Glauco Sbrana

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.

Infrared spectra and reactivity of DI-μ-halobis(halotricarbonylruthenium)

The IR spectra of the di-μ-halobis(halotricarbonylruthenium) complexes of formula [Ru(CO)3X2]2 (X = Cl, Br) have been studied in different solvents and a tentative assignment of the bands observed made. The change with time of the IR spectra in chloroform solution observed by several authors is due to the interaction of the compounds with the ethanol present in the solvent as stabilizer. The reactions of [Ru(CO)3X2]2 (X = Cl, Br) with oxygenated solvents, nitrogen and phosphorous ligands are described. Some complexes of type RuX2(CO)3L and RuX2(CO)2L2 (L = nitriles, pyridine or triphenylphosphine) have been isolated and characterized.

Anionic ruthenium iodorcarbonyl complexes as selective dehydroxylation catalysts in aqueous solution

The selective dehydroxylation in aqueous solution of C3C5 polyols and C6 sugars in the presence of homogeneous ruthenium iodocarbonyl catalysts, [Ru(CO)3I3]− species, has been studied. Glycerol, pure or in dilute aqueous solution, is dehydroxylated to give n-propanol and its ethers with selectivities of up to 90%. Xylitol and C6 sugars, glucose and fructose, are dehydrated and hydrogenated through initial formation of levulinic acid to give γ-valerolactone with high yields. The dehydroxylation of these polyhydroxylic substrates is made possible in water solution by the bifunctional nature (acidity and hydrogenating ability) of the ruthenium catalytic system. The requirements necessary for the catalytic system to be active and stable in water have been studied, and the mechanism of the reaction discussed.

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.

Selective synthesis of octadienyl and butenyl ethers via reaction of 1,3-butadiene with alcohols catalyzed by homogeneous palladium complexes

The selective synthesis, by telomerization of 1,3-butadiene with alcohols in the presence of palladium catalysts, both of octadienyl ethers (especially from higher linear primary alcohols) and of butenyl ethers is reported. The variation of the alcohol/diene molar ratio plays a decisive role in both the cases, excess of alcohol favouring in the former case the synthesis of octadienyl ethers with respect to octatrienes, being useful in the latter case, together with other factors such as high P/Pd and low Pd/diene molar ratios, to favour the formation of butenyl ethers. It has in fact been discovered that, for palladium catalysts, the formation of butenyl ethers is ruled by a complex mechanism involving both the reversible formation of butenyl ethers and their direct transformation into octadienyl ethers.

Copolymerization of ethylene with methyl methacrylate by ziegler-natta-type catalysts based on nickel salicylaldiminate/methylalumoxane systems†

Bis(salicylaldiminate)nickel(II) complexes, such as bis[N(2,6-diisopropylphenyl) salicylaldiminate]nickel(II) and bis(N-isopropylsalicylaldiminate)nickel(II), were activated by methylalumoxane (MAO) to give catalytic systems able to copolymerize ethylene (E) with methyl methacrylate (MMA), thus producing low molecular weight copolymers with a rather high content of MMA co-units (50- 80 mol-%). On the contrary, when catalytic systems, obtain- ed by oxidative addition of salicylaldimine ligands such as 5-nitro-N-(2,6-diisopropylphenyl)salicylaldimine (NPS) and 3,5-dinitro-N-(2,6-diisopropylphenyl)salicylaldimine (DNPS) to bis(cyclooctadienyl)nickel(0) [Ni(cod) 2 ], were activated with MAO, high viscometric average molecular weight (M v 10-30 × 10 4 Da) E/MMA copolymers with a low content of MMA co-units (3-6 mol-%) were formed, thus allowing to obtain directly by synthesis functionalized highly linear poly(ethylene)s (T m up to 130 °C) to be potentially applied as new materials with improved surface properties.

Homogeneous telomerization of 1,3-butadiene with alcohols in the presence of palladium catalysts modified by hybrid chelate ligands

Abstract 1,3-Butadiene telomerization with methanol and higher alcohols was investigated in the presence of different palladium(0) and palladium(II) complexes based on hybrid chelate ligands. When P ∩ O ligands were used, the resulting palladium complexes displayed poor activity and low selectivity to telomers, also in the presence of alkoxide promoters. Even worse performances were found when ionic palladium(II) or neutral palladium(0) and palladium(II) complexes based on N ∩ N chelate ligands were employed in combination with alkoxide promoters. Better results were obtained by using ionic palladium(II) complexes with P ∩ N ∩ N ligands in combination with an alkoxide promoter. Very promising results were achieved when the telomerization reaction was catalyzed by palladium(0) complexes obtained in situ from Pd(dba) 2 and P ∩ N ligands. The data are discussed and interpreted in terms of different capability of the chelate ligands, depending on their size and donor power, to give palladium complexes with metal sites at low oxidation state characterized at the same time by a sufficient stability and coordinative unsaturation to promote high catalytic activity and selectivity.