Unraveling the surface reactions during liquid-phase oxidation of benzyl alcohol on Pd/Al2O3: an in situ ATR-IR study

The palladium-catalyzed liquid-phase reaction of benzyl alcohol to benzaldehyde was investigated in the presence and absence of oxygen by attenuated total reflection infrared (ATR-IR) spectroscopy. The 5 wt % Pd/Al2O3 catalyst was fixed in a flow-through ATR-IR cell serving as a continuous-flow reactor. The reaction conditions (cyclohexane solvent, 323 K, 1 bar) were set in the range commonly applied in the heterogeneous catalytic aerobic oxidation of alcohols. The in situ ATR-IR study of the solid-liquid interface revealed a complex reaction network, including dehydrogenation of benzyl alcohol to benzaldehyde, decarbonylation of benzaldehyde, oxidation of hydrogen and CO on Pd, and formation of benzoic acid catalyzed by both Pd and Al2O3. Continuous formation of CO and its oxidative removal by air resulted in significant steady-state CO coverage of Pd during oxidation of benzyl alcohol. Unexpectedly, benzoic acid formed already in the early stage of the reaction and adsorbed strongly (irreversibly) on the basic sites of Al2O3 and thus remained undetectable in the effluent. This observation questions the reliability of product distributions conventionally determined from the liquid phase. The occurrence of the hydrogenolysis of the C-O bond of benzyl alcohol and formation of toluene indicates that Pd was present in a reduced state (Pd0) even in the presence of oxygen, in agreement with the dehydrogenation mechanism of alcohol oxidation.     

汽车尾气净化反应的UBI-QEP法研究

应用单位键指标-二次指数势(UBI-QEP)方法对汽车尾气净化反应中氮氧化物的分解进行了理论分析.结果表明,NOx的分解的可能途径为氮氧化物的直接分解、CO还原助解和氮助解离.在富氧条件下,以CO助解为主.NO的解离存在N2O中间态.Ni与Rh一样,也是优秀的还原NOx催化剂,若能有效克服表面氧的共吸附,Ni-Cu可能是良好的汽车尾气净化催化剂的主体成份.     

The catalytic hydrogenolysis of benzylamine derivatives

The hydrogenolysis of optically active ethyl 2-amino-2-phenylpropionate (I), its N-methyl (II), and N,N-dimethyl (III) derivatives was studied using Raney Ni and Pd as the catalysts. The Raney Ni catalysed hydrogenolysis of II and III, as well as the reaction catalysed by Pd, occurred predominantly with inversion of configuration; this is not in accord with the hydrogenolysis of corresponding benzyl alcohols. This difference can be ascribed to the difference of the affinity for Ni between N and O atoms. The “SN_Ni” process may be inhibited in the Raney Ni catalysed hydrogenolysis of II and III since the amino group acts as a self-catalyst poison, and the “S_N2” process appears to be preferable to the “S_Ni” one. The predominance of the configurationally inversion was also observed in the Pd catalysed hydrogenolysis of I. These results over Pd are reasonable in reflecting that the N atom has not so high affinity for Pd. The hydrogenolysis of a quarternary ammonium bromide of I was also reported.     

A Convenient Synthesis of the Echinacea‐Derived Immunostimulator and HIV‐1 Integrase Inhibitor (−)‐(2R,3R)‐Chicoric Acid

The Echinacea‐derived immunostimulator and HIV‐1 integrase inhibitor (−)‐chicoric acid (=2,3‐bis{[3‐(3,4‐dihydroxyphenyl)‐1‐oxoprop‐2‐enyl]oxy}butanedioic acid; 1a ) was conveniently prepared via a silane‐promoted Pd‐mediated chemoselective hydrogenolysis of its perbenzylated derivative 12a , which was generated from an efficient and reliable carbodiimide‐mediated coupling reaction between the caffeic acid dibenzyl ether derivative 7 and commercially available (+)‐dibenzyl L ‐tartrate ( 9a ). The other naturally occurring dextrorotatory chicoric acid ( 1b ) can be similarly prepared.     

A Study of Carbon Deposition on Catalysts During the Catalytic Partial Oxidation of Methane to Syngas in a Fluidized bed

The deposition of carbon on catalysts during the partial oxidation of methane to syngas has been investigated in a fluidized bed. It was found that the relative rate of carbon deposition follows the order Ni>>Pd>Pt, Rh. Although the rate of carbon deposition in the fluidized bed was much lower than that in the fixed bed, carbon deposition could still be detected in the fluidized bed if a CH₄ /O₂ ratio in greater than 2.3 was used.     

