Selective oxidation of betulin to biologically active betulinic aldehyde is demonstrated for the first time over Ru/C catalyst mixed with a basic hydrotalcite and using SiO 2 as a dehydrating agent in synthetic air at 108 8C in toluene with conversion of 41 % in 24 h and 67 % selectivity to betulinic aldehyde, whereas without SiO 2 with Ru/C the corresponding conversion and selectivity values were 20 % and 66 %, respectively. Over another, acidic Ru/C catalyst even higher conversion was achieved, giving, however, allobetulin as a main product. These results indicate that basicity and absence of water are crucial for selective botulin oxidation over Ru catalysts. The conversion levels are comparative with the results in the oxidation of hydroxymathylfurfural, which contains a hydroxymethyl group attached to the heterocyclic ring.Pharmaceuticals are conventionally synthesized in multistep procedures using several organic solvents and stoichiometric reagents, therefore the E-factor, i. e. the amount of waste per formed product is very high. [1] Currently there is a high interest to develop more environmentally friendly methods for production of pharmaceuticals, moreover starting the synthesis from naturally occurring compounds. A potential compound for medical applications is betulin, which is present in the bark of some tree species, such as Betula sp. [2,3] Betulinic acid is present in birch bark or cork of cork oak (Quercus suber L.) and can be isolated and extracted, [2] whereas the stem bark of Tectona grandis contains betulinic aldehyde. [4] In this work betulin oxi-dation was investigated using heterogeneous catalysts and air as an oxidant (Figure 1).Oxidation of betulin produces both betulonic and betulinic aldehydes and acids, respectively, as products ( Figure 1). Betulinic acid has been conventionally prepared from betulin in socalled Jones oxidation process using Cr 2 O 3 as an oxidant. The formed betulonic acid can be reduced to betulinic acid with NaBH 4 in tetrahydrofuran. [18] Betulinic acid was also synthesized via oxidation of betulin using Keggin type tungstophosphoric acid together with potassium dichromate between 15-35 8C during 60 to 240 min giving betulonic acid, which is reduced to betulinic acid with NaBH 4 in an organic solvent. [19] TEMPO (2,2,6,6-teramethylpiperidine -oxyl) catalyst has also been used in the oxidation of betulin to betulinic acid with iodine or (diacetoxyiodo)benzene DIB as oxidants. 2 Furthermore, a high isolated yield of betulinic acid (86 %) was achieved, using 4-acetamido-TEMPO as a catalyst together with NaClO 2 /NaOCl at 50 8C. [20] The above-mentioned betulin derivatives exhibit several biological and medicinal properties. [5][6][7][8][9][10][11][12][13][14][15][16][17] Several examples were given from betulin oxidation with homogeneous catalysts, e. g. RuCl 2 (PPh 3 ) 3 and TEMPO as a cocatalyst in oxygen at 1 atm and 105 8C giving 15 % yield of betulinic aldehyde at 17 % conversion in 27 h and in 8 h at 100 8C under 8 bar 69 % of betulinic aldehyde, respectively...
Here, for the first time, we developed a catalytic composite by forming a thin layer of a cross-linked hyperbranched pyridylphenylene polymer (PPP) on the surface of mesoporous magnetic silica (Fe 3 O 4 − SiO 2 , MS) followed by complexation with Pd species. The interaction of Pd acetate (PdAc) with pyridine units of the polymer results in the formation of Pd 2+ complexes which are evenly distributed through the PPP layer. The MS-PPP-PdAc catalyst was tested in the Suzuki−Miyaura crosscoupling reaction with four different para-Br-substituted arenes, demonstrating enhanced catalytic properties for substrates containing electron withdrawing groups, and especially, for 4-bromobenzaldehyde. In this case, 100% selectivity and conversion were achieved with TOF of >23 000 h −1 at a very low Pd loading (0.032 mol %), a remarkable performance in this reaction. We believe these exceptional catalytic properties are due to the hyperbranched polymer architecture, which allows excellent stabilization of catalytic species as well as a favorable space for reacting molecules. Additionally, the magnetic character of the support allows for easy magnetic separation during the catalyst synthesis, purification, and reuse, resulting in energy and materials savings. These factors and excellent reusability of MS-PPP-PdAc in five consecutive uses make this catalyst promising for a variety of catalytic reactions.
Here, we report on the development of novel Cr-containing magnetic oxide nanoparticles (NPs) as catalysts for a syngas-tomethanol reaction which constitutes a sustainable route to obtain value-added chemicals. These NPs have been synthesized in a one-pot reaction by thermal decomposition of Cr acetylacetonate and doping metal acetylacetonates (if used) in the reaction solution of preformed magnetite NPs stabilized by polyphenylquinoxaline. For all the samples, the NP surface is enriched with Cr. At the same time, the Cr species are finely dispersed in the magnetite phase. This exposes Cr catalytic species to reacting molecules and creates an intimate contact between Cr 3 + and Fe 3 O 4 . As a result, the methanol productivity rate for the Cr-containing magnetic oxide prepared with 0.5 mmol of the Cr precursor is approximately three orders of magnitude higher than that for the conventional Cu/ZnO/Al 2 O 3 catalyst. Additional doping of this Cr-containing magnetic oxide with small amounts of Ni or La leads to even higher catalytic activity (by 40-49%).
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