylene, seven times more product could be obtained in the case of hydrodynamic cavitation than in the case of acoustic cavitation. The reaction was found to be considerably accelerated at ambient temperature.

Oxidation of alkylarenes to the corresponding acids using aqueous potassium permanganate by hydrodynamic cavitation

Oxidation of toluene using aqueous potassium permanganate was studied under heterogeneous condition in the presence of hydrodynamic cavitation and compared with the results of the reaction under acoustic cavitation. Various parameters, such as quantity of potassium permanganate, toluene to aqueous phase ratio, reaction time and cavitation parameters such as orifice plate, and pump discharge pressure were optimized. The reaction was found to be considerably accelerated at ambient temperature in the presence of cavitation. On comparison, it was found that when 1 kJ of energy was passed to the reaction mixture in the case of acoustic cavitation, the product obtained was 4.63 x 10(-6) mol, whereas when 1 kJ of energy was passed to the reaction mixture in the case of hydrodynamic cavitation the product obtained was 2.70 x 10(-5) mol. Hence, about six times more product would be obtained in the case of hydrodynamic cavitation than in the case of acoustic cavitation at same energy dissipation. It has been observed that further optimization is possible.

Sonochemical bromination of acetophenones using p-toluenesulfonic acid-N-bromosuccinimide

Substituted acetophenones react with N-bromosuccinimide (NBS) and p-toluenesulfonic acid (p-TsOH) in the presence of ultrasound in methanol at 35 +/- 2 degrees C to give alpha-bromoacetophenones in high yield. In the absence of ultrasound the reaction takes place at the boiling point of methanol (65 degrees C) and takes longer time. The reaction does not take place in the absence of p-TsOH thermally or sonically. However the reaction is possible under photochemical conditions in the absence of p-TsOH. The best solvent for the reaction was found to be methanol.

Sonochemical chloro-oxidation of phenols using HCl-H2O2

The reaction of phenol, 2-nitrophenol, thymol, 1-naphthol and 1-hydroxy-2-naphthoic acid with HCl-H2O2 was carried out in the presence and in the absence of ultrasound. In the presence of ultrasound phenol, 2-nitrophenol and thymol gave only the chlorinated products, while 1-naphthol and 1-hydroxy-2-naphthoic acid gave chlorinated quinones as the major products. The reactions with ultrasound were compared with those without ultrasound.

Ultrasound assisted PTC catalyzed saponification of vegetable oils using aqueous alkali

A few vegetable oils were saponified using aqueous KOH and different PTCs at room temperature in the presence of ultrasound. The extent of saponification was studied using the saponification value as a reference. Optimizations of various parameters such as time, selection of PTC, quantity of PTC, quantity of KOH and quantity of water were carried out using soyabean oil as a sample oil under sonication with stirring. To study the effect of ultrasound, the saponification was also carried out at 35 +/- 2 degrees C under different conditions, namely stirring, sonication, stirring and sonication, and heating at 100 degrees C. It was found that the heterogeneous liquid-liquid phase saponification of different vegetable oils using aq. KOH/CTAB was remarkably accelerated at 35 +/- 2 degrees C in the presence of ultrasound along with stirring.