Crown-Containing N-(Thio)Phosphoryl-(Thio)Ureas,their Ligand Properties and Analytical Application

Abstract

Crown-containing N-(thio)phosphoryl(thio)ureas are related to a class of NH-acids due to the presence of two acceptor-groups: (thio)phosphorylic and (thio)acylic. In agreement with structure of lariat ether, it was observed a stage corresponding to the step ejection of two H* ion on the potentiometric titration curve of ligand by alkaline. Calculated step ionization constants demonstrate that these compounds are weak acids with relative values of pK₁ and pK₂.     

Dissociation constants of n,n'-bis(2-carboxyethyl)dithiooxamide

The dissociation constants of N,N'-bis(2-carboxyethyl)dithiooxamide have been determined by potentiometric and spectrophotometric methods. They were calculated by a modified Ricci formula and by a weighted least-squares treatment. The thermodynamic constant pK₃^T is 12.32. At ionic strength 1.00, pK₁=3.76, pK₂=4.74, pK₃=11.41 and pK₄=14.19.     

Multimode Retention Behavior of Azaarenes in Size Exclusion Chromatography with Poly(Divinylbenzene)

Abstract

The size exclusion retention behavior of azaarenes on poly(divinylbenzene) is described. With dichloromethane as the mobile phase a strong nonsize effect was evident and retention was found to be governed by the pK_a of the eluate. By changing the mobile phase to N-methylpyrrolidinone, retention became independent of pK_a and components eluted in order of decreasing molecular weight. Some degree of nonsize behavior was still evident and separation proceeded through a multimode mechanism. LogMW for both the azaarenes and PAH. However, in the case of the azaarenes, a less than ideal correlation coefficient (-.705) suggests that retention is not purely size-dependent.     

Synthesis and Structural Characterisation of Two Copper(II) Complexes of <Emphasis Type="Italic">N</Emphasis>-(1-acetyl-2-propylidene) (2-pyridylmethyl) amine

Two new complexes [CuBr(C₁₁H₁₃N₂O)] (1) and [Cu(NCO)(C₁₁H₁₃N₂O)] (2) containing the tridentate Schiff base ligand, N-(1-acetyl-2-propylidene)(2-pyridylmethyl) amine which is the 1:1 condensation product of acetylacetone and 2-aminomethylpyridine, have been synthesised and characterised by elemental analysis, IR and electronic spectra, electrochemical study and single crystal X-ray diffraction study. Crystal structures reveal that the copper atom in both the complexes are in square geometry formed by the N₂O donor set of the Schiff base and a bromine atom in 1 and one cyanate ligand in 2. Both bromide and isocyanate ligands act in a terminal monodentate fashion.     

Unexplored metallic cation effect in the acidity constants of p-t-butylthiacalix[4]arene,p-t-butylcalix[4]arene and p-t-butylcalix[6]arene in aqueous-organic media

The influence of the metallic cation of the base (Li⁺, Na⁺ or K⁺) was determined on the acid–base constants of p-t-butylthiacalix[4]arene (TC4), p-t-butylcalix[4]arene (CA4) and p-t-butylcalix[6]arene (CA6) in ethanol/water in an large interval of pH values by potentiometry and spectrophotometry. The pK_a values determined by both methods correlate very well and these are characteristic for each macrocycle with influence of the cation of the base without a straight evidence of an effect by the size of the metallic cation. In the case of TC4, pK_a1 and pK_a2 were lower to Li⁺ and Na⁺ than with K⁺. For CA4, an effect of K⁺ on the pK_a2 with respect to Li⁺ was observed. A very different behaviour was observed for CA6 with Li⁺ and K⁺ showing a lower pK_a2 and a higher pK_a3 than with Na⁺. These effects were interpreted on the basis of the interaction/complexation of each cation with each macrocycle.     

The reversible cation-anion isomerisation of 2-imino-2H-pyrido [1,2-b][1,2,4]thia(oxa)diazole hydrobromide

The title compounds exist in pH-dependent equilibrium between cation and ring-opened anion; since pK₂ <pK₁, the hypothetical neutral species is always metastable.     

