Negative ion chemical ionization mass spectra of (η6-arene)Cr(CO)3

The negative ion chemical ionization mass spectra, with ammonia and methane as reagent gases, of the (η⁶-arene)Cr(CO)₃ complexes, where the arene is C₆H₅COCH₃, C₆H₅COC₂H₅, C₆H₅COC₃H₇, C₆H₅COC(CH₃)₃, 2-CH₃C₆H₄COC₃H₇, C₆H₅COOCH₃, C₆H₅CH₃, 1,3,5-(CH₃)₃C₆H₃ and C₆H₅CH₂COC₂H₅, are reported. Similar behaviour is observed with the two reagent gases, but ammonia shows a much higher abundance for the ions produced by reactions of [NH₂]^? with sample molecules. The compounds containing the C₆H₅CO group display an abundant [M]^{? ˙}, whereas the other compounds exhibit [M? H]^? as base peak, produced by ion/molecule reactions. A comparison of the negative ion chemical ionization mass spectra of the (η⁶-arene)Cr(CO)₃ complexes with those of the corresponding ligands shows the strong electron withdrawing power of the Cr(CO)₃ group in the gas phase.     

Transition metal-catalysed sequences of nucleophilic addition

Summary In presence of nickel or palladium catalysts, nucleophiles can attack vinylcyclopropanes with concomitant ring cleavage. With palladium catalysts in presence of appropriate substituents the terminal carbon atom of the resulting open chain is able to add to two molecules of a conjugated diene giving rise to long-chain unsaturated compounds.     

Standard pH values for potassium hydrogenphthalate reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water mixed solvents at temperatures from 288.15 to 318.15 K

Standard pH(S) values for 0.05 mol kg^?1 potassium hydrogenphthalate (KHpH) reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water solvent mixtures within the temperature range 288.15–318.15 K are determined from e.m.f. measurements of the cell without transference Pt|H₂|KHPh + KCl|AgCl|Ag|Pt. The consistency of the results is analysed by a recently described method of multilinear regression of the quantity p(a_Hγ_Cl) as a function of both solution composition and temperature. The standard pH(S) determined can be reproduced to within ±0.01 by the equation pH(S) - 4.004 + 3.309w + 0.408z + 1.037w³ - 14.95zw² + 27.1zw³, where w is the weight fraction of dioxane in the solvent mixture,z = (T –θ)/θ, and θ - 298.15 K. Values of the first ionization constant of phthalic acid (H₂Ph; benzene-1,2-dicarboxylic acid) in the above solvent mixtures are also determined from e.m.f. measurements of the cell without transference Pt|H₂|H₂Ph + KHPh + KCl|AgCl|Ag|Pt.     

Synthesis of some 3,7-disubstituted quino[3,2-c][1,8]naphthyridines

The preparation of some 3,7-disubstituted-5,6-dihydroquino[3,2-c][1,8]naphthyridines ( 6 ) by the condensation of 7-substituted-2,3-dihydro-1,8-naphthyridin-4-(1H)ones ( 5 ) with o-aminoacetophenone or o-aminobenzophenone is described. All the 5,6-dihydroderivatives 6 were transformed into the fully aromatic compounds 7 by heating with nitrobenzene. Only a few quino[3,2-c][1,8]naphthyridines were previously described.     

Simultaneous determination of concentration,diffusion coefficient and number of electrons for electroactive species by combining suitable electroanalytical measurements

The electroanalytical method described for the simultaneous determination of concentration, the number of electrons involved in the redox process and diffusion coefficient is based on evaluation of the ratios between the currents recorded for the analyte and for an easily standardized reference species dissolved in the same medium. Three different electroanalytical techniques are used in which the currents exhibit, for two techniques at least, different dependences on both the diffusion coefficient and electron number. The approach is applicable to diffusion-controlled processes, regardless of the degree of reversibility involved. Reliability tests with electroactive organic compounds dissolved in dimethyl sulphoxide show that both accuracy and precision are within 10% depending on the chosen combination of techniques.     

