Isophytol Research Articles

Size-Effect of Pd-(Poly(N-vinyl-2-pyrrolidone)) Nanocatalysts on Selective Hydrogenation of Alkynols with Different Alkyl Chains

We have studied the effect of unsupported Pd nanoparticle (NP) size in the selective C≡C semi-hydrogenation of alkynols with different alkyl chains, i.e., C16 in dehydroisophytol (DIP) (to isophytol (IP)) vs C1 in 2-methyl-3-butyn-2-ol (MBY) (to 2-methyl-3-buten-2-ol (MBE)). The Pd NPs were synthesized via colloidal technique with poly(N-vinyl-2-pyrrolidone) (PVP) as stabilizing agent where a range of crystal sizes (2.1–9.8 nm; confirmed by HRTEM) was generated. Both reactions show antipathetic structure sensitivity consistent with higher specific activity (TOF) over larger Pd NPs where the structure sensitivity effect is more pronounced for NPs ≤ 3.0 nm. All the Pd NPs exhibit high (≥88%) selectivity to the target alkenol product at almost complete (98%) conversion. Increased IP selectivity (SIP; XDIP=98%ca. 95%) was observed over smaller (2.1–3.0 nm) Pd NPs while ca. 98% selectivity to MBE (SMBE; XDIP=98%) is obtained irrespective of particle size. The kinetic results were consistent with a Langmuir–Hin...

Continuous synthesis of d, l-α-tocopherol catalyzed by sulfonic acid-functionalized ionic liquid in supercritical carbon dioxide

Continuous synthesis of d, l-α-tocopherol catalyzed by a sulfonic acid-functionalized ionic liquid was conducted in supercritical carbon dioxide (SC-CO 2). The product was continuously separated from the reaction mixture by SC-CO 2 extraction during the course of reaction. Decompression of the supercritical fluid mixture downstream gave the product free of ionic liquid. The yield of d, l-α-tocopherol was improved with non-polar SC-CO 2 and polar propylene carbonate as solvents. The selectivity of d, l-α-tocopherol to trimethylhydroquinone (TMHQ) between CO 2-rich and ionic liquid-rich phase increased with the increase of pressure, and decreased with the increase of temperature at temperatures from 70 to 115 °C and pressures from 15 to 25 MPa. Effect of temperature, pressure and flow rate on the continuous synthesis of d, l-α-tocopherol was studied. The conversion of isophytol (IP) and the yield of d, l-α-tocopherol increased with decreasing pressure. The extraction rate of d, l-α-tocopherol increased with increasing pressure and decreased with increasing temperature. d, l-α-Tocopherol yield of 90.4% was obtained at 100 °C, 20 MPa and a CO 2 residence time of 12.6 min.

Novel Sol–Gel Synthesis of Acidic MgF2−x(OH)x Materials

Novel magnesium fluorides have been prepared by a new fluorolytic sol-gel synthesis for fluoride materials based on aqueous HF. By changing the amount of water at constant stoichiometric amount of HF, it is possible to tune the surface acidity of the resulting partly hydroxylated magnesium fluorides. These materials possess medium-strength Lewis acid sites and, by increasing the amount of water, Brønsted acid sites as well. Magnesium hydroxyl groups normally have a basic nature and only with this new synthetic route is it possible to create Brønsted acidic magnesium hydroxyl groups. XRD, MAS NMR, TEM, thermal analysis, and elemental analysis have been applied to study the structure, composition, and thermal behaviour of the bulk materials. XPS measurements, FTIR with probe molecules, and the determination of N(2)/Ar adsorption-desorption isotherms have been carried out to investigate the surface properties. Furthermore, activity data have indicated that the tuning of the acidic properties makes these materials versatile catalysts for different classes of reactions, such as the synthesis of (all-rac)-[alpha]-tocopherol through the condensation of 2,3,6-trimethylhydroquinone (TMHQ) with isophytol (IP).

Catalytic Performance of Nanoscopic, Aluminium Trifluoride‐Based Catalysts in the Synthesis of (all‐rac)‐α‐Tocopherol

AbstractA novel nanoscopic, partly hydroxylated aluminium fluoride was prepared in a sol‐gel fluorination synthesis and characterised by IR probe molecules. It was shown that this material has, in contrast to high surface area aluminium fluoride (HS‐AlF3) which is one of the strongest Lewis acids, a low amount of strong Lewis acid sites combined with weak and medium strength Brønsted sites. Both materials were tested in the synthesis of (all‐rac)‐α‐tocopherol through the condensation of 2,3,6‐trimethylhydroquinone (TMHQ) with isophytol (IP). The activity data indicate the partly hydroxylated aluminium fluoride to be a very efficient and highly selective catalyst for (all‐rac)‐α‐tocopherol (>99.9%, for an IP conversion of 100%) whereas high surface area aluminium fluoride is a poor catalyst for this reaction.

