Mechanism of formation of organic carbonates from aliphatic alcohols and carbon dioxide under mild conditions promoted by carbodiimides. DFT calculation and experimental study

Dicyclohexylcarbodiimide (CyN=C=NCy, DCC) promotes the facile formation of organic carbonates from aliphatic alcohols and carbon dioxide at temperatures as low as 310 K and moderate pressure of CO2 (from 0.1 MPa) with an acceptable rate. The conversion yield of DCC is quantitative, and the reaction has a very high selectivity toward carbonates at 330 K; increasing the temperature increases the conversion rate, but lowers the selectivity. A detailed study has allowed us to isolate or identify the intermediates formed in the reaction of an alcohol with DCC in the presence or absence of carbon dioxide. The first step is the addition of alcohol to the cumulene (a known reaction) with formation of an O-alkyl isourea [RHNC(OR')=NR] that may interact with a second alcohol molecule via H-bond (a reaction never described thus far). Such an adduct can be detected by NMR. In alcohol, in absence of CO2, it converts into a carbamate and a secondary amine, while in the presence of CO2, the dialkyl carbonate, (RO)2CO, is formed together with urea [CyHN-CO-NHCy]. The reaction has been tested with various aliphatic alcohols such as methanol, ethanol, and allyl alcohol. It results in being a convenient route to the synthesis of diallyl carbonate, in particular. O-Methyl-N,N'-dicyclohexyl isourea also reacts with phenol in the presence of CO2 to directly afford for the very first time a mixed aliphatic-aromatic carbonate, (MeO)(PhO)CO. A DFT study has allowed us to estimate the energy of each intermediate and the relevant kinetic barriers in the described reactions, providing reasonable mechanistic details. Calculated data match very well the experimental results. The driving force of the reaction is the conversion of carbodiimide into the relevant urea, which is some 35 kcal/mol downhill with respect to the parent compound. The best operative conditions have been defined for achieving a quantitative yield of carbonate from carbodiimide. The role of temperature, pressure, and catalysts (Lewis acids and bases) has been established. As the urea can be reconverted into DCC, the reaction described in this article may further be developed for application to the synthesis of organic carbonates under selective and mild conditions.     

Intercalation of tris-(2,2′-bipyridyl) ruthenium (II) in α- and γ-zirconium phosphate: synthesis, thermal behaviour and X-ray characterization

Intercalation compounds such as the ruthenium trisbipyridyl complex in inorganic layered ion-exchangers (α- and γ-zirconium phosphate) have been synthesized using the batch method. There is no loss of bipyridyl ligand from the metal ion during the exchange of the ruthenium trisbipyridyl complex in these host matrices. The materials obtained are thermally stable up to ~330 °C (γ-phase) or ~380 °C (α-phase). The complex decomposition occurs in one or more steps and at ~600 °C the complex decomposition is complete. The X-ray patterns of ruthenium materials show a new phase with an increase in the interlayer distance with respect to the initial phase. Microanalysis measurements confirm the fact that the ruthenium complex is not modified when exchanged and the complex decomposition depends on its position in the host matrices.     

Supply chain cooperation in industrial districts: A simulation analysis

In the past few years the literature on supply chain management has widely emphasized that cooperation among supply chain (SC) firms is a key source of competitive advantage. This paper explores the topic in a particular context, i.e. the industrial district (ID), which constitutes a specific production model where complex SC networks can be identified. SC cooperation may take on several forms in IDs and may produce several benefits (e.g. upgrading quality and reducing costs) so this paper also analyzes the benefits of a specific form of SC cooperation in different competitive scenarios and for diverse ID organizational structures. An agent-based model of SC cooperation in IDs has been developed and a simulation analysis carried out.     

Thermal behaviour of g-zirconium phosphate intercalation compounds with template surfactants

Long chain alkylammonium cations can be exchanged into a preswelled phase of g-zirconium phosphate, a layered inorganic ion-exchanger. The derived materials are used as templates to give organic-inorganic composite materials. The cationic exchange occurs very quickly. These intercalation compounds behave in a very similar way. They are still layered and exhibit an interlayer distance d notably greater than that of its precursor whose behavior depends on the chain length. By thermal and microanalyser characterizations it can be observed that the surfactant is lost in two stages, the second one as a result of the fragmentation of the chain. The layered structure with the expanded interlayer distance is maintained up to ~350°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Updating of a lumped model for an experimental web tension control system using a multivariable optimization method

The modelling and the control of web handling systems have been studied for a long time; correct modelling is necessary in order to design a better control system or to identify the plant parameters experimentally. On the web dynamics itself, lumped parameters expressions may be used to designate a web section between two adjacent drive rolls, and there is the necessity of incorporating the property of viscoelasticity to the web.     

Evidence for spontaneous release of acrylates from a transition-metal complex upon coupling ethene or propene with a carboxylic moiety or CO(2)

The development of a new synthetic approach to acrylates based on the formation of alkyl esters of acrylic acids has been studied. A preformed Pd-COOMe moiety is used as a model system to investigate the insertion of an olefin into the Pd--C bond. The fast elimination of acrylate is observed. Density functional calculations support the experimental findings and allow the characterization of transition states along the reaction pathway. The first example of olefin/CO(2) coupling with facile release of ethyl acrylate is also presented.     

New catalytic system for the hydrogenation of ketones

Alcohols are produced in high yield by hydrogenation of several aliphatic and aromatic ketones with rhodium complexes as catalysts in the presence of strong alkali.     

Rhodium and iridium complexes containing nitrosoarene ligands

A number of new nitrosoarene complexes of rhodium(I) and iridium(I) have been prepared, and characterized by elemental analysis, IR spectroscopy and ¹H NMR spectroscopy. Some reactions of the complexes have been studied.     

Reactivity of mono- and di-methoxycarbonyl complexes of Pd towards amines and copper amine complexes: role of copper in the catalyzed palladium-copper oxidative carbonylation of amines

The reactivity of mono- and di-methoxycarbonyl complexes of palladium of formula [PdL₂Cl_2-n(COOCH₃)_n] (n = 1 or 2; L₂ = chelating ligand) towards amines in the presence of [RNH₃]Cl or CuCl₂ has been studied. The reactions yield N,N′-disubstituted ureas or carbamates, respectively. These results are compared with the dioxygen-induced carbonylative oxidation of amines catalyzed by palladium-based systems.     

A kinematic approach based on an equivalent track for a skid-steering vehicle

The skid-steering principle is based on controlling the relative velocities of both the tracks as differential drive wheeled vehicles. However, control of tracked locomotion poses a more complex problem because variation of the relative velocity of the two tracks results often in slippage of the vehicle [1]. It is possible to define a kinematic approach able to describe and to improve the motion control and dead-reckoning of a skid-steering robot by considering the effects of the slippage but without introducing the complexity of dynamics computation. The equivalent track approach has been applied to a skid-steering robot characterized by an high maximum payload (75 kg) and by a high power than makes it able to move in very difficult conditions (snow, iced terrains, mud) where the slippage effects become predominant. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)