1,721,099 research outputs found
Phosgene-free synthesis of 1,3-diphenylurea via catalyzed reductive carbonylation of nitrobenzene
Full text link1,3-Diphenylurea (DPU) has been proposed as a synthetic intermediate for phosgene-free synthesis of methyl N-phenylcarbamate and phenyl isocyanate, which are easily
obtained from the urea by reaction with methanol. Such an alternative route to synthesis of carbamates and isocyanates necessitates an improved phosgene-free synthesis of the corresponding urea. In this work, it is reported that Pd(II)-diphosphine catalyzed reductive carbonylation of nitrobenzene in acetic acid (AcOH)-methanol proceeds in high yield and selectivity
as a one-step synthesis of DPU. We have found that the catalytic activity and selectivity of this process depends on solvent composition and on the bite angle of the diphosphine ligands.
Under optimum reaction conditions, yields in excess of 90 molar % and near-quantitative selectivity can be achieved
Multistep Electron Transfer Catalytic System for the Oxidative Carbonylation of Phenol to Diphenyl Carbonate
Full text linkHigh molecular weight poly(1-oxo-trimethylene) solution obtained by the catalytic copolymerization of CO with ethene in phenol-H2O as a solvent
No full textThe CO-ethene copolymerization, catalyzed by Pd(II)-diphosphine complexes, affords to the perfectly alternate poly(1-oxo-trimethylene), a high-performance thermoplastic with interesting physical and chemical properties [1]. The catalysis is efficiently carried out in methanol where the Pd(II) precursors are soluble while the polymer is insoluble [1]. As a consequence of this, during the reaction the Pd(II) intermediates, bonded with the growing polymer chain, precipitate after insertion of only a few monomers units and the polymer growth continues through a liquid-solid heterogeneous catalysis. We propose the homogeneous CO-ethene copolymerization carried out in phenol-H2O as a solvent and the influence of such a solvent on the molecular weight and on the productivity have been investigated
Solvent Effect on the CO-Ethylene Copolymerization Catalyzed by the System Pd(acetate)2/1,3-bis(diphenylphosphine)propane/Formic acid
No full text
Carbon Monoxide-Ethylene Copolymerization Catalyzed by a Pd(OAc)2/dppp/formic acid System [dppp = 1,3 bis-(diphenylphosphino)propane]
No full textOn the mechanism of the organocatalyzed Beckmann rearrangement of cyclohexanone oxime by trifluoroacetic acid in aprotic solvent
No full textThe Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam in high yield catalyzed by trifluoroacetic acid in aprotic solvents is described. The influence of the concentration of reagents, intermediates, solvents on reaction rate and selectivity in ɛ-caprolactam is studied. The identification of the key intermediate and its role in the catalysis are reported together with the influence of the acid on the reaction rate. In addition, the study of the hydrolysis reactions of reagent and intermediates highlights what are the parameters that influence the selectivity to ɛ-caprolactam. On the basis of these results a likely catalytic cycle based only on the experimentally verified intermediates is also given
Recommendation for future actions in research and developments
Full text linkThe Sustainable Chemistry Issue Team has been active within the OECD Environment Health and Safety Programme since 1998 and has held many meetings in Germany and in Italy.
Although Italy has organized two meetings (Venice, 1998 and 2001) and has an excellent scientific and technological background in the field, the coordination among research, academy and industry, necessary to undertake actions among the
leader countries of this area, has not yet been activated. At this end the University Ca’ Foscari of Venice, in collaboration with the Istituto Superiore di Sanità (ISS – Italian Institute for Health) that co-ordinates in Italy the OECD activities in the framework of
the Environment, Health and Safety Programme, has organized this Workshop aimed to the establishment of the Italian network on green and sustainable chemistry.
The connection with EU achievements and with the recently instituted OECD Green Growth Knowledge Platform has been highlighted.
The first part of the Workshop has addressed European activities carried out in this field. OECD, EuCheMS, UNESCO have participated. The second part, organised in collaboration with pertinent Italian ministries, universities, public research institutes and industries has highlighted the different point of views inherent to the sustainable development and in particular the state of art of the green and sustainable chemistry in Italy in connection with its international perspectives
Carbon monoxide-ethylene copolymerization catalyzed by a Pd(OAc)2/dppp/TsOH system: the promoting effect of water and of the acid
Full text linkSynthesis of phenyl isocyanate and derivates via oxidative carbonylation of aniline catalyzed by Pd(II)-based redox systems
No full textOne of the challenges in current day catalysis is to replace wasteful and dangerous industrial processes by more environmentally friendly and safer ones. An example of such a challenge is to replace the highly toxic and corrosive phosgene often used as carbonylating agent. An important example, from an industrial point of view, is represented by the synthesis of isocyanates, starting materials for the production of polyurethanes, actually performed by treating amines with phosgene. Among the numerous phosgene-free methods reported in the literature to produce isocyanates, carbamates and ureas, the reductive carbonylation of nitro compounds and the direct oxidative carbonylation of amines represents a valid alternative to the traditional methods. The Pd-catalyzed carbonylation of aniline to phenylisocyanate, phenylcarbamate or 1,3-diphenylurea has been deeply studied and appears particularly attractive from the standpoint of atom economy. In such a systems, the catalyst consists of a Pd(II) salt that, to form the desiderated products, is reduced to inactive Pd(0) species. The reoxidation of such species to Pd(II) active ones is a key step which permits the restarting of the catalytic cycle. As a matter of fact, the direct reoxidation of Pd(0) species by molecular oxygen is so slow that the precipitation of inactive palladium metal (palladium black) often competes with the reoxidation itself, making inefficient the catalysis. Several methods have been proposed and developed to circumvent this problem mainly based on two strategies which can work at the same time: 1) the stabilization of reoxidable Pd(0) complexes, avoiding the formation of Pd metal; 2) the increasing of the Pd(0) reoxidation rate. An interesting proposal widely adopted in literature is to increase the rate of Pd(0) reoxidation step by inserting an electron-transfer mediator (ETM) between the substrate-selective catalyst and O2 or H2O2 as terminal oxidant. This ETM would then carry the electrons from the metal to the oxidant along a low-energy pathway which would compete kinetically with side reactions of the reduced form of the metal (precipitation, decomposition). Actually, the ETM’s (redox cocatalysts) proposed in literature are mainly metal compounds of varying valences. Salts of Cu, Fe, Ag and heteropolyacids like H3PMo12O40 are the most frequently used cocatalysts, which are able to oxidize Pd(0) to Pd(II), allowing to restart the main reaction cycle. In the present work we synthesized directly phenyl isocyanate through the oxidative carbonylation of aniline catalyzed by a Pd(II)-based multistep redox system in which oxygen is used as terminal oxidant
- …
