Complexes of copper(II) with 3-(ortho-substituted phenylhydrazo)pentane-2,4-diones: syntheses,properties and catalytic activity for cyclohexane oxidation

Reactions of copper(II) with 3-phenylhydrazopentane-2,4-diones X-2-C6H4-NHN = C{C(= O)CH3}(2) bearing a substituent in the ortho-position [X = OH (H2L1) 1, AsO3H2 (H3L2) 2, Cl (HL3) 3, SO3H (H2L4) 4, COOCH3 (HL5) 5, COOH (H2L6) 6, NO2 (HL7) 7 or H (HL8) 8] lead to a variety of complexes including the monomeric [CuL4(H2O)(2)]center dot H2O 10, [CuL4(H2O)(2)] 11 and [Cu(HL4)(2)(H2O)(4)] 12, the dimeric [Cu-2(H2O)(2)(mu-HL2)(2)] 9 and the polymeric [Cu(mu-L-6)](n)] 13 ones, often bearing two fused six-membered metallacycles. Complexes 10-12 can interconvert, depending on pH and temperature, whereas the Cu(II) reactions with 4 in the presence of cyanoguanidine or imidazole (im) afford the monomeric compound [Cu(H2O)(4){NCNC(NH2)(2)}(2)](HL4)(2)center dot 6H(2)O 14 and the heteroligand polymer [Cu(mu-L-4)(im)](n) 15, respectively. The compounds were characterized by single crystal X-ray diffraction (complexes), electrochemical and thermogravimetric studies, as well as elemental analysis, IR, H-1 and C-13 NMR spectroscopies (diones) and ESI-MS. The effects of the substituents in 1-8 on the HOMO-LUMO gap and the relative stability of the model compounds [Cu(OH)(L-8)(H2O)]center dot H2O, [Cu(L-1)(H2O)(2)]center dot H2O and [Cu(L-4)(H2O)(2)]center dot H2O are discussed on the basis of DFT calculations that show the stabilization follows the order: two fused 6-membered > two fused 6-membered/5-membered > one 6-membered metallacycles. Complexes 9, 10, 12 and 13 act as catalyst precursors for the peroxidative oxidation (with H2O2) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H2O (total yields of ca. 20% with TONs up to 566), under mild conditions.

Desenvolvimento de quelantes macrocíclicos para complexação de iões metálicos de transição e lantanídeos com interesse em aplicações médicas

A investigação de novos compostos macrocíclicos tetraaza tem sido intensificada ao longo das últimas décadas, uma vez que estes estão entre os melhores ligandos para complexação de iões metálicos. Desta forma, tanto a síntese destes compostos, como as propriedades dos seus complexos com iões metálicos provocaram o seu crescente interesse em variadíssimas áreas, das quais são exemplo a medicina, a biologia, a catálise, e a química analítica. Procuram-se ligandos específicos para determinados iões metálicos, mas que ao mesmo tempo se preparem por processos de síntese simples e eficazes que permitam uma maior utilização ao nível industrial. Com este trabalho procurou-se dar continuidade aos estudos desenvolvidos nesta área desde 1980 pelo grupo de investigação onde me encontro inserida e assim obter ligandos novos com vista à formação de complexos com iões metálicos estáveis e aplicáveis ao nível da medicina e da farmacologia, com destaque para as aplicações relacionadas com o diagnóstico e a terapia de tumores. Assim, foram sintetizados quatro novos ligandos derivados de macrociclos tetraaza com 12 átomos no anel, dois deles com ponte cruzada curta tipo etano. A síntes baseou-se na funcionalização destes macrociclos com braços pendentes metilnitrofenol ou metilfenol, originando assim os seguintes compostos: cb-do2nph, do2nph, cb-do2ph e do do2ph. Todos os compostos sintetizados foram caracterizados por diversas técnicas analíticas. Os compostos cb-do2nph e do2nph mostraram reduzida solubilidade em água e em metanol:água, pelo que não foi possível a determinação de constantes por potenciometria. Preparam-se alguns complexos que se estudaram em solução por espectroscopia electrónica e no estado sólido por difracção de raios X. O composto do2ph só se obteve em pequena quantidade sem revelar a pureza necessária e, a sua síntese ainda terá de ser optimizada. Finalmente, o composto cb-do2ph foi sintetizado em quantidade suficiente para se poderem determinar as suas constantes de protonação e as constantes de estabilidade dos seus complexos com Cu 2+ e Zn 2+, pelo método potenciomátrico, em solução aquosa, à temperatura de 298,2 K e à força iónica 0,10M em N(CH 3)4NO3. Determinaram-se ainda por potenciometria as constantes de protonação bem como as constantes de estabilidade dos complexos com Mg2+, Cu2+, Zn 2+, Fe3+, Ga3+, In3+, Gd3+, do composto cbdbf-do2a, igualmente em solução aquosa, à temperatura de 298,2K e à força iónica 0,10M em N(CH 3)4NO3. Para ambos os compostos, cb-do2ph e cbdbf-do2a, recorreu-se a titulações por espectroscopia de RMN de 1H para a determinação da primeira constante, por esta ter um valor muito elevado (log K1 ≥ 14), ou seja, estes compostos comportaram-se como “esponjas de protão”. Para obter informações estruturais dos complexos de alguns ligandos com cobre (II) realizaram-se estudos por espectroscopia de absorção de UV-Vis e de RPE, tendo-se ainda obtido cristais de tamanho suficiente para a determinação de estruturas por difracção de raios X de alguns compostos e complexos de cobre (II) e Zinco(II).

