Regina Buffon

Direct selective oxidation of benzene to phenol using molecular oxygen in the presence of palladium and heteropolyacids

Abstract The use of heteropolyacids as a reoxidant for palladium in the direct oxidation of benzene to phenol with molecular oxygen was studied as a function of the variables involved. It was shown that the oxidation system is very effective even if a molar ratio of HOAc:H2O of 1:2 is used. After 4 h at 130°C the benzene conversion is 15% and the selectivity for phenol is above 70%. The quantity of palladium acetate can be drastically reduced allowing turnover numbers as high as 800.

Metathesis in Oleochemistry

Metathesis is an attractive reaction for the conversion of oleochemical feedstocks into useful chemical products. Thus, metathesis of unsaturated fatty acid esters (the oleochemical raw materials) provides a convenient route to unsaturated diesters which can be used as intermediates for the production of polymers and specialty chemicals. Cross-metathesis with olefins is a means to change the chain length of fatty acids and derivatives; cross-metathesis with ethene (ethenolysis) gives compounds with terminal double bonds, having a broad range of applications. Ethenolysis of fatty oils or triglycerides allows the transformation of long-chain fatty acid triglycerides into fatty oils of lower molecular weight. Several highly selective catalyst systems - homogeneous as well as heterogeneous - have proven to be successful for the metathesis of unsaturated esters. Especially modified heterogeneous rhenium- and molybdenum-based catalysts have attracted much attention. Considering catalyst activation and regeneration procedures, rhenium-based catalysts are to be preferred.

Sol–gel derived hybrid materials as heterogeneous catalysts for the epoxidation of olefins

Abstract CH 3 ReO 3 has been heterogenized inside the porous system of hybrid silica matrixes via the sol–gel method using 1,4- bis (triethoxysilyl)benzene as a co-condensation agent and 4-((3-triethoxysilyl)propylamino)pyridine hydrochloride as a hydrolysable ligand. The resulting solids are stable and recyclable epoxidation catalysts.

Heterogenization of H6PMo9V3O40 and palladium acetate in VPI-5 and MCM-41 and their use in the catalytic oxidation of benzene to phenol

Abstract The heteropolyacid H 6 PMo 9 V 3 O 40 (HPA) was encapsulated in MCM-41 and VPI-5. When HPA/MCM-41 is used in the direct oxidation of benzene to phenol, the heteropolyacid leaches from the MCM-41 and oxidation takes place in the homogeneous phase. VPI-5 retains the HPA and palladium acetate more efficiently than MCM-41, and can be used as a heterogeneous oxidation catalyst for benzene. However, its activity is very low since only the active species at the pore entrances of VPI-5 are accessible to the reactants.

Heterogenization of alkene epoxidation catalysts

This account describes our efforts to heterogenize epoxidation catalysts. Anchored and sol-gel entrapped molybdenum were shown to be very selective, but had a strongly reduced activity. On the other hand, molybdenum silicates were very active and stable as long as no diols were present in the reaction mixture. Heterogenized rhenium catalysts were less active but allowed the use of anhydrous hydrogen peroxide as oxidant. However, the high cost and difficult regeneration prevents the industrial use of these catalysts. During these investigations, we found that alumina alone is active in the epoxidation with anhydrous hydrogen peroxide, giving good conversions to epoxides with high selectivity. More research is needed in order to clarify the nature of the hydroxyl groups responsible for its catalytic activity and thus to produce an appropriate material which would allow the obtention of epoxides with high selectivity under industrial conditions.

