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Kinetics and mechanism of nitration of aromatic compounds using trichloroisocyanuric acid (TCCA)/NaNO2, TCCA‐N,N‐dimethyl formamide (TCCA‐DMF)/NaNO2, and TCCA‐N,N‐dimethyl acetamide (TCCA‐DMA)/NaNO2 under acid‐free and Vilsmeier‐Haack conditions. Reactions followed second‐order kinetics with a first‐order dependence on [Phenol] and [Nitrating agent] ([TCCA], [(TCCA‐DMF)], or [(TCCA‐DMA)] >> [NaNO2]). Reaction rates accelerated with the introduction of electron‐donating groups and retarded with electron‐withdrawing groups, but did not fit well into the Hammett's theory of linear free energy relationship or its modified forms like Brown‐Okamoto or Yukawa‐Tsuno equations. Rate data were analyzed by Charton's multiple linear regression analysis. Isokinetic temperature (β) values, obtained from Exner's theory for different protocols, are 403.7 K (TCCA‐NaNO2), 365.8 K (TCCA‐DMF)/NaNO2, and 358 K (TCCA‐DMA)/NaNO2. These values are far above the experimental temperature range (303‐323 K), indicating that the enthalpy factors are probably more important in controlling the reaction. [ABSTRACT FROM AUTHOR]

Sodium perborate (SPB) was used as efficient green catalyst for NaNO2/KHSO4-mediated nitration of aromatic compounds in aqueous acetonitrile medium. Synthesis of nitroaromatic compounds was achieved under both conventional and solvent-free microwave conditions. Reaction times were comparatively shorter in the microwave-assisted than conventional reaction. The reaction kinetics for nitration of phenols in aqueous bisulfate and acetonitrile medium indicated first-order dependence on [Phenol], [NaNO2], and [SPB]. Reaction rates accelerated with introduction of electron-donating groups but retarded with electron-withdrawing groups. Kinetic results did not fit well quantitatively with Hammett’s equation. Observed deviations from linearity were addressed in terms of exalted Hammett’s constants (σ¯ or σeff), para resonance interaction energy (ΔΔGp) parameter, and Yukawa-Tsuno parameter (r). This term provides a measure of the extent of resonance stabilization for a reactive structure that builds up charge (positive) in its transition state. The observed negative entropy of activation (−ΔS#) suggests greater solvation and/or cyclic transition state before yielding products. [ABSTRACT FROM AUTHOR]

Abstract: Ammonium metavanadate (AMV)/NaNO2-triggered nitration of phenols (Ar-OH) in aqueous KHSO4-acetonitrile medium is too sluggish, even at elevated temperature. However, addition of surfactant [sodium dodecyl sulfate (SDS) or Triton X-100 (TX-100)] remarkably accelerates the nitration rate in a concentration-dependent fashion. The reaction kinetics are first order in [AMV], [Ar-OH], and [NaNO2]. Addition of acrylamide or acrylonitrile to the reaction mixture does not result in polymerization, indicating absence of free-radical intermediates. Ultraviolet-visible (UV-Vis) spectroscopic studies of AMV with SDS and TX-100 revealed binding interactions of AMV with micelles. Scanning electron microscopy studies revealed formation of nanostructured micelles with SDS as well as TX-100. On the basis of these observations, the rate acceleration in micellar media can be explained based on formation of more reactive micelle-bound AMV species that partake in the reaction by triggering nitration.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Silica-supported perchloric acid and bisulfate (SiO2/HClO4 and SiO2/KHSO4) have been developed as reusable green catalysts for nitration of aromatic compounds using NaNO2 in acetonitrile medium under conventional and solvent-free microwave conditions. The reaction times under microwave irradiation are significantly shorter than conventional method even though the yields obtained in microwave-assisted reactions are comparable with those obtained under reflux conditions. [ABSTRACT FROM AUTHOR]

Peroxy compounds such as H2O2, peroxydisulfate (PDS), peroxymonosulfate (PMS), sodium perborate (SPB), and tert-butyl hydroperoxide (TBHP) have been used as efficient catalysts for nitration of aromatic and heteroaromatic compounds in presence of NaNO2O/KHSO4O under mineral acid-free conditions. The reactions afforded very good yields of under different conditions. Depending on the nature of peroxide and substrate, reaction times recorded under conventional conditions reduced from (2 to 7hrs) hours to (25 to 60) minutes with grindstone technique, which in turn reduced to (25 to 120) seconds in microwave assisted reactions. Product yields are also increased from 6 to 10% under microwave irradiation as compared to conventional procedures. All synthesized compounds were characterized by 1H NMR and mass spectral studies. [ABSTRACT FROM AUTHOR]

ABSTRACT The reaction kinetics of Prussian blue (PB)/NaNO2 initiated for the nitration of phenols by in aqueous bisulfate and acetonitrile medium indicated first-order dependence on [phenol], [NaNO2], and [PB]. An increase in [KHSO4] accelerated the rate of nitration under otherwise similar conditions. The rate of nitration was faster in the solvent of higher dielectric constant ( D). Observed results were in accordance with Amis and Kirkwood plots [log k′ vs. (1/ D) and [( D − 1)/(2 D + 1)]. These findings together with the linearity of plots, log k′ versus (vol% of acetonitrile (ACN)) and mole fraction of ( nx) ACN, probably indicate the importance of both eloctrostatic and nonelctrostatic forces, solvent-solute interactions during nitration of phenols. Reaction rates accelerated with the introduction of electron-donating groups and retarded with electron-withdrawing groups, which are interpreted by Hammett's theory of linear free energy relationship. Hammett's reaction constant (ρ) is a fairly large negative (ρ < 0) value, indicating attack of an electrophile on the aromatic ring. Furthermore, an increase in temperature decreased the reaction constant (ρ) values. This trend was useful in obtaining isokinetic temperature ( β) from Exner's plot of ρ versus 1/ T. Observed β value (337.8 K) is above the experimental temperature range (303-323 K), indicating that the enthalpy factors are probably more important in controlling the reaction. [ABSTRACT FROM AUTHOR]

Ultrasonic and microwave-assisted practical methods have been developed for the nitration of phenols using metal nitrates in aqueous polyethylene glycol (PEG) media. Solvent is recycled three times for reproducibility. It was recycled with minimum loss and decomposition. Developed protocols were cost effective, simple and efficient, which afforded nitration products in good to excellent yields. The observed hyperchromic/hypochromic shifts in the UV/VIS spectra of metal nitrates in PEG solutions could be due to the plausiblein situformation of “PEG-bound M(II) nitrate” and thereby the release of nitronium ion () during the course of reaction when metal nitrate [M(II)nitrate] is added to PEG. Nitronium thus formed most likely is captured by aromatic compound to afforded nitro aromatics. [ABSTRACT FROM AUTHOR]

Polyethylene glycols (PEGs) were found to be efficient media for decarboxylative nitration of α,β-unsaturated aromatic carboxylic acids by ceric ammonium nitrate (CAN) in acetonitrile to give β-nitrostyrene derivatives. Kinetics of the reaction exhibited second order kinetics with a first order dependence on [CAN] and [substrate]. Reactions were too sluggish to be studied in the absence of PEG; therefore detailed kinetics were not taken up. Reaction times were reduced from 24 hrs to few hours. The catalytic activity was found to be in the increasing order PEG-300 > PEG-400 > PEG-600 > PEG-200. Mechanism of PEG-mediated reactions was explained by Menger-Portnoy's scheme as applied in micellar kinetics. [ABSTRACT FROM AUTHOR]