0000000000103812
AUTHOR
Giuseppe Silvestri
showing 60 related works from this author
Anodic abatement of organic pollutants in water in micro reactors
2010
The electrochemical oxidation of oxalic acid (OA) was performed in a micro flow cell equipped with a boron doped diamond (BDD) anode. This preliminary study demonstrates that a flow cell with a micrometric distance between the cathode and the anode can be used to perform the electrochemical treatment of waters contaminated by organic pollutants in the absence of added supporting electrolytes with high abatements. The effect of the distance between the cathode and the anode, the flow rate and the current density on the abatement of oxalic acid and on the current efficiency was in particular studied.
A filter-press electrolytic cell with semi-continuous renewal of sacrifical electrodes
1989
Etude d'une cellule electrolytique dans laquelle une des electrodes est consummee avec remplacement de l'element sacrifie sans demontage de la cellule. Cette cellule est testee lors de l'electrocarboxylation de la N-phenylbenzalimine en acide amine
Oxide anodes in electro-organic oxidation. Oxidation of maleic addon tungsten oxide anodes
1982
The electrochemical oxidation of maleic acid on tungsten anodes has been investigated. Glyoxal and carbon dioxide were the main products together with tartaric acid and acetaldehyde. Glyoxal is also obtained as the main product from the oxidation ofd-tartaric acid. Under the same conditions succinic acid is completely oxidized to carbon dioxide and water. The anodic dissolution of tungsten and the oxidation of water to oxygen become predominant in the final stages of the electrolyses.
Supercritical-fluid extraction of chlorofluoroalkanes from rigid polyurethane foams
1996
Abstract Preliminary results about a process for recovering expanding agents chlorofluoroalkanes (CFCs) both trapped in the cavities and dissolved in the polymer from rigid polyurethane foams are reported. The performances of liquid and supercritical carbon dioxide, and of CO2-propane supercritical mixtures were compared. Better results in terms of extraction time and amount of extracted CFCs were obtained with finely ground materials and supercritical propane-carbon dioxide fluids.
Carboxylation of a linear low density polyethylene via gamma irradiation in presence of carbon dioxide in subcritical and supercritical conditions
1994
Abstract In this work the molecular modifications induced in a linear low density polyethylene gamma irradiated in presence of carbon dioxide both in subcritical and supercritical conditions are presented. The obtained results indicate that this process can be a new and interesting way in order to graft oxidized groups in the polyethylene chains. Moreover it is worth noting that, together with these functionalization reactions, also a significant crosslinking occurs, with improvement in some mechanical tensile behaviour.
Electrochemical carboxylation of aldehydes and ketones with sacrificial aluminum anodes.
1986
Abstract The electrocarboxylation of aldehydes to the corresponding α-hydroxyacids was described as impossible with conventional electrochemical systems. It is reported here that it is possible to realize it in diaphragmless cells making of sacrificial aluminum anodes. The method can be used also for the electrocarboxylation of ketones with good yields.
