Search

The Z/E photoisomerization of a series of 5-arylmethylenehydantoins and a series of 5-pyridylmethylenehydantoins by direct irradiation in methanol or ethanol solvent was investigated. The isomeric ratios at the photostationary state are dependent on the excitation wavelength and are related to the relative absorption coefficients of the two isomers. Measurements of quantum yields show the absence of quenching effects by oxygen or azulene, suggesting that triplet states either are not involved or are too short-lived for quenching to be observed. Preparative photoisomerization provides a route to the isomer which is not isolated or obtained only as a minor product by the usual method of synthesis.

The patterns of the NH stretching vibrations in the solid-state IR spectra of a series of 5-pyridylmethylenehydantoins revealed the presence of various modes of hydrogen bonding: intermolecular NH&4nldr; &4nldr;OC and intermolecular or intramolecular NH&4nldr; ‥‥N(py). These variations are related to the orientation of the pyridyl nitrogen and to stereochemistry. A distinction between intramolecularly and intermolecularly hydrogen-bonded compounds was also provided by comparison of the 1H NMR spectra in (CD3)2SO and in CDCl3.

The cobalt(II) complex of an unsymmetrical bis-Schiff base. Co(dha, salen), has been prepared. In the presence of pyridine, it forms both monomeric superoxo and dimeric peroxo adducts with dioxygen. At −10°C and lower temperatures, the adduct formed in pyridine solution is mainly superoxo as shown by electronic and e.s.r. spectra as well as volumetric measurement of oxygen uptake. The solid adduct precipitated by addition of toluene is predominantly peroxo as shown by elemental analysis, i.r. spectrum, magnetic and thermogravimetric measurements. Comparison of the oxygen affinities of this complex and of the symmetrical Co(salen) is discussed.

The ionization constants of nine amphoteric 5-pyridylmethylenehydantoins were measured in 80% (w/w) dimethyl sulphoxide–water at 25 °C. The effects of structure and Z/E configuration on both pK and pK values are discussed. The especially low basicity and acidity of the Z-isomers of the N-unsubstituted and 3-methyl-substituted 5-(2-pyridylmethylene)hydantoin are attributed to the formation of intramolecular N(1)H…N hydrogen bond in the s-cis conformation of these compounds. The existence of N(1)CH3…N attraction is also postulated for the Z-isomer of 1-methyl-5-(2-pyridylmethylene)hydantoin.

Nine 5-pyridylmethylenehydantoins were prepared. Each of the 1-methyl-substitute compounds was obtained in two stereoisomeric forms. Only one form of each of the 3-methyl-substituted and N-unsubstituted compounds was obtained directly from synthesis but could be partially converted into the other stereoisomer photochemically. The Z/E configurations and the conformational relationship between the pyridine and hydantoin rings were studied by 1H and 13C NMR spectroscopy, including variable-temperature 1H NMR. The existence of NH…N or CH…N interactions and the possibility of tautomerism are suggested for some of the compounds. The Z-isomers of compounds with 2- or 3-pyridyl rings prefer an s-cis conformation whereas the E-isomers prefer an s-trans conformation.

The nickel(II) and copper(II) complexes ofN,N′-bis(dehydroaceto) ethylenediimine are monomeric and hydrated. In both compounds, coordination occurs at the C(4) carbonyl of the dehydroacetic acid moiety. The Ni atom has square-planar geometry with a water molecule at a substantial distance away. Both structurally distinct Cu atoms have square-pyramidal geometry, the apical position of one being occupied by an oxygen atom of the C(2) carbonyl group in a neighbouring molecule, and that of the other by a water molecule which participates in hydrogen-bond formation.

The copper(II)-phenolate oxygen interaction in several mixed-ligand complexes of copper(II) containing a 2,2′,2″-terpyridyl and a phenolate has been studied by i.r., electronic, e.p.r. spectroscopies and conductometric and polarographic measurements. Electronic spectral results demonstrate the dependence of such interaction on the nature of the phenol as well as the solvent. Partial dissociation of the phenolate from the complex was detected in methanol at low concentrations (≤1×10−4M). In dimethyl sulphoxide the complexes remain intact. The X-band e.p.r. spectral data obtained at ambient temperature and at 77 K are consistent with the results from the electronic spectral and conductometric study.

