Effect of aqueous solutions of various alcohols on kinetics of aromatic nucleophilic substitution reaction of 1-fluoro-2,4-dinitrobenzene with piperidine

895-899Reaction kinetics of 1-fluoro-2, 4-dinitrobenzene with piperidine has been studied spectrophotometrically in aqueous solutions of methanol, ethanol, propan-2-ol and 2-methylpropan-2-ol at 10°C. The reaction in the aqueous solutions is not catalyzed by nucleophile(piperidine). Second-order rate constants of the reaction decrease with increasing mole fraction of water and ETN(normalized polarity parameter). Therefore, polarity of the reactants of the reaction is higher than that of the activated complex. Single-parameter correlations of log kA vs ETN give satisfactory results (regression coefficients in aqueous solutions of methanol, ethanol, propan-2-ol and 2-methylpropan-2-ol are 0.988, 0.994, 0.995 and 0.996, respectively). Single-parameter correlations of log kA vs π*(dipolarity/ polarizability) and a ( hydrogen-bond donor acidity) do not give acceptable results(fore example, in the all aqueous solutions regression coefficients are 0.893 and 0.789, respectively), hence π* and α are not individually major factors in determining the reaction rate. Dual-parameter correlations of log kA vs π* and α in the all solutions represent significant improvement in statistical factors with regard to the single parameter models. Dipolarity/polarizability and hydrogen-bond donor acidity (HBD) of media have parallel and approximately equal effects on the reaction rate. Increasing of hydrogen-bond donor acidity of media stabilizes piperidine via hydrogen bonding interactions (one of the reactants) and hence the reaction rate decreases. A dual -parameter equation of log kA vs π* and α is obtai ned in the all aqueous solutions (n = 41, r= 0.990, s.e = 0.070, F2,38 = 968.10) in which π* and α have parallel and approximately equal effects on the reaction rate

Nanoarchitecturing TiO2/NiCr2O4 p-n heterojunction photocatalysts for visible-light-induced activation of persulfate to remove tetracycline hydrochloride

Herein, TiO2/NiCr2O4 nanocomposites with p-n heterojunctions were synthesized via a refluxing method and used with peroxydisulfate (PDS) to produce extensive reactive radicals. Textural, optical, photoelectrochemical, structural, and morphological properties of the prepared materials were extensively investigated. After adding 1.48 mM PDS, the removal rate constant of tetracycline hydrochloride (TH) over the TiO2/NiCr2O4 (20%)/PDS system was almost 20.5, 7.24, and 5.91-times as high as the pristine TiO2, TiO2/PDS, and TiO2/NiCr2O4 (20%) samples, respectively. Therefore, the synergistic effect of PDS and heterogeneous photocatalysis remarkably impacted the degradation reaction of TH. It was proposed that all h+, •O2−, •OH, and SO4•- contributed to the degradation reaction. According to the formation of heterojunction between n-TiO2, and p-NiCr2O4 semiconductors, a plausible mechanism for removal of different contaminants in the TiO2/NiCr2O4/PDS system was discussed. © 2022 Elsevier Lt

General acid catalysis of boric acid and water on dehydration step in formation of phenylhydrazone from salicylaldehyde

976-978Hydrazone formation from salicylaldehyde and phenylhydrazine has been studied in water-ethanol (60:40 volume) solution at 35°C and ionic strength of 0.25 (with KCI). The reaction exhibits specific acid (in pH<4) and general acid catalysis (in 4pHpH<4 attack of phenylhydrazine to salicylaldehyde, and in pH>4 dehydration of intermediate is rate detennining step. Apparent catalytic rate constants of water and boric acid in the reaction are in good agreement with predicted values from Bronsted relationship. The kinetic results, UV, IR and NMR spectroscopic analyses exhibit general acid catalysis by boric acid and water.</span

Novel visible-light-driven photocatalyst of NiO/Cd/g-C3N4 for enhanced degradation of methylene blue

Novel NiO/Cd/g-C3N4 photocatalysts were synthesized using a green and straightforward microwave-assisted method and characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), the Brunauer�Emmett�Teller (BET) method, transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and ultraviolet�visible spectroscopy (UV�Vis). The ternary NiO/Cd/g-C3N4 nanocomposites were evaluated for the degradation of methylene blue (MB) at room temperature under the visible light irradiation. Experimental results revealed that the weight percent of cadmium had a remarkable effect on the photodegradation efficiency. The NiO/Cd/g-C3N4 (0.1) sample exhibited superior activity in the degradation reaction. The activity of this nanocomposite was about 4.5 and 3.25 fold higher than those of the pure g-C3N4 and NiO/g-C3N4 samples in the degradation of MB, respectively. The enhanced photocatalytic activity was attributed to the low energy gap, increased absorption capacity of the visible light, and efficient suppression of the recombination of photogenerated electron-hole pairs. A detailed photocatalytic mechanism over the nanocomposite of NiO/Cd/g-C3N4 (0.1) was proposed with superoxide radical anion radO2� as the main reactive species. The stability of the nanocomposite was confirmed after four consecutive runs as well. © 202