The nickel-catalysed carbonylation of 2-mercaptoethanol

2-Mercapthoethanol undergoes carbonylation in pyridine solution in the presence of oxygen and of [Ni(CO)₃Pyl as a catalyst to give cyclic O, S-ethylelnethiorcarbonate. The isolation of thiolatonickel compound [Ni(SCH₂CH₂OH)₂] by the oxidation of a solution containing [Ni(CO)₃Py] and 2-mercaptoethanol, and its reaction with carbon monoxide to give the cyclic thiocarbonate and [Ni(CO)₃Py] prove that the reaction proceeds in at least two steps.     

Fibrazioni di una classe di near-field regolari di dimensionet+1 sul nucleo

Il contenuto di questo lavoro consiste nel mostrare che le fibrazioni dei near-field regolari di dimensionet+1 sul nucleo , quando , si ottengono da fibrazioni regolari con una operazione di scambio fra alcuni sistemi di matrici, che generalizza il procedimento di sostituzione di regoli con regoli opposti di quadriche rigate nel caso di dimensione due sul nucleo.     

Fast solid-phase extraction-gas chromatography-mass spectrometry procedure for oil fingerprinting. Application to the Prestige oil spill

A rapid and simple fractionation procedure using solid-phase extraction (SPE) cartridges was developed for an accurate determination of aliphatic and polycyclic aromatic hydrocarbons in petroleum residues and further application in chemical fingerprinting of oil spills by gas chromatography-mass spectrometry (GC-MS). Among the adsorbents evaluated, SiO2/C3-CN exhibited the best selectivity, providing, by elution with n-hexane (4 ml) and n-hexane-CH2Cl2 (1:1) (5 ml), two well-resolved aliphatic and aromatic hydrocarbon fractions, with recoveries of 97 +/- 7.2 and 99.7 +/- 13.9%, respectively. The SPE fractionation procedure was compared with the conventional silica-alumina adsorption chromatography showing similar results but practical advantages in terms of reproducibility, analysis time, solvent reduction and cost. Moreover, is particularly suitable for routine analysis with a high sample throughput. The developed methodology was tested in the characterization of fuel-oil samples collected along the Spanish north-west coast, after the Prestige oil spill accident.     

Low-Cost Potentiometric Sensor for Chloride Measurement in Continuous Industrial Process Control

Recently, the new updates in legislation about drinking water control and human health have increased the demand for novel electrochemical low-cost sensors, such as potentiometric ones. Nowadays, the determination of chloride ion in aqueous solutions has attracted great attention in several fields, from industrial processes to drinking water control. Indeed, chloride plays a crucial role in corrosion, also influencing the final taste of beverages, especially coffee. The main goal is to obtain devices suitable for continuous and real-time analysis. For these reasons, we investigated the possibility to develop an easy, low-cost potentiometric chloride sensor, able to perform analysis in aqueous mediums for long immersion time and reducing the need of periodic calibration. We realized a chloride ion selective electrode made of Ag/AgCl sintered pellet and we tested its response in model solutions compatible with drinking water. The sensor was able to produce a stable, reproducible, and accurate quantification of chloride in 900 s, without the need for a preliminary calibration test. This opens the route to potential applications of this sensor in continuous, in situ, and real time measurement of chloride ions in industrial processes, with a reduced need for periodic maintenance.     

Switchable photocatalysis for the chemodivergent benzylation of 4-cyanopyridines

We report a photocatalytic strategy for the chemodivergent radical benzylation of 4-cyanopyridines. The chemistry uses a single photoredox catalyst to generate benzyl radicals upon N–F bond activation of 2-alkyl N-fluorobenzamides. The judicious choice of different photocatalyst quenchers allowed us to select at will between mechanistically divergent processes. The two reaction manifolds, an ipso-substitution path proceeding via radical coupling and a Minisci-type addition, enabled selective access to regioisomeric C4 or C2 benzylated pyridines, respectively. Mechanistic investigations shed light on the origin of the chemoselectivity switch.

We report a photocatalytic strategy for the chemodivergent radical benzylation of 4-cyanopyridines. The chemistry uses a single photoredox catalyst to generate benzyl radicals upon N–F bond activation of 2-alkyl N-fluorobenzamides.