Applied Reaction Conditions Research Articles

Rigid bis-zinc(ii) salphen building blocks for the formation of template-assisted bidentate ligands and their application in catalysis

The template-induced formation of chelating bidentate ligands by the selective self-assembly of two monodentate pyridyl phosphorus ligands on a rigid bis-zinc(II) salphen template with two identical binding sites was studied. Using UV-vis, NMR-spectroscopy and X-ray analysis the formed structures were unambiguously proven. The application of these templated bidentate ligands in transition metal catalysis showed, in most cases, typical bidentate character. Compared to previous work based on a more flexible bis-zinc(II) porphyrin template, the current catalytic data suggest that the rigidity of the template is not an important factor for the improvement of the regio- and enantioselectivity under the applied reaction conditions.

Palladium-Catalyzed N-Arylation Reactions with Aziridine and Azetidine

Studies on the viability of palladium-catalyzed cross-coupling reactions of aryl- or hetaryl bromides with the parent aziridine or azetidine showed that a wide range of N-arylaziridines and N-arylazetidines are accessible by this method. Ring cleavage of the N-arylaziridines or -azetidines thus produced does not occur under the applied reaction conditions. The synthetic utility of the method is illustrated by examples of double N-arylations with either aziridine or azetidine.

Direct Boronation of Allyl Alcohols with Diboronic Acid Using Palladium Pincer-Complex Catalysis. A Remarkably Facile Allylic Displacement of the Hydroxy Group under Mild Reaction Conditions

Allyl alcohols were converted to allyl boronic acids and subsequently to trifluoro(allyl)borates with tetrahydroxy diboron using palladium pincer-complex catalysis. These reactions are regio- and stereoselective proceeding with high isolated yields. Competitive boronation experiments indicate that under the applied reaction conditions the allylic displacement of a hydroxy group is faster than the displacement of an acetate leaving group. It is assumed that the hydroxy group of the allyl alcohol is converted to a diboronic acid ester functionality, which can easily be substituted.

Palladium Pincer Complex Catalyzed Cross‐Coupling of Vinyl Epoxides and Aziridines with Organoboronic Acids

Palladium-catalyzed cross-coupling of vinyl epoxides and aziridines with organoboronic acids was performed by using 0.5-2.5 mol % pincer-complex catalyst. The reactions proceed under mild conditions affording allyl alcohols and amines with high regioselectivity and in good to excellent yields. Under the applied reaction conditions aromatic chloro-, bromo- and iodo substituents are tolerated. Our results indicate that the mechanism of the pincer complex catalyzed and the corresponding palladium(0) catalyzed process is substantially different. It was concluded that the transformations proceed via transmetalation of the organoboronic acids to the pincer-complex catalyst followed by an S(N)2'-type opening of the vinyl epoxide or aziridine substrate. In this process the palladium atom is kept in oxidation state +2 under the entire catalytic process, and therefore oxidative side reactions can be avoided.

Analysis of a technical-grade w/o-microemulsion and its application for the precipitation of calcium carbonate nanoparticles

For a directed synthesis of inorganic nanoparticles in water-in-oil (w/o)-microemulsions the detailed investigation of the microemulsion system is of particular importance. This study illustrates that the phase behavior of the ternary as well as of the quaternary mixture (with reactants) has to be analyzed to identify microemulsion regions suitable for particle synthesis. Besides detailed phase prism investigations the microemulsion, consisting of water/reactant, cyclohexane and Marlipal O13/40, was further characterized. Dynamic light scattering studies have been conducted for determining the droplet size and viscosity measurements have been undertaken to clarify the internal structure. A time scale analysis of the involved processes during particle formation (e.g., droplet exchange, reaction, nucleation, growth and mixing) points out, that the utilization of w/o-microemulsions for precipitation reactions is an effective way to overcome mixing problems, which usually are present in bulk precipitation. This is demonstrated for the precipitation of CaCO 3 from two microemulsions containing dissolved Na 2CO 3 and CaCl 2, respectively. The influence of microemulsion composition, initial reactant concentration and holding time on the final particle size and shape was investigated. The resulting CaCO 3 nanoparticles have been characterized by means of a transmission electron microscope. Depending on the applied reaction conditions it is shown that different particle sizes and morphologies can be obtained.