INFLUENCE OF THE EXPERIMENTAL SYSTEM AND OPTIMIZATION OF THE SELECTIVITY FOR THE ELECTROCARBOXYLATION OF CHLOROACETONITRILE TO CYANOACETIC ACID
2004
The electrocarboxylation of chloroacetonitrile (ClACN) to cyanoacetic acid in undivided cells equipped with sacrificial anodes was investigated both in a bench-scale electrochemical batch reactor and in a continuous batch recirculation reaction system equipped with a parallel-plate electrochemical cell. Selectivity and faradaic yields higher than 90% were obtained by working under anhydrous conditions with low halide concentrations and at more negative potentials. It was found that the instantaneous selectivity in the carboxylate compound depends mainly on the [CO 2 ]/[ClACN] ratio at high substrate concentration and is close to 100% for low ClACN concentration. These results were consisten…
Electrochemical oxidation of organics in water: Role of operative parameters in the absence and in the presence of NaCl
2008
The electrochemical oxidation of organics in water was investigated theoretically and experimentally to determine the role of several operative parameters on the performances of the process in the presence and in the absence of sodium chloride. Theoretical considerations were used to design the experimental investigation and were confirmed by the results of the electrochemical oxidation of oxalic acid (OA) at boron doped diamond (BDD) or IrO(2)-Ta(2)O(5) (DSA-O(2)) anodes in a continuous batch recirculation reaction system equipped with a parallel plate undivided electrochemical cell. Polarization curves and chronoamperometric measurements indicated that, in the presence of chlorides, the a…
Mechanism of the palladium-catalysed electrosynthesis of diethyl carbonate from carbon monoxide and ethanol
2004
Abstract A mechanism is proposed for the PdBr2(PPh3)2-catalysed electrosynthesis of diethyl carbonate from carbon monoxide and ethanol, proceeding at room temperature and atmospheric CO pressure. The mechanism is investigated by cyclic voltammetry and 31P NMR spectroscopy. The active Pd0 complex able to coordinate CO is generated by the chemical reduction of PdBr2(PPh3)2 by EtO– ions generated from EtOH at the cathode. After reaction of EtO– ions with Pd0(PPh3)2(CO), the ensuing anionic complex [(PPh3)2Pd0–COOEt]– is oxidized at the anode in a key step leading to BrPdII–COOEt(PPh3)2. A nucleophilic attack of ethoxide on the latter generates diethyl carbonate and the Pd0 complex active in th…
Electroactivation of Transition Metal Redox Couples for the Carbonylation of Alcohols to Dialkylcarbonates
1998
Electrochemical systems which promote the carbonylation of methanol to dimethylcarbonate, based on the anodic activation of transition metal redox couples, or the Br−/Br2 couple, are poorly active for the carbonylation of ethanol to diethylcarbonate at room temperature and atmospheric pressure. Positive results have been obtained by combined addiction of PdBr2 and Bu4NBr to the system. In this way yields up to 50% in diethylcarbonate were obtained, with very good conductivities in long range electrolyses.
Electrochemical oxidation of substituted pyrroles.III.Anodic oxidation of 2,5-diphenyl-3-acetylpyrrole
1991
The electrochemical oxidation of 2,5-diphenyl-3-acetylpyrrole (I) is described. The cyclic derivative 1,6a-dihydro-2,5,6a-triphenyl-3,4-diacetylbenzo[g]pyrrolo[3,2-e]indole (II) was obtained in very good yield. However, when water was present in the reaction medium, a different derivative, 4-acetyl-2-hydroxy-2,5-diphenyl-3-(4′-acetyl-2′,5′-diphenyl-3′-yl)-2H-pyrrole (III), was obtained as the main product. 2,2′,5,5′-Tetraphenyl-4,4′-diacetyl-3,3′-dipyrryl (IV), a potentially useful intermediate for the synthesis of condensed pyrroles, was synthesized by zinc reduction of III.
Synthetic Application of Homogeneous Charge Transfer Catalysis in the Electrocarboxylation of Benzyl Halides
1998
The results of an investigation on the performances of some outer sphere electron transfer homogeneous catalysts in the electrocarboxylation of 1-(p-isobutyl-phenyl)-1-chloroethane to 2-(p-isobutyl-phenyl)-propionic acid (Ibuprofen), using as catalysts the esters of benzoic and o-, m-, and p-phtalic acids, are reported. The performances of the catalysts are evaluated on the basis of the following parameters: faradic yields of the carboxylation and decomposition of the catalyst. The performances of dimethylisophtalate have been examined in greater detail. The rate of decomposition of the catalyst is related to the molar ratio [halide]/[catalyst].