Greener Selective Cycloalkane Oxidations with Hydrogen Peroxide Catalyzed by Copper-5-(4-pyridyl)tetrazolate Metal-Organic Frameworks

Microwave assisted synthesis of the Cu(I) compound [Cu(µ4-4-ptz)]n [1, 4-ptz = 5-(4-pyridyl)tetrazolate] has been performed by employing a relatively easy method and within a shorter period of time compared to its sister compounds. The syntheses of the Cu(II) compounds [Cu3(µ3-4-ptz)4(µ2-N3)2(DMF)2]n∙(DMF)2n (2) and [Cu(µ2-4-ptz)2(H2O)2]n (3) using a similar method were reported previously by us. MOFs 1-3 revealed high catalytic activity toward oxidation of cyclic alkanes (cyclopentane, -hexane and -octane) with aqueous hydrogen peroxide, under very mild conditions (at room temperature), without any added solvent or additive. The most efficient system (2/H2O2) showed, for the oxidation of cyclohexane, a turnover number (TON) of 396 (TOF of 40 h−1), with an overall product yield (cyclohexanol and cyclohexanone) of 40% relative to the substrate. Moreover, the heterogeneous catalytic systems 1–3 allowed an easy catalyst recovery and reuse, at least for four consecutive cycles, maintaining ca. 90% of the initial high activity and concomitant high selectivity.

Effects of copper on the photosynthesis of intact chloroplasts: interaction with manganese

Highly purified, intact chloroplasts were prepared from pea (Pisum sativum L.) and spinach (Spinacia oleracea L.) following an identical procedure, and were used to investigate the cupric cation inhibition on the photosynthetic activity. In both species, copper inhibition showed a similar inhibitor concentration that decreases the enzyme activity by 50% (IC(50) approximately 1.8 microM) and did not depend on the internal or external phosphate (Pi) concentration, indicating that copper did not interact with the Pi translocator. Fluorescence analysis suggested that the presence of copper did not facilitate photoinhibition, because there were no changes in maximal fluorescence (F(m)) nor in basal fluorescence (F(o)) of copper-treated samples. The electron transport through the photosystem II (PSII) was also not affected (operating efficiency of PSII-F'v/F'm similar in all conditions). Yet, under Cu(2+) stress, the proportion of open PSII reaction centers was dramatically decreased, and the first quinone acceptor (Q(A)) reoxidation was fully inhibited, as demonstrated by the constant photochemical quenching (q(P)) along experiment time. The quantum yield of PSII electron transport (Phi(PSII)) was also clearly affected by copper, and therefore reduced the photochemistry efficiency. Manganese, when added simultaneously with copper, delayed the inhibition, as measured by oxygen evolution and chlorophyll fluorescence, but neither reversed the copper effect when added to copper-inhibited plastids, nor prevented the inhibition of the Hill activity of isolated copper-treated thylakoids. Our results suggest that manganese competed with copper to penetrate the chloroplast envelope. This competition seems to be specific because other divalent cations e.g. magnesium and calcium, did not interfere with the copper action in intact chloroplasts. All results do suggest that, under these conditions, the stroma proteins, such as the Calvin-Benson cycle enzymes or others are the most probable first target for the Cu(2+) action, resulting in the total inhibition of chloroplast photosynthesis and in the consequent unbalanced rate of production and consumption of the reducing power.