Acid-Base and Photochemical Reactions of Selenious Acid

Abstract

Spectrophotometric data used in connection with H_A acidity function yield pK₁=?3.3(K₁= [H₂SeO₃][H⁺]/[H₃SeO₃ ⁺]);potentiometric and spectral measurements give for pK₂ and pK₃ data in agreement with the literature. At pH > 10 selenite undergoes a fast photochemical reaction, preceded by a rapidly established acid-base equilibrium. Products of this reaction undergo a slow reaction which is second order in selenite.     

Reaktivität der Pyrrolpigmente, 2. Mitt.: Deprotonierung von 3-Pyrrolin-2-onen

Deprotonation of 3,4-dimethyl-3-pyrrolin-2-on (1) int-butyl alcohol/potassiumt-butoxide solutions takes place on the N atom, as shown by¹H/²H exchange andpK _a determinations of1 (pK=17.1), 1,3,4-trimethyl-3-pyrrolin-2-one (pK _a =17.6), and 3,4-dimethyl-5-methoxy-2_H-pyrrole (pK _a =16.7). The SCF-MO approximation MINDO/3 indicates, however, that in the gas phase deprotonation of1 should occur at the C atom.

1.Mitt.:Ribó, J. M., Trull, F., Mh. Chem.110, 201 (1979).     

Preparation,spectral and structural characterization of (2-benzoylpyridine N(4)-methyl-N(4)-phenylthiosemicarbazonato) chloropalladium(II)

The synthesis, as well as spectral and structural characterization, of (2-benzoylpyridine-N(4)-methyl-N(4)-phenylthiosemicarbazonato)chloropalladium(II), [Pd(Bz4MePh)Cl], is described. The unit cell contains two crystallographically independent molecules [Pd(1)(Bz4MePh)Cl], (1), and [Pd(2)(Bz4MePh)Cl], (2), stabilized by intra- and intermolecular hydrogen bonding. The distance between the Pd(1) and Pd(2) centres is 3.5038(11) Å. The spectroscopic techniques used in this study are the following: u.v.-visible, i.r. and ¹H n.m.r. The protonation constants, determined spectrophotometrically, of the uncoordinated HBz4MePh are pK_a1 = 10.82 ± 0.03 and pK_a2 = 4.09 ± 0.02.     

The influence of ionic surfactants on the acid-base properties and tautomeric equilibrium of 2-dimethylaminomethylphenol

Shifts in the acid-base and tautomeric equilibria have been observed in aqueous solutions of 2-dimethylaminomethylphenol (DAMP) containing surfactants. Cationic micelles of cetyltrimethylammonium bromide increase the dissociation constants of DAMP (pK₁ 0.3, pK₂ 0.5), and anionic micelles of sodium dodecyl sulfate reduce them (pK₁ 1.5, pK₂ 0.3). The constant of tautomeric equilibrium decreases when ionic surfactants are added. This is connected with the better solubilization of the neutral form by micelles.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1215–1218, July, 1994.     

Copper(I) bromide complexes of two 15-memberd O2S2-macrocycles with different sulfur-to-sulfur separations: dimer and one-dimensional coordination polymer

Abstract

A comparative study on the exo-coordination-based networking of 15-membered O₂S₂-macrocycle isomers (L¹ and L²) induced by interdonor distances is reported. In copper(I) bromide complexation, the isomer L¹ incorporating a shorter sulfur-to-sulfur separation yielded a discrete dimer complex [(μ-Cu₂Br₂)(L¹)₂] (1) in which two macrocycles are bridged by a Cu₂Br₂ square cluster. While, the reaction of copper(I) bromide with the isomer L² incorporating a longer sulfur-to-sulfur separation afforded a double-stranded one-dimensional (1D) coordination polymer {[(μ₄-Cu₂Br₂)(L²)₂]·CH₂Cl₂}_n (2) as a kinetic product which converted to [(μ₄-Cu₂Br₂)(L²)₂]_n (3) with different 1D connectivity pattern as a thermodynamic product. The results indicate as examples of programmed self-assembly that the proposed interdonor distances and the ligand isomerism play decisive roles cooperatively in the topologies of the supramolecular products via different coordination modes.     

