Acid-catalyzed hydrolysis of some diazoacetophenones in aqueous dioxan

Rate constants and activation parameters for the acid-catalyzed hydrolysis of eight ring-substituted diazoacetophenones have been measured in three dioxan–water mixtures. An isokinetic relationship applies to the results obtained using a 50% dioxan–water mixture as solvent. Solvent and substituent effects are discussed together with some mechanistic aspects. Substituent constants are reported for the ? COCHN₂ group.     

Protonation of some cyclic triphosphenium ions

Several cyclic triphosphenium ions of various ring sizes have been successfully protonated to form the corresponding triphosphane di‐ium dications, either by a ^tBuCl/AlCl₃ mixture and/or by triflic acid. The latter reagent appears to be harsher, however, sometimes leading to decomposition. The new dications have been identified in solution by ³¹P NMR spectroscopy; recording the spectra proton coupled as well as decoupled has enabled ¹J_PH as well as ¹J_PP to be evaluated in most cases. The protonated derivatives of three compounds could not be observed, with only decomposition products being detected. In the case of the triphosphenium ion derived from bis‐1,4‐diphenylphosphinobutane (dppb), clear spectroscopic evidence for an intermediate in the decomposition process of the di‐ium dication has been obtained, enabling a plausible mechanism to be proposed. In addition, a novel triphosphorus‐containing trication with a norbornane‐like structure has been detected, and characterized by single crystal X‐ray diffraction, as a minor product from the protonation of the triphosphenium ion derived from cis‐bis‐1,2‐diphenylphosphinoethene (dppE). © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:447–452, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20124     

Protonation of some cyclopropylarenes in the gas phase

The capability of the cyclopropyl group to conjugate with Unsaturated systems or to delocalize an adjacent positive charge is compared with that of a double bond, and is tested by the determination of the gas-phase basicity (GB) of various methyl-substituted cyclopropylbenzenes, α-methyl styrenes, and biphenyls by Fourier-transform ion cyclotron resonance. The site of the gas-phase protonation in the cyclopropylbenzene is established at the three-membered ring, based on analogy with the trends of GBs in the styrene system upon methyl substitution at the aromatic meta and para positions. The diverse nature of the conjugative interaction of a cyclopropyl group and of a double bond toward an aromatic ring is manifested, instead, in the different behaviour toward a steric perturbation. The cyclopropyl group adopts the bisected conformation in cyclopropylbenzene, because it tolerates the steric perturbation of a methyl group, intentionally placed in the ortho position, more easily than the double bond, which adopts a coplanar conformation in the isomeric α-methyl styrene.     

Protonation constant of salicylidene (N-benzoyl)glycyl hydrazone and its coordination behaviour towards some bivalent metal ions

Protonation constant of an unsymmetrical Schiff base, salicylidene(N-benzoyl)glycyl hydrazone (SalBzGH), and formation constants of its complexes have been determined potentiometrically at different temperatures in aqueous dioxane medium. Complexes of SalBzGH with VO(IV), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) have been prepared. Elemental analyses, pH-metric, molar conductance, magnetic susceptibility, electronic, IR, ESR, XRD (powder) and NMR studies have been carried out to study the coordination behaviour of SalBzGH toward these metal ions. pH-metric and 1H NMR studies show the presence of two dissociable protons in the ligand. IR and NMR spectra suggest the tridentate nature of the ligand, coordinating as a uninegative species in the Mn(II) complex and as a dinegative species in all the other complexes. Presence of two different conformers of the ligand at room temperature and stabilization of a single conformer upon complex formation have been established from¹H NMR spectra of the metal-free ligand, Zn(II) and Hg(II) complexes recorded at 296 K. Electronic and ESR spectra indicate highly distorted tetragonal geometry for VO(IV) and Cu(II) complexes. XRD powder patterns of the Zn(II) complexes are indexed for an orthorhombic crystal system.     

