Safe Removal of the Allyl Protecting Groups of Allyl Esters using a Recyclable,Low‐Leaching and Ligand‐Free Palladium Nanoparticle Catalyst

A safe, facile and low‐leaching (up to 0.04 ppm) method has been developed for the removal of allyl, prenyl and benzyl protecting groups from the corresponding esters, using a sulfur‐modified gold‐supported palladium (SAPd) nanoparticle catalyst, which is known to be non‐flammable. The catalyst itself was found to be recyclable and the reaction appeared to proceed on the surface of the SAPd.

     

Low‐Pressure Hydrogenation of Arenecarboxylic Acids to Aryl Aldehydes

A highly effective palladium catalyst has been developed that allows the selective hydrogenation of arenecarboxylic acids to the aryl aldehydes in the presence of pivalic anhydride already at 5 bar hydrogen pressure. With the new catalyst, diversely functionalized aromatic and heteroaromatic aldehydes are conveniently accessible from the corresponding carboxylic acids in a single reaction step without any overreduction to the alcohols.     

Palladium‐Catalyzed Reduction of Carboxylic Acids to Aldehydes with Hydrosilanes in the Presence of Pivalic Anhydride

A palladium catalyst system that allows the reduction of carboxylic acids to the corresponding aldehydes with hydrosilanes as reducing agent and pivalic anhydride as an indispensable reagent has been developed. A simple mixture of commercially available bis(dibenzylideneacetone)palladium(0) [Pd(dba)₂], tri(para‐tolyl)phosphane and methylphenylsilane realized the reduction of various aliphatic carboxylic acids as well as benzoic acids to aldehydes in good to high yields.

     

Hydrolysis of Alkyl Ester on Lipase/Silicalite-1 Catalyst

Pure silica zeolites have been prepared in powder and pellets form with different surface chemical properties in order to investigate how the binding forces in the lipase enzyme adsorption influence the final conformation of the immobilized enzyme and its catalytic activity. The catalytic activity of the adsorbed lipase have been tested in the alkyl esters hydrolysis reaction. The higher alkyl-esters conversion is observed for the lipase immobilized on the supports prepared in OH⁻ media compared to the fluoride media supports. The obtained results can be explained by the two different non-covalent interactions between the external surface of zeolites and the enzyme.     

Recyclable Solid Ruthenium Catalysts Supported on Metal Oxides for the Addition of Carboxylic Acids to Terminal Alkynes

Ceria‐supported ruthenium catalysts (Ru/CeO₂) were found to be quite effective for the addition of various carboxylic acids to terminal alkynes, which gave the corresponding enol esters in moderate to high yields. The major products of the reaction were E‐isomers of anti‐Markovnikov adducts. Among the ceria‐supported ruthenium catalysts examined, those prepared using ruthenium precursors with chloride ligands showed high activities. The zirconia‐supported ruthenium catalyst (Ru/ZrO₂) showed activity comparable to that of the ceria‐supported catalyst. These catalysts were recyclable without a significant loss of activity, and the leaching of ruthenium species into the liquid phase was negligible after cooling the reaction mixture, which indicates marked superiority of the present solid oxide catalysts to conventional homogeneous catalysts.     

功能化松香丙烯醇酯聚合物吸附分离银杏黄酮

研究了功能化松香丙烯醇酯聚合物吸附分离银杏黄酮的效果.结果表明,功能化松香丙烯醇酯聚合物对银杏黄酮的静态吸附量为22.6 mg·g-1,洗脱液为70%乙醇水溶液,动态吸附量为4.7 mg·g-1,功能化交联松香丙烯醇酯聚合物对银杏黄酮的静态吸附量和动态吸附量分别为14.2 mg·g-1和5.5 mg·g-1.经过再生,功能化松香丙烯醇酯聚合物可以重复使用,3次使用后对银杏黄酮的吸附能力没有明显降低.     