Ethylene-bridged periodic mesoporous organosilicas with Fm3m symmetry

Divalent surfactant [CH3(CH2)15N(CH3)2(CH2)3N(CH3)3]2+2Br− (C16-3-1) was exploited as a structure directing agent (SDA) for the synthesis of highly ordered periodic mesoporous organosilicas (PMOs) from 1,2-bis(triethoxysilyl)ethane (BTEE) as organosilica source under basic conditions. The mesophase structure/symmetry and the physical parameters could be controlled/optimized by adjusting synthetic parameters such as surfactant and base concentration, hydrothermal aging temperature and time, and crucially the type (charge, shape, aliphatic tail chain length) of the surfactant. Cubic PMO[KIT-5]-n reveals a face-centred Fm3m symmetry similar to that of the previously reported purely siliceous material KIT-5. Under the applied reaction conditions, lower aging temperatures generally afforded PMO[KIT-5] materials with increased BET surface area (max. 840 m2 g−1) and pore volume (max. 0.93 cm3 g−1), however, similar pore size (ca. 3.0 nm). Lower divalent surfactant concentrations (C16-3-1) caused a mesophase transformation from cubic Fm3m to hexagonal P6mm symmetry. Upon relative increase of the base (NaOH) concentration, the PMO mesostructure transformed from hexagonal to cubic, then from cubic to hexagonal symmetry. Surfactants [CH3(CH2)17N(CH3)2(CH2)3N(CH3)3]2+2Br− (C18-3-1), [CH3(CH2)15N(CH3)2(CH2)3-N(C2H5)3]2+2Br− (C16-3-2), and [CH3(CH2)15N(CH3)3]+Br− (C16) were found to encode for PMO[SBA-1]-n and PMO[MCM-41]-n with cubic Pm3n (former) and hexagonal P6mm symmetry (latter two), respectively. All these periodic mesoporous organosilicas were characterized by powder X-ray diffraction (PXRD), nitrogen physisorption, FTIR spectroscopy, 13C and 29Si solid state NMR spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Thermally Induced Reaction of Potato Starch with Thiourea

Thermally induced reaction of thiourea with potato starch was carried out with involvement of either conventional or microwave heating. Under applied reaction conditions conventional heating provided a higher degree of transformation. The course of reaction was complex. Thiourea reacted with starch but the reaction products underwent further decompositions. Dextrins contaminated with isothiocyanates were obtained. Not necessarily they underwent alpha-amylolysis more readily than original starch.

Catalytic olefin epoxidation with cyclopentadienyl–molybdenum complexes in room temperature ionic liquids

Complexes of the type (η 5-C 5R 5)Mo(CO) 3X (X = Me, Cl; R = H, Me), being efficient homogeneous catalysts for the epoxidation of olefins, have been examined for their catalytic performance at 55 °C in systems containing room temperature ionic liquids (RTILs) of composition [BMIM]NTf 2, [BMIM]PF 6, [C 8MIM]PF 6 and [BMIM]BF 4. The catalytic performance for cyclooctene epoxidation depends strongly on the water content of the system, the catalyst solubility in the RTIL, and the reaction behaviour of the RTIL under the applied reaction conditions. The catalysts can be recycled without significant loss of activity when a reaction system containing [BMIM]NTf 2 and [BMIM]PF 6 in a 4:1 relationship is used. High proportions of [BMIM]PF 6 lead to a ring opening reaction (diol formation), due to HF formation and the presence of residual water.

