Search

The iron metalation of the known free‐base porphyrins H2P2 and H2P3, obtained by structural modification of the well‐known TPPF20 (H2P1) with galactose dendritic units, gave the corresponding iron(III) porphyrin complex FeP2 and the solid hybrid material FeP3S. Their synthesis, characterization and catalytic efficacy toward the oxidation of the organic substrates (Z)‐cyclooctene, cyclohexane and heptane, are reported. In this work, the possibility to modulate selectivity and chemical efficiency of the catalytic system by using simple and more sophisticated metalloporphyrins is demonstrated. Furthermore, the presence of the galactose dendrimer units at the meso‐porphyrin ring positions can tune the oxidation at the terminal positions in linear alkanes. In addition, the FeP3S material was easily recovered and reused at least 3 times for the cyclooctene oxidation. The catalytic performance of material FeP3S, associated with their possibility of reuse, makes this material a promising catalyst. [ABSTRACT FROM AUTHOR]

Abstract: It is well established that the transformation of abundant and cheap natural products, such as terpenoids, can produce other more valuable compounds. Thymoquinone, which has a commercial value significantly higher than that of its precursors, can be obtained by oxidation of carvacrol and thymol. In this work, a new water‐soluble MnIII PEG‐porphyrin is reported as catalyst in a water/hexane (1:1) biphasic medium for the oxidation of carvacrol and thymol into thymoquinone. The reactions were performed using tert‐butyl hydroperoxide as oxidant in the presence of ammonium acetate as co‐catalyst, reaching 94 and 78 % of conversion after 5 h of reaction for thymol and carvacrol, respectively. Experiments with oregano essential oil as substrate revealed selective transformation of thymol and carvacrol into thymoquinone. The main advantage of this biphasic system based on a water‐soluble catalyst and on substrates and products soluble in hexane, is the straightforward isolation, recovery and recycling of the catalyst by simple phase separation. Recycling studies of the MnIII PEG‐porphyrin using thymol as substrate showed high conversion values throughout four catalytic cycles. [ABSTRACT FROM AUTHOR]

The synthesis and structural characterization of novel metal-organic-framework-type materials obtained from the reaction of 5,10,15,20-tetrakis[2,3,5,6-tetrafluoro-4-(4-pyridylsulfanyl)phenyl]porphyrin ( H2P1) and 5,10,15,20-tetrakis(4-pyridyl)porphyrin ( H2P2) with copper(II) acetate is reported. The new material, CuP1S, shows higher heterogeneous catalytic activity than the homogeneous porphyrin-copper(II) complex CuP1 in the oxidation of catechol into ortho-benzoquinone in the presence of air (O2) or H2O2 (30 %). [ABSTRACT FROM AUTHOR]

New sulfonyl-lapachones were efficiently obtained through the catalytic oxidation of arylthio- and cyclohexylthio-lapachone derivatives with hydrogen peroxide in the presence of a Mn(III) porphyrin complex. The antibacterial activities of the non-oxidized and oxidized lapachone derivatives against the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus aureus were evaluated after their incorporation into polyvinylpyrrolidone (PVP) micelles. The obtained results show that the PVP-formulations of the lapachones 4b-g and of the sulfonyl-lapachones 7e and 7g reduced the growth of S. aureus. [ABSTRACT FROM AUTHOR]

Porphyrin-based Metal-Organic Frameworks (Por-MOFs) constitute a special branch of the wide MOF family that has proven its own value and high potential in different applications. In this mini-review the application of these materials as catalysts in oxidation reactions is highlighted. [ABSTRACT FROM AUTHOR]

Synthetic metalloporphyrins are catalysts that can efficiently insert oxygen and other atoms such as nitrogen and sulfur in hydrocarbons and in a wide variety of other organic compounds. This work reports on a synthetic strategy to prepare new metalloporphyrins via structural modification of [5,10,15,20-tetrakis (pentafluorophenyl)porphyrin], or [H 2 (TPFPP)], with 4-mercaptobenzoic acid; it also describes their characterization and catalytic activity. The substituent groups present in the structure of the resulting porphyrins furnished structured solids, which could potentially serve as catalysts in heterogeneous medium. Investigation of the catalytic activity of the new derivatives in the oxidation of (Z)-cyclooctene, cyclohexane, and heptane, under homogeneous conditions, and in the oxidation of (Z)-cyclooctene, in heterogeneous medium, proved that the new metalloporphyrins constituted excellent catalysts for (Z)-cyclooctene epoxidation. As for alkane oxidation, they selectively gave the corresponding alcohol in good yields. [ABSTRACT FROM AUTHOR]