Molecularly imprinted solid phase extraction of fluconazole from pharmaceutical formulations

This work encompasses a direct and coherent strategy to synthesise a molecularly imprinted polymer (MIP) capable of extracting fluconazole from its sample. The MIP was successfully prepared from methacrylic acid (functional monomer), ethyleneglycoldimethacrylate (crosslinker) and acetonitrile (porogenic solvent) in the presence of fluconazole as the template molecule through a non-covalent approach. The non-imprinted polymer (NIP) was prepared following the same synthetic scheme, but in the absence of the template. The data obtained from scanning electronic microscopy, infrared spectroscopy, thermogravimetric and nitrogen Brunauer-Emmett-Teller plot helped to elucidate the structural as well as the morphological characteristics of the MIP and NIP. The application of MIP as a sorbent was demonstrated by packing it in solid phase extraction cartridges to extract fluconazole from commercial capsule samples through an offline analytical procedure. The quantification of fluconazole was accomplished through UPLC-MS, which resulted in LOD≤1.63×10(-10) mM. Furthermore, a high percentage recovery of 91±10% (n=9) was obtained. The ability of the MIP for selective recognition of fluconazole was evaluated by comparison with the structural analogues, miconazole, tioconazole and secnidazole, resulting in percentage recoveries of 51, 35 and 32%, respectively.

Ethenolysis of esters of vegetable oils: Effect of B2O3 addition to Re2O7/SiO2.Al2O3-SnBu4 and CH3ReO3/SiO2.Al2O3 metathesis catalysts

Impregnation of SiO2.Al2O3 (24.3% Al2O3 with 6% B2O3 increases the activity of supported Re2O7 in the ethenolysis of methyl oleate, but reduces the activity of CH3ReO3 on the same support. Re2O7/SiO2.Al2O3/B2O3-SnBu4 is shown to be an effective catalyst for the ethenolysis of methyl linoleate and of the methyl esters of olive oil, and can be recycled after calcination at least five times without loss of activity.

Pd complexes based on phosphine-linked cyclophosphazenes: synthesis, characterization and application in Suzuki coupling reactions

Palladium complexes were obtained by reaction of phosphine-linked cyclophosphazenes, (P3N3)(O-C6H4-PR2)6, where R = phenyl, i-propyl or cyclohexyl, with using a Pd/ligand molar ratio of 3/1. The (P3N3)(O-C6H4-PR2)6Pd3(dba)x complexes were characterized by elemental analyses, mass spectrometry, 31P NMR and FT-IR where a characteristic νC=C band of dba coordinated to palladium was always observed. All complexes were tested in Suzuki coupling reactions between phenylboronic acid and aryl halides. Turnover numbers as high as ca. 17,500 for the coupling of 2-bromotoluene with chlorophenylboronic acid could be obtained for R = cyclohexyl. The complex based on -PPh2 was also immobilized in silica matrixes by the sol-gel method. Preliminary experiments showed that the immobilized catalyst could be used in at least three consecutive Suzuki reactions with the same catalytic activity.

On the interaction of Schrock Mo–alkylidene complexes with the surface of inorganic oxides

Abstract This work describes the reactivity of Schrock-type alkylidenemolybdenum(VI) complexes, Mo(=CHCPhMe 2 )(=NAr)(O t Bu) 2 , I , or Mo(=CHCPhMe 2 )(=NAr)[OCMe(CF 3 ) 2 ] 2 , II , with the surface of silica, silica–alumina and niobia. In situ FT-IR studies suggest that I and II are attached to the surface of silica via a Lewis acid base adduct; on silica–alumina, an OH addition to the MoN bond seems to take place. Grafting of I and II causes a decrease in their intrinsic catalytic activity as well as a change in the stereoselectivity of II in ROMP of norbornene.

Catalyst recycling in the epoxidation of alkenes catalyzed by MoO2(acac)2 through precipitation with poly(ethylene oxide)

Addition of poly(ethylene oxide) (PEO) to the catalytic system MoO2(acac)2/TBHP/t-butanol used for epoxidation of olefins allowed an easy strategy for catalyst recycling and product recovery. This procedure is based upon catalyst removal by precipitation of a complex with the polymer, being advantageous over other similar recycling methodologies in that there is no requirement for specially prepared catalysts or solvents. Although some catalyst leaching is detected, the epoxidation of cis-cyclooctene was achieved with global turnover numbers close to 650.