Molecular rearrangements—II: The pyrolysis of benzyl-β-naphthyl ether

When purified benzyl-β-naphthyl ether was heated at 260°, in absence of any promotor, the benzyl group migrated to the α-position of the naphthol nucleus. β-Naphthol, toluene, dibenzyl and 9-phenyl-1,2,7,8-dibenzoxanthene also were formed. When quinoline was used as a solvent, the normal rearrangement products were obtained together with 2- and 4-benzylquinolines and 1(2-quinolyl)2-naphthol and its isomeric 1(4-quinolyl)2-naphthol. When phenol and anisole were used as solvents, the rearrangement was accompanied with benzylation of the solvent.     

Phase relationships and thermodynamic interactions in isotactic polypropylene–diluent systems

Phase relationships of isotactic polypropylene in various organic diluents were investigated. The diluents used were aliphatic alcohols, alkyl phenols, aryl phenols, diphenyl derivatives, alkyl aryl ethers, esters, and others. Among the diluents examined, n-butyl alcohol, p-tert-butyl phenol, p-tert-amyl phenol, diphenyl, diphenyl ether, benzyl phenyl ether, dibenzyl ether, and benzyl propionate were found to be theta solvents for isotactic polypropylene at temperatures in the range 120–190°C. For these theta solvents, the thermodynamic interaction parameters were determined. The results are discussed in relation to the type of diluent.     

Synthesis of Stereoisomers of Cryptofolione 6'-Mono- and 4', 6'-Di-O-benzyl Ethers

Synthesis of stereoisomers of 6′‐mono‐ and 4′,6′‐di‐O‐benzyl cryptofolione is described through a key intermediate 6 , which was prepared by coupling of iodobenzene 8 with chiral propargyl alcohol 9 under Cosford protocol conditions. Monobenzyl ether 4 is obtained via epoxide 6 opening with vinyl Grignard, followed by cross‐metathesis reaction with a vinyl lactone 11 . Whereas, dibenzyl ether 5 is prepared by epoxide 6 opening with chiral propargyl alcohol 7 followed by simple transformations and finally cis‐Wittig olefination.     

Skeletal rearrangements of protonated molecular ions of some ethers

Skeletal rearrangements are reported of protonated molecular ions in the chemical ionization mass spectra of allyl cyclohexyl ether, benzyl cyclohexyl ether, t-butyl cyclohexyl ether and dibenzyl ether.     

Etherification of benzyl alcohol under microwave irradiation using a heteropoly acid as catalyst

Selective dehydration of benzyl alcohol to dibenzyl ether using heteropoly acid as catalyst in solvent-free conditions under microwave irradiation has been studied. The microwave power and irradiation time, and concentration of heteropoly acid are key factors, and under the severe conditions dibenzyl ether was polymerized. This revised version was published online in August 2006 with corrections to the Cover Date.     

Alkyne Insertion into the M?P and M?H Bonds (M=Pd,Ni, Pt,and Rh): A Theoretical Mechanistic Study of the C?P and C?H Bond‐Formation Steps

In hydrogen‐metal‐phosphorus (H M P) transition metal complexes (proposed as intermediates of H P bond addition to alkynes in the catalytic hydrophosphorylation, hydrophosphinylation, and hydrophospination reactions), alkyne insertion into the metal‐hydrogen bond was found much more facile compared to alkyne insertion into the metal‐phosphorus bond. The conclusion was verified for different metals (Pd, Ni, Pt, and Rh), ligands, and phosphorus groups at various theory levels (B3LYP, B3PW91, BLYP, MP2, and ONIOM). The relative reactivity of the metal complexes in the reaction with alkynes was estimated and decreased in the order of Ni>Pd>Rh>Pt. A trend in relative reactivity was established for various types of phosphorus groups: PR₂>P(O)R₂>P(O)(OR)₂, which showed a decrease in rate upon increasing the number of the oxygen atoms attached to the phosphorus center.     

