Search results for "MRH"

The influence of steric effects on the strength of some organic acids in toluene and water

Effect of ionic liquids in acid-promoted heterocyclic rearrangement reaction

Reactivity of phenylhydrazones in ionic liquids solution: the effect of copper(II) salts

MULTIPLE CLIMATE-DRIVEN CASCADING ECOSYSTEM EFFECTS AFTER THE LOSS OF A FOUNDATION SPECIES

2021

Abstract Climate change is evolving so fast that the related adverse effects on the environment are becoming noticeable. Thus, there is an urgent need to explore and understand the effects generated by multiple extreme climatic events (MECEs) on marine ecosystem functioning and the services provided. Accordingly, we combined long-term in-situ empirical observations in the Mediterranean Sea with a mesocosm manipulation to investigate the concurrence of increasing temperature and hypoxia events. By focussing on a foundation mussel species, we were able to detect several cascade events triggered by a mass mortality event caused by stressful temperature and oxygen conditions, and resulting in a…

Reazioni di isomerizzazione e trasposizione di fenilidrazoni in liquidi ionici: catalisi da sali di rame (II)

Ionic Liquids: as the different structural order degree can affect the outcome of a reaction

Acid- and Base-Catalysis in the Mononuclear Rearrangement of Some (Z)-arylhydrazones of 5-Amino-3-benzoyl-1,2,4-oxadiazole in Toluene: Effect of Subs…

2011

The reaction rates for the rearrangement of eleven (Z)-arylhydrazones of 5-amino-3-benzoyl-1,2,4-oxadiazole 3a-k into the relevant (2-aryl-5-phenyl-2H-1, 2,3-triazol-4-yl)ureas 4a-k in the presence of trichloroacetic acid or of piperidine have been determined in toluene at 313.1 K. The results have been related to the effect of the aryl substituent by using Hammett and/or Ingold-Yukawa-Tsuno correlations and have been compared with those previously collected in a protic polar solvent (dioxane/water) as well as with those on the analogous rearrangement of the corresponding (Z)-arylhydrazones of 3-benzoyl-5-phenyl-1,2,4-oxadiazole 1a-k in benzene. Some light can thus be shed on the general di…

The ionic liquid effect on the Boulton-Katritzky reaction: a comparison between substrates of different structure

2015

The mononuclear rearrangement of heterocycles, also called Boulton–Katritzky reaction, was studied in ionic liquid solution using N-(5-phenyl-1,2,4-oxadiazol-3-yl)-N′-(4-nitrophenyl)-formamidine as substrate. The investigation was carried out using piperidine as basic catalyst and several ionic liquids differing in both cation and anion structure. Kinetic data collected were compared with the ones previously reported using (Z)-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole to have information about the effect due to the different structure of the alkyl chain borne on the substrate. Furthermore, data were analysed on the grounds of polarity, Kamlet–Taft solvent parameters, but taking…

The effect of the cation p-surface area on the 3D organization and catalytic ability of imidazolium-based ionic liquids

2011

The dichotomic nature of ionic liquids (ILs, simple solvents or supramolecular fluids) induced us to carry out a structural investigation of some mono-and dicationic ionic liquids using 1D and 2D NMR, resonance light scattering, and UV/Vis spectroscopy. Ionic liquids with different cation π-surface areas were used, namely [bmim][NTf2], [Bzmim][NTf 2], [Bzbim][NTf2], [p-Xyl-(bim)2][NTf 2]2, and [m-Xyl-(bim)2][NTf2] 2 [bmim = 1-butyl-3-methylimidazolium, Bzmim = 1-benzyl-3- methylimidazolium, Bzbim = 1-benzyl-3-butylimidazolium, NTf2 = bis(trifluoromethansulfonyl)imide]. In order to verify to what extent the structural investigation, coupled with the determination of solvent parameters, could…

Convergent results from experimental and theoretical DFT studies of the intramolecular rearrangement of Z-hydrazones of 3-acetyl-1,2,4-oxadiazoles

2004

A combined kinetic and theoretical study of the monocyclic rearrangements of heterocycles (MRH) has been carried out. The interconversion of the Z-hydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into the corresponding triazole has been experimentally investigated in dioxane/water in the pS(+) range 5.5(5)-13.9. The uncatalyzed region has been examined at the DFT level using a model system formed by the Z-hydrazone of 3-formyl-1,2,4-oxadiazole and one or two water molecules. The environmental effect of the solvent has been emulated using a continuum model (COSMO) approach. The kinetic data suggest a concerted process where the magnitude of the activation barrier is determined by the interpl…