Mechanism and catalysis for phenylhydrazone formation from aromatic heterocyclic aldehydes

Moscovici, R.; Ferraz, Julio P.; Neves, Eduardo Almeida; TOGNOLI, J. O.; Seoud, Monica I. El; Amaral, Luciano

doi:10.1021/jo00888a010

Cited by 9 publications

(7 citation statements)

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“…Previous work has shown that rate constants for phenylhydrazone formation are ca. 10 3 M −2 s −1 19. We will see presently how this compares with our measured product formation rate constants.…”

Section: Resultsmentioning

confidence: 53%

“…Stage 1 is a preequilibrium between the arylhydrazine and acid, leading to complete inhibition of the condensation when [acid] ≥ [arylhydrazine]. At lower acid concentrations, the second stage of the reaction commences via a preassociative complex consisting of the phenylhydrazine, diketone, and acid, similar to the complex proposed for acid‐catalyzed hydrazine additions to ketones 19,23,25,26. We include not only nucleophilic addition to the carbonyl of the diketone and enol 2 tautomers but also a Michael‐fashion attack on enol 1 as well, since that possibility cannot be ruled out.…”

Section: Resultsmentioning

confidence: 93%

“…1 1 Chemical shift differences of approximately 2 ppm were noted under the acidic, ethanolic reaction conditions relative to CDCl 3 . See 19 for additional information. …”

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confidence: 99%

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Pyrazole formation: Examination of kinetics, substituent effects, and mechanistic pathways

Sloop

Lechner

Washington

et al. 2008

Int J of Chemical Kinetics

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Reaction kinetics for the condensation of 1,3-diketones 1a-o with selected arylhydrazines (aryl = Ph, 4-NO 2 Ph, 4-CH 3 OPh, and 2,4-diNO 2 Ph) was studied using 19 F NMR spectroscopy. Product regioselectivity is modulated by reactant ratios, substituents, and acidity. Reaction rates were found to be influenced by substituents on the diketones and on phenylhydrazines as well as by acidity of the reaction medium with rates varying as much as 1000-fold. Hammett ρ values for these cyclizations were determined. The reaction was found to be first order in both the diketone and arylhydrazine. The rate-determining step for pyrazole formation shifts as a function of pH. Mechanistic details and reaction pathways supporting these findings are proposed.

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Section: Resultsmentioning

confidence: 53%

Section: Resultsmentioning

confidence: 93%

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Pyrazole formation: Examination of kinetics, substituent effects, and mechanistic pathways

Sloop

Lechner

Washington

et al. 2008

Int J of Chemical Kinetics

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“…A carbinolamine then reacts to form imine by the loss of water. In the homogeneous system of imine formation, it was reported that under slightly acidic conditions, formation of the carbinolamine intermediate is slow, while under neutral or basic conditions, dehydration of the carbinolamine becomes the slow step [36]. An electron-withdrawing group on benzaldehyde would favor the formation of carbinolamine intermediate but hinder the dehydration process and imine formation, resulting in a decrease of the conversion.…”

Section: Catalytic Performancementioning

confidence: 99%

Applications of Amine-functionalized Mesoporous Silica in Fine Chemical Synthesis

2009

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SBA-15 silica containing homogeneously distributed amine-functional groups and of fiber or platelet morphology was prepared through a modified co-condensation method using P123 copolymer as template under acidic condition. Synthetic factors which led to wellordered mesoporous materials with high loadings of various amine groups were discussed. The resultant mesoporous materials were efficient base catalysts in Knoevenagel and Claisen-Schmidt addition reactions. The activities over SBA-15 materials with different aminofunctional groups are compared. Moreover, the advantage of ordered large mesopores of SBA-15 in catalyzing liquid phase reactions was demonstrated, and the reaction rate could be further increased when SBA-15 was with platelet morphology and short mesochannels.

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“…The Schiff base (HL, Fig. 1) was been prepared according to the previous procedure [14,15]: An ethanolic solution of 2-thiophenecarboxaldehyde (1 mmol, 25 mL) was added to an ethanolic solution of 2-chlorophenyl hydrazine (1 mmol, 25 mL) and refluxed for 2 hour in a water bath. After concentration of the solution, the precipitate was separated, filtered, washed with ethanol, and dried over anhydrous calcium chloride under vacuum.…”

Section: Synthesis Of Schiff Base (Hl)mentioning

confidence: 99%

Nano Sized Schiff Base Complexes with Mn(II), Co(II), Cu(II), Ni(II) and Zn(II) Metals : Synthesis, Spectroscopic and Medicinal Studies

2014

Can Chem Trans

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Metal chelates, [M(HL)2(H2O)2]X2 (where M= Mn(II), Co(II), Cu(II), Ni(II) or Zn(II), X= NO3-or Cl-and HL= Schiff base moiety), have been prepared and characterized by elemental analysis, magnetic and spectroscopic measurements (infrared, X-ray powder diffraction and scanning electron microscopy). Elemental analysis of the metal complexes was suggested that the stoichiometry is 1:2 (metal-ligand). Infrared spectra of the complexes agree with the coordination to the central metal atom through the nitrogen of the 2-chlorophenyl hydrazine (-Ph-NH-) group and the sulfur atom of the thiophene ring. The electronic spectra suggest a distorted octahedral geometry for all Schiff base complexes. The Schiff base and its metal chelates have been screened for their in vitro antibacterial activity against four bacteria, gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to possess more antibacterial activity than the free Schiff-base chelate.

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Mechanism and catalysis for phenylhydrazone formation from aromatic heterocyclic aldehydes

Cited by 9 publications

References 0 publications

Pyrazole formation: Examination of kinetics, substituent effects, and mechanistic pathways

Pyrazole formation: Examination of kinetics, substituent effects, and mechanistic pathways

Applications of Amine-functionalized Mesoporous Silica in Fine Chemical Synthesis

Nano Sized Schiff Base Complexes with Mn(II), Co(II), Cu(II), Ni(II) and Zn(II) Metals : Synthesis, Spectroscopic and Medicinal Studies

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