Following our approach on the use of metalloporphyrins as catalysts and hydrogen peroxide as oxidant in the oxidation of organosulfur compounds (e.g. sulfides, benzothiophenes and dibenzothiophenes), herein the excellent catalytic performance of a homogeneous iron(III) porphyrin complex is demonstrated. Beyond the better results obtained, when compared with those with manganese(III) complexes, the present procedure involves a cleaner approach because ethanol is used as solvent and a co-catalyst is not required. For all the studied substrates (1-10), conversions higher than 95% were achieved with Fe(TF4NMe2PP)Cl (I). More significantly, catalyst (I) is also efficient in the oxidation of a model fuel, constituted by a mixture of benzothiophene (3), 3-methylbenzothiophene (5), 4-methyldibenzothiophene (8) and 4,6-diethyldibenzothiophene (10) in hexane, affording an overall conversion of 84%. [ABSTRACT FROM AUTHOR]

Three-dimensional graphene oxide foam (3DGO) was found to be a highly efficient and recyclable catalyst for the oxidation of thioanisole. We found that 3DGO is more efficient than 2DGO, and that the efficiency increases with the number of cycles for 3DGO, in contrast to the 2D counterpart. [ABSTRACT FROM AUTHOR]

Metalloporphyrins (MPs) are known to catalyze in vitro a broad range of cytochrome P450-mediated reactions occurring in vivo. Most of the biomimetic research using MPs in oxidative catalysis has been directed towards the oxidation of organic compounds presenting significant reactivity features in one functional group. Much less effort has been made to imitate the oxidation of more complex molecules, with a range of functionalities, such as drugs or other xenobiotics. By varying the structure of the porphyrin, the metal ion, the oxidant, and the reaction conditions, it is possible to modulate the regioselectivity of the oxidation reactions. Recently, and along with studies on the synthesis and reactivity of porphyrins, chlorins, and phthalocyanines, our group was able to develop an interesting line of research in the field of biomimetic oxidation of organic compounds using environmentally benign hydrogen peroxide as oxidant and Mn(III) or Fe(III) porphyrin complexes as catalysts. The more up to date results obtained in such work are reviewed here. [ABSTRACT FROM AUTHOR]

Abstract: The oxidation of styrene and derivatives with H2O2 catalyzed by manganese porphyrins in acetonitrile is described. The effect of the imidazolium substituent on the catalytic efficiency has been also considered. The thermodynamic analysis has indicated that enthalpy rules styrene oxidation when catalysts Mn(Porph)-1 and Mn(Porph)-2 are used whereas the entropy is the driven force for Mn(Porph)-3 and Mn(Porph)-4 catalyzed reactions. Interestingly, an enthalpy–entropy compensation phenomenon is observed when comparing the thermodynamic results obtained for catalysts Mn(Porph)-3 and Mn(Porph)-4. Hammett plots for the studied manganese porphyrins provided small ρ-values, and this is typical for multi-step reactions, indicating that there is no significant charge separation in the transition state. For Mn(Porph)-1 and Mn(Porph)-2 the formation of multiple active species can be put forward whereas for Mn(Porph)-3 and Mn(Porph)-4 a concerted-type mechanism, via metalloxetane intermediate, fits well with the values obtained for those catalysts. The imidazolium-based catalysts have shown to be efficient catalysts in styrene and derivatives oxidation with hydrogen peroxide. [Copyright &y& Elsevier]

Abstract: The biomimetic oxidation of caffeine with hydrogen peroxide using metalloporphyrins as catalysts, which are known to be good biomimetic models of cytochrome P450 enzymes, is investigated. The two manganese porphyrins tested, chloro[5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinato]manganese(III), [Mn(TDCPP)Cl], and chloro [5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]manganese(III), [Mn(TPFPP)Cl], afford high conversions of caffeine for all substrate/catalyst molar ratios. Selectivity was found to be dependent on the catalyst employed, and a new spiro racemic compound is described and fully characterized in the solid state from X-ray diffraction studies. [Copyright &y& Elsevier]

Abstract: In the past few years, borohydrides have gathered a lot of attention as an energy carrier for fuel cell application. Numerous investigations on both hydrogen generation and direct oxidation of NaBH4 have been published. Nonetheless, in our knowledge, only a few catalysts are capable to completely perform the direct oxidation of NaBH4 at low potentials without hydrogen evolution. In this work, carbon supported Pd1−x Bi x /C and Pt1−x Bi x /C nanocatalysts were synthesized by a “water in oil” microemulsion method. The influence of surface modifications of Pt and Pd by Bi on the electrooxidation of sodium borohydride in alkaline media was evaluated. Physical and electrochemical methods were applied to characterize the structure and surface of the synthesized catalysts. It was verified that bismuth is present at the surface of the bimetallic catalysts and that hydrogen adsorption/desorption reactions are strongly limited on Pt and Pd surfaces with high bismuth coverage. Although the onset potential for NaBH4 oxidation on Pd x Bi1−x /C catalysts is ca. 0.2V higher than that for Pd/C, the presence of bismuth on palladium surface influences the reaction mechanism, limiting hydrogen evolution and oxidation in the case of Pd0.8Bi0.2 catalyst. On Pt0.9Bi0.1 catalyst the onset potential remains unchanged comparing to Pt/C and negligible hydrogen evolution was observed in the whole potential range where the catalyst is active. The number of exchanged electrons was calculated using the Koutecky–Levich equation and it was found that for Pt0.9Bi0.1 catalyst, ca. 8 electrons are exchanged per BH4 − ion at low potentials. The presented results are remarkable evidencing that NaBH4 can be directly oxidized at low potentials with high energy efficiency. [Copyright &y& Elsevier]