Bioconversion of D-glucose into D-glucosone by Glucose 2-oxidase from Coriolus versicolor at Moderate Pressures

Glucose 2-oxidase (pyranose oxidase, pyranose: oxygen-2-oxidoreductase, EC 1.1.3.10) from Coriolus versicolor catalyses the oxidation of D-glucose at carbon 2 in the presence of molecular O(2) producing D-glucosone (2-keto-glucose and D-arabino-2-hexosulose) and H(2)O(2). It was used to convert D-glucose into D-glucosone at moderate pressures (i.e. up to 150 bar) with compressed air in a modified commercial batch reactor. Several parameters affecting biocatalysis at moderate pressures were investigated as follows: pressure, [enzyme], [glucose], pH, temperature, nature of fluid and the presence of catalase. Glucose 2-oxidase was purified by immobilized metal affinity chromatography on epoxy-activated Sepharose 6B-IDA-Cu(II) column at pH 6.0. The rate of bioconversion of D-glucose increased with the pressure since an increase in the pressure with compressed air resulted in higher rates of conversion. On the other hand, the presence of catalase increased the rate of reaction which strongly suggests that H(2)O(2) acted as inhibitor for this reaction. The rate of bioconversion of D-glucose by glucose 2-oxidase in the presence of either nitrogen or supercritical CO(2) at 110 bar was very low compared with the use of compressed air at the same pressure. The optimum temperature (55 degrees C) and pH (5.0) of D-glucose bioconversion as well as kinetic parameters for this enzyme were determined under moderate pressure. The activation energy (E(a)) was 32.08 kJmol(-1) and kinetic parameters (V(max), K(m), K(cat) and K(cat)/K(m)) for this bioconversion were 8.8 Umg(-1) protein, 2.95 mM, 30.81 s(-1) and 10,444.06 s(-1)M(-1), respectively. The biomass of C. versicolor as well as the cell-free extract containing glucose 2-oxidase activity were also useful for bioconversion of D-glucose at moderate pressures. The enzyme was apparently stable at moderate pressures since such pressures did not affect significantly the enzyme activity.

Bioconversion of D-glucose into D-glucosone by immobilized glucose 2-oxidase from Coriolus versicolorat moderate pressures

The immobilized glucose 2-oxidase (pyranose oxidase, pyranose:oxygen-2-oxidoreductase, EC 1.1.3.10) from Coriolus versicolor was used to convert D-glucose into D-glucosone at moderate pressures, up to 150 bar, with compressed air in a modified commercial batch reactor. Several parameters affecting biocatalysis at moderate pressures were investigated as follows: pressure, different forms of immobilized biocatalysts, glucose concentration, pH, temperature and the presence of catalase. Glucose 2-oxidase (GOX2) was purified by immobilized metal affinity chromatography on epoxy-activated Sepharose 6B-IDA-Cu(II) column at pH 6.0. Purified enzyme and catalase were immobilized into a polyethersulfone (PES) membrane in the presence of glutaraldehyde and gelatin. Enhancement of the bioconversion of D-glucose was done by the pressure since an increase in the pressure with compressed air increases the conversion rates. The optimum temperature and pH for bioconversion of D-glucose were found to be 62 degrees C and pH 6.0, respectively and the activation energy (E(a)) was 28.01 kJ mol(-1). The apparent kinetic constants (V(max)' K(m)', K(cat)' and K(cat)/K(m)') for this bioconversion were 2.27 U mg(-1) protein, 11.15 mM, 8.33 s(-1) and 747.38 s(-1) M(-1), respectively. The immobilized biomass of C. versicolor as well as crude extract containing GOX2 activity were also useful for bioconversion of D-glucose at 65 bar with a yield of 69.9 +/- 3.8% and 91.3 +/- 1.2%, respectively. The immobilized enzyme was apparently stable for several months without any significant loss of enzyme activity. On the other hand, this immobilized enzyme was also stable at moderate pressures, since such pressures did not affect significantly the enzyme activity. (C) 2010 Elsevier Ltd. All rights reserved.

