Cationic ruthenium complex of the formula [RuCl(2,6-diacetylpyridine)(PPh3)2]BArF and its catalytic activity in the formation of enol esters

A new ruthenium 2,6-diacetylpyridine complex was synthesized and applied in the atom-economic synthesis of enol esters through Markovnikov-directed addition of carboxylic acids to terminal alkynes. The ruthenium complex [RuCl(dap)(PPh₃)₂]⁺BArF^? was synthesized from [RuCl₂(PPh₃)₂] and the corresponding ligand 2,6-diacetylpyridine (dap). The complex was characterized structurally. The new ruthenium complex was utilized under ambient conditions as a catalyst in the Markovnikov addition of carboxylic acids to terminal alkynes to afford the corresponding enol esters in 93% to 52% isolated yields (85?°C, 16?h reaction time, 1?mol% catalyst loading).     

Synthesis of fluorine-containing tetraketones and diketo esters and luminescence-spectral properties of their complexes with lanthanide ions

The Claisen condensation of diesters of fluorinated dicarboxylic acids with 2-acetyl-naphthalene affords the corresponding naphthyl-containing tetraketones and diketo esters. The luminescence-spectral properties and stability constants of complexes of these compounds with Eu³⁺ ions were estimated. The characteristics of the complexes are comparable with those of fluorinated β-diketones containing chromophoric substituents, which are widely used in luminescence analysis. The synthesized naphthyl-containing diketo esters are efficiently conjugated with proteins and can be used for detection of biospecific interactions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 269—273, February, 2006.     

A novel method for the synthesis of biodiesel from soybean oil and urea

The increasing demand for energy has encouraged the development of renewable resources and environmentally benign fuel such as biodiesel. In this study, ethyl fatty esters (EFEs), a major component of biodiesel fuel, were synthesized from soybean oil using sodium ethoxide as a catalyst. By-products were glycerol and difatty acyl urea (DFAU), which has biological characteristics, as antibiotics and antifungal medications. Both EFEs and DFAU have been characterized using Fourier transform infrared (FTIR) spectroscopy, and ¹H nuclear magnetic resonance (NMR) technique. The optimum conditions were studied as a function of reaction time, reactant molar ratios, catalyst percentage and the effect of organic solvents. The conversion ratio of soybean oil into pure EFEs was 76% after 10 h of reaction. The highest conversion yield of EFEs is obtained when the urea/soybean oil ratio was from 6.2 mmol to 1 mmol, while the highest production of DFAU is obtained when the ethoxide (as a catalyst)/soybean oil ratio is from 6.4 mmol to 1 mmol in hexane as the reaction medium.     

The Determination of Protonation Constants of Some Amino Acids and Their Esters by Potentiometry in Different Media

In this study, stoichiometric protonation constants of L-tyrosine, L-cysteine, L-tryptophane, L-lysine, and L-histidine, and their methyl and ethyl esters in water and ethanol–water mixtures of 30, 50, and 70% ethanol (v/v), were determined potentiometrically using a combined pH electrode system calibrated as the concentration of hydrogen ion. Titrations were performed at 25^∘C and the ionic strength of the medium was maintained at 0.10 mol⋅L⁻¹ using sodium chloride. Protonation constants were calculated by using the BEST computer program. The effect of solvent composition on the protonation constants is discussed. The log₁₀ K₂ values of esters generally decreased with increasing ethanol content. However, the log₁₀ K₁ values of the esters of L-tyrosine, L-cysteine, and L-tryptophane were found to increase with increasing ethanol content in contrast those of L-lysine and L-histidine esters.     

Preparation of benzoate esters of morphine and its derivatives

Abstract  

Sustained analgesia is crucial for patients suffering from long-acting pain. Ester derivatives of morphine could enhance the lipophilicity of morphine; consequently its transdermal delivery as well as its duration of action are also increased. Therefore, twenty-one 3-O-, 6-O-, and 14-O-benzoate esters of morphine and their derivatives were synthesized in order to elaborate different synthetic methods suitable for esterification of these widely used compounds. Schotten–Baumann reaction was applied with sodium hydrogen carbonate, triethylamine, or pyridine in methylene chloride or 1,2-dichloroethane as solvents. The presence of 4-dimethylaminopyridine catalyst was also successfully utilized mainly in the case of tertiary alcohols. A novel synthesis of dihydromorphine via diacetyl morphine free of by-products is also presented. Structures of all synthesized compounds were elucidated by ¹H nuclear magnetic resonance (NMR), ¹³C NMR, high-resolution mass spectrometry (HRMS), and electron ionization mass spectrometry (EI-MS). The log D (pH 7.4) values of the synthesized compounds were determined by a reversed-phase high-performance liquid chromatography (HPLC)–MS-based method, and calculated hydrolysis rate constants are also provided. The synthesized benzoate esters are potential prodrugs of the parent morphine with enhanced lipophilicity, derivatives which can also be used in transdermal drug delivery as prospective long-acting narcotic analgesics.     

Optimization of biodiesel production via transesterification of soybean oil using α-MoO3 catalyst obtained by the combustion method

A catalyst based on MoO₃ was synthesized by a simple and fast pilot-scale combustion reaction