New heterogeneous catalysts for greener routes in the synthesis of fine chemicals

New strong Lewis acid SnTf-MCM-41 and SnTf-UVM-7 catalysts with unimodal and bimodal pore systems were prepared in a two-step synthesis in which the triflic acid (Tf) was incorporated to previously synthesized mesoporous tin-containing silicas. The Sn incorporation inside the pore walls was carried out through the Atrane method. The SnTf-UVM-7 catalysts were prepared by aggregating nanometric mesoporous particles defining a hierarchic textural-type additional pore system. Following these procedures, catalysts with different Si/Sn ratios—21.8 to 50.8 for SnTf-MCM-41 and 18.4 for SnTf-UVM-7—were prepared. These new materials were tested in the acylation of aromatic sulfonamides using acetic acid as the acylating agent and in the synthesis of (dl)-[α]-tocopherol through the condensation of 2,3,6-trimethylhydroquinone (TMHQ) with isophytol (IP). The activity data indicate that these heterogeneous catalysts are very active, corresponding to high yields in acylated compounds as 65.5% and very high selectivity to (dl)-[α]-tocopherol (94%, for a conversion of 98%).

Catalytic performance of Nafion/SiO 2 nanocomposites for the synthesis of α-tocopherol

Synthesis of α-tocopherol starting from trimethylhydroquinone (TMHQ) and isophytol (IP) was performed over Nafion/SiO 2 nanocomposite catalysts (Nafion content: 5–20 wt.%) and Nafion ® NR50 resin. The nanocomposites were made by in situ hydrolysis of tetraethoxysilane in the presence of home-made Nafion solution. Nitrogen adsorption and catalytic dehydration of 2-propanol were used, respectively, to characterize the texture and acid properties of the nanocomposites. It is found that acid strength of the Nafion-based acidic sites was weakened in the nanocomposites and the weakening disappeared when the amount of Nafion exceeded 30 wt.% of the nanocomposite. The pore structure and accessibility of the Nafion-based acidic sites in the nanocomposite catalysts showed pronounced effects on the catalytic efficiency toward the desired α-tocopherol. In comparison with Nafion resin in the condensed phase (Nafion ® NR50), 5 and 13 wt.% Nafion/SiO 2 catalysts showed tenfold higher catalytic activities by turnover frequency for α-tocopherol formation owing to increased Nafion dispersion and accessibility of the Nafion-based acid sites. Though the acid sites in the 20 wt.% Nafion/SiO 2 catalyst had similar accessibility to those in the 5 and 13 wt.% Nafion/SiO 2 catalysts by the dehydration of 2-propanol, smaller pore sizes of the 20 wt.% Nafion/SiO 2 catalyst induced severe side reactions of the IP reactant, such as dehydration to form phytadienes and furan derivatives, which resulted in much lower yield (or selectivity) and turnover frequency for α-tocopherol.

Industrial application of Nafion-systems in rearrangement-aromatisation, transesterification, alkylation, and ring-closure reactions

Nafion, a perfluorinated sulphonic acid ion-exchange polymer, is known to be a very strong Brønsted acid. Thus, Nafion NR 50 and Nafion/SiO 2 with 15 wt.% Nafion-loading were selected, in order to elucidate the potential for rearrangement-aromatisation of ketoisophorone (KIP) to 2,3,5-trimethylhydroquinone diacetate (TMHQ-DA) in presence of acetic acid anhydride as acylating agent, transesterification of TMHQ-DA to 2,3,6-trimethylhydroquinone monoacetate (TMHQ-1-MA) and reaction of isophytol (IP) with trimethylhydroquinone (TMHQ) to (all- rac)-α-tocopherol. For the rearrangement-aromatisation of KIP to TMHQ-DA supported Nafion/SiO 2 was markedly more active than the unsupported Nafion NR 50. Both Nafion-systems generally revealed remarkably high selectivity, which ranged up to 94 GC-a% TMHQ-DA at high conversion. The major side-product was 3,4,5-trimethylcatechol diacetate. In case of Nafion/SiO 2, pre-treatment under vacuum and especially grinding of the extrudates seemed to increase activity at comparably high selectivity. Recycling Nafion/SiO 2 after filtering and rinsing with acetic acid anhydride led to gradually decreasing activity. Without intermediate isolation of TMHQ-DA, Nafion/SiO 2 was active and selective for the formation of TMHQ-1-MA. Using the Nafion systems in the reaction of IP and TMHQ revealed that remarkably high conversion of IP (>95%) and compared with zinc chloride/Brønsted acid or BF 3-catalysed reaction good yields (≈92%) and selectivities were obtained. We found a strong dependency on the solvent polarity. In further experiments, the recovery of the catalyst was tested.

The synthesis of d, l-α-tocopherol in supercritical media

The synthesis of d, l-α-tocopherol in supercritical carbon dioxide or nitrous oxide by condensation of trimethylhydroquinone (TMHQ) with isophytol (IP) in the presence of various Brönsted or Lewis acids, especially an imide or its metal salts, as catalysts is described. The product is obtained in high yield. The method represents an interesting alternative to existing processes. A quasi-reaction mechanism is being proposed together with kinetics, which are needed for the reactor analysis and design.