Chromatographic behaviour of monoclonal antibodies against wild-type amidase from Pseudomonasaeruginosa on immobilized metal chelates

The aim of this work was to devise a one-step purification procedure for monoclonal antibodies (MAbs) of IgG class by immobilized metal affinity chromatography (IMAC). Therefore, several stationary phases were prepared containing immobilized metal chelates in order to study the chromatographic behaviour of MAbs against wild-type amidase from Pseudomonas aeruginosa. Such MAbs adsorbed to Cu(II), Ni(II), Zn(II) and Co(II)-IDA agarose columns. The increase in ligand concentration and the use of longer spacer arms and higher pH values resulted in higher adsorption of MAbs into immobilized metal chelates. The dynamic binding capacity and the maximum binding capacity were 1.33 +/- 0.015 and 3.214 +/- 0.021 mg IgG/mL of sedimented commercial matrix, respectively. A K(D) of 4.53 x 10(-7) M was obtained from batch isotherm measurements. The combination of tailor-made stationary phases of IMAC and the correct selection of adsorption conditions permitted a one-step purification procedure to be devised for MAbs of IgG class. Culture supernatants containing MAbs were purified by IMAC on commercial-Zn(II) and EPI-30-IDA-Zn(II) Sepharose 6B columns and by affinity chromatography on Protein A-Sepharose CL-4B. This MAb preparation revealed on SDS-PAGE two protein bands with M(r) of 50 and 22 kDa corresponding to the heavy and light chains, respectively. Copyright (C) 2011 John Wiley & Sons, Ltd.

Development of a biosensor for urea assay based on amidase inhibition, using an ion-selective electrode

A biosensor for urea has been developed based on the observation that urea is a powerful active-site inhibitor of amidase, which catalyzes the hydrolysis of amides such as acetamide to produce ammonia and the corresponding organic acid. Cell-free extract from Pseudomonas aeruginosa was the source of amidase (acylamide hydrolase, EC 3.5.1.4) which was immobilized on a polyethersulfone membrane in the presence of glutaraldehyde; anion-selective electrode for ammonium ions was used for biosensor development. Analysis of variance was used for optimization of the biosensorresponse and showed that 30 mu L of cell-free extract containing 7.47 mg protein mL(-1), 2 mu L of glutaraldehyde (5%, v/v) and 10 mu L of gelatin (15%, w/v) exhibited the highest response. Optimization of other parameters showed that pH 7.2 and 30 min incubation time were optimum for incubation ofmembranes in urea. The biosensor exhibited a linear response in the range of 4.0-10.0 mu M urea, a detection limit of 2.0 mu M for urea, a response timeof 20 s, a sensitivity of 58.245 % per mu M urea and a storage stability of over 4 months. It was successfully used for quantification of urea in samples such as wine and milk; recovery experiments were carried out which revealed an average substrate recovery of 94.9%. The urea analogs hydroxyurea, methylurea and thiourea inhibited amidase activity by about 90%, 10% and 0%, respectively, compared with urea inhibition.

The effect of the angle of incidence on the aqueous corrosion of ion implanted M50 steel substrates

Following work on tantalum and chromium implanted flat M50 steel substrates, this work reports on the electrochemical behaviour of M50 steel implanted with tantalum and chromium and the effect of the angle of incidence. Proposed optimum doses for resistance to chloride attack were based on the interpretation of results obtained during long-term and accelerated electrochemical testing. After dose optimization from the corrosion viewpoint, substrates were implanted at different angles of incidence (15°, 30°, 45°, 60°, 75°, 90°) and their susceptibility to localized corrosion assessed using open-circuit measurements, step by step polarization and cyclic voltammetry at several scan rates (5–50 mV s-1). Results showed, for tantalum implanted samples, an ennoblement of the pitting potential of approximately 0.5 V for an angle of incidence of 90°. A retained dose of 5 × 1016 atoms cm-2 was found by depth profiling with Rutherford backscattering spectrometry. The retained dose decreases rapidly with angle of incidence. The breakdown potential varies roughly linearly with the angle of incidence up to 30° falling fast to reach -0.1 V (vs. a saturated calomel electrode (SCE)) for 15°. Chromium was found to behave differently. Maximum corrosion resistance was found for angles of 45°–60° according to current densities and breakdown potentials. Cr+ depth profiles ((p,γ) resonance broadening method), showed that retained doses up to an angle of 60° did not change much from the implanted dose at 90°, 2 × 1017 Cr atoms cm-2. The retained implantation dose for tantalum and chromium was found to follow a (cos θ)8/3 dependence where θ is the angle between the sample normal and the beam direction.

