Carlo Carlini

Selective saccharides dehydration to 5-hydroxymethyl-2-furaldehyde by heterogeneous niobium catalysts

Selective dehydration of different substrates, such as fructose, sucrose and inulin, to 5-hydroxymethyl-2-furaldehyde has been studied in aqueous medium by using heterogeneous niobium-based catalysts. Batch experiments have been performed in the presence of both commercial niobium phosphates and catalysts prepared by treatment of niobic acid with phosphoric acid. Flow experiments on catalyst packed beds have been also examined. Finally, batch catalytic experiments, characterized by combination of reaction and products extraction steps, have been also carried out.

Acid sites characterization of niobium phosphate catalysts and their activity in fructose dehydration to 5-hydroxymethyl-2-furaldehyde

Abstract The nature of different acid sites on the surface of various niobium-based catalysts has been spectroscopically investigated by means of FT-IR and UV–VIS techniques. Surface acidity has been further characterized by acetonitrile adsorption and subsequent FT-IR analysis. The catalytic activity of the different examined samples has been preliminarily tested in the fructose dehydration to 5-hydroxymethyl-2-furaldehyde, a reaction of relevant industrial interest.

Selective synthesis of isobutanol by means of the Guerbet reaction: Part 2: Reaction of methanol/ethanol and methanol/ethanol/n-propanol mixtures over copper based/MeONa catalytic systems

The synthesis of isobutanol via the Guerbet condensation between methanol and ethanol was studied by using sodium methoxide (MeONa) as soluble basic component and copper-based catalysts as heterogeneous dehydrogenating/hydrogenating metal species. The effect of the nature of the catalyst and the relative amount of its individual components with respect to the reacting alcohols as well as of temperature on productivity and selectivity of the process was investigated. The collected data indicated that the copper chromite/MeONa was more active than Cu-Raney/MeONa system. The reaction was shown to proceed with the formation only of n-propanol and isobutanol. Ethanol conversion up to 61% with selectivity to isobutanol up to 98.4% was obtained. The same catalytic systems were also employed in the reaction of the methanol/ethanol/n-propanol ternary mixture. Again copper chromite/MeONa resulted more active than the Cu-Raney/MeONa system. Finally, experiments were carried out on methanol/n-propanol mixtures in the presence of the copper chromite/MeONa catalytic system by recycling both the recovered solid copper component and the liquid reaction mixture for evidencing eventual copper leaching by MeONa. On the basis of the obtained results it was concluded that in the Guerbet reaction copper chromite works as heterogeneous catalyst.

Ethylene oligomerization by novel catalysts based on bis(salicylaldiminate)nickel(II) complexes and organoaluminum co-catalysts

The reactivity of bis(salicylaldiminate)nickel(II) complexes ( I) with organoaluminum compounds under ethylene atmosphere, eventually in the presence of an ancillary phosphine ligand, has been studied by UV–VIS spectroscopy. When a large excess of methylaluminoxane (MAO) (Al/Ni molar ratio = 100) was used, in absence of phosphine ligands, the formation of an alkyl(monosalicylaldiminate)nickel(II) species absorbing at about 380 nm, active in the oligomerization of ethylene, was supposed to occur. Accordingly, when an equimolar I/phosphine mixture was treated with an excess of MAO (Al/Ni molar ratio = 100) an analogous absorption band was detected and the subsequent addition of an equivalent amount of Et3Al was supposed to cause the formation of the corresponding [alkyl(phosphino)monosalicylaldiminate)]nickel(II) species, as evidenced by 31 P-NMR analysis. The catalytic behavior of the homogeneous systems prepared in situ from I and different organoaluminum co-catalysts in the activation of ethylene was also investigated. In particular, the effect of reaction parameters, such as temperature and PC2H4 , as well as the type of salicylaldiminate ligand in the nickel precursor, the Al/Ni molar ratio and eventually the presence of a phosphine ancillary ligand, was studied. The catalysts evidenced very high activity with turnover frequencies (TOFs) up to 10 5 –10 7 h −1 , mainly oriented to the oligomerization rather than to the polymerization of ethylene. Changing the nature of I and reaction parameters it was possible to strongly modify the chemo- and regioselectivity of the catalytic process towards the formation of target olefin products, particularly 1-hexene. Depending on the type of I, minor amounts of polymeric products were also obtained. The heterogenization of the catalysts, either by precipitation in n-hexane of the reaction product from I and MAO, or by anchoring I to a SiO2-bound MAO, in order to increase the formation of polyethylene through a matrix effect, was also described.

Polymeric photoinitiators having benzoin methylether moieties connected to the main chain through the benzyl aromatic ring and their activity for ultraviolet-curable coatings

Abstract New polymeric UV photoinitiators, bearing the benzoin methyl ether moiety linked to the side chain through the 4′ position, were synthetized by radical homopolymerization of the corresponding monomers, 4′-methacryloyloxy benzoin methyl ether and 4′-methacryloyloxy α-methyl benzoin methyl ether, prepared in turn after a thorough investigation of synthetic methods. For comparison, low molecular weight structural models of the repeating co-units of the polymers having the pivaloyloxy group linked to the 4′ position of the benzoin methyl ether moiety were also prepared. All polymeric and model compounds were fully characterized and employed in the photoinitiated polymerization and crosslinking of a standard acrylic formulation for clear UV curable coatings. The photoinitiating activity of these systems, measured by microwave dielectrometry, indicates a higher cure fastness for the model compounds with respect to the corresponding polymeric derivatives, and such a behaviour is tentatively interpreted in terms of the fragmentation mechanism of the benzyl methyl ether radicals formed on α-photocleavage of the benzoin moiety.