Application of the pKa rule to synthesize salts of bezafibrate

ABSTRACT

Co-crystallization frequently employs forces such as hydrogen bonds, halogen bonds, and π-π stacking to assemble molecules in a multi-component crystal. In an effort to increase the strength of the intermolecular interaction between the anti-cholesterol drug bezafibrate (BEZA), a wastewater contaminant, and hydrogen-bond-acceptor molecules, we modified the pK_a values of the acceptors. Here, we describe the first series of salts incorporating BEZA and achieve a variety of supramolecular architectures including discrete assemblies, 1D chains, tapes, and 2D sheets. We discuss exceptions to the pK_a rule, and demonstrate that the presence of hydrogen-bond-donor atoms on the acceptor molecule supports salt formation.     

Kinetics and mechanism of the base hydrolysis of thecis-chlorobis(ethylenediamme)(benzimidazole)cobalt(III) cation

Summary The hydrolysis ofcis-[CoCl(en)₂(bzmH)]²⁺ (en=ethylenediamine, bzmH=benzimidazole) has been studied over the pH range 8.31–11.58 at I=0.1 mol dm^–3 and 25°. Potentiometric titration of aqueous solutions of the [Co(en)₂(bzmH)OH₂]³⁺ complex obtained by silver(I) catalysed aquation of the chloro-complex give pK₁=5.81 and pK₂ = 8.84 for Equilibria (1) and (2) at 25° and I=0.1 mol dm^–3. Spectrophotometric titration of the hydroxy complex also gives a value of pK₂=8.88 for the ionisation of the coordinated benzimidazole. The kinetic data can be interpreted in terms of base hydrolysis ofcis-[CoCl(en)₂(bzmH)]²⁺ (k_OH=220 dm³ mol^–1s^–1) andcis-[CoCl(en)₂(bzm)]⁺ (k_OH=14.9 dm³ mol^–1s^–1). Comparisons with the corresponding imidazole and pyridine complexes are made.     

TRANSITION METAL COMPLEXES WITH HYDRAZIDES AND HYDRAZONES. PART 81. X-RAY CRYSTAL STRUCTURE OF A CATENA-POLYBROMO (ACETONE-1-NAPHTHOYLHYDRAZONE) COPPER(II)-COPPER(I) COMPLEX

Abstract

The title compound [Cu₃Br₄C₂₈H₂₈N₄O₂] is a type of polymeric three-centre octahedral-trigonal planar coordination complex. The copper(II) atom located at a centre of symmetry is six-coordinate with two bidentate (N3, O1) ligands of acetone-1-naphthoylhydrazone forming the equatorial plane and two bromine ions in axial positions (Cul-Brl = 2.946(1)Å). The ligands are in trans positions. The Cu(I) atoms are in trigonal planar coordination by two bridging Br^? ions (Cu2-Br2 = 2.412(1)Å, Cu2-Br2? = 2.407(2)Å) which connect two Cu(I) atoms and a third bromine ion shared with the octahedral Cu(II) ion (Cu2-Br1 = 2.304(1)Å). The arrangement forms an infinite chain along the b axis.     

