Cristian Gambarotti

Selective functionalisation of hydrocarbons by nitric acid and aerobic oxidation catalysed by N-hydroxyphthalimide and iodine under mild conditions

Alkylbenzenes are selectively functionalised to the corresponding acetates by nitric aerobic oxidation catalysed by N-hydroxyphthalimide and iodine. With cyclohexane the oxidation leads to a mixture of cyclohexyl acetate and trans-2-iodocyclohexyl acetate. The mechanism is discussed.

TiO2 in Organic Photosynthesis: Sunlight Induced Functionalization of Heterocyclic Bases

In the last decades photocatalyzed organic processes have attracted the great interest, due to their low environmental impact. Various oxidation and reduction processes of organic substrates have been developed as alternative routes to the “classical” synthesis of more complex molecules. In this attempt TiO2 is actually largely studied and employed, especially as catalyst in the organic pollutants photodegradation to products with less environmental impact. From the synthetic point of view, the attention has been focused particularly on the TiO2-mediated synthesis of alcohols, carbonyl- and carboxylic- derivatives. Recently our group has developed new TiO2-photocatalyzed synthetic protocols for the functionalization of N heteroaromatic bases as an alternative to the “classic” well known redox metal-catalyzed methods. These substrates are suitable for the nucleophilic free-radical addition and the photocatalytic activity of microcrystalline TiO2 has shown a key role in the success of our protocol.

Sunlight induced functionalisation of some heterocyclic bases in the presence of polycrystalline TiO2

The functionalisation of various heterocyclic bases induced by sunlight is reported. The photoreaction occurred with higher yield in a liquid-solid heterogeneous system in the presence of polycrystalline TiO2 (anatase) than in a homogeneous system under the same experimental conditions.

A green approach to the amidation of heterocyclic bases: the use of sunlight and air

A easy and environmentally friendly method for the photochemical functionalisation of the heterocyclic bases is described. The selective introduction of the amido group of formamide, using sunlight and air in the presence of TiO2, has allowed to obtain the desired products in mild conditions with high conversions. The comparison of these results with those previously reported, in the presence of H2O2 instead of air, clarifies some aspects of the reaction mechanism.

Functionalization of aliphatic polyesters by nitroxide radical coupling

Functionalized poly(butylene succinate) (PBS) samples were prepared by a post-polymerization method based on the coupling reaction between TEMPO derivatives bearing different functionalities and PBS macroradicals generated by H-abstraction using a peroxide. 4-Benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (BzO-TEMPO) and 4-(1-naphthoate)-2,2,6,6-tetramethylpiperidine-1-oxyl (NfO-TEMPO), a pro-fluorescent nitroxide, were successfully grafted on PBS, as revealed by MALDI TOF MS and UV-Vis spectroscopy. The functionalization degrees were accurately determined by UV-Vis analysis and confirmed by 1H-NMR spectroscopy. The grafting site was identified by combining theoretical calculations with experimental evidence. This evidence was collected by both EPR analysis of a functionalized sample subjected to controlled heating in the EPR cavity, and by 1H-NMR spectroscopy. Our functionalization method, which was also tested for poly(lactic acid) (PLA), preserves the original polymer structure. This avoids the crosslinking-branching side reaction, which generally affects the free radical treatment of biodegradable aliphatic polyesters. In addition, using a pro-fluorescent nitroxide to form functionalized samples is a significant step towards unambiguously demonstrating the radical grafting on these types of polymer. It also proves that well-defined fluorescently labeled biodegradable polyesters can be tailored.