Abstract: Carbon supported Pd, Pt, Au and bimetallic PdAu and PdNi nano-catalysts with different compositions were synthesized. Their catalytic activity toward glycerol electro-oxidation was evaluated in alkaline medium. Physical and electrochemical methods where used to characterize the structure and the surface of the catalysts. It was shown that the Pd x Au1−x /C catalysts were alloys, which present an increase of crystallite (XRD) and particle (TEM) sizes with increasing Au atomic fraction. Their surfaces were palladium rich whatever the Pd atomic ratio. The structure of the Pd0.5Ni0.5/C catalyst is much more difficult to understand, but it seems to be composed of a palladium phase in interaction with a Ni(OH)2 phase. The onset potential of glycerol oxidation is ca. 0.15V lower on Pt/C than on Pd/C and Au/C. All Pd x Me1−x /C catalysts presented lower onset potential than monometallic Au/C and Pd/C ones, but higher than Pt/C. For bimetallic catalysts, the order of activity at low potentials is: Pd0.3Au0.7/C>Pd0.5Au0.5/C>Pd0.5Ni0.5/C. Electrochemical experiments and in situ infrared spectroscopy measurements have shown that glycerol electro-oxidation mechanism is dependent on the catalyst, leading to different reaction products. Adsorbed CO species are detected on monometallic Pt and on Pd rich catalysts, but not on Au and Pd0.3Au0.7 catalysts, indicating that they are not able to break the C–C bond. The formation of hydroxypyruvate ion, which is a costly chemical product, is detected on pure gold catalyst. [Copyright &y& Elsevier]

Abstract: The homogeneous liquid phase oxidation of indane and tetralin with hydrogen peroxide catalysed by tetrabutylammonium salts of iron(III)-substituted polyoxotungstates of general formula [XW11Fe(H2O)O39] n−, X=P, Si or B is described. The system presented here gives rise to benzylic monooxygenation and dioxygenation products. Indane oxidation reactions produce also dehydrogenation and hydroperoxidation products. As a result, 1H-indene and indane hydroperoxide are formed. Interestingly, tetralin gives rise to the cleavage of carbon–carbon bond, producing 4-(2-hydroxyphenyl)butanal. In the present conditions, this aldehyde is probably arising from tetralin hydroperoxide. Depending on the reaction conditions, moderate selectivities for the corresponding ketones are obtained, affording conversions as high as 59% and 34% for indane and tetralin, respectively. In order to understand the reactions pathway, the oxidation of 1-indanol, 1-indanone, 1H-indene, 1-tetralol and 1-tetralone is also carried out with an iron(III)-substituted polyoxotungstate as catalyst and H2O2 as oxidant. The results show that 1-indanol and 1-tetralol give an important contribution for the formation of the corresponding ketones. As far as we know, the use of iron-substituted polyoxotungstates in the oxidation of these arenes is presented for the first time. [Copyright &y& Elsevier]

The oxidation of 1 H-indene and 1,2-dihydronaphthalene with hydrogen peroxide in the presence of Mn(III) or Fe(III) substituted Keggin-type polyoxotungstates is described. The products obtained depend on the catalyst and reaction conditions. Ring cleavage was observed, affording dialdehydes under mild and environmentally friendly conditions. Other main products were the α-hydroxy-ketones. The resulting epoxides seem to be intermediates to other oxygenated products. [ABSTRACT FROM AUTHOR]

Abstract: Several manganese(III) porphyrin complexes were evaluated as catalysts in the oxidation of indane and tetralin with hydrogen peroxide, in the presence of ammonium acetate as a co-catalyst. Catalysis by Mn(III) meso-tetra-2,6-dichlorophenylporphyrins gave rise, in a first stage, to benzylic monooxygenation products (1-alcohols and 1-ketones). However, addition of excess of oxidant gave rise to over-oxidation products and, in certain conditions, hydroxy-keto compounds were selectively obtained. Reactions catalysed by Mn(III) meso-tetra-pentafluorophenylporphyrins showed higher capability to generate dehydrogenated products. As a result, 1H-indene and naphthalene were formed. To understand the reactions’ pathway, the oxidations of 1-indanol, 1-indanone, 2-indanol, 1H-indene, 1-tetralol, 1-tetralone, 1,4-dihydroxytetralin and 4-hydroxy-1-tetralone were also considered with manganese (III) meso-tetra-2,6-dichlorophenylporphyrin chloride, Mn(TDCPP)Cl, as catalyst. [Copyright &y& Elsevier]