A Novel QSAR Approach for Estimating Toxicity of Phenols

Abstract

Toxicity values (log IGC^?1 ₅₀) for 60 phenols tested in the 2-d static population growth inhibition assay with the ciliate Tetrahymena pyriformis were tabulated. Each chemical was selected so the series formed uniform coverage of the hydrophobicity/ionization surface. A high quality hydrophobicity-dependent (log K _ow) structure-toxicity relationship (log IGC^?1 ₅₀ = 0.741 (log K_ow) ?1.433; n = 17; r² = 0.970; s = 0.134; F = 486.55; Pr > F = 0.0001) was developed for phenols with pK_a values > 9.8. Similarly, separate hydrophobicity-dependent relationships were developed for phenols with pK_a values of 4.0, 5.1, 6.3, 7.5, and 8.7. Comparisons of intercepts and slopes, respectively, revealed phenols with pK_a values of 6.3 to be the most toxic and the least influenced by hydrophobicity. These relationships were reversed for the more acidic and basic phenols. Plots of toxicity versus pK_a for nitro-substituted phenols and phenols with log K_ow values of either 1.75 or 2.50 further demonstrated bilinearity between toxicity and ionization. In an effort to more accurately model the relationship between toxicity and ionization, the absolute value function |6.3-pK_a| was used to model ionization affects for derivatives with pK_a values between 0 and 9.8. For derivatives with pK_a value > 9.8, a value of 3.50 was used to quantitate ionization effects. The use of log K_ow in conjunction with this modified pK_a (ΔpK_a) resulted in the structure-toxicity relationship (log IGC^?1 ₅₀ = 0.567 (log K_ow)-0.226 (ΔpK_a-0.079; n = 54; r² = 0.926; s = 0.215; F = 321.06; Pr > F = 0.0001). Derivatives with a nitro group in the 4-position typically did not model well with the above equation.     

Determination of acidic constants of some phenyl-hydroxyiminoethyl quinolinium compounds

Mixed acidic constants (pK _a ) of quinolinium oximes [1-(2-phenyl-2-hydroxyiminoethyl)-1-quinolinium chloride (F-1), 1-(2-phenyl-2-hydroxyiminoethyl)-1-isoquinolinium chloride (F-2), 1-(2-phenyl-2-hydroxyiminoethyl)-1-(4-methyl)-quinolinium chloride (F-3), and 1-(2-phenyl-2-hydroxyiminoethyl)-1-(6-methyl)-quinolinium chloride (F-4)] have been determined via their UV absorption spectra recorded in the series ofBritton-Robinson's buffer solutions in thepH region 8.74–11.28 (t=25±0.5°C, =0.2). The obtainedpK _a values are in good agreement with those achieved by applying graphical methods. The followingpK _a values have been obtained: 9.93 forF-1, 9.90 forF-2, and 10.02 forF-3 andF-4.On the basis of potentiometric titrations thermodynamic acidic constants (pK _a ) of compoundsF-1,F-2,F-3, andF-4 have been determined and they were found to be 9.82, 9.71, 9.91, and 9.86, respectively. The values obtained by transferringpK _a intopK _a are in good agreement with the values obtained spectrophotometrically.

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Bestimmung der Aciditätskonstanten einiger Phenyl-hydroxyiminoethylchinolin-Verbindungen

Zusammenfassung Die Mischaciditätskonstanten (pK _a ) der Chinolin-Oxime 1-(2-Phenyl-2-hydroxyiminoethyl)-1-chinolinium chlorid (F-1), 1-(2-Phenyl-2-hydroxyiminoethyl)-1-isochinolium chlorid (F-2), 1-(2-Phenyl-2-hydroxyiminoethyl)-1-(4-methyl)-chinolinium chlorid (F-3) und 1-(2-Phenyl-2-hydroxyiminoethyl)-1-(6-methyl)-chinolinium chlorid (F-4) wurden durch ihre UV-Absorptionspektren in einer Reihe vonBritton-Robinson-Pufferlösungen impH-Intervall 8.74–11.28 (t=25±0.5°C; =0.2) bestimmt. Die berechnetenpK _a -Werte stimmen mit den über graphische Methoden erhaltenen Ergebnissen überein. DerpK _a -Wert beträgt 9.93 für die VerbindungF-1 und 9.90 fürF-2, sowie 10.02 fürF-3 andF-4.Auf Grund der potentiometrischen Titration wurden auch die thermodynamischen Aciditätskonstanten (pK _a ) berechnet: 9.82 fürF-1, 9.71 fürF-2, 9.91 fürF-3 und 9.86 fürF-4. Wenn man diese Konstanten in Mischaciditätskonstanten überträgt, erhält man Werte, die mit den durch spektrophotometrischen Bestimmungen erhaltenen Werten gut übereinstimmen.

