A. Arcoria

Oxidations with peroxotungsten complexes: rates and mechanism of stoichiometric olefin epoxidations

Abstract The stoichiometric epoxidation reactions of a series of olefins with WO-(O2)2HMPT and MoO(O2)2HMPT have been studied in dichloroethane at 40 °C. The data obtained point out the superior oxidizing ability of W(VI) over Mo(VI). However, the two peroxo groups in WO(O2)2HMPT appear to react with the substrates at different rates, the transfer of the first peroxide oxygen being faster than of the second one, contrary to that observed in the behavior of MoO(O2)2HMPT. The crystal structure of WO(O2)2HMPT·H2O, determined by diffractometric techniques, does not show any significant difference compared to that reported for MoO(O2)2HMPT·-H2O, indicating that it might be difficult to correlate the solid state structures with the different behaviors experimentally observed in solution. In spite of the different features shown by the two peroxo complexes, the data collected in this investigation suggest that an identical mechanism of oxygen transfer from the two oxidants is operating. Moreover, this mechanism should not involve the occurrence of substrate-oxidant intermediates.

The relevance of acid-base equilibria in the catalytic oxidations by tungsten and molybdenum peroxo complexes

Abstract The catalytic behaviour of the two peroxo complexes MO(O 2 ) 2 HMPT· H 2 O (M = W(VI), Mo(VI); HMPT = hexamethylphosphoric acid triamide) in the oxidations by hydrogen peroxide in ethanol has been examined. Rate data, obtained in a model reaction, i.e. the oxidation of organic sulphides to the corresponding sulphoxides, indicate that in ‘neutral’ ethanol the Mo(VI)-catalyzed system is more efficient than the W(VI) one. Spectroscopic ( 1 H NMR), potentiometric and kinetic experiments suggest that this is mainly due to the much stronger acidity of the W(VI)-peroxo complex which is almost completely dissociated into its anionic form, and which is a poor electrophilic oxidant. In fact, when the anions are neutralized upon addition of methanesulphonic acid, the neutral peroxotungsten complex appears to be a much more effective oxidizing agent than the structurally similar peroxomolybdenum compound. An additional advantage of the W(VI)-catalyzed system may be found in the reduced affinity of W(VI)-peroxo species, as compared with Mo(VI), for neutral ligands. Therefore HMPT, even at the highest catalytic concentrations employed, is completely removed from the coordination sphere of tungsten.

Reactions of aromatic sulphonyl chlorides with anilines : Studies of solvent effects by the approach of multiparameter empirical correlations

Abstract The reaction kinetics of 5-substituted 2-thiophenesulphonyl chlorides with anilines were studied in fourteen pure solvents (protic and aprotic) and in mixed solvents at 25°. The approach of multiparameter equations to describe solvent effects according to the Palm-Koppel and Krygowski-Fawcett models was unsuccessful. Instead satisfactory single parameter linear correlations, one for protic solvents with positive slope and another for aprotic solvents with negative slope, were found by using the dielectric constant ϵ. An S A N mechanism for these reactions was proposed, bond-making being the rate-determining step for protic solvents and bond-breaking for aprotic ones. The analysis of some data for the reactions of benzenesulphonyl chloride showed that the mechanism is analogous also for this substrate and the rate-determining step is depending on both solvent and nucleophile. Hammett ρ-values for the reactions of substituted 2-thiophenesulphonyl chlorides with aniline are in accord with the proposed mechanism. ϱ-Values for the reactions of 2-thiophenesulphonyl chloride with substituted anilines are related to the solvent effects by equation ϱ = − 15.7 f(ϵ) + 0.113E + 3.94. The solvent effects on these values can be interpreted by the effect of the dielectric constant and the influence of H-bonding. Mixed solvents are characterized by the presence of a maximum rate.

Carrier dyeing of polyester fibre with some disperse azo dyes

Abstract This paper reports the effects of phenol, as a carrier, on the kinetics and thermodynamics of the dyeing of polyester fibre with some substituted benzothiazolyl azo dyes. The dyeing rate constants, the thermodynamic affinity and the apparent diffusion coefficients depend on the carrier concentration and on the dye structure, i.e. the presence of hydroxy groups in the N,N-diethylamino moiety of the coupler and of the phenyl ring between the thiazole and azo group. The results indicate the phenol does not behave by plasticizing the fibre, but it mainly acts as dispersant of the dye in the dyebath.

Infrared and ultraviolet spectra of some 2-thiophenecarboxamides

Abstract The i.r. spectra of some 2-thiophene-carboxamides have been investigated for identification of the N-H stretching, CO stretching and N-H deformation bands. The u.v. spectra have been recorded in order to get information about the chromophores responsible for absorption.

Nucleophilic substitution in the side chain of 5-membered heterocycles—I : Reactions of furfuryl, 2-thenyl and benzyl chlorides with aniline in acetonitrile and in benzene

Abstract The reaction kinetics of furfuryl, 2-thenyl and benzyl chlorides with aniline has been studied in acetonitrile and benzene solutions, The reactions are third order overall, first order with respect to the chloromethyl compound and second order with respect to aniline. In benzene solutions the kinetics at high aniline concentrations (≥0·8 M) deviate from the third order equation. The remarkable increase in k3, not depending on the polarity of the reaction medium, is ascribed to the association of aniline in benzene. The reactions in acetonitrile are faster than in benzene; in both solvents furfuryl chloride reacts faster than 2-thenyl and benzyl chlorides, the latter being the less reactive. The large negative activation entropies, consistent with an ordered and highly polar transition state, determine the observed rate sequence. The rate constants were correlated with the polar constants for heterocycles.

Dyeing properties of basic azo-dyes from 2-amino thiadiazole

Abstract Some new basic azo-dyes derived from thiadiazole were synthesized to evaluate the dyeing parameters on polyester fibre (PET) for optimizing the dyeing process. The kinetics of dyeing were performed at various temperatures (80°, 90° and 100°C) in the absence and in the presence of phenol, benzoic acid and salicylic acid as carriers. Thermodynamic affinities were also measured. The dyeing rate constants increase on increasing the concentration of carrier, while low affinity values were observed for the dyes bearing hydroxyl groups, owing to increased solubility of the dye in the dyebath. This behaviour is less evident in the dyes bearing a methyl group in the thiadiazole ring. The dyes show good fastness to light, perspiration and dry cleaning.

Infrared and ultraviolet spectra of 2-thienyl-phenyl-ketone nitro-derivatives

Abstract The i.r. spectra of 2-thienyl-phenyl-ketone nitro-derivatives have been investigated for the identification of the main absorption frequencies. The u.v. spectra are also reported in order to get information about the chromophores responsible for the absorption.

Electronic spectra and infrared characteristics of trans-2-styrylthiophene and some nitro derivatives

Abstract The electronic spectra of trans -2-styrylthiophene and its nitro derivatives have been discussed in order to get information about the chromophores responsible for the absorption. The electronic transition energies of these compounds have been compared with those of trans -stilbene, 2-phenylthiophene and some nitro derivatives. The i.r. spectra have been investigated for the identification of the main absorption frequencies.

Effects of the phenol on the dyeing of polyester fibre with some disperse azo-dyes

Abstract The effects of the phenol, as carrier, on the dyeing rates, apparent diffusion coefficients, solubilities, thermodynamic affinities and T D values of some disperse azo-dyes on polyester fibre are reported. The dyeing rates of less soluble dyes are higher than those of more soluble hydrophilic dyes, while the affinity and T D values show a reversed behaviour. The carrier efficiency on the dyeing parameters studied appears to be correlated with the structure of dyes.