Analysis of acid-base properties of some p-substituted aromatic hydrazones in aqueous perchloric acid by spectrophotometric and semiempirical methods

Jankulovska, Mirjana; Spirevska, Ilinka

doi:10.20450/mjcce.2014.370

Cited by 5 publications

(3 citation statements)

References 26 publications

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“…At this pH only the protonated form of the compounds is present in the solution. The substituents present in the molecule of the investigated hydrazones have not significant influence on the protonation process, presented with Scheme 1 [36]: Scheme 1. Protonation process of investigated hydrazones.…”

Section: From Thementioning

confidence: 98%

UV Spectrophotometric Determination of Thermodynamic Dissociation Constants of Some Aromatic Hydrazones in Acid Media

et al. 2019

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The spectral behavior of some p-nitro-p-substituted benzoylhydrazones in the perchloric acid media was followed, applying the UV spectroscopy. The position of the absorption maximum in the spectra was defined in acidic media and the electronic transitions were discussed, as well (7<pH<1). The equilibrium between neutral and protonated form was investigated in the ethanol-water (V/V, 1:1) solutions. The observed changes in the UV spectra suggested that protonation process took place in one step. The pH region of protonation ranges between 1.4 and 2.9. Using the changes in the UV spectra which appear as a result of the protonation reaction the stoichiometric dissociation constants were determined numerically (pKBH+ = n·pH + logI) and graphically (intercept of the dependence of logI on pH). Thermodynamic dissociation constants were estimated as an intercept of dependence of pKBH+ on square root of the ionic strength. In order to achieve that, measurements were performed at different ionic strengths: 0.1, 0.25 and 0.5 mol/dm3, adjusted with sodium perchlorate. The obtained thermodynamic pKBH+ values ranged between 2.07 and 2.58. In order to predict proton transfer at a given pH, semiempirical methods AM1 and PM3 were applied. The influence of the substituents present in the p-position of the benzene ring on pKBH+ values of investigated hydrazones was discussed, too. Total energy, binding energy, enthalpy of formation, Gibbs energies of formation, atomic charge and proton affinity values were used to predict protonation site in hydrazone molecule. Furthermore, the stability and the proton affinity of the isomers (E and Z) in which hydrazones exist and their protonated forms were defined.

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Section: From Thementioning

confidence: 98%

UV Spectrophotometric Determination of Thermodynamic Dissociation Constants of Some Aromatic Hydrazones in Acid Media

et al. 2019

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“…1 and 2). The appearance of the absorption band at around 195-200 nm is due to a  * electronic transition in benzene ring, while the absorption band at around 330 nm is as a result of n * electron transition in the azomethine group [17]. For further investigation we followed the changes in the absorption band that appeared at wavelength around 330 nm.…”

Section: Uv Spectramentioning

confidence: 99%

Investigation Od Acid-Base Properties of Aromatic Hydrazones in Basic Media at Constant Ionic Strength

Jankulovska¹,

Dimova²,

Spirevska³

2017

RAD Conference Proceedings

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Abstract. UV spectroscopic methods were used in order to determine dissociation constants of some aromatic hydrazones. The acid-base properties of investigated hydrazones were followed in sodium hydroxide media at constant ionic strength of 0.5 mol/dm 3 adjusted with sodium perchlorate. Absorption band with the maximum of 330 nm was noticed in neutral media. A batochromic shift of this band was observed in basic media, probably due to the dissociation process. The dissociation process took place in one step for four investigated hydrazones and in two steps for the hydrazone with a phenol group in its molecule. The absorbance data from the UV spectra were used for the calculation of dissociation constants. The obtained pKHA values were between 2.11 and 2.62 which suggested that the influence of the substituents is not significant. At the same time, pKHA values were determined graphically from the intercept of the dependence of logI on pH. There are no important differences between calculated and graphically determined dissociation constant values.

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“…Experimental gas‐phase proton affinities of hydrazones have not been reported. Available quantum computations have been limited to semi‐empirical studies and have been mainly focused on determination of protonation sites (Zverev et al, ; Jankulovska & Spirevska, ). In these studies, phenylhydrazones were found to be preferentially protonated at the imino‐nitrogen atom, but for alkylhydrazones, Zverev and coworkers () predicted protonation of the amino nitrogen atom to be more favorable.…”

Section: Iminesmentioning

confidence: 99%

Gas phase basicities of polyfunctional molecules. Part 5: Non‐aromatic sp² nitrogen containing compounds

Bouchoux

Eckert‐Maksić

2016

Mass Spectrometry Reviews

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This paper constitutes the fifth part of a general review of the gas-phase protonation thermochemistry of polyfunctional molecules (Part 1: Theory and methods, Mass Spectrom Rev 2007, 26:775-835, Part 2: Saturated basic sites, Mass Spectrom Rev 2012, 31:353-390, Part 3: Amino acids, Mass Spectrom Rev 2012, 31:391-435, Part 4: Carbonyl as basic site, Mass Spectrom Rev 2015, 34:493-534). This part is devoted to non-aromatic molecules characterized by a lone pair located on a sp nitrogen atom, it embraces functional groups such as imines, amidines, guanidines, diazenes, hydrazines, oximes, and phosphazenes. Specific examples are examined under five major chapters. In the first one, aliphatic and unsaturated (conjugated and cyclic) imines, hydrazones, and oximes are considered. A second chapter describes the protonation energetic of aliphatic, conjugated, or cyclic amidines. Guanidines, polyguanides, and biomolecules containing guanidine were examined in the third chapter. A fourth chapter describes the particular case of the phosphazene molecules. Finally, diazenes and azides were considered in the last chapter. Experimental data were re-evaluated according to the presently adopted basicity scale, i.e., PA(NH ) = 853.6 kJ/mol, GB (NH ) = 819 kJ/mol. Structural and energetic information given by G4MP2 quantum chemistry computations on typical systems are presented. © 2016 Wiley Periodicals, Inc. Mass Spec Rev 37:139-170, 2018.

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Analysis of acid-base properties of some p-substituted aromatic hydrazones in aqueous perchloric acid by spectrophotometric and semiempirical methods

Cited by 5 publications

References 26 publications

UV Spectrophotometric Determination of Thermodynamic Dissociation Constants of Some Aromatic Hydrazones in Acid Media

UV Spectrophotometric Determination of Thermodynamic Dissociation Constants of Some Aromatic Hydrazones in Acid Media

Investigation Od Acid-Base Properties of Aromatic Hydrazones in Basic Media at Constant Ionic Strength

Gas phase basicities of polyfunctional molecules. Part 5: Non‐aromatic sp² nitrogen containing compounds

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Analysis of acid-base properties of some p-substituted aromatic hydrazones in aqueous perchloric acid by spectrophotometric and semiempirical methods

Cited by 5 publications

References 26 publications

UV Spectrophotometric Determination of Thermodynamic Dissociation Constants of Some Aromatic Hydrazones in Acid Media

UV Spectrophotometric Determination of Thermodynamic Dissociation Constants of Some Aromatic Hydrazones in Acid Media

Investigation Od Acid-Base Properties of Aromatic Hydrazones in Basic Media at Constant Ionic Strength

Gas phase basicities of polyfunctional molecules. Part 5: Non‐aromatic sp2 nitrogen containing compounds

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Gas phase basicities of polyfunctional molecules. Part 5: Non‐aromatic sp² nitrogen containing compounds