Electrochemical reduction and carboxylation of halobenzophenones
2002
Abstract The electrochemical reduction of a series of halogenated benzophenones XC6H4COC6H4Y (1) was studied in aprotic solvents, in the absence and presence of CO2, by cyclic voltammetry (CV) and controlled-potential electrolysis. The mechanism of electroreduction in dimethylformamide (DMF) has been investigated in some detail. Most of the compounds undergo reductive carbonhalogen bond cleavage in the time window of CV. The radical anions derived from difluorobenzophenones (X=Y=4-F; X=2-F, Y=4-F) as well as from the 3-chloro derivative are quite stable with a cleavage rate constant (kc) of the order of 10−2 s−1 or less. With 4-chloro-, 2-chloro-, 4,4′-dichloro- and 2,4′-dichorobenzophen…
Electrochemical Syntheses Involving Carbon Dioxide
1990
The recent developments of electrosynthetic processes involving carbon dioxide are reviewed. Both processes involving carbon dioxide alone and electrocarboxylations are taken under consideration. The first of these two fields, mainly projected towards the production of basic chemicals such as methanol or carbon monoxide, is at present at a stage of fundamental research. Some interesting developments have recently appeared in the literature, concerning the use of electrode materials, or of transition metal complexes with particular catalytic activity. Electrocarboxylations are at a stage of more applicative development: some processes have reached the stage of pilot plant, and other have int…
Irradiation of low density and high density polyethylenes in presence of carbon dioxide in subcritical and supercritical conditions
1998
Abstract The grafting of carboxylated and oxygenated functions on low density and high density polyethylenes is carried out by gamma irradiation in the presence of carbon dioxide. Both crosslinking and grafting of oxidised groups occur. The extent of these molecular modifications depends on the physical conditions of the gas phase and on the nature of the polymer matrix.
Copolymerization of vinylidene fluoride and acrylic acid in supercritical carbon dioxide
2009
The free-radical copolymerization of vinylidene fluoride (VDF) and acrylic acid (AA) was carried out in supercritical carbon dioxide using both precipitation and dispersion techniques in the presence of an ammonium carboxylate perfluoropolyether compound. Formation of a copolymer was confirmed by variable contact time CP MAS NMR spectroscopy. Macromolecular matrices were significantly enriched in AA with respect to the initial feed composition and we found that the nonfluorinated monomer has a much higher reactivity ratio with respect to VDF. The cumulative concentration, crystallinity, and water affinity of the synthesized copolymers could be modified changing the initial feed composition,…
Electrocarboxylation of Benzyl Halides through Redox Catalysis on the Preparative Scale
2006
The electrocarboxylation of benzyl halides to the corresponding carboxylic acids through homogeneous charge-transfer catalysis was investigated both theoretically and experimentally to determine the influence of the operative parameters on the yield of the process and on the catalyst consumption. Theoretical considerations, based on fast kinetics of redox catalysis, were confirmed by the electrocarboxylation of 1-phenyl-1-chloroethane catalyzed by 1,3-benzenedicarboxylic acid di methyl ester performed at a carbon cathode under different operative conditions. We obtained high yields of the target carboxylic acid and experienced a low catalyst consumption by operating with optimized [RX]bulk/…
Catalytic systems based on transition metals for the carbonylation of methanol to dimethylcarbonate
1997
Abstract The results of an investigation on catalytic systems arising from the electrochemical activation of salts and complexes of several transition metals for the carbonylation of methanol to dimethylcarbonate (DMC) are reported. Metals were tested as inorganic salts or complexes with ligands such as 2,2′-bipyridine (bipy), 1,6-bis (2-oxyphenyl)-2,5-diaza-1,5-hexadiene (salen), 2,4-pentanedionate (acac), triphenylphosphine (TPP) in methanol at room temperature saturated with carbon monoxide at atmospheric pressure. Best faradic yields vs DMC were observed as follows: CuCl(bipy): 84.8%; PdCl 2 (bipy): 64.0%; CoCl 2 : 26.0%; RhCl 3 : 25.0%; AgBF 4 (bipy): 10.2%; AuCl 3 : 9.4%; Cr(acac) 3 :…
Recent Scientific and Technological Developments in Electrochemical Carboxylation Based on Carbon Dioxide
2010
The electrochemistry of carbon monoxide reductive cyclotetramerization to squarate anion
1978
Abstract The electrochemical reduction, of carbon monoxide to C4O2−4 squarate anion is investigated. Particular attention is devoted to the influence that solvents, electrolytes, electrodes and carbon monoxide pressure have on the yields. The main feature appears to be that strictly controlled conditions are not necessary for cyclotetramerization. In dmf — Bu4NBr the following yields vs reacted CO and circulated charge were obtained with different cathodes: Pt(49%, 34%); Au(48%, 29%); Al(47%, 38%); stainless steel (36%, 33%); graphite (39%, 31%). A distinct influence of the supporting electrolyte (inorganic and tetraalkylammonium halides) was however observed.