Using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry for the characterization of functionalized carbon nanotubes

RATIONALE Functionalization of carbon nanotubes (CNTs) generates complex systems that require the development of suitable characterization protocols. New techniques have been explored, and existing analytical and spectroscopic methods to characterize functionalized CNTs have been adapted. Presently, chemical characterization of functionalized CNTs (f-CNTs) remains a difficult task. METHODS Matrix-assisted laser desorption/ionization (MALDI) analysis is performed on f-MWCNT samples prepared via grafting or absorption of anti-oxidant (AO) molecules on both MWCNT-COOH and MWCNT-OH. Covalently functionalized MWCNTs were subjected to thermal degradation and/or hydrolysis reaction before analysis, whereas MWCNTs with a physical adsorption of the functionalizing molecules were directly spotted in the target sample. Noteworthy, in our approach f-MWCNTs constitute at the same time analyte and MALDI matrix. RESULTS The identification of functionalizing AO molecules is ascertained after degradation or hydrolysis reactions in both MWCNT-COOH and MWCNT-OH grafted samples. Absorbed AO molecules, as well as organic impurities derived from grafting reactions, are also revealed by MALDI MS without any preliminary cleavage reaction. CONCLUSIONS A simple MALDI-TOF mass spectrometry method permits to obtain the unambiguous discrimination between grafted or adsorbed functionalized molecules onto the surface of MWCNTs.

One-pot synthesis of aryloxypropanediols from glycerol: towards valuable chemicals from renewable sources

Glycerol offers an easy and green route for the synthesis of aryloxypropanediols of known pharmacological activity. Glycerol is selectively converted to aryloxypropanediols in a one-pot reaction, through in situ formed glycerol carbonate, under benign and solvent-free conditions. Catalyst and unreacted reagent can be recycled.

A novel, selective free-radical carbamoylation of heteroaromatic bases by Ce(IV) oxidation of formamide, catalysed by N-hydroxyphthalimide

The Ce(IV)-NHPI system was used to generate a carbamoyl radical by oxidation of formamide; this nucleophilic radical has been successfully used in the carbamoylation of heteroaromatic bases.

Advanced nano-hybrids for thermo-oxidative-resistant nanocomposites

In the present work, trisilanol phenyl polyhedral olygomeric silsesquiosane (TSPh-POSS) has been physically immobilized onto carbon nanotubes (CNTs) bearing covalently linked Br-terminated long-alkyl chain (Br-alkyl-f-CNTs), and the so obtained hybrid nanoparticles (Br-alkyl-f-CNTs/TSPh-POSS) have been used to prepare ultra-high molecular weight polyethylene (UHMWPE)-based nanocomposites with enhanced thermo-oxidative resistance. The effective immobilization of the TSPh-POSS molecules has been confirmed by spectroscopic and thermo-gravimetric analyses. Besides, the influence of the hybrid nanoparticles on the rheological and mechanical behaviour and morphology of the nanocomposites have been fully investigated. The obtained results show that the rheological and thermo-mechanical behaviour of UHMWPE/Br-alkyl-f-CNTs/TSPh-POSS nanocomposite is affected by two different opposite contributions: reinforcement effect of CNTs and plasticizing action induced by TSPh-POSS molecules. The unexpected excellent thermo-oxidative resistance of the nanocomposite containing hybrid nanoparticles seems to be due to a synergistic effect of TSPh-POSS and CNTs. Moreover, TSPh-POSS molecules, upon thermo-oxidative treatment, are able to migrate toward film surface, forming a TSPh-POSS-rich protective layer that hinders the oxygen diffusion.

Immobilization of natural anti-oxidants on carbon nanotubes and aging behavior of ultra-high molecular weight polyethylene-based nanocomposites

The use of natural antioxidants is an attractive way to formulate nanocomposites with extended durability and with potential applications in bio-medical field. In this work, Vitamin E (VE) in the form of α-tocopherol and Quercetin (Q) are physically immobilized on the outer surface of multi-walled carbon nanotubes (CNTs). Afterward, the CNTs-VE and CNTs-Q are used to formulate thermally stable ultra high molecular weight polyethylene based nanocomposites. The obtained results in the study of the thermo-oxidation behavior suggest a beneficial effect of the natural anti-oxidant carbon nanotubes systems. The unexpected excellent thermo-resistance of the nanocomposites seems to be due to a synergistic effect of the natural anti-oxidant and carbon nanotubes, i.e. strong interaction between CNT surface and anti-oxidant molecules. Particularly, these interactions cause the formation of structural defects onto outer CNT surfaces, which, in turn, increase the CNT radical scavenging activity.