聚(对乙烯基苄基丁二酰亚胺)树脂的合成及其催化酯水解反应活性

在碱性条件下,氯甲基化聚苯乙烯与丁二酰亚胺反应合成了聚(对乙烯基苄基丁二酰亚胺)树脂(简称为丁二酰亚胺树脂),采用元素分析、红外光谱对合成树脂的组成进行了表征。并考察了该树脂在酯水解反应中的催化活性。结果表明,在合成反应12h后,树脂增重最多,其中氮含量为4.08%,残余氯含量为2.51%,IR谱图中1640cm-1处出现较强酰胺羰基峰。在催化酯水解反应中,酸收率均大于85%,且催化稳定性好。     

Tandem Catalysis: Access to Ketones from Aldehydes and Arylboronic Acids via Rhodium‐Catalyzed Addition/Oxidation

Direct cross‐coupling reactions of aromatic aldehydes with arylboronic acids afforded ketones in high yields and under mild conditions in the presence of a rhodium catalyst, acetone and a base. This new reaction, involving a formal aldehyde C H bond activation, is believed to proceed via a tandem process involving addition of the organometallic species to the aldehyde followed by oxidation by β‐hydride transfer.     

Chemistry of Pyruvate Enolates: anti‐Selective Direct Aldol Reactions of Pyruvate Ester with Sugar Aldehydes Promoted by a Dinuclear Zinc Catalyst

A chiral dinuclear zinc complex can effectively catalyse the direct aldol reactions of pyruvic acid ester with various chiral sugar aldehydes, thus functionally mimicking the pyruvate‐dependent type II aldolases. Application of sterically hindered aryl esters allows for the elusive aldol reaction of the pyruvate donor with controlled anti‐selectivity en route to the short and efficient synthesis of 3‐deoxy‐2‐ulosonic acids. Pyruvic acid ester is here used as a chemical equivalent of phosphoenol pyruvate (PEP) in imitation of the synthetic principle used in nature. The presented biomimetic methodologies use enol formation for the highly efficient and flexible formation of various C₆–C₉ ulosonic acids. Particularly, efficient and concise syntheses of 3‐deoxy‐D ‐erythro‐hex‐2‐ulosonic acid (KDG, overall 50% yield), 3‐deoxy‐D ‐ribo‐hept‐2‐ulosonic acid (DRH, overall 53% yield) and 3‐deoxy‐D ‐glycero‐D ‐talo‐non‐2‐ulosonic acid (4‐epi‐KDN, overall 78% yield) are described. This direct efficient application of pyruvic esters does not require additional demasking steps and thus surpassess previously methodologies utilising masked pyruvic synthons such 2‐acetylthiazole and pyruvic aldehyde dimethyl acetal.

     

A Comprehensive Evaluation of the Melting Points of Fatty Acids and Esters Determined by Differential Scanning Calorimetry

The melting point is one of the most important physical properties of a chemical compound and it plays a significant role in determining possible applications. For fatty acid esters the melting point is essential for a variety of food and non-food applications, the latter including biodiesel and its cold-flow properties. In this work, the melting points of fatty acids and esters (methyl, ethyl, propyl, butyl) in the C₈–C₂₄ range were determined by differential scanning calorimetry (DSC), many of which for the first time. Data for triacylglycerols as well as ricinoleic acid and its methyl and ethyl esters were also acquired. For some compounds whose melting points have been previously reported, data discrepancies exist and a comprehensive determination by DSC has not been available. Variations in the present data up to several °C compared to data in prior literature were observed. The melting points of some methyl-branched iso- and anteiso-acids and esters were also determined. Previously unreported systematic effects of compound structure on melting point are presented, including those for ω-9 monounsaturated fatty acids and esters as well as for methyl-branched iso and anteiso fatty acids and esters. The melting point of a pure fatty acid or ester as determined by DSC can vary up to approximately 1 °C. Other thermal data, including heat flow and melting onset temperatures are briefly discussed. Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable.     

The Catalytic Diastereo‐ and Enantioselective Claisen Rearrangement of 2‐Alkoxycarbonyl‐Substituted Allyl Vinyl Ether

The catalytic asymmetric Claisen rearrangement of 2‐alkoxycarbonyl‐substituted allyl vinyl ethers that contain two stereogenic double bonds is described. A combination of the highly Lewis acidic [Cu{(S,S)‐tert‐Bu‐box}](H₂O)₂(SbF₆)₂ complex and molecular sieves served as catalyst and afforded the Claisen rearrangement products, substituted and functionalized α‐keto esters, in high yield with a remarkable diastereo‐ and enantioselectivity. The influence of ligand structure, counterion and allyl vinyl ether double bond configuration on the stereoselectivity of the rearrangement was briefly investigated. We propose an explanation for the rate accelerating effect of the Lewis acid as well as a stereochemical model which serve to explain and predict the stereochemical course of the copper bis(oxazoline) catalyzed Claisen rearrangement.     