Protonation and solvent extraction of N-p-tolylbenzohydroxamic acid in hydrochloric acid medium

the protonation of N-p-tolylbenzohydroxamic acid (p-TBHA) in aqueous hydrochloric acid has been investigated by determination of its distribution between cyclohexane and hydrochloric acid. The pK(a) value found was - 2.30 +/- 0.02 at 30 degrees . The solubility of p-TBHA as a function of hydrochloric acid concentration has also been determined. At lower acid concentrations the solubility decreases owing to a salting-out effect, whereas at higher concentrations it increases because of formation of the more hydrophilic protonated species and a salting-in effect. Intramolecular hydrogen-bonding observed in p-TBHA provides evidence for protonation of the nitrogen atom.     

Protonation of some cyclic β-Aminovinylthiones and β-aminovinylketones

Conclusions The NMR method was used to study the protonation of 3-N,N-dimethylammo-5,5-dimethyl-3-cyclohexene-1-thione, 3-N,N-dimethylamino-2-phenylidene-1-thione, and their oxygen analogs. The protonation center for these compounds is different, and is, respectively, N and O, and S and 2-C.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2091–2094, September, 1976.     

Determination of sulpha-drugs with ion-selective membrane electrodes--II

Two liquid-membrane electrodes, one sensitive to Cu(2+) and the other to Ag(+), were used for the determination of various sulpha-drugs with pK(a) > or = 6 (as the sodium salts) by potentiometric titration with CuSO(4) and AgNO(3). The construction and basic characteristics of these two electrodes are discussed.     

Protonation of anion radicals and dianions of some dinitro aromatics

A simple electrochemical method developed to study reactions of reactive intermediates (neutralfree readical, cation-, anion- radicals etc.) was employed to study the protonation reaction of anion radicals and dianions of some dinitroaromatics. Rate constants thus obtained and the mechanism of protonation reaction invesitgated, are reported. It is suggested that the reactions do not involve a direct electron transfer. The possible role of various ion-pairs was investigated. Positions of nucleophilic attack were investigated through M.O. calculations.     

Protonation constants of some substituted 2-hydroxy-1-naphthalideneanilines in dioxan-water mixtures

The protonation constants of ten Schiff's bases synthesized by the condensation of 2-hydroxy-1-naphthaldehyde with aniline and o-, m-, and p-substituted methylanilines, ethylanilines and methoxyanilines in various dioxan-water mixtures have been determined potentiometrically using an electrode system calibrated in concentration units of the hydrogen ion. The influence of substituents in the molecular structure on the protonation constants is discussed. The log K₂ values relating to the protonation of imine nitrogen atoms are in accordance with the Hammett relationship for all solvent compositions. A reverse relationship is observed between log K₂ for all Schiff's bases and the mole fraction of dioxan. However, the log K₁ values corresponding to the protonation of naphtholate O-ions have been found to increase with the increase in concentration of dioxan. Both electrostatic and non-electrostatic contributions influencing these constants are briefly discussed.     

Determination of sulpha-drugs with ion-selective membrane electrodes

A liquid-membrane mercury(II)-sensitive electrode is used for determination of various sulpha drugs by addition of excess of mercuric nitrate and potentiometric back-titration of the surplus mercury(II) with EDTA. The performance of the electrode is compared with that of an Ag(2)S crystal-membrane electrode. Attempts to prepare a sulphamethoxazole-sensitive electrode failed.     

Determination of sulpha-drugs with a piezoelectric sensor

A piezoelectric sensor is used for the determination of sulpha-drugs, as pure substances and in their dosage forms, by an indirect micro method based on reaction of the sulpha-drug with bromine and reduction of the resultant N-bromoderivative with iodide to form iodine, which after extraction is monitored with a piezoelectric quartz sensor. The response of the sensor is linear from 2 x 10(-5) to 4 x 10(-4)M sulpha-drug.     