Aqua(malonato-O,O′)(1,10-phenanthroline)copper(II) crystallizes in the triclinic space group P with a= 11.560(4), b= 11.734(5), c= 12.491(2)A, α= 92.12(2), β= 105.50(2), γ= 109.28(3)°, and Z= 2. The structure consists of two independent monomeric [Cu(phen)(mal)(H2O)] molecules with three water molecules in the lattice. The CuN2O2O′ chromophore is distorted square pyramidal with a symmetrically co-ordinated phen molecule (mean Cu–N 2.018 A) and a symmetrically co-ordinated malonate ion (mean Cu–O 1.914 A) in the plane of the square pyramid and a water molecule at 2.266 A. The relatively short Cu–O distance has been attributed to phen being a stronger π-acid. The compound and its several related complexes show complete loss of water molecules at ca. 100 °C followed by stepwise degradation of the organic ligands. Thermogravimetric analysis and visible reflectance spectral results are discussed in relation to the known structure of the title compound.

The dissociation constants ofm-nitroanilinium ion have been determined in seven water-acetone mixtures at 25°C. The results are compared with similar data for water-dimethyl sulfoxide solvent mixtures.

A hydroxocobalt(III) complex (1a), has been obtained by reaction of bis(dehydroacetato)ethylenediimine (H2dhaen) with cobalt(II) hydroxide or acetate in the presence of air. Addition of a second complexing agent leads to the formation of a series of mixed-ligand complexes (2)-(26) having either the trans- or cis-β configuration. In the cis-β complexes, the quadridentate ligand dhaen adopts a nonplanar conformation. Configurations are distinguishable from characteristic differences in the electronic and n.m.r. spectra.

Tri-and quadri-dentate Schiff bases have been synthesized from the reaction of dehydroacetic acid with diamines, aminoacids, aminophenols and aminoalcohols. The copper(II) and some nickel(II) and palladium(II) chelates of these ligands as well as copper(II) complexes of bidentate Schiff bases of dehydroacetic acid with anilines have been prepared and characterised by electronic, i.r. and n.m.r. spectral measurements and magnetic moments.

Partial displacement of the symmetrical bis-Schiff bases (1)–(4) of ethylenediamine and salicyladehyde, o-hydroxyacetophenone, acetylacetone or benzoylacetone by dehydroacetic acid have led to the formation and isolation of the unsymmetrical bis-Schiff base ligands (6)–(9). Attempted partial displacements of the symmetrical bis-Schiff base (5) of dehydroacetic acid or (1)–(4) by each of the other four carbonyl compounds have been unsuccessful. The Ni(II) and Cu(II) complexes of (6)–(9) have been prepared and characterized.

The reactions of rhodium trichloride, iridium trichloride and chloroauric acid with thianthrene and phenoxathiin were studied. Solid complexes were isolated and characterized by electronic, IR and nuclear magnetic resonance spectra and by conductivity measurements.

Ionization constants of 2,4- and 2,5-dinitrophenol in dimethylsulfoxide were measured by the conductance method at five temperatures ranging from 20 to 40 °C. The ionization constants of 2,4-dinitrophenol are much larger than those of 2,5-dinitrophenol, and in both cases they increase with temperature. The thermodynamic functions of ionization are discussed in terms of Hepler's theory for substituent and solvent effects. The ionization of phenols in dimethylsulfoxide is controlled by the enthalpy factor, both internal and environmental, which is in contrast to the entropy-controlled process in water.

The ionization constants of 2,4-dinitrophenol were measured in water-dimethylsulphoxide solvent mixtures at five temperatures ranging from 20 to 40°C. The enthalpy and entropy contributions to the ionization process are discussed. The results indicate that in water-rich solvent mixtures the ionization process is controlled by the entropy factor while in the dimethylsulphoxide-rich solvent mixtures it is controlled by the enthalpy factor.

The pK values of (Z)-5-arylmethylenehydrantoins, (Z)-5-arylmethylene-3-methylhydantoins, and (Z)- and (E)-5-arylmethylene-1-methylhydantoins with various para-substituents in the phenyl ring have been measured. The effects of structure and stereochemistry on acidity are discussed. For each series, a good linear correlation is obtained between the pK values and Hammett constants σ and σ– in spite of the considerable distance of the site of deprotonation from the phenyl ring. The ρ values show that substituent effects are significantly greater on the acidity of N(1)–H than on that of N(3)–H, and are also greater for the E- than the Z-isomers of the 5-arylmethylene-1-methylhydantoins.

Mixed-ligand complex formation of copper(I) with 2,2′,2″-terpyridine (terpy) and various biologically significant sulfurcontaining amino acids, L′ [L′ = cysteine, penicillamine,N-acetylcysteine andN-acetylpenicillamine] was investigated. WithN-acetylcysteine andN-acetylpenicillamine, copper(I) complexes [Cu(terpy)L′]HCl have been isolated and characterised. The amino acid in each case bonds to the copper(I) through the sulfur atom only. These complexes are readily oxidised to the corresponding copper(II) complexes which contain a CuII-S(mercaptide) bond as demonstrated by the π(S)→CuII LMCT at 420 nm. The e.p.r. and electronic spectroscopic results are consistent with a distorted octahedral structure. Reactions of copper(I) with terpy and cysteine/ penicillamine in weakly acidic medium produce complexes containing two different copper(II) centres. From a strongly acidic medium, a binary copper(I) terpyridine complex is obtained instead and is shown from i.r. spectral absorptions to contain a protonated pyridyl ring.