The catalytic homogeneous oxidation of cyclohexane and cyclooctane in acetonitrile with hydrogen peroxide in the presence of the tetrabutylammonium salts of Keggin-type polyoxotungstates [XW11O39]n- and [XW11MO39](n-m)- (X=P, Si, B and MIII=Fe, Mn) afforded substantial amounts of the corresponding alkyl hydroperoxides. The cyclododecane oxidation reactions only gave rise to the alcohol and ketone. Under the used reaction conditions, high turnover numbers were obtained, reaching 614 in the cyclooctane oxidation after 9 h of reaction. These oxidation reactions appear to be radical processes, since they were totally inhibited in the presence of 2,6-di-tert-butyl-4-methylphenol or I2, two well-known radical scavengers. [Copyright &y& Elsevier]

The first remarkable property associated to metallophthalocyanines (MPcs) was their chemical "inertness", which made and make them very attractive as stable and durable industrial dyes. Nevertheless, their rich redox chemistry was also explored in the last decades, making available a solid and detailed knowledge background for further studies on the suitability of MPcs as redox catalysts. An overlook of MPcs and their catalytic activity with dioxygen as oxidants will be discussed here with a special emphasis on the last decade. The mini-review begins with a short introduction to phthalocyanines, from their structure to their main features, going then through the redox chemistry of metallophthalocyanines and their catalytic activity in aerobic oxidation reactions. The most significant systems described in the literature comprise the oxidation of organosulfur compounds such as thiols and thiophenes, the functionalization of alkyl arenes, alcohols, olefins, among other substrates. [ABSTRACT FROM AUTHOR]

The synthesis, characterisation and homogeneous catalytic oxidation results of two manganese(III) porphyrins of the so-called second-generation of metalloporphyrin catalysts, containing one or four 3,5-dichloropyridyl substituents at the meso positions are reported for the first time. The catalytic efficiency of these novel manganese(III) porphyrins was evaluated in the oxidation of cyclooctene and styrene using aqueous hydrogen peroxide as the oxidant, under homogeneous conditions. High conversions were obtained in the presence of both catalysts, obtaining the corresponding epoxide as the major product. The asymmetric metalloporphyrin, chloro[5,10,15-tris(2,6-dichlorophenyl)-20-(3,5-dichloropyridin-4-yl)porphyrinate]manganese(III), CAT-4, evidences a similar activity to that obtained with the well-known and highly efficient second-generation metalloporphyrin catalyst, chloro[5,10,15,20-tetrakis(2,6-dichlorophenyl)porphyrinate]manganese(III), CAT-2. CAT-4 was covalently attached onto Merrifield resin and 3-bromopropylsilica supports. The solid materials obtained were characterized by several techniques including diffuse reflectance, UV—VIS spectrophotometry, SEM and XPS. The catalytic results for the oxidation of cyclooctene and styrene using the immobilized catalysts are also presented. The Merrifield-supported catalyst showed to be very efficient, leading to five catalytic cycles in the oxidation of cyclooctene, using tert-butyl hydroperoxide as the oxidant. [ABSTRACT FROM AUTHOR]

The catalytic efficiency and selectivity of a series of manganese(III) complexes of meso -tetrakis(pentafluorophenyl)porphyrin H 2 (TPFPP) derivatives bearing one to four ethylene glycol moieties are compared in the oxidation of cis -cyclooctene and cyclohexane in the presence of H 2 O 2 at ambient temperature. The results show that the catalysts’ performance depends on the number of ethylene glycol moieties present and on the cocatalyst used; for both substrates, the most efficient catalyst in the presence of H 2 O 2 is the Mn(III) complex bearing three ethylene glycol moieties (MnP 3 ). Moreover, in the oxidation of cyclohexane in the presence of iodosylbenzene (PhIO) as oxidant, all the substituted Mn(III) complexes are more efficient than the parent non-substituted Mn(III) porphyrin complex. In addition, during the preparation of this series of derivatives, the tetrasubstituted free-base porphyrin (P 4 ) was further isolated and studied in the solid state, by using single-crystal X-ray diffraction studies. [ABSTRACT FROM AUTHOR]

A new catalytic system based on an immobilized imidazolyl manganese porphyrin for the oxidation of olefins is presented. Merrifield resin (MR) and functionalized silica gel (SG) were chosen as supports. The results indicate that the MR system shows high reaction rates, high efficiency with hydrogen peroxide as oxidant and good recyclability up to four times, without a dramatic loss in the catalytic efficiency. The catalytic behavior seems to be strongly influenced by the immobilization reaction conditions. The oxidation reactions performed for cis -cyclooctene, styrene, cyclohexene and geraniol give the corresponding epoxides, with very high selectivity, when the MR system is used. Some considerations concerning the high efficiency of the MR system are put forward. [ABSTRACT FROM AUTHOR]