Bis(enamino-Cp) Group 4 metal complex chemistry: developing a Mannich-type carbon–carbon coupling reaction at the bent metallocene famework

Treatment of 6-methyl-6-dimethylaminofulvene ( 2a) with methyl lithium in ether results in a deprotonation reaction to yield the enamino-substituted lithium cyclopentadienide reagent 3a. Its reaction with zirconium tetrachloride (0.5 molar equivalents) results in the formation of the [1-dimethylaminobutadien-1,3-diyl-bis(cyclopentadienyl)]zirconium dichloride product 4a. The unsaturated ansa-metallocene is probably formed via a Lewis acid-catalyzed Mannich-type carbon–carbon coupling reaction of an in situ generated bis[(dimethylaminoethenyl)cyclopentadienyl]ZrCl 2 intermediate. A number of related examples of this condensation reaction at the intact Group 4 bent metallocene framework is described, using different amino-substituents and Ti, Zr and Hf systems. Three examples of the unsaturated ansa-metallocene systems were characterized by X-ray diffraction. In a few cases it was possible to isolate the open (enamino-Cp) 2ZrCl 2 complexes. In the case of, e.g., (piperidinoethenylcyclopentadienyl) 2ZrCl 2 ( 13c) treatment with a catalytic quantity of the Lewis acid ZrCl 4 or the Brønsted acid [ PhNMe 2 H + ] [ BPh 4 - ] resulted in a clean conversion to the respective Mannich condensation product, here the ansa-metallocene complex 4c. The strongly electrophilic borane HB(C 6F 5) 2 did not catalyze the CC-coupling reaction under the applied reaction conditions but added cleanly to the enamino-C C double bond of, e.g., 13c to yield a cyclic nitrogen donor-stabilized hydroboration product ( 19).

Solid‐ and Solution‐Phase Synthesis of a Library of Mixed‐Metal Complexes

AbstractA solid‐phase synthesis protocol has been developed for the stepwise assembly of mixed‐metal dinuclear complexes built from chromium, molybdenum and tungsten and a directional bridging ligand. Complexes with all nine possible metal combinations have been prepared on polystyrene/divinylbenzene copolymer employing a metal‐complex‐compatible silyl ether linker. Release of the metal complexes from the polymeric support is accomplished by fluoridolysis under mild conditions. The metal sequence in these complexes is precisely determined by the reaction sequence and is retained under the applied reaction conditions as shown by IR, NMR and UV/Vis spectroscopic analysis of the cleaved soluble products. Additionally, the same complex library has been prepared by conventional solution‐phase synthesis to allow evaluation of the advantages and disadvantages of the solid‐phase synthesis method. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Heterogeneously catalysed partial oxidation of cyclohexane in supercritical carbon dioxide

Heterogeneously catalysed partial oxidation of cyclohexane to cyclohexanol and cyclohexanone in supercritical carbon dioxide was investigated realising batch experiments and continuous runs within the temperature range from 353 to 673 K at pressures between 80 and 160 bar. Before catalytic runs, phase behaviour of the reaction mixture was studied by means of a high-pressure optical cell and the results indicate that: (i) the system is supercritical at the applied reaction conditions; and (ii) results agree well to estimated values using the Peng–Robinson equation of state. Mainly two classes of catalysts were tested in oxidation runs: (i) conventional metal oxide catalysts (active metals Co, Mn, Fe) on alumina or silica as well as microporous (MOR, AlPO-31) and mesoporous materials (Al-MCM-41) as supports; and (ii) organometallic complexes (salenes) of those metals immobilised on mesoporous molecular sieve (MCM-41) or microporous material (EMT). In general, the use of supported metal oxides leads to higher yields for target products cyclohexanone and cyclohexanol compared to the immobilised complexes. Maximum selectivity for these products reached 26% (-one) respective 16% (-ol) at 10% conversion.

Opportunities and Limits of the Use of Azides in Industrial Production. Implementation of Safety Measures