The dissociation constants ofm-nitroanilinium ion have been determined in water and nine water-sulfolane mixtures at 25°C. The behavior is compared to results for several other aqueous solvent mixtures.

The ionization constants of some hydroxypyrones have been measured spectrophotometrically at 25 °C in water and in 80%(w/w) dimethyl sulphoxide–water. A few of them are exceptionally strongly acidic. The pKa values of these compounds are discussed in relation to their molecular structures. A plot of the pKa in water against the corresponding pKa in 80%(w/w) dimethyl sulphoxide–water is linear, although ΔpKa varies from negative values for the weaker acids to positive values for the stronger acids. Possible solvent effects have been suggested.

A series of eight carbon acids, α,α-bis(benzylsulfonyl)toluene and 7 substituted α,α-bis-(benzylsulfonyl)toluenes, was synthesized and their equilibrium ionization constants were determined by spectrophotometric measurement in 80% (w/w) dimethyl sulfoxide – water solvent at 25 °C. From a plot of −log K versus σ for the 'well-behaved' substituents and σ− for para-cyano and para-nitro substituents, a ρ value of 2.53 is obtained. The correlation co-efficient is 0.99. Comparing this ρ value with the reported ρ value of 12 for the substituted toluenes in dimethyl sulfoxide, it shows that the acidities of the disulfonyl toluenes are at least 8 to 9 orders of magnitude less sensitive to substituent effects than are the acidities of substituted toluenes implying that, for disulfonyl toluenes, the negative charge on the benzylic carbon is extensively delocalised into the two adjacent sulfonyl groups.

First ionization of (Z)-5-arylmethylenehydantoins in aqueous dimethyl sulphoxide yields a tautomeric mixture of monoanions by deprotonation at N-1 or N-3. By using appropriate 3-methyl and 1-methyl derivatives as models, the equilibrium proportions of the monoanions of the N-unsubstituted compounds have been estimated from the electronic spectra. The percentage of the N-1 anion increases with electron-withdrawing substituents in the benzene ring and with increasing concentration of dimethyl sulphoxide in the solvent mixture.

Standard free energy differences between the Z- and E-isomers of 14 hydantoins such as (I) and (II) are estimated by thermal equilibration in DMSO.

A series of eight ternary complexes, viz.[Cu(dmphen)L](dmphen = 2,9-dimethyl-1,10-phenanthroline, L = a bidentate oxygen-donor ligand), has been synthesised and characterised. In those complexes containing a β-diketonate, substitution of CF3 for CH3 of the acetylacetonate is accompanied by a shift of the C–O and C–C stretching vibrations to higher frequencies and that of the M–O to lower frequencies, indicative of the strong positive inductive effect of the CF3 group. The 1H n.m.r. spectral results indicate that the eight ternary systems, unlike [Cu(dmphen)2Cl], remain essentially undissociated in chloroform solution.

Substituent effects in para-substituted 5-arylmethylenehydantoins have been studied by correlations of 1H and 13C chemical shifts with Hammett constants. In addition to the expected correlations for the 1H chemical shift of the vinyl proton and the 13C chemical shift of the β-carbon C-5, good linear correlations are also obtained for the chemical shifts of the N-1 and N-3 protons which are respectively four and five atoms away from the benzene ring as well as for the α-carbon C-6.

Complexes of [Cu(dmphen)n]+(dmphen = 2,9-dimethyl-1,10-phenanthroline; n= 1 or 2) with several of the biologically relevant sulphur amino acids L (L = cysteine, penicillamine, methionine, N-acetylcysteine, and N-acetylpenicillamine) have been synthesized and characterised. I.r, and 1H n.m.r. spectral results indicate that the amino group is protonated in the complexes containing sulphydryl amino acids; the carboxylic group remains unionised in complexes isolated from strongly acidic media while that in complexes isolated from nearly neutral solution ionises and co-ordinates to the CuI centre through one of the oxygen atoms. The CuI–S(sulphydryl) interaction in all complexes is exclusively one of sulphur→copper(I)σ donation, as supported by the relative magnitudes of the Cu–S stretching frequencies.