Highlights: [•] Iron(III) enzymes involved on indigo synthesis were mimicked for dye production. [•] Indole is oxidized by H2O2 in the presence of a Fe(III)porphyrin in ethanol. [•] A simpler and more efficient methodology is obtained relatively to bio-catalysis. [•] The yields of indigo and indolinoid co-products were dependent on the metalloporphyrin system. [•] The results were justified by the formation of different active species. [ABSTRACT FROM AUTHOR]

Highlights: [•] Indole is oxidized by H2O2 in the presence of Mn(III)porphyrins in mild conditions. [•] The biomimetic oxidation of indole can replace biocatalytic and natural processes. [•] Optimization of the reaction allowed the isolation of indigo and indirubin pigments. [•] 2-Oxoindole, isatin, indoxyl and other coupling derivatives were produced. [•] The reaction has relevance for biomedical studies and dye industry. [Copyright &y& Elsevier]

Abstract: The preparation and characterization (FT-IR, FT-Raman, 11B MAS NMR, diffuse reflectance, elemental analysis) of a novel boron peroxotungstate (BTBA)4H[BW4O24] (BTBA=benzyltributylammonium) is reported, along with its use in the homogeneous oxidation of cis-cyclooctene, geraniol, linalool and (−)-carveol with H2O2 as oxidant and acetonitrile as solvent. High catalytic activity was registered for all the substrates studied under homogeneous conditions, namely 99% of conversion of geraniol after 2h, 93% for linalool after 5h, 74% for cis-cyclooctene after 6h, and 100% for (−)-carveol after 2h of reaction. Some oxidation studies were carried out with the Venturello complex, [PW4O24]3−, in the same conditions. Furthermore, the boron peroxotungstate (BW4) was immobilized using two different strategies: (a) BW4 anchored into a functionalized silica (aptesSiO2) giving BW4@aptesSiO2 and (b) BW4 encapsulated on a metal organic framework, commonly referred as MIL-101, giving BW4@MIL-101. The catalytic activity of both heterogeneous materials was investigated for geraniol oxidation and the results were compared with those obtained with BW4 under homogeneous conditions. The encapsulated boron peroxotungstate (BW4@MIL-101) gave rise to the best results, reaching complete conversion of geraniol after 3h of reaction and 78% selectivity for 2,3-epoxygeraniol. Additionally, this heterogeneous catalyst could be reused without appreciable loss of catalytic activity, affording similar 2,3-epoxygeraniol selectivity. The heterogeneous catalysts’ stability was also investigated after the oxidation reactions by different characterization techniques. [Copyright &y& Elsevier]

Abstract: An integrated methodology for the identification and quantification of linoleic acid hydroperoxides (HPODEs) mixtures, obtained by the Fenton''s reaction and by enzymatic oxidation, is reported. Unambiguous identification of the HPODEs formed (13-hydroperoxy-(9Z,11E)-octadecadienoic acid, 13-hydroperoxy-(9E,11E)-octadecadienoic acid and 9-hydroperoxyoctadecadienoic acid) was performed by HPLC–MS/MS analysis, while quantification was carried out by HPLC–UV using an external calibration, based on the collection of chromatographic peaks, and measuring of total hydroperoxides by ferrous oxidation-xylenol orange (FOX) method. [Copyright &y& Elsevier]

Abstract: Silica nanoparticles supporting polyoxometalates (POMs), namely an iron(III) mono-substituted Keggin-type polyoxotungstate of formula α-[PW11FeIII(H2O)O39]4− and a sandwich-type tungstophosphate with the formula B-α-[(PW9O34)2FeIII 4(H2O)2]6− were synthesized. The POM/SiO2 nanocomposites were obtained by alkaline hydrolysis of tetraethoxysilane using a reverse micelle and sol–gel technique. The spectroscopic studies suggest that the POMs were successfully immobilized on the silica nanoparticles. The catalytic activity of POM/SiO2 nanomaterials was tested in the epoxidation of geraniol using H2O2 as oxygen donor. The α-[PW11FeIII(H2O)O39]4−/SiO2 nanocomposite was the most efficient catalyst with high geraniol conversion and good regioselectivity for 2,3-epoxygeraniol. [ABSTRACT FROM AUTHOR]