Azides are very versatile precursors of organic synthesis functionalities such as amines, isocyanates, sulfonamides, triazoles, tetrazoles, triazolines, aziridines, amino acids and diazo compounds. In industry, one of the favourite starting materials for these syntheses is sodium azide which can generate hydrazoic acid whose toxicity and detonation potential is of major safety concern. However sodium azide is used daily in large tonnage in the air-bags of vehicles, in biologic institutes as a bactericide and in agriculture as a herbicide. In industrial synthesis, sodium azide is actually the starting material of herbicides, anti-HIV pharmaceuticals, anti-pain compounds and hypo tensors. This massive use of sodium azide represents severe toxicological and physical damage risks. The industrial synthesis under the scope of this presentation will be the manufacture of a tetrazole produced in several tens of tons per year. A risk assessment concluded that it would be necessary to conduct the reaction in a 'Bunker' and to minimise risks by absolutely avoiding generation of hydrazoic acid. This can be achieved by a careful design of the process and by strict organisational measures. Furthermore, the reaction equipment was designed to prevent any condensation of hydrazoic acid. One way to prevent its formation is to maintain the reaction medium under basic conditions at all times. This is achieved by using triethylamine hydrochloride as a buffer. In the applied reaction conditions it could be demonstrated that triethylamine was the refluxing compound at 130 °C and that a thermally stable triethyl ammonium azide was formed. The environmental problem could be resolved by incineration of the wastewaters. In conclusion, reactions with sodium azide are safe, they only need a stabilising agent. A search for such compounds could be an interesting but rather dangerous research project.

Liquid-phase hydrogenation kinetics of isooctenes on Co/SiO 2

The kinetics of the hydrogenation of isooctenes (2,4,4-trimethyl-1-pentene, TMP-1, and 2,4,4-trimethyl-2-pentene, TMP-2) to isooctane (2,2,4-trimethylpentane) was studied on a commercial Co/SiO 2 catalyst in a three-phase laboratory-scale reactor. The terminal double bond in TMP-1 was substantially faster hydrogenated than the internal double bond in TMP-2. Double bond isomerization was found to be of no importance under the applied reaction conditions. Kinetic parameters were estimated for power-law rate equations as well as for equations based on the Horiuti–Polanyi mechanism assuming competitive and non-competitive adsorption of the alkenes and hydrogen. All models described the experimental data accurately with physically reasonable values of parameters ( E app 34–35 kJ/mol for TMP-1 and 40–43 kJ/mol for TMP-2). The hydrogenation rate per catalyst mass was considerably lower on cobalt than on nickel, evidently mainly due to the smaller number of active sites.

The role of the active phase of Raney-type Ni catalysts in the selective hydrogenation of d-glucose to d-sorbitol

Bulk and surface properties of homemade Raney-type Ni catalysts and their Ni–Al alloy precursors have been studied and compared with commercial samples, both promoted and unpromoted. The two starting alloys had a different Ni 2Al 3 concentration, resulting in Raney-type Ni catalysts with different Ni–Al composition. All catalysts have been screened in the hydrogenation of an aqueous solution of d-glucose (10 wt.%) using a three-phase slurry reactor at 4.0 MPa and 393 K. The promoters are segregated at the surface of the catalysts and have a beneficial effect on the reaction rate, essentially due to an increased surface area and stability of the active phase while an enhanced interaction of d-glucose with Ni seems to play a secondary role. The Raney-type Ni catalysts lose Ni and Al at the applied reaction conditions. Mo does not leach at all. Fe leaches severely from the catalyst surface, but about 30% of the Fe at the surface is present as inactive, bulk iron. The major cause of deactivation of the Raney-type Ni catalysts is the presence of d-gluconic acid formed during the reaction. The effect of d-gluconic acid is two-fold: firstly it blocks the Ni sites making them inactive in d-glucose processing. The poisoned catalytic sites can be recovered again by a regeneration treatment in hydrogen at 393 K. Secondly, the formation of d-gluconic acid leads to a severe loss of Ni, which makes product purification necessary.

Preparation of chelate bis(imine)nickel allyl systems by reaction of their corresponding butadiene complexes with electrophiles