Halogen-bonded tris (2,4-Bis(trichloromethyl)-1,3,5,triazapentadienato)-M(III) [M = Mn, Fe, Co] complexes and their catalytic activity in the peroxidative oxidation of 1-phenylethanol to acetophenone

One-pot template condensation of CCl3C=N with ammonia on a metal source [MnCl2 center dot 4H(2)O, FeCl3 center dot 6H(2)O or Co(CH3COO)(2)center dot 4H(2)O] in DMSO led to the formation of tris(2,4-bis(trichloromethyl)-1,3,5-triazapentadienato)-M(III) complexes, [M(NH=C(CCl3)NC(CCl3)=-NH}(3)]center dot n(CH3)(2)SO [M = Mn, n = 1 (1); M = Fe, n = 2 (2); M = Co, n = 2 (3)1, which were characterized using elemental analysis, and IR, ESI-MS and single-crystal X-ray analysis. The role of inter- and intramolecular non-covalent halogen and hydrogen bonds in the synthesis of 1-3 is discussed. It is shown that the crystal ionic radii of the metal ions [68.5 (Co) < 69 (Fe) < 72 (Mn), pm] are related to the corresponding Cl center dot center dot center dot Cl distances [3.178 (3) > 3.155 (2) > 3.133 (1) Al. Compounds 1-3 and the related di(triazapentadienato)-Cu(v) complex [Cu(NH=C(CCl3)NC(CCl3)=NH}2]center dot 2(CH3)(2)SO (4) act as catalyst precursors for the additive-free microwave (MW) assisted homogeneous oxidation of 1-phenylethanol with tert-butylhydroperoxide (TBHP), leading to the formation of acetophenone with yields up to 99% and TONs up to 5.0 x 10(3) after 1 h of low power (10 W) MW irradiation.

The solvation and electrochemical behaviour of Copper acetylacetonate complexes in ionic liquids

The behavior of copper(II) complexes of pentane-2,4-dione and 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, [Cu(acac)(2) (1) and [Cu(HFacac)(2)(H2O)] (2), in ionic liquids and molecular organic solvents, was studied by spectroscopic and electrochemical techniques. The electron paramagnetic resonance characterization (EPR) showed well-resolved spectra in most solvents. In general the EPR spectra of [Cu(acac)(2)] show higher g(z) values and lower hyperfine coupling constants, A(z), in ionic liquids than in organic solvents, in agreement with longer Cu-O bond lengths and higher electron charge in the copper ion in the ionic liquids, suggesting coordination of the ionic liquid anions. For [Cu(HFacac)(2)(H2O)] the opposite was observed suggesting that in ionic liquids there is no coordination of the anions and that the complex is tetrahedrically distorted. The redox properties of the Cu(II) complexes were investigated by cyclic voltammetry (CV) at a Pt electrode (d = 1 mm), in bmimBF(4) and bmimNTf(2) ionic liquids and, for comparative purposes, in neat organic solvents. The neutral copper(II) complexes undergo irreversible reductions to Cu(I) and Cu(0) species in both ILs and common organic solvents (CH2Cl2 or acetonitrile), but, in ILs, they are usually more easier to reduce (less cathodic reduction potential) than in the organic solvents. Moreover, 1 and 2 are easier to reduce in bmimNTf(2) than in bmimBF(4) ionic liquid. (C) 2013 Elsevier B.V. All rights reserved.

