Reactivity of organic azo-compounds. VIII. Dissociation constants of hydroxyl group and electronic spectra of 3'- and 4'-substituted 2-hydroxy-5-chloroazobenzenes

1969 ◽  
Vol 34 (12) ◽  
pp. 3740-3745 ◽  
Author(s):  
J. Socha ◽  
M. Večeřa
Keyword(s):  
Electronic Spectra ◽  
Dissociation Constants ◽  
Azo Compounds ◽  
Hydroxyl Group

scholarly journals ACID-BASE PROPERTIES OF -UNSATURATED KETONES OBTAINED FROM REACTION OF 5-FORMYL-8-HYDROXYQUINOLINE WITH P-SUBSTITUTED ACETOPHENONES

2019 ◽  
Vol 16 (31) ◽  
pp. 755-764
Author(s):  
Roberto FERNANDEZ-MAESTRE ◽  
Alonso J MARRUGO-GONZÁLEZ
Keyword(s):  
Electron Donor ◽  
Opposite Effect ◽  
Dissociation Constants ◽  
Phenyl Group ◽  
Hydroxyl Group ◽  
Ultraviolet Spectroscopy ◽  
Acid Base ◽  
Unsaturated Ketones ◽  
Ph Values ◽  
Phenyl Fragment

Chalcones (α,β-unsaturated ketones) containing aromatic or heterocyclic radicals are highly reactive, allowing the synthesis of novel organic compounds. In this study, the dissociation constants (pKa) of seven chalcones derived from 8-hydroxyquinoline were determined and the influence on dissociation of substituents in the phenyl group (-CH3, -OCH3, -N(CH3)2, -Cl, -Br, and -NO2) was analysed. pKa values are important because they determine the pH at which ligands are fully deprotonated -when they show their maximum chelating properties- and determine the ligands interactions at different pH values. The chalcones’ pKa’s were calculated by visible ultraviolet spectroscopy in a water-ethanol (1:1) mixture using the Henderson-Hasselbach equation. It was shown that the 8-hydroxyquinolinic fragment has a large electron donor effect on the π system of the chalcones. The introduction of substituents (R) in the phenyl fragment of the chalcones slightly affected the dissociation of the hydroxyl group and the protonation of the nitrogen in the hydroxyquinoline fragment. The acceptor substituents (Cl, Br, NO2) increased the polarity of OH- and its acidity. Nitrogen protonation decreased electron donor properties of this fragment, and deprotonation of the hydroxyl caused the opposite effect. Substituents introduction in the phenyl fragment slightly affected hydroxyl group dissociation and nitrogen protonation.

scholarly journals Acid dissociation constants of glycopeptides

1977 ◽  
Vol 163 (1) ◽  
pp. 31-38 ◽  
Author(s):  
B M Austen ◽  
R D Marshall
Keyword(s):  
Amino Acid ◽  
Dissociation Constants ◽  
Acid Dissociation ◽  
Hydroxyl Group ◽  
Amino Acid Residues ◽  
Acid Base ◽  
Titration Curves ◽  
Pka Value ◽  
Hen’S Egg ◽  
Additional Amino Acid

Glycopeptides containing mainly four amino acid residues in the sequence Asn-Leu-Thr-Ser, with small amounts of additional amino acid residues, were isolated from enzymic hydrolysates of hen's-egg albumin. Heterogeneity of the carbohydrate moiety was confirmed. Acid-base titrations showed that the alpha-amino group has a pKa value of 6.43 at 25 degrees C. The standard free engery and entropy changes associated with the ionization at 25 degrees C were 37.2kJ-mol-1 and -0.014kJ-mol-1- K-1 respectively. The complications arising in the interpretation of titration curves of the glycopeptides, which are heterogeneous with respect to the peptide chain, were considered and discussed in the light of the earlier suggestion that the titration curve of the glycopeptide might be interpreted as being due in part to a structure in which the hydroxyl group of the threonine residue is hydrogen-bonded to the beta-aspartamido oxygen atom [Neuberger & Marshall (1968) in Symposium on Foods - Carbohydrates and their Roles (Schultz, H.W., Cain, R.F. & Wrolstad, R.W., eds.), pp. 115-132, Avi Publishing Co., Westport, CT]. It is concluded that either the glycopeptides do not contain a hydrogen bond of that type, or, if they do, that it cannot be recognized by acid-base-titration studies.