The chelate 1,2-bis(imine)nickel(butadiene) complex 4a (chelate ligand derived from condensation of biacetyl with 2,6-diisopropylaniline) adds the strong Lewis acid B(C 6F 5) 3 at the terminal carbon atom of the butadiene ligand to yield the dipolar substituted π-allyl-type betaine complex (lig)Ni[η 3-C 3H 4-CH 2B(C 6F 5) 3] ( Z- 6a). At 90 °C the kinetically formed product equilibrated with its E- 6a isomer. Similarly, 4a adds the boron Lewis acid (pyrrolyl)B(C 6F 5) 2 to yield the corresponding neutral dipolar π-allyl betaine complex Z- 7a, that slowly equilibrated with E- 7a over several hours at ambient temperature. Protonation of the butadiene ligand of complex 4a was achieved by treatment with the neutral Brønsted acid (2H-pyrrol)B(C 6F 5) 3 to yield the [(lig)Ni(η 3-crotyl) +][(pyrrolyl)B(C 6F 5) 3 −] salt 9a ( Z-/ E- 9a ratio=90:10 upon preparation). At 298 K this salt rearranged to a 5:95 mixture of Z- 9a/ E- 9a with a Gibbs activation energy of Δ G ‡ (298 K)=22.3±0.2 kcal mol −1. Complex 4a added [Ph 3C +] to the butadiene ligand to yield the salt [(lig)Ni(η 3-C 3H 4-CH 2CPh 3) +][B(C 6F 5) 4 −] ( Z- 12a), that proved isomerically stable under the applied reaction conditions. Similar reactions were carried out starting from the acenaphthylene 1,2-dione derived chelate bis(imine)Ni(butadiene) complex 4b. The systems 6, 7, 9 and 12 were found to be active ethene polymerization catalysts in the presence of Al( i-Bu) 3.

Monoterpenes oxidation in the presence of Y zeolite-entrapped manganese(III) tetra(4-N-benzylpyridyl)porphyrin

Under homogeneous conditions and as a Y zeolite supported complex, manganese(III) tetra(4-N-benzylpyridyl)porphyrin (MnTBzPyP) is an active catalyst in the epoxidation of (R)-(+)-limonene and α-pinene, and in the hydroxylation of carvacrol and thymol, using H2O2/ammonium acetate, at room temperature and atmospheric pressure. A combined study on the characterization and catalytic performance of MnTBzPyP–NaY suggests that its preparation led to a successful inclusion of MnTBzPyP inside the zeolite during the hydrothermal synthesis. Unfortunately, irreversible catalyst deactivation occurs in the presence of H2O2. Changes in the crystalline structure of MnTBzPyP–NaY during the oxidative transformations are accompanied by leaching of the porphyrin complex to the reaction solution, accounting for the nearly complete loss of activity when the catalyst is re-used. Higher substrate conversions were achieved with the zeolite-impregnated complex. The iron analogue is inactive, under the applied reaction conditions.

Synthesis and structural characterization of Group 4 metallocene complexes that contain remote carboxamide functionalities at their Cp-side chains

Treatment of the levulinic acid amides CH3COCH2CH2CONR27 [–NR2 = NMe2 (a), NEt2 (b), pyrrolidino (c)] with cyclopentadiene in the presence of excess pyrrolidine gave the corresponding pentafulvene derivatives 8(a–c). Their subsequent reaction with [Me2CuLi] followed by hydrolysis furnished the corresponding C-methylated cyclopentadienes 9(a–c), each obtained as a mixture of isomers (9-A and 9-B). Deprotonation of the cyclopentadiene units in these compounds was achieved by treatment with lithium diisopropylamide (LDA) to yield the substituted lithium cyclopentadienide reagents [(C5H4)–CMe2CH2CH2CONR2]Li (10a–c), that were resistant to intramolecular cyclization under the applied reaction conditions. The transmetalation reaction of 10a with FeCl2 furnished the ferrocene derivative [(C5H4)–CMe2CH2CH2CONMe2]2Fe (11a). Treatment of 10a–c with CpTiCl3 gave the Group 4 bent metallocene complexes Cp[(C5H4)–CMe2CH2CH2CONR2]TiCl2 (12a–c). Similarly, the reaction of 10b with CpZrCl3 led to formation of the complex Cp[(C5H4)CMe2CH2CH2CONEt2]ZrCl2 (13b). Treatment of 12a with Meerwein's reagent [(Et3O+)(BF4−)] resulted in chloride abstraction with formation of the metallocene cation complex 16 (with BF4− anion), in which, contrary to the 16-electron systems 12 and 13, the carboxamido oxygen atom intramolecularly coordinates to the electron deficient Group 4 metal cation. The organic reagents 8a and 9a as well as the transition metal complexes 11a, 13b, and 16[BF4−] were characterized by X-ray crystal structure analyses.