     

Acid-Base Properties of the Ground and Excited States of Ruthenium(II) Tris(4′-methyl-2,2′-bipyridine-4-carboxylic Acid)

The acid dissociation constant, pK_a, for the ground and excited states of ruthenium tris(4′-methyl-2,2′-bipyridine-4-carboxylic acid) complex have been measured. The ground state pK_a obtained from the pH titration curve of the complex absorption at 454 nm was 2.5. The lifetimes of the excited-state for deprotonated and protonated ruthenium complexes are 595 and 150 ns, respectively. The excited-state pK_a* is obtained from the emission titration curve at 630 nm and corrected for the excited-state lifetime to be 4.2. The increase of 1.7 pH units in the acid dissociation constant in the excited-state indicates that the ligand is much more basic in the excited-state. This result confirms the MLCT assignment for the lowest electronic transition of [Ru(mbpyCOOH)₃]²⁺.     

Multiwavelength Spectrophotometric Determination of Acid Dissociation Constants. Deconvolution of Binary Mixtures of Ionizable Compounds

ABSTRACT

A spectral deconvolution method based on target factor analysis has been developed to determine pK_a values of binary mixtures of monoprotic and/or diprotic ionizable compounds. The technique makes use of the approach of Frans and Harris, which has been implemented previously for mixtures of monoprotic compounds (Anal. Chem. 1985, 57, 1718-1721), to extract the unknown pK_a values. The method has been illustrated by using the multiwavelength spectrophotometrictitation data of binary mixtures of: I. benzoic acid and phenol, 2. benzoic acid and nicotinic acid, 3. p-aminosalicylic acid and phthalic acid. It was demonstrated that the pK_a values as determined in this study are in good agreement with the literature.     

Acid-base properties of silica-based ion-exchanger having covalently bonded aminodi(methylphosphonic) acid

Acid-base properties of an organophosphorous silica-based ion-exchanger with covalently bonded complexone groups—N-propylaminodi(methylphosphonic) acid (AdPA-SiO₂) were studied. By comparison of AdPA-SiO₂ chemical analysis and data of pH and conductometric titration it was demonstrated that the composition of immobilised layer differ from sample to sample and might consist of 60-88% aminodi(methylphosphonic) acid and 12-40% of residual aminopropyl groups. Regardless of the multifunctional nature of AdPA-SiO₂ interfacial layer, its acid-base properties can be predicted. All studied AdPA-SiO₂ samples have the properties of strong multiprotic H₄L acids with pK₁ < 2.6. Incomplete transformation of amino groups to aminodiphosphonic acid plays the key role in determination of the conditions of AdPA-SiO₂ ionisation in neutral and weak-basic media. Linear correlation was found for pK₂ and amine-to-acid conversion degree (ω) with pK₂ = 8.8 − 4.0ω. It allows us to determine the conditions of AdPA ionisation for all AdPA-SiO₂ samples. The established correlation can be used to check the quality (the degree of interfacial layer heterogeneity) of AdPA-SiO₂. The final measurable ionisation constant for AdPA-SiO₂, pK₃ = 7.9 ± 0.6 is 2-orders of magnitude higher then acidity constant for AdPA homogeneous analogue. It seems that such reduction is caused by increase of electro static interaction between movable counter-ions and negatively charged surface groups. Conductometric study of AdPA-SiO₂ also suggests firm fixation of counter-ions in the interfacial layer.     

A New Method for the Oxybromination of Aromatic Compounds with Copper(II)bromide and Potassium Dichromate

Abstract

A new and mild method for oxybromination of aromatic compounds with CuBr ₂ and K ₂ Cr ₂ O ₇ in HOAC is reported.