Ultraviolet absorption of flavonoids VI. Protonation constants of some dihydroxyflavones

Summary The protonation (basicity) constants of six disubstituted flavones have been determined by the spectrophotometric method.Irkutsk Institute of Organic Chemistry, Siberian Branch of the Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 587–590, September–October, 1975.     

Protonation studies on the oximes of some 7-acetyl-1,2-benzisothiazoles

Three 7-acetyl-1,2-benzisothiazoles have been made by cyclisation of the monooximes of 2-methylthio-1,3-diacetylbenzenes. The oximes of these ketones dissolved in acidic media give only protonated forms, and no indication of the formation of stable bridged sulfonium ions.     

Protonation and silver(I) complex-formation equilibria of some amino-alcohols

Formation constants of the silver(I) complexes with some amino-alcohols have been determined at 25 degrees C in 0.5 M KNO(3) by means of two independent potentiometric measurements employing glass and silver electrode. The ligands considered are: sec-butylamine, 2-amino-1-propanol, 2-amino-1-methoxy-propane, 2-amino-2-methyl-1-propanol, 2-amino-1-butanol, 2-amino-1-pentanol, 2-amino-1-hexanol, 2-amino-1,3-propanediol, 2-amino-1,3-hexandiol, 2-amino-2-methyl-1,3-propanediol and Tris(hydroxymethyl)-aminomethane. Protonation constants of the selected ligands have also been determined. Calculations were made using HYPERQUAD computer program. The influence exerted by the introduction of hydroxy groups and by the presence of alkyl residuals in the ligand structure on the formation equilibria, is discussed.     

Protonation of water clusters induced by hydroperoxyl radical surface adsorption

We have investigated the HO(2) adsorption and acid dissociation process on the surface of (H(2)O)(20) and (H(2)O)(21) clusters by using quantum-chemistry calculations. Our results show that the radical forms a stable hydrogen-bond complex on the cluster. The HO(2) acid dissociation is more favorable in the case of the (H(2)O)(21) cluster, for which the inner water molecule plays a crucial role. In fact, acid dissociation of HO(2) is found to occur in two steps. The first step involves H(2) O autoionization in the cluster, and the second one involves the proton transfer from the HO(2) radical to the hydroxide anion. The presence of the HO(2) radicals on the surface of the cluster facilitates water autoionization in the cluster.     

Ultraviolet absorption of flavonoids IV. Protonation constants of some monohydroxy flavones

Summary 1. The protonation constants of flavone, 3-hydroxyflavone and its methyl ether, and 7-, 5-, and 4-hydroxyflavones have been determined by a spectrophotometric method.2. It has been shown that the basicities of the monohydroxyflavones change fundamentally according to the position of electron-donating substituents in the molecule.Irkutsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 25–28, January–February, 1973.     

Synthesis of some new bis-Schiff bases of isatin and 5-fluoroisatin in a water suspension medium

Condensation of aromatic primary bis-amines with isatin (1H-indole-2,3-dione) and 5-flouroisatin occurred cleanly and efficiently in a water suspension medium without using any organic solvent or acid catalyst. The corresponding bis-Schiff bases were obtained in good yields and were easily isolated by filtration. Their structures were confirmed by (1)H-NMR, (13)C-NMR, IR and mass spectra.     

Acid-base equilibria in binary water/organic solvent systems Dissociation of citric acid in water/dioxan and water/methanol solvent systems at 25 degrees

The thermodynamic constants of citric acid were determined at 25 degrees in water/dioxan and water/methanol mixtures with 10, 20, 30, 40 and 50% v/v organic co-solvent content. Simple relations allowing the calculation of palpha*(H) of citrate buffer solutions are proposed (alpha*(H) being the hydrogen-ion activity referred to the standard state in the corresponding medium). The palpha*(H) values of some citrate buffer solutions, suitable for standardization, are reported. The pK values obtained are discussed in relation to the nature and composition of the solvent, as well as the structure of the acid molecule.