Pyridyl enamines and dienamines as models of mycobacterial pigments

1970 ◽  
Vol 23 (10) ◽  
pp. 2109 ◽  
Author(s):  
GM Renwick
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Electronic Spectra ◽  
Dissociation Constants ◽  
Related Compounds

N,N'-Tetramethylformamidinium perchlorate and its higher vinylogue react with 4-picolylsodium to yield 4-(2-dimethylaminovinyl)pyridine (1) and l-dimethyl-amino-4-(4-pyridyl)buta-1,3-diene (3), and with 2-picolylsodium to yield the 2-pyridine isomers (2) and (4). The N.M.R. spectra and dissociation constants of these products are reported. The electronic spectra of the bases, their mono- and di-cations, and of some related compounds are described, and comparisons are drawn with coloured alkaloids which are produced by Mycobacterium tuberculosis in the presence of isonicotinoylhydrazide.

scholarly journals Electrochemical and Spectrastudies of Some Sulfa Drug Azodyes and Their Metal Complexes in Aqueous Solution

2017 ◽  
Vol 14 (1) ◽  
pp. 6021-6032 ◽  
Author(s):  
E.M. Mabrouk ◽  
Kh.A.Al Omary ◽  
A.S.Al- Omary ◽  
E.H. El-Mossalamy
Keyword(s):  
Dissociation Constants ◽  
Mercury Electrode ◽  
Reduction Process ◽  
Electrode Reaction ◽  
Formation Constants ◽  
Azo Compounds ◽  
Alkaline Solutions ◽  
Sulfa Drugs ◽  
Sulfa Drug ◽  
Buffer Solutions

The electrochemical behavior of some azo compounds derived from sulfa drugs derivatives in B.R. buffer solutions of different pH containing 20 (v/v) ethanol was investigated at the mercury  electrode using different techniques (DC,DPP,CV and Coulometry) to investigate the effect of medium on the electro reduction process and suggestion the electrode reaction mechanism. The obtained results denoted that these compounds were reduced undergo a single irreversible 4- electron polarographic wave in acid and neutral solutions which represent the cleavage of the N=N center to the amine stage, whereas in alkaline solution, two wave are obtained the second is 2-electron irreversible wave corresponding to the reduction ofCHO group to CH2OH. The DPP and CV data showed a single peak in solutions of pH< 8, whereas three peaks are in alkaline solutions. The dissociation constants of the investigated compounds were determined by using spectrophotometric and potentiometric methods. Also the metal – ligand formation constants were determined potentiometrically and found in the order Cu˃ Co˃ Ni ˃Zn.

scholarly journals Polarographic Performance of Some Azo Derivatives Derived from 2-amino-4-hydroxy Pyridine and Its Inhibitory Effect on C-steel Corrosion in Hydrochloric acid

2019 ◽  
Vol 35 (1) ◽  
pp. 98-109 ◽  
Author(s):  
M. Abdallah ◽  
M. M. Alfakeer ◽  
N. F. Hasan ◽  
E. M. Mabrouk ◽  
Ahmed. M. Alharbi
Keyword(s):  
Dissociation Constants ◽  
Steel Corrosion ◽  
Transition Metal Ions ◽  
Electrode Reaction ◽  
Formation Constants ◽  
Inhibitory Effect ◽  
Azo Compounds ◽  
Alkaline Solutions ◽  
Acidic Solutions ◽  
Mechanistic Pathway

