Angela Dibenedetto

Utilisation of CO2 as a chemical feedstock: opportunities and challenges

The need to reduce the accumulation of CO(2) into the atmosphere requires new technologies able to reduce the CO(2) emission. The utilization of CO(2) as a building block may represent an interesting approach to synthetic methodologies less intensive in carbon and energy. In this paper the general properties of carbon dioxide and its interaction with metal centres is first considered. The potential of carbon dioxide as a raw material in the synthesis of chemicals such as carboxylates, carbonates, carbamates is then discussed. The utilization of CO(2) as source of carbon for the synthesis of fuels or other C(1) molecules such as formic acid and methanol is also described and the conditions for its implementation are outlined. A comparison of chemical and biotechnological conversion routes of CO(2) is made and the barriers to their exploitation are highlighted.

Carbon dioxide as building block for the synthesis of organic carbonates: Behavior of homogeneous and heterogeneous catalysts in the oxidative carboxylation of olefins

Abstract The increasing world market of organic carbonates demands for the development of new synthetic methodologies, alternative to phosgene which represents the starting material for their conventional synthesis. Innovative technologies based on CO 2 are attracting much attention as they are environmentally acceptable and may respond to the atom-economy principle. The oxidative carboxylation of olefins catalyzed by homogeneous or heterogeneous catalysts has a good potential as it uses simple starting materials to produce valuable chemicals. In this paper the conversion of styrene into styrene carbonate is discussed with emphasis on the reaction mechanism and product distribution considering either homogeneous or heterogeneous catalysts.

Nb(V) compounds as epoxides carboxylation catalysts: the role of the solvent

The synthesis of organic cyclic carbonates from epoxides and CO2 is described. The role of the solvent is discussed, together with that of Nb(V) catalysts (Nb2O5 and NbCl5). The reaction is very selective and affords the conversion of epoxides into the relevant carbonates in high yield.

Direct synthesis of organic carbonates by oxidative carboxylation of olefins catalyzed by metal oxides : developing green chemistry based on carbon dioxide

In this paper we report on the ‘oxidative-carboxylation’ of olefins catalysed by either transition metal complexes or metal oxides. We discuss the oxidation mechanism under homogeneous and heterogeneous conditions. In the former case the process is driven by co-ordination to the metal centre, in the latter a radical reaction takes place. The yield of carbonate is strongly dependent on the catalyst used. Copyright

Biorefinery : from biomass to chemicals and fuels

This book provides an introduction to the basic science and technologies for the conversion of biomass (terrestrial and aquatic) into chemicals and fuels, as well as an overview of innovations in the field. The entire value chain for converting raw materials into platform molecules and their transformation into final productsare presented in detail. Both cellulosic and oleaginous biomassare considered.Thebook contains contributionsby both academic scientists and industrial technologists so that each topic combines state-of-the-art scientific knowledge with innovative technologies relevant to chemical industries.

Reaction of silylalkylmono- and silylalkyldi-amines with carbon dioxide: evidence of formation of inter- and intra-molecular ammonium carbamates and their conversion into organic carbamates of industrial interest under carbon dioxide catalysis

The reactivity of industrially relevant silylalkylamines towards CO2 and dialkyl/arylcarbonates is discussed. The kinetics of uptake of carbon dioxide at various temperatures shows that at 295 K, silylalkylmonoamines react with carbon dioxide in a 2∶1 molar ratio, affording classic intermolecular ammonium carbamates of formula RNHCOO−+NH3R, while at 273 K, dimeric carbammic acids, (RNHCOOH)2, are formed. Conversely, silylalkyldiamines react at 297 K with carbon dioxide to afford zwitterionic intramolecular six-membered cyclic ammonium carbamates of formula RNH2+CH2CH2NHCOO−, a unique example of CO2 uptake by an amine with a 1∶1 molar ratio. Such systems may have a potential application in CO2 separation. The catalytic role of carbon dioxide in the carbamation of the above mentioned amines by reaction with organic carbonates is described.

The first synthesis of a cyclic carbonate from a ketal in SC-CO2

Abstract In this paper the synthesis of a cyclic organic carbonate by a halogen-free route is described. The ketal formed from cyclohexanone and 1,2-ethanediol was reacted with carbon dioxide, either in SC-CO2 or in organic solvents under CO2 pressure. Transition-metal complexes with functionalized fluorinated di-ketone ligands were used as catalyst. The synthetic methodology based on SC-CO2 is effective for the synthesis of ethylene carbonate. The use of methanol as co-solvent in SC-CO2 prevents the formation of the ethylene carbonate and only the alcoholysis of the ketal is observed. In organic solvents, no reaction takes place.

Enantioselective synthesis of organic carbonates promoted by Nb(IV) and Nb(V) catalysts

In this paper, we describe the use of Nb(IV) and Nb(V) catalysts in the carboxylation of either pure enantiomers of chiral epoxides or racemic mixtures. The carboxylation of pure enantiomers with Nb(V)-oxide is very selective (100%), proceeds with a good TON and occurs with total retention of the configuration. Optically active Nb(IV) complexes have been synthesised and used in the conversion of a racemic mixture of epoxides. An enantiomeric excess (ee, up to 22%) has been observed, that varies with the catalyst and the reaction conditions. The enantiomeric excess depends on the liability of the chiral ligands on Nb(IV).

Synthesis, Characterization, and Use of NbV/CeIV‐Mixed Oxides in the Direct Carboxylation of Ethanol by using Pervaporation Membranes for Water Removal

New catalytic systems based on ceria have been used in the direct carboxylation of ethanol. The catalytic behavior of Al(2)O(3) and Nb(2)O(5) loaded ceria is compared, the latter showing a better performance. A morphological and structural study has been carried out on Nb(2)O(5)/CeO(2) catalysts in order to explain their behavior in catalysis. Pervaporation membranes have been used for water separation. The synthesis of diethylcarbonate (DEC) has been carried out either in a liquid phase (ethanol) pressurized with CO(2) or in supercritical conditions. A set-up has been developed that allows the production of quite pure DEC (>90%) with recycling of CO(2) and ethanol.

Reaction of aromatic diamines with diphenylcarbonate catalyzed by phosphorous acids: a new clean synthetic route to mono- and dicarbamates

Abstract In the presence of organophosphorus acids [Ph 2 P(O)OH, (PhO) 2 P(O)OH, (BuO) 2 P(O)OH, (BuO)P(O)(OH) 2 ], aromatic diamines, such as 4,4′-methylendianiline (MDA) or 2,4-diaminotoluene (TDA), react with diphenylcarbonate (DPC) to afford in a very selective way mono- and dicarbamate phenyl esters. The carbamation process is strongly influenced by the temperature and solvent. The influence of both these factors on carbamate yield and selectivity has been investigated and we present in this study the kinetics of formation of both mono- and dicarbamate esters.