Growth of (Perylene)(2) [PD(MNT)(2)] crystals

The conditions for [pd(mnt)(2)]he growth of [pd(mnt)(2)]Perylene) [pd(mnt)(2)] [Pd(mnt) [pd(mnt)(2)]] crystals either by chemical oxidation and electrochemical routes are [pd(mnt)(2)]escribed. The electrocrystallisation is limited by close [pd(mnt)(2)]roximity of [pd(mnt)(2)]he oxidation [pd(mnt)(2)]otentials of [pd(mnt)(2)]he [pd(mnt)(2)]erylene [pd(mnt)(2)]onor and [Pd(mnt) [pd(mnt)(2)]] - anion, and [pd(mnt)(2)]epending on [pd(mnt)(2)]he experimental conditions [pd(mnt)(2)]ifferent [pd(mnt)(2)]orphologies can be obtained. [pd(mnt)(2)]Per) [pd(mnt)(2)] [Pd(mnt) [pd(mnt)(2)]] crystals obtained by elecrocrystallisation were found [pd(mnt)(2)]o be [pd(mnt)(2)]ainly of [pd(mnt)(2)]he β-polymorph with [pd(mnt)(2)]roperties comparable [pd(mnt)(2)]o [pd(mnt)(2)]he Cu, Ni and Pt analogues [pd(mnt)(2)]reviously [pd(mnt)(2)]escribed at variance with [pd(mnt)(2)]hose obtained by chemical oxidation which are [pd(mnt)(2)]ainly of [pd(mnt)(2)]he α-polymorph.

Y Trinuclear Cu-II structural isomers coordination, magnetism, electrochemistry and catalytic activity towards the oxidation of alkanes

The reaction of the Schiff base (3,5-di-tert-butyl-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H3L) with copper(II) nitrate, acetate or metaborate has led to the isomeric complexes [Cu-3(L)(2)(MeOH)(4)] (1), [Cu-3(L)(2)(MeOH)(2)]2MeOH (2) and [Cu-3(L)(2)(MeOH)(4)] (3), respectively, in which the ligand L exhibits dianionic (HL2-, in 1) or trianionic (L3-, in 2 and 3) pentadentate 1O,O,N:2N,O chelation modes. Complexes 1-3 were characterized by elemental analysis, IR spectroscopy, single-crystal X-ray crystallography, electrochemical methods and variable-temperature magnetic susceptibility measurements, which indicated that the intratrimer antiferromagnetic coupling is strong in the three complexes and that there exists very weak ferromagnetic intermolecular interactions in 1 but weak antiferromagnetic intermolecular interactions in both 2 and 3. Electrochemical experiments showed that in complexes 1-3 the Cu-II ions can be reduced, in distinct steps, to Cu-I and Cu-0. All the complexes act as efficient catalyst precursors under mild conditions for the peroxidative oxidation of cyclohexane to cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone, leading to overall yields (based on the alkane) of up to 31% (TON = 1.55x10(3)) after 6 h in the presence of pyrazinecarboxylic acid.

Mn-II and Cu-II complexes with arylhydrazones of active methylene compounds as effective heterogeneous catalysts for solvent- and additive-free microwave-assisted peroxidative oxidation of alcohols

A one-pot template reaction of sodium 2-(2-(dicyanomethylene) hydrazinyl) benzenesulfonate (NaHL1) with water and manganese(II) acetate tetrahydrate led to the mononuclear complex [Mn(H2O)(6)](HL1a)(2)center dot 4H(2)O (1), where (HL1a) -= 2-(SO3-)C6H4(NH)=N=C(C N) (CONH2) is the carboxamide species derived from nucleophilic attack of water on a cyano group of (HL1) . The copper tetramer [Cu-4(H2O)(10)(-) (1 kappa N: kappa O-2: kappa O, 2 kappa N: k(O)-L-2)(2)]center dot 2H(2)O (2) was obtained from reaction of Cu(NO3)(2)center dot 2.5H(2)O with sodium 5-(2( 4,4-dimethyl-2,6-dioxocyclohexylidene) hydrazinyl)-4-hydroxybenzene-1,3-disulfonate (Na2H2L2). Both complexes were characterized by elemental analysis, IR spectroscopy, ESI-MS and single crystal X-ray diffraction. They exhibit a high catalytic activity for the solvent-and additive-free microwave (MW) assisted oxidation of primary and secondary alcohols with tert-butylhydroperoxide, leading to yields of the oxidized products up to 85.5% and TOFs up to 1.90 x 103 h(-1) after 1 h under low power (5-10 W) MW irradiation. Moreover, the heterogeneous catalysts are easily recovered and reused, at least for three consecutive cycles, maintaining 89% of the initial activity and a high selectivity.