Abstract: The preparation and characterization (FT-IR, FT-Raman, diffuse reflectance, elemental analysis) of novel catalysts with iron or manganese substituted polyoxotungstates [XMIII(H2O)W11O39] n− (X=P, M=Fe or Mn; X=Si or B, M=Fe) immobilized on a functionalized silica matrix are reported. The new materials were tested as heterogeneous catalysts in the oxidation of cis-cyclooctene and cyclooctane at 80°C, using environmentally safe hydrogen peroxide as oxidant and acetonitrile as solvent. Some of these novel heterogeneous catalysts could be reused several times without appreciable loss of catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: A new manganese chlorin has been successfully immobilized on a silica matrix by a nucleophilic substitution reaction. The potential application of this new material as a biomimetic oxidation catalyst was tested, using cis-cyclooctene as substrate. Different reaction conditions were studied, including hydrogen peroxide and t-butyl hydroperoxide as oxidants. The new silica-supported manganese chlorin exhibits high catalytic efficiency and a good recyclability was observed with t-butyl hydroperoxide. [Copyright &y& Elsevier]

Abstract: Tetravalent metal phosphates and phosphonates form highly insoluble inorganic polymers and can act as good catalysts in some oxidative reactions. In the present work, zirconium phosphate amorphous (ZrPA), scandium exchanged zirconium phosphate amorphous (ScZrPA), sodium exchanged zirconium phosphate amorphous (NaZrPA), potassium exchanged zirconium phosphate amorphous (KZrPA), zirconium phenylphosphonate amorphous (ZrPPA) and zirconium phenylphosphonate phosphate amorphous (ZrPA/ZrPPA), were prepared and evaluated as catalysts for the oxidation of 3,7,7-trimethylbicyclo[4.1.0]hept-3-ene [(+)-3-carene)] by hydrogen peroxide, in different solvents. It was found that the oxidation reaction of (+)-3-carene yielded three major products, namely α-3,4-epoxycarane, carane-3β,4α-diol and 3β-acetoxycaran-4α-ol, depending on the catalyst and solvent conditions. No β-3,4-epoxycarane was detected in the studied conditions. [Copyright &y& Elsevier]

Abstract: The tetrahexylammonium (THA) salt of the peroxocomplex [W2O3(O2)4]2− was used as catalyst for the oxidation of cis-cyclooctene, geraniol and cyclooctane, with hydrogen peroxide, in acetonitrile. High catalytic activity for all substrates, with high efficiency of use of hydrogen peroxide, was found. Under the conditions used, the oxidation of cyclooctane gives rise to cyclooctanone, cyclooctanol and cyclooctyl hydroperoxide, with 90% and 97% of conversion after 6 and 12h, respectively, reaching turnover numbers higher than 600. A possible mechanism for the oxidation of cyclooctane is proposed. The oxidation of cis-cyclooctene gives the corresponding epoxide with 100% conversion after 4h, whereas geraniol yields mainly the 2,3-epoxide (94% selectivity) with 88% of conversion after 5h of reaction. The crystal structure of (THA)2[W2O3(O2)4] is reported. The anion has two types of coordinated peroxide ligands, namely symmetrical and unsymmetrical bridging peroxo groups. This study indicates that the peroxocomplex [W2O3(O2)4]2− is catalytically active both in epoxidation reactions in acetonitrile and in the oxyfunctionalization of a cycloalkane. [Copyright &y& Elsevier]

Abstract: New evidence concerning the mechanism of oxidation reactions of alkenes and aromatic compounds catalyzed by metalloporphyrins with H2O2 were obtained based on the evaluation of results from structurally different substrates. A systematic change in metalloporphyrin structure and reaction conditions was accomplished with cis-cyclooctene as a model. Two maximum performance systems were obtained and then applied to the oxidation of selected substrates, namely 17β-acetoxy-4-androstene, (+)-3-carene, geraniol, and naphthalene. Substantial differences in reaction conversion and product selectivity were found. These systematic studies confirmed the evidence of two different active oxidation species, assigned as the hydroperoxy or oxo ones. The use of more electronegative porphyrins, iron as central metal, and protic solvent and the absence of co-catalyst favor the formation of a hydroperoxy active species. On the other hand, the oxo species was considered to be the main acting entity in the presence of less electronegative porphyrin ligands, manganese as central atom, aprotic solvent, and a buffering substance as co-catalyst. This state of knowledge makes it possible to modulate the reaction selectivity by the selection of the appropriate catalytic system. [Copyright &y& Elsevier]

The tetrabutylammonium (TBA) salts of the Keggin-type polyoxotungstates [XW12O40]n-, [XW11O39](n+4)-, [XW11VO40]m- and [XW11MIII(H2O)O39]p-, X = P or Si and M = Fe or Mn, proved to be effective catalysts for the oxidation of cyclooctane with hydrogen peroxide, in acetonitrile, to the corresponding alkyl hydroperoxide, ketone, and alcohol. High turnover numbers and selectivity for cyclooctyl hydroperoxide were obtained, with values of cyclooctane conversion, after 9h, between 13 and 96%, depending on the catalyst and reaction conditions. In general tungstosilicates were less active than tungstophosphates but presented higher selectivity for cyclooctyl hydroperoxide. Results obtained with H2O2 near the stoichiometric ratio and in excess are compared. Excess of hydrogen peroxide afforded higher selectivity for cyclooctyl hydroperoxide.In the presence of (TBA)4[PW11Fe(H2O)O39], 74% of cyclooctane conversion and 80% of selectivity for cyclooctyl hydroperoxide were obtained after 2h of reaction, using an excess of H2O2. In the same conditions, 100% of cyclooctyl hydroperoxide was obtained with (TBA)4H4SiW11O39, after 9h (55% conversion). These results indicate that these are very promising systems for the oxidation of alkanes. [Copyright &y& Elsevier]