Ru/Al_2O_3催化剂上邻苯二甲酸二丁酯加氢合成1,2-环己烷二甲酸二丁酯

以浸渍法制备Ru/Al2O3催化剂,研究在高压反应釜中Ru/Al2O3上催化加氢邻苯二甲酸二丁酯(DBP)合成1,2-环己烷二甲酸二丁酯(CDADE)。采用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、扫描电镜(SEM)、X射线能谱仪(EDS)和透射电子显微镜(TEM)对催化剂进行表征。结果表明,Ru负载量为3.0%(质量分数),200℃氢气气氛中还原的Ru/Al2O3催化剂,在催化DBP合成CDADE的反应中具有较高的催化活性。在反应温度80℃、反应压力2.0~2.5 MPa和搅拌转速800 r/min下,DBP转化率和CDADE选择性分别达到99.972%和99.904%,催化剂重复使用9次后仍有较高活性,但继续使用,由于活性组分Ru部分流失、团聚和催化剂表面积炭,催化剂活性有所下降。     

Nitrilase‐Catalyzed Selective Hydrolysis of Dinitriles and Green Access to the Cyanocarboxylic Acids of Pharmaceutical Importance

To further explore its synthetic applications, the nitrilase bll6402 from Bradyrhizobium japonicum strain USDA110 has been examined toward the hydrolysis of various dinitriles. It has been found that nitrilase bll6402 effectively hydrolyzed α,ω‐dinitriles to ω‐cyanocarboxylic acids, and the selectivity was independent of the substrate chain length. This feature is distinct from all the known nitrilases of various sources. Nitrilase bll6402 was thus applied to the synthesis of 1‐cyanocycloalkaneacetic acids, the useful precursors for the synthesis of gabapentin and its analogues.     

A Novel and Efficient Synthesis of Tocopheryl Quinones by Homogeneous and Heterogeneous Methyltrioxorhenium/Hydrogen Peroxide Catalytic Systems

A convenient and efficient application of heterogeneous poly(4‐vinylpyridine), poly(4‐vinylpyridine N‐oxide), and polystyrene/methylrhenium trioxide systems for the selective oxidation of tocopherols and tocopherol derivatives to the corresponding ortho‐ and para‐tocopherylquinones is described. Environment friendly, easily available, and low‐cost hydrogen peroxide (H₂O₂) was used as the oxygen atom donor. The antiviral activity of the newly synthesized tocopherylquinones and their parent tocopherols against influenza A virus is also reported. On the basis of the biological assay, the activity of tocopherols against influenza virus is higher than that showed by the corresponding tocopherylquinones, thus suggesting, for the first time, a drawback effect of the oxidative metabolism on the antiviral activity of these compounds.     

Catalytic Conversions in Aqueous Media. Part 2. A Novel and Highly Efficient Biphasic Hydrogenation of Renewable Methyl Esters of Linseed and Sunflower Oils to High Quality Biodiesel Employing Rh/TPPTS Complexes

An unusual high catalytic activity (TOF = 117,000 h⁻¹) and high catalyst productivity (TON = 9,700) have been achieved in the first example of partial hydrogenation of renewable polyunsaturated crude methyl esters of linseed and sunflower oils catalyzed by water soluble Rh/TPPTS complexes [TPPTS = P(C₆H₄-m-SO₃Na)₃] in aqueous/organic two-phase systems to afford monounsaturated fatty esters which is biodiesel first generation of improved oxidative stability, energy and environmental performance at a low pour point. This exceptionally high catalytic activity contrast with the general perception that industrially applied water soluble Rh/TPPTS catalysts normally exhibit very low rates in the conversions of higher molecular weight starting materials in aqueous/organic two-phase systems. For part 1 of this series see Ref. [14].