Electrochemical production of initiators for polymerization processes
2007
The most important technological interest in initiator production lies, in the electrosynthesis of complex catalytic systems, i. e. coordination compounds and Ziegler-Natta catalysts, although the choice of olefins to be polymerized with these electrosynthesized complexes is still limited to ethylene and to very few other monomers.
Direct electrochemical detosylation of tetratosylcyclen to cyclen with carbon cathodes
2005
The electrochemical detosylation of tetratosylcyclen to cyclen (1,4,7,10-tetraazacyclododecane) in aprotic solvents at a carbon cathode was investigated both in a bench-scale batch electrochemical reactor and in a continuous batch recirculation reaction system equipped with a parallel-plate electrochemical cell. Yields and faradaic efficiency in cyclen, respectively, of 80 and 55% were obtained in the bench-scale reactor working in acetonitrile. It was found that the faradaic efficiency in cyclen depends on the competition between the reduction of the tetratosylcyclen and parasitic processes as the reduction of the tetraalkylammonium cations present in the supporting electrolyte. We have ob…
Sacrificial Anodes in the Electrocarboxylation of Organic Chlorides
1984
Electrochemical oxidation of 2,4,5-triaryl-substituted pyrroles.II. Oxidative dimerization of 4,5-diphenyl-2-mesitylylpyrrole
1989
2,4,5-Triaryl-substituted pyrroles lead, upon chemical or electrochemical oxidation, to an intermediate β-β'-dimer, which, in the course of the reaction, undergoes further oxidation to a tetracyclic derivative. To improve the selectivity towards the uncyclized dimer the oxidation of a triarylpyrrole in which the ortho positions of the phenyl group in position 2 are hindered by the presence of methyl groups was attempted. The cyclization was hindered, but an α-β'-dimer was obtained as the major product. An unexspected isomeric α-β'-dimer, in which the mesitylyl group is shifted into the β position of the pyrrole ring which undergoes the oxidation, was obtained in minor amounts. Electroanalyt…
Electrochemical carboxylation of benzal chloride
1984
Abstract The clectrocarboxylation of benzal chloride to -chlorophenylacetic and phenylmalonic acids is realized in diaphragmless cells with aluminium sacrificial anodes. Yields respectively up to 50% and 30% can be obtained. Phenylacetic acid is always present among the products.
Elektrocarboxylierung organischer Chloride mit Zehrandon
1984
Carboxylation par CO 2 de chloro-1 propane, -butane, α-chlorotoluene, dichlorobenzene, chloro-1 naphtalene et chloro-1p ethylbenzene en presence d'une anode de Al dans DMF-bromure de tetrabutylammonium
Synthesis of cyanoacetic acid by carbon dioxide and electrogenerated acetonitrile anion in undivided cells equipped with sacrificial anodes
2008
The electrochemical synthesis of cyanoacetic acid was performed by cathodic reduction of tetraalkylammonium salts (R4NX) in acetonitrile in undivided cells equipped with sacrificial anodes with concomitant or subsequent addition of carbon dioxide. These syntheses avoid the use of dangerous reagents, yield cyanoacetic acid in moderate faradic yields and confirm that the cathodic reduction of tetraalkylammonium salts in the presence of acetonitrile leads to the formation of the anion CNCH2-.