The urgency to reduce CO 2 emissions and energy costs has driven the investment in solar and wind technologies. However, these sources of energy are intermittent and heavily influenced by weather conditions. To overcome this limitation, it is necessary to combine electricity production with a stable and low-carbon energy source, and biofuels have emerged as a promising option. Nonetheless, other challenges have arisen, including the oversupply of glycerol. To address this issue, one of the most sought-after solutions is to convert glycerol into value-added products, such as polymer precursors, solvents, and fuel additives. The production of these products involves catalytic reactions such as oxidation, reduction, reforming, dehydration, acetalization, and carbonylation. Here, we review the latest advances in the conversion of glycerol into value-added products using zeolite-based catalysts and discuss the remaining challenges in this field. [Display omitted] • Glycerol is convertible into chemicals used as polymer precursors, solvents, fuel additives, etc. • Oxidation of glycerol over Al-containing zeolites requires doping with metals such as Fe. • Zeolite's acidity plays a pivotal role in the glycerol reactions. • Catalytic acetalization of glycerol over zeolites is selective towards solketal. • Zeolites glycerol conversion and selectivity to acrolein are better than over other types of catalysts. [ABSTRACT FROM AUTHOR]

Catalytic efficiency of tetrabutylammonium salts of sandwich tungstophosphates B‐α‐[M 4 (H 2 O) 2 (PW 9 O 34 ) 2 ] n− , M = Co II , Mn II , Fe III , was studied in the oxidation of ( R )-(+)-limonene, geraniol, linalool, linalyl acetate, carveol, and cis -cyclooctene with hydrogen peroxide, in acetonitrile. Oxidation of ( R )-(+)-limonene gave limonene-1,2-diol as main product. Epoxidation of linalool takes place preferentially at the more substituted 6,7-double bond, the corresponding 6,7-epoxide reacting further, yielding furano- and pyrano-oxides, via intramolecular cyclization. Oxidation of linalyl acetate occurred preferentially at the more substituted 6,7-double bond for Mn 4 (PW 9 ) 2 , affording 6,7-epoxide at 82% selectivity. Linalyl acetate 1,2-epoxide was the major product with 51% and 77% selectivity for Co 4 (PW 9 ) 2 and Fe 4 (PW 9 ) 2 , respectively. Oxidation of carveol occurred with very good conversions in the presence of Mn 4 (PW 9 ) 2 , Co 4 (PW 9 ) 2 and Fe 4 (PW 9 ) 2 , yielding carvone and carveol 1,2-epoxide in similar amounts. Oxidation of cis -cyclooctene gave only the epoxide, while oxidation of geraniol at room temperature afforded 2,3-epoxygeraniol as the major product. [ABSTRACT FROM AUTHOR]

Synthetic strategies that comply with the principles of green chemistry represent a challenge: they will enable chemists to conduct reactions that maximize the yield of products with commercial interest while minimizing by-products formation. The search for catalysts that promote the selective oxidation of organic compounds under mild and environmentally friendly conditions constitutes one of the most important quests of organic chemistry. In this context, metalloporphyrins and analogues are excellent catalysts for oxidative transformations under mild conditions. In fact, their reduced derivatives chlorins are also able to catalyze organic compounds oxidation effectively, although they have been still little explored. In this study, we synthesized two chlorins through porphyrin cycloaddition reactions with 1.3-dipoles and prepared the corresponding manganese chlorins (MnCHL) using adequate manganese(II) salts. These MnCHL were posteriorly immobilized on silica by following the sol–gel process and the resulting solids were characterized by powder X-ray diffraction (PXRD), UVVIS spectroscopy, FTIR, XPS, and EDS. The catalytic activity of the immobilized MnCHL was investigated in the oxidation of cyclooctene, cyclohexene and cyclohexane and the results were compared with the ones obtained under homogeneous conditions. [ABSTRACT FROM AUTHOR]

Two efficient methods are reported for the oxidation of 1,3-dihydrobenzo[ c ]thiophenes to sulfones in good to high yields using H 2 O 2 in the presence of catalytic amounts of porphyrin-based catalysts in ethanol or acetonitrile as solvents at room temperature. The presence of electron-donating or electron-withdrawing groups, in the benzene ring of 1,3-dihydrobenzo[ c ]thiophene, is well tolerated. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hydroperoxides were produced from linoleic acid by cloned Pseudomonas aeruginosa lipoxygenase (PALOX). [•] Hydroperoxide yield (HY) and regioselectivity of the process were optimized. [•] Results: HY>75% and high selectivity for the 13-hydroperoxy-(9Z,11E)-octadecadienoic acid. [•] Comparison with the Gaeumannomyces graminis tritici lipoxygenase (GGLOX). [•] The PALOX system was more efficient than the GGLOX system. [Copyright &y& Elsevier]