Hydrogenolysis of Furfuryl Alcohol to 1,2-Pentanediol Over Supported Ruthenium Catalysts

Hydrogenolysis of the furan rings of furfural and furfuryl alcohol, which can be obtained from biomass, has attracted attention as a method for obtaining valuable chemicals such as 1,2-pentanediol. In this study, we examined the hydrogenolysis of furfuryl alcohol to 1,2-pentanediol over Pd/C, Pt/C, Rh/C, and various supported Ru catalysts in several solvents. In particular, we investigated the effects of combinations of solvents and supports on the reaction outcome. Of all the tested combinations, Ru/MgO in water gave the best selectivity for 1,2-pentanediol: with this catalyst, 42 % selectivity for 1,2-pentanediol was achieved upon hydrogenolysis of furfuryl alcohol for 1 h at 463 K. In contrast, reaction in water in the presence of Ru/Al₂O₃ afforded cyclopentanone and cyclopentanol by means of hydrogenation and rearrangement reactions.     

2-(Trimethylsilyl)äthylester als Carboxylschutzgruppe; Anwendung bei der Synthese des (−)-(S)-Curvularins

2-(Trimethylsilyl)ethyl Esters as Carboxyl Protecting Group; Application in the Synthesis of (?)-(S)-Curvularin The mould metabolite curvularin (VIII) has been synthesized with the help of a new carboxyl protecting group that can be removed selectively with fluoride ions. 2-(Trimethylsilyl)ethyl 7-hydroxy-octanoate (III) was acylated with 3,5-dibenzyloxy-phenacetyl chloride (IV) to form V with two different ester groups. Tetrabutyl-ammonium fluoride in tetrahydrofuran cleaved the 2-(trimethylsilyl)ethyl ester in V selectively to form the carboxylate anion of VI together with ethylene and trimethylsilyl fluoride. Curvularin dibenzyl ether (VII) was formed by intramolecular acylation of VI. Removal of the benzyl ether groups in VII by hydrogenolysis led to (±)-curvularin (VIII). The naturally occurring (?)-enantiomer was formed when (+)-(S)-III served as starting material.     

Reductions of Benzene Derivatives Whose Benzylic Positions Bear Oxygen Atoms under Mild Conditions

Reductions of compounds whose benzylic positions bear O‐atoms, such as benzyl alcohol, dibenzyl ether, styrene oxide, benzaldehyde, acetophenone, and benzophenone, to the corresponding non‐conjugated dienes were performed by using t‐BuOH, Li, and gaseous NH₃ in THF at room temperature. In these reductions, it was observed that the functional groups at benzylic positions were reduced first.     

Special features of gas chromatography determination of dibenzyl ether hydroperoxide impurity in benzyl alcohol

Chromato–mass spectrometric analysis of a benzyl alcohol sample has revealed the presence of dibenzyl ether hydroperoxide C₆H₅CH(OOH)OCH₂C₆H₅ impurity showing the retention index 1894±10 on a standard stationary phase (RTX-5). A special feature of this hydroperoxide is its stability under conditions of gas chromatography separation (retention temperature 190°С). This has been confirmed by the measurement of the analytical signal between the chromatographic peaks of the hydroperoxide and the major product of its decomposition (benzyl benzoate). From this criterion, dibenzyl ether hydroperoxide is more stable that, for instance, monomethyl phthalate.     

负载型Pd-Ni双金属纳米颗粒在无溶剂苯甲醇氧化中有效抑制甲苯的生成

醇类化合物的选择性氧化是实验室和工业应用中一类重要的官能团转化反应.以分子氧为氧化剂,在液相无溶剂条件下温和氧化符合绿色化学的要求.负载型Pd基催化剂因其优异的催化活性而在该反应中得到广泛应用.但是,单金属Pd催化剂对反应目标产物醛类化合物的选择性还有待提高.例如,在苯甲醇液相无溶剂氧化中,甲苯是在单金属Pd催化剂上的主要副产物.针对这一问题,除了对载体进行改性和修饰外,开发双金属Pd基催化剂也是一种有效的选择性调控策略.虽然已有的Pd-Au双金属催化剂可以在一定程度上降低甲苯的选择性,但是在较高温度和较高转化率下仍然难以控制甲苯的大量生成.本文采用固相合金化法合成了负载型Pd-Ni双金属纳米颗粒.该方法首先以硝酸镍为镍的前驱体浸渍介孔二氧化硅,然后负载钯纳米颗粒.在高温固相还原条件下,作为种子的钯纳米颗粒和镍通过原子迁移和生长,形成Pd-Ni双金属纳米颗粒.扫描透射电镜、能量色散X射线光谱、X射线衍射和X射线光电子能谱等表征证实了Pd-Ni双金属纳米颗粒的生成.上述催化剂用于苯甲醇液相无溶剂氧化,催化结果显示Ni的加入可以抑制副产物甲苯的生成,并且随Ni负载量增加,甲苯的选择性(在80%等转化率下)由22.6%(单金属Pd)降低至1.6%(双金属Pd1Ni20).尽管Ni的加入降低了单金属Pd的活性,但是由于提高了目标产物苯甲醛的选择性,醛的最终产率得到提升.进一步催化研究表明,Ni的加入可以抑制无氧氛围下甲苯的生成,说明Ni可以抑制歧化反应和降低表面氢浓度.这种作用可归结于Pd-Ni双金属的协同效应.该效应得到了CO吸附的傅里叶变换漫反射红外光谱和密度泛函理论研究的证实.双金属的几何效应和电子效应均减弱了苯甲醇在双金属纳米颗粒表面的解离吸附和相互作用,导致苯甲醇的吸附减弱,同时C–O键断裂不易进行.另外,由于Ni的亲氧性,双金属纳米颗粒表面有利于氧的吸附,降低吸附氢的浓度,减少C–H键生成,从而抑制甲苯的生成.     