Elektrochemische Prozesse in superkritischen Phasen
2006
Electrochemical Syntheses of Carboxylic Acids from Carbon Dioxide
1987
The first report on the reduction of carbon dioxide is due to the venerable name of Hermann Kolbe, who, in 1861, published with R. Schmitt the reduction of carbon dioxide to formate with metallic potassium (1). Seven years later he introduced to the Chemical Society in London his assistant E. Drechsel, who “after many unsuccessful experiments, made during several years” (2) at the end succeeded in reducing carbon dioxide to oxalate with metallic sodium or with potassium amalgam in anhydrous conditions. Soon afterwards Beketov (3) and Royer (4) opened the series of papers dealing with the direct involvement of carbon dioxide in electrolytic processes. Since then the reduction of carbon dioxi…
Optimization of selectivity for the electrocarboxylation of chloroacetonitrile
2004
Electrocarboxylation of benzyl halides at silver cathodes
2006
Electrochemical Incineration of Dichloroethane. Influence of the anode material
2007
Electrochemical incineration of organic pollutants: effect of the nature of the pollutants and of the operative conditions
2010
Copolymerization of Vinylidene Fluoride and Acrylic Acid in Supercritical Carbon Dioxide
2010
The free-radical copolymerization of vinylidene fluoride (VDF) and acrylic acid (AA) was carried out in supercritical carbon dioxide using both precipitation and dispersion techniques in the presence of an ammonium carboxylate perfluoropolyether compound. Formation of a copolymer was confirmed by variable contact time CP MAS NMR spectroscopy. Macromolecular matrices were significantly enriched in AA with respect to the initial feed composition and we found that the nonfluorinated monomer has a much higher reactivity ratio with respect to VDF. The cumulative concentration, crystallinity, and water affinity of the synthesized copolymers could be modified changing the initial feed composition,…
Metodologie di fabbricazione di microreattori elettrochimici
2008
A Gas Chromatographic Method To Measure Sorption of Supercritical Carbon Dioxide in Poly(vinylidenefluoride): a Comparison between two Different Tech…
2005
Incineration of oxalic acid at boron doped diamonds. In: Giornate dell'elettrochimica italiana
2007
Two electrochemical methodologies for the synthesis of cyanoacetic acid
2005
Electrochemical incineraton of oxalic acid at boron doped diamond electrodes: influence of operative parameters
2006
Electrocarboxylation of chloroacetonitrile to cyanoacetic acid
2004
Incenerimento elettrochimico di acido ossalico in presenza di NaCl
2008
Influence of operative parameters on the electrochemical incineration of oxalic acid.
2008
Electrochemical incineration in a micro flow reactor: influence of operative parameters
2010
Electrochemical processes for the treatment of chlorinated ethanes in water solutions
In the present work, the electrochemical treatment of water solutions containing chloro ethanes was performed by cathodic reduction, anodic oxidation and coupled processes with the aim of evaluate the effectiveness of these methodologies.
Free radical copolymerization of vinylidene fluoride and acrylic acid in supercritical carbon dioxide
2010
Electrochemical incineration of oxalic acid in a micro-gap flow cell
2009
Elettrocarbossilazione di alogenuri benzilici su scala preparativa tramite catalisi omogenea di trasferimento di carica e catalisi eterogenea su arge…
2007
Electrochemical incineration of organic pollutants: effect of the nature of the pollutants and of the temperature
2009
The electrochemical oxidation of some organic pollutants, including three carboxylic acids (oxalic, formic and maleic), at boron doped diamond (BDD) and DSA anodes, using galvanostatic alimentation, was investigated in order to study the effect of the temperature and of the nature of the pollutants on the process. In incineration electrolyses, the performances of the process in terms of carboxylic acid conversion and current efficiency dramatically depend on the adopted operative conditions. The abatement of the organic pollutant depends on the nature of the carboxylic acid. Quite interestingly, the opposite effect of the nature of the substrate on the performances of the process was observ…