The 1H and 13C n.m.r. spectra of 3-acetyl-6-methyl-2H-pyran-2,4(3H)-dione (I) and 3,5-diacetyltetrahydropyran-2,4,6-trione (III) and their Schiff's bases were studied in CDCl3 over a range of temperatures for elucidation of possible tautomerism. Whereas compound (I) appears to exist in only one form, at least two forms have been detected for compound (III). The Schiff's bases exist predominantly in keto-amine forms and the rotational barrier due to substantial double bond character of the exocyclic carbon to carbon bonds allows ready detection of rotamers. Structures of the predominant rotamers are deduced from the 1Hand 13C spectra and the assignments of NH proton signals are based on the relative strengths of the intramolecular hydrogen-bonds. The chemical shifts of NH protons correlate linearly with the pKa of the amine precursors. The 15N spectra of some 15N-enriched Schiff's bases were obtained in CDCl3 and in (CD3)2SO and the considerable downfield shifts of the 15N resonances, compared with those of typical amides, are indicative of extensive electron delocalisation.

The conductance of calcium sulphate and that of magnesium sulphate were measured at different temperatures (15–35 °C), pressures (1–1500 bar) and concentrations (up to 10–4 mol dm–3). The association constant, KA, equivalent conductance at infinite dilution, Λ°, partial molar volume change, Δtext-decoration:overlineV, and the distance of closest approach, a, have been calculated. The maximum value of Λ°p/Λ°1 for CaSO4 and that for MgSO4 occur at higher pressures than that for KCl; this observation is interpreted in terms of the dissociation of the ion pair at high pressure. With increasing pressure Walden's rule can no longer be applied, owing to a change in size of the hydrated ion. The phenomenon is closely related to the change in the dielectric constant of the solvent and the distance of closest approach, in agreement with the prediction of Bond's electrostatic model. The ion pair of calcium sulphate is more likely to be a contact ion pair than that of magnesium sulphate. Plots of the specific volume as a function of change in partial molar volume at three temperatures extrapolate to a point which may be taken to represent the situation where the structure of water around the ion is similar to that of bulk water.

The effects of 5-acyl substituents on the tautomerism of pyran-2,4-diones are revealed by comparison of the u.v.,i.r., 1H, and 13C n.m.r. spectral properties of 5-acetyl-6-methyl-,5-acetyl-6-phenyl-,5-benzoyl-6-methyl-, and 3,5-diacetyl-6-methyl-pyran-2,4-diones (3)–(6), with those of 6-methyl-(1) and 3-acetyl-6-methyl-pyran-2,4-done (2). The differences in the behaviour of the 5-acyl and 3-acyl derivatives towards primary amines are also discussed. Compound (6) reacts with aniline to form 5-acetyl-2,6-dimethyl-1-phenyl-4-oxopyridine-3-carboxylic acid (7).

A series of eight ternary complexes, viz.[Cu(dmphen)L](dmphen = 2,9-dimethyl-1,10-phenanthroline, L = a bidentate oxygen-donor ligand), has been synthesised and characterised. In those complexes containing a β-diketonate, substitution of CF3 for CH3 of the acetylacetonate is accompanied by a shift of the C–O and C–C stretching vibrations to higher frequencies and that of the M–O to lower frequencies, indicative of the strong positive inductive effect of the CF3 group. The 1H n.m.r. spectral results indicate that the eight ternary systems, unlike [Cu(dmphen)2Cl], remain essentially undissociated in chloroform solution.

First ionization of (Z)-5-arylmethylenehydantoins in aqueous dimethyl sulphoxide yields a tautomeric mixture of monoanions by deprotonation at N-1 or N-3. By using appropriate 3-methyl and 1-methyl derivatives as models, the equilibrium proportions of the monoanions of the N-unsubstituted compounds have been estimated from the electronic spectra. The percentage of the N-1 anion increases with electron-withdrawing substituents in the benzene ring and with increasing concentration of dimethyl sulphoxide in the solvent mixture.

A modified electrode has been prepared by electrodeposition of Pt particles into Nafion-coated glassy carbon (GC). The electrochemical properties of the Pt-Nafion-GC electrode were compared with those of Pt, GC and Pt-modified GC electrodes. The Pt-Nafion-GC electrode showed good stability and was used for the determination of hydrogen peroxide. An application of this electrode to flow injection analysis-electrochemical detection is also described.

The i.r., u.v., and 1H- and 13C-n.m.r. spectra of some acetylpyran-2,6-diones are discussed in relation to their tautomeric structures and compared with those of the acetylpyran-2,4-diones. Their reactions with primary amines to give Schiff bases, salts, pyridones or open-chain products as well as a thermal rearrangement of the Schiff bases are reported.