The polarographic performance of five azo compounds derived from 2-amino-4-hydroxypyridine was studied in BR buffer series of pH 2-12. The polarograms of all azo compounds in strong acidic solutions gave a single irreversible diffusion-controlled 4-electron wave representing the splitting of the N=N group to the amine stage but in alkaline solutions 2-electron irreversible wave is obtained corresponding to the reduction of the azo center to the hydrazo stage. For NO2 substituted derivative, approximately two equal waves were observed in the acidic solutions, , but in the alkali, the rise of the second wave is approximately twice that of the first wave. The effect of substituents on electrode reaction was investigated and the kinetic parameters were calculated. The mechanistic pathway was proposed and interpreted. The dissociation constants of the tested azo compounds were examined by potentiometric methods and the M-L formation constants of their complexes with some transition metal ions were computed. Application of the investigated azo compounds as inhibitors of dissolution of carbon steel in in 1MHCl solutions was inspected using potentiodynamic polarization technique. The results indicated that these compounds inhibit C-steel corrosion in HCl solutions and the inhibition efficiency reached 81% in presence of 1x10-3 M of the inhibitors. The efficiency of the inhibitors follows the following sequence: III> II > I > IV > V This arrangement is consistent with the sequence of the E1/2 and the pka values of these azo compounds.

Spectroscopic Determination of Dissociation Constants of Some 4-nitrobenzaldehyde-4-substitutedphenyl-1-carbonylhydrazones in Sodium Hydroxide Media

2020 ◽  
Vol 16 ◽  
Author(s):  
Mirjana S. Jankulovska ◽  
Ilinka Spirevska ◽  
Vesna Dimova ◽  
Milena Jankulovska
Keyword(s):  
Sodium Hydroxide ◽  
Dissociation Constants ◽  
Wide Spectrum ◽  
Amide Group ◽  
Hydroxyl Group ◽  
Semiempirical Methods ◽  
Dissociation Process ◽  
Vis Spectroscopy ◽  
The Media

Purpose: Hydrazones are a class of azomethines with a wide spectrum of pharmacological properties which are influenced by pH of the media. The purpose of this study was investigation of acid-base properties of five 4-nitrobenzaldehyde-4-substitutedphenyl1-carbonylhydrazones in sodium hydroxide media (14>pH>7). Method: The dissociation process was followed by UV-Vis spectroscopy, in the ethanol-water (V/V, 1:1) solutions, at room temperature. Semiempirical methods AM1 and PM3 were applied for determination of the deprotonation enthalpies. Results: The changes in the UV-Vis spectra, as well as the deprotonation enthalpies suggested that dissociation process for four investigated hydrazones with amide group took place in one step. The exception with two dissociation steps was hydrazone with amide and hydroxyl group. The pH region of dissociation was from pH 10.8 to pH 11.6 for the first step and between pH 11.7 and pH 12.1 for the second step of dissociation. The influence of the ethanol on the UV-Vis spectra was eliminated by the method of Characteristic Vector Analyses (CVA). The stoichiometric dissociation constants were determined numerically (pKHA = n·pH + logI) and graphically (intercept of the dependence of logI on pH) from the absorbance data using experimental and reconstructed UV-Vis spectra, at three different ionic strengths. Thermodynamic dissociation constants were estimated graphically as an intercept of dependence of dissociation constant on square root of the ionic strength. Conclusion: The obtained results demonstrated that the influence of the substituents on pKHA values was not significant, except for hydrazone with amide and hydroxyl group. Namely, the dissociation of amide group of this hydrazone was retarded due to the influence of phenolic group.

Medium Effect on the Acid Dissociation Constants of Some Heterocyclic Azo Compounds

1999 ◽  
Vol 44 (3) ◽  
pp. 451-455 ◽  
Author(s):  
Said A. Ibrahim ◽  
Nasr M. Rageh ◽  
Ahmed A. Mohamad ◽  
Youssif H. Ebead
Keyword(s):  
Dissociation Constants ◽  
Acid Dissociation ◽  
Medium Effect ◽  
Azo Compounds ◽  
Acid Dissociation Constants

Effect of H-bond formation on the electronic spectra of some azo compounds derived from 3-amino-1,2,4-triazole

1998 ◽  
Vol 129 (1-2) ◽  
pp. 133-138 ◽  
Author(s):  
Mahmoud A. El-Taher ◽  
Mohamed T. El-Haty ◽  
Atiat A. Montaser
Keyword(s):  
Electronic Spectra ◽  
Bond Formation ◽  
Azo Compounds
Sign in / Sign up

Export Citation Format

Share Document