Photochemistry of trifluromethyl substituted 1‐methylpyrazoles

Trifluromethyl substitution on the pyrazole ring was found to enhance photoreactivity via the P₄ pathway which involves interchange of the N2‐C3 ring atoms. Thus, 1‐methyl‐3‐(trifluromethyl)pyrazole (1) and 1‐methyl‐5‐(trifluromethyl)pyrazole (3) transposed with a P₄/P₆ or P₄/P₆+P₇ ratio of 2.1:1. 1‐methyl‐4‐(trifluromethyl)pyrazole (2) transposed regiospecifically by the P₄ transposition pathway. Compounds 2 and 3 were also observed to undergo photocleavage to yield enaminonitrile and enaminoisocyanide products.     

Effect of Static Magnetic Field on Photocatalytic Degradation of Methylene Blue over ZnO and TiO2 Powders

Magnetic field effects (MFEs) on photocatalytic degradation of methylene blue (MB) solution over ZnO and TiO₂ powders are investigated under static magnetic field up to 0.7 T with light irradiation by ultraviolet (UV) light emitting diode. The UV–visible-near-infrared spectrometer is used to monitor the MB concentrations. The positive MFE is observed for ZnO, while the negative MFE for TiO₂, and both MFEs are increased with the increase in the magnetic field applied. By increasing the settling time (the time interval between the preparation of MB solution and the powder dispersion into the MB solution), the photodegradation abilities under MFEs are decreased for both the catalysts. The cause of MFE is discussed in terms of dissolved oxygen in the MB solution and magnetic adsorption of the constituent molecules.     

A Novel Trihybrid Material Based on Renewables: An Efficient Recyclable Heterogeneous Catalyst for C−C Coupling and Reduction Reactions

The generation of organic–inorganic hybrid materials from renewable resources and their utilization in basic and applied areas has been at the forefront of research in recent years for sustainable development. Herein, a novel organic–inorganic trihybrid material was synthesized by in situ generation of palladium nanoparticles (PdNPs) in a hybrid gel matrix based on renewable chemicals. Constituents of the hybrid gel included a pentacyclic triterpenoid arjunolic acid extractable from Terminalia arjuna and the leaf extract of Chrysophyllum cainito rich in flavonoids. We took advantage of the presence of flavonoid molecules in this hybrid gel to generate an advanced trihybrid gel through in situ reduction of doped Pd^II salts to stable PdNPs. The xerogel of this trihybrid material was used as a recyclable heterogeneous catalyst for C?C coupling and reduction reactions in aqueous media. We also demonstrated that the in situ generated PdNPs containing trihybrid material was a more efficient catalyst than the trihybrid material generated with presynthesized PdNPs.     

Semiconducting polymers from triphenylamine derivatives‐benzaldehyde polymers by oxidization with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ)

4‐Tolyldiphenylamine (TDPA) and N,N′‐diphenyl‐N,N′‐bis(4‐methylphenyl)‐1,1′‐biphenyl‐4,4′‐diamine (TPD), were reacted with benzaldehyde (BA) using p‐toluenesulfonic acid as a catalyst to yield linear polymers. The polymers were reacted with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) in tetrahydrofuran (THF) at room temperature. ¹H‐NMR showed that all the methine protons in the residue of BA were completely removed at the mole ratio of repeating unit : DDQ, 2 : 1. The resulting polymers showed good solubility in chloroform or THF. The reacted TDPA‐BA and TPD‐BA polymers gave new UV absorption peaks at 697.0 and 722.5 nm and showed reversible redox potentials about 0.994 and 1.021 V, respectively. Direct current (d.c.) conductivity of the reacted polymers was in the range of 10^?11 S/cm, which is more than two orders higher than the unreacted polymers. The polymer showed pentad split electron spin resonance (ESR) signal, whose concentration was one in 670 or 230 repeating unit for TDPA‐BA and TPD‐BA polymers, respectively. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis of some trifluoromethyl substituted 1‐methylpyrazoles

The major products from the reaction of β‐alkoxyvinyl trifluoromethyl ketones 1a‐c with methylhydrazine ( 2 ) in absolute ethanol are the 3‐(trifluoromethyl)‐substituted‐1‐methylpyrazoles 3a‐3c with lesser amounts of the 5‐(trifluoromethyl)‐substituted products 4a‐4c and 5a‐5c. Carrying out the reaction in non‐polar, aprotic solvents can further enhance the regioselectivity favoring the 3‐ (trifluoromethyl) ‐substituted isomers.     

Synthesis of some pyrano[2,3‐c]pyrazoles

Synthetic methods have been developed to prepare pyrano[2,3‐c]pyrazoles with various substituents at ring positions 1, 3, and 6. The ¹H‐ and ¹³C‐NMR properties of these products and their precursors are presented and discussed. J. Heterocyclic Chem., (2011).     

Synthesis and spectroscopic properties of 15n‐labelled 1,2,4‐thiadiazoles

5‐Phenyl‐1,2,4‐thiadiazole‐4‐¹⁵N and 3‐methyl‐5‐phenyl‐1,2,4‐thiadiazole‐4‐¹⁵N were synthesized from commercially available benazmide‐¹⁵N. The mass spectra and the ¹H, ¹³C, and ¹⁵N‐nmr spectra of these compounds, which show various long‐range heteronuclear coupling with the ¹⁵N‐nucleus, are discussed.