Catalytic reduction of aromatic polynitro compounds

The liquid-phase catalytic hydrogenation of 3,5-dinitrophenyl phenyl ether to give 3,5-diaminophenyl phenyl ether in the presence of Group VIII metals as catalysts has been investigated. The main kinetic characteristics of the process have been established. The reduction occursvia the formation of 5-amino-3-nitrophenyl phenyl ether. In terms of their activity, the catalysts studied can be arranged in the following sequence: 1% Pd/Sibunit> 2 % Pd/C > Lindlare Pd > 5% Ru/Sibunit > Raney Ni. The selectivity of the process with respect to intermediate 5-amino-3-nitrophenyl phenyl ether depends on the relative adsorption abilities of mono- and dinitro compounds. A promoting effect of water during hydrogenation of 3,5-dinitrophenyl phenyl ether in isopropanol or 1,4-dioxane has been noted. Catalytic synthesis of 3,5-diaminophenyl phenyl ether has been carried out for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1716–1719, September, 1995.     

溴化苄的合成工艺研究

以二苄醚和氢溴酸为原料,SO42-/TiO2为催化剂,环已烷为带水剂,合成了溴化苄。实验分别考察了反应物摩尔比、反应时间、反应温度、带水剂的用量,催化剂的使用量等因素对溴化苄收率的影响,得出了用此方法合成溴化苄的最佳反应条件:氢溴酸与二苄醚的摩尔比为3:1,反应时间为8 h,环已烷为8 mL,SO42-/TiO2催化剂的用量为0.5 g,溴化苄的收率达80.2%。     

Pyrolytic Chemistry of Benzyl Benzoate

Flash vacuum pyrolysis of benzyl benzoate ( 3 ) at temperatures in the range 750–900 °C and at 10² torr gave diphcnylmethane ( 5 ) as the major product with toluene ( 6 ) and eight other trace products, namely bipbenyl ( 7 ), dibenzyl ( 8 ), 2-, 3-, 4-phenyltoluenes ( 9,10,11 , respectively), fluorcne ( 12 ), benzyl alcohol ( 4 ) and benzaldehyde ( 13 ). The mechanism of formation of these products is proposed to involve benzyl and phenyl radicals.     

Thermal study of Cu(II), Ni(II) and Pd(II) chelates of resacetophenoneoxime

Summary Thermal analysis of resacetophenoneoxime and its chelates of Cu(II), Ni(II) and Pd(II) is carried out. A comparison is made between the thermal stability and the solution stability of chelates and found that they oppose each other. The thermal stability for the chelates studied is PdNi>Cu and the solution stability on the other hand is Pd>Cu>Ni. The results obtained were compared with the data available in the literature for structurally similar oximes. The advantages of the reagent for gravimetric and thermogravimetric analysis of metal ions were discussed.

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Thermochemische Untersuchung der Cu(II)-, Ni(II)- und Pd(II)-Chelate von Resacetophenonoxim

Zusammenfassung Die thermische Stabilität der Chelate und ihre Stabilität in Lösung wurden verglichen und festgestellt, daß diese sich nicht entsprechen. Die erste nimmt ab in der Reihenfolge PdNi>Cu, die zweite in die Reihenfolge Pd>Cu>Ni. Die erhaltenen Ergebnisse wurden denen aus der Literatur für strukturell ähnliche Oxime gegenübergestellt. Die Vorteile des Reagenses für gravimetrische und thermogravimetrische Bestimmungen werden diskutiert.