Abstract: The tetrabutylammonium salts of sandwich-type tungstophosphates of general formula B-α-[M4(H2O)2(PW9O34)2] n−, M=CoII, MnII and FeIII, proved to be catalysts or catalyst precursors for the oxidation of cyclohexane and cyclooctane with hydrogen peroxide, affording the corresponding alcohol, ketone and alkyl hydroperoxide in variable proportions. Depending on the tungstophosphate used, the oxidation of cyclooctane could also give 1,2-epoxycyclooctane or a cyclooctanedione. With the Fe sandwich anion, cycloalkyl hydroperoxide was generally the most abundant product. The conversion of cycloalkanes was always higher than 68% after 12h of reaction. Oxidation of cyclooctane into cyclooctanone could be obtained with high selectivity (83%) and conversion (92%) using B-α-[Co4(H2O)2(PW9O34)2]10−. The Fe sandwich complex showed to be the most effective catalyst, with turnover numbers of 1333 for cyclohexane and of 1930 for cyclooctane, after 12h. [Copyright &y& Elsevier]

Abstract: The novel fluorinated metallochlorin 5,10,15,20-tetrakis(pentafluorophenyl)-tetrahydro-1H-N-methyl-pyrrolo[3,4-b]-porphyrinato manganese(III), Mn(chlor)-1, and its methylated derivative, Mn(chlor)-2, have been studied as catalysts in the oxyfunctionalisation of cyclohexane with two oxidants, namely iodosylbenzene (PhIO) and H2O2. For comparison reasons two metalloporphyrins have been also used: the neutral 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato manganese(III), Mn(porph)-1, and the cationic 5,10,15,20-tetrakis(2,3,5,6-tetrafluoro-4-trimethylammoniumphenyl)porphyrinato manganese(III), Mn(porph)-2. It has been possible to verify a different reactivity in the H2O2-oxyfunctionalisation of alkanes from studies using the radical inhibitor bromotrichloromethane and competitive cyclooctane/cis-cyclooctene oxidations. The results suggest that the formation of alcohols and ketones from the oxidation of cyclohexane occurs mainly from a free alkyl radical mechanism, which requires a MnV to abstract a hydrogen atom from the alkane to generate the alkyl radical. On the other hand, the Mn(chlor)/H2O2 system possibly yields, in a first step, the MnIII es, but this is not reactive enough to generate MnV (chlor) hydroperoxy complex shows low efficiency in the production of the alkyl radical, leading to small amounts of alcohol and ketone. However, it seems to be an efficient species for selective epoxidation, as can be observed in the competitive cyclooctane/cis-cyclooctene oxidation reaction. [Copyright &y& Elsevier]

Abstract: New compounds based on the association of polyoxometalates and cationic porphyrins or metalloporphyrins were prepared with the aim of obtaining new bi-functional catalysts. A combined study on the syntheses, characterization and catalytic activity of these compounds was performed. The new compounds have the general formula (porphyrin) x H y [XM12O40]·z solv, x =0.75 or 1, X=P or Si and M=W or Mo. The porphyrins used were 5,10,15,20-tetrakis(4-pyridyl)porphyrin, 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin, 5,10,15-tris(2,6-dichorophenyl)-20-(4-pyridyl)porphyrin, and 5,10,15-tris(2,6-dichlorophenyl)-20-(1-methyl-4-pyridinio)porphyrin, either as free bases or complexed with MnIII (one case with ZnII). A few compounds with metal substituted Keggin anions ([PW11Y(H2O)O39] n−, Y=Mn, Fe, Ni, Zn) were also prepared. All compounds were characterized by spectroscopic and analytical techniques. The oxidation of cis-cyclooctene, geraniol and (+)-3-carene by hydrogen peroxide catalysed by the polyoxometalate/MnIIIporphyrin associations and co-catalysed by ammonium acetate was examined. Some of the associations significantly increased the percentage of conversion of the substrates relatively to the respective metalloporphyrin alone. However, the regio-, chemo- and stereoselectivity of the oxidation reactions catalysed by metalloporphyrins were globally preserved: cis-cyclooctene was selectively epoxidised to epoxycyclooctane; geraniol gave 6,7-epoxygeraniol as the major product and (+)-3-carene was preferably oxidised to the α-3,4-epoxycarane. In the conditions studied, the polyoxoanions seem to contribute mainly to stabilise the metalloporphyrin against deactivation during catalytic cycles. [Copyright &y& Elsevier]