Hydrolysis and oxidative decomposition of ethyl acetate in sub- and super-critical water

Hydrolysis of ethyl acetate in sub-critical (633K, 200bar) and super-critical water (673K, 240bar) has been investigated in a tubular flow reactor as a model reaction for the depolymerisation of polyesters. Super-critical reaction conditions enable approximately a 10-fold hydrolysis rate in comparison to sub-critical process. The reaction products ethanol and acetic acid are stable under these conditions. Additionally, oxidative decomposition experiments were carried out using ethyl acetate, ethanol and acetic acid as feed in the presence of air, non-catalysed as well as in the presence of a heterogeneous MnO2–CuO/Al2O3 catalyst (Carulite 150®). The catalyst caused only slight increase of ethyl acetate conversion in oxidation compared to hydrolysis, but a noticeable increase in CO2 formation due to destruction of ethanol and acetic acid. In absence of catalyst, the degrees of conversion and selectivities were not affected by addition of oxygen. Fresh and spent catalysts were characterised with standard methods (BET, ICP), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The catalyst material was identified as chemically and mechanically stable under the applied reaction conditions, however, a significant sintering accompanied by a deep structural alteration and a slight reduction were observed. Additionally, the stability of reactor material regarding to corrosion was also tested.

Activity, Selectivity, and Long-Term Stability of Different Metal Oxide Supported Gold Catalysts for the Preferential CO Oxidation in H2-Rich Gas

A comparative study of the catalytic performance and long-term stability of various metal oxide supported gold catalysts during preferential CO oxidation at 80°C in a H2-containing atmosphere (PROX) reveals significant support effects. Compared to Au/γ-Al2O3, where the support is believed to behave neutrally in the reaction process, catalysts supported on reducible transition metal oxides, such as Fe2O3, CeO2, or TiO2, exhibit a CO oxidation activity of up to one magnitude higher at comparable gold particle sizes. The selectivity is also found to strongly depend on the employed metal oxide, amounting, e.g., up to 75% for Au/Co3O4 and down to 35% over Au/SnO2. The deactivation, which is observed for all samples with increasing time on stream, except for Au/γ-Al2O3, is related to the build-up of surface carbonate species. The long-term stability of the investigated catalysts in simulated methanol reformate depends crucially on the ability to form such by-products, with magnesia and Co3O4 supported catalysts being most negatively affected. Overall, Au/CeO2 and, in particular, Au/α-Fe2O3 represent the best compromise under the applied reaction conditions, especially due to the superior activity and the easily reversible deactivation of the latter catalyst.

00/00702 Characterization of recycle solvent and solvent hydrogenation in 150 ton/day pilot plant for NEDOL process

In the search for active catalysts for the conversion of refractory sulfur compounds in diesel fuel, the activity, the role of the support, and the nature of the active sites on Pt/ASA catalysts in deep HDS reactions were studied and compared to Pt/γ-Al2O3 and Pt/XVUSY (stabilised Y zeolite). Pt/ASA appears to be much more active than Pt/γ-Al2O3 but is initially less active than Pt/XVUSY. The latter however, showed strong deactivation after short reaction times. It is concluded that an appropriate tuning of the support acidity is crucial for this reaction. In contrast to the activity, the H2S sensitivity of the tested Pt based catalysts is hardly influenced by acidity of the support. Adsorption of H2S on these sulfur vacancies leads to strong competitive adsorption with the reacting sulfur compound. It is proposed that the stabilisation of small platinum clusters in the presence of H2S is an important effect of acidic supports. In addition, the strength and nature of the acidic sites on the support may affect the Pt–S bond strength of the active sites on small platinum particles. It is concluded that no sulfur-free platinum metal sites are present under the applied reaction conditions. It is therefore proposed that the conversion of 4-E,6-MDBT over Pt/ASA proceeds over sulfur vacancies on small platinum particles. The creation of sulfur vacancies on these small platinum particles may be related to their electron-deficient character on acidic supports.