Synthesis, chiroptical properties and photoresponsive behaviour of optically active poly[(S)-4-(2-methacryloyloxypropanoyloxy)azobenzene]

Abstract A novel optically active monomer containing a photochromic chromophore, such as trans-(S)-4-(2-methacryloyloxypropanoyloxy)azobenzene and its low molecular weight model compound trans-(S)-4-(2-pivaloyloxypropanoyloxy)azobenzene were prepared. Free radically initiated homopolymerization of the methacrylic monomer afforded in fairly high yield a rather high molecular weight polymer which was molecularly and structurally characterized. The molecular mobility of the polymer in all trans configuration, as well as chiroptical properties, photoisomerization kinetics and photochromic behaviour were investigated and compared with those of the low and high molecular weight related compounds. The polymer photoresponsive properties were evaluated by circular dichroism measurements at various extents of photoisomerization. All the results are discussed in terms of structural requirements of the macromolecules.

Synthesis of isobutanol by the Guerbet condensation of methanol with n-propanol in the presence of heterogeneous and homogeneous palladium-based catalytic systems

AbstractThe catalytic synthesis of isobutanol ( i BuOH), via the Guerbet condensation of methanol with n-propanol is described.In particular, bifunctional catalysts based on either heterogeneous or homogeneous dehydrogenating/hydrogenating pal-ladium species and on sodium methoxide (MeONa) as basic component were investigated. When heterogeneous Pd/Cand MeONa was used as catalytic system a high activity was obtained with turnover numbers up to about 110mol of i BuOH/(mol of Pdh). The increase of the MeONa/Pd molar ratio increased the activity of the catalyst. However, differentlyfrom Cu-based/MeONa catalysts, a significant metal leaching was observed; recycle experiments indicated that both hetero-geneous and homogeneous palladium species are involved in the catalysis. When homogeneous palladium complexes, such astetrakis(triphenylphosphine)palladium(0) [Pd(PPh 3 ) 4 ], diphenylphosphinoethane(dichloro)palladium(II) [Pd(dppe)Cl 2 ] andbis(dibenzylideneacetone)palladium(0) [Pd(dba) 2 ], were used in combination with MeONa a remarkable activity was alsoobtained, independently of the oxidation state of the palladium precursor. During the reaction deposition of a solid was ob-served and recycle experiments carried out both on the recovered solid and on the liquid phase suggested that also in this casethe activity has to be addressed to both heterogeneous and homogeneous (or colloidal) palladium species.© 2003 Elsevier Science B.V. All rights reserved.

Light-induced conformational changes in chiral polymers with photochromic side chains

Preparation de polymeres optiquement actifs avec un squelette hydrocarbure et peptide portant des groupes photoisomerisables azobenzene et stilbene dans les chaines laterales par copolymerisation et par modification chimique de polymeres preformes. Etude du comportement photochrome et de la conformation en solution par absorption UV, fluorescence et dichroisme circulaire

Recent advances on photosensitive polymers: Polymeric photoinitiators

This overview deals with recent developments on structure—activity relationships in polymeric photoinitiators for UV curable coatings. In particular, polymeric systems bearing side-chain benzoin methyl ether moieties are examined and the effect on the photoinitiation activity discussed in connection with the different anchorage positions of the photosensitive group to the polymer backbone. In addition, novel polymeric photoinitiators based on acyldiphenylphosphinoxide moieties are discribed and their photoinitiation activity related to the nature of the acyl group in the photoreactive molecule. Finally, polymeric systems having pendant thioxanthone and α-morpholino acetophenone moieties in the same macromolecule that are able to behave as photosensitizing and photoinitiating species, respectively, are reported. The much higher photoinitiation activity found for the above copolymers, compared with the mixtures of the corresponding low molecular weight analogs, is interpreted in terms of excitation energy transfer from the side-chain thioxanthone to α-morpholino acetophenone moieties, favored by their forced proximity along the polymer chain.

Optically active polymers containing side-chain benzophenone chromophores

Abstract Optically active copolymers of (—)menthyl acrylate (MtA) with 4-hydroxybenzophenone acrylate (ABP) have been prepared by radical initiation. Reactivity ratios, mean sequence lengths and the statistical distribution of the sequence lengths of both co-units have been evaluated. Chiroptical properties of the copolymers indicate that a chiral perturbation of side-chain benzophenone chromophores occurs, due to the dissymetric arrangement of the macromolecules. C.d. data in the spectral region connected with the naπ°∗ electronic transition of benzophenone chromophore, combined with statistical distribution of sequence lengths of monomeric units in the macromolecules suggest that the observed ellipticity is essentially due to the isolated ABP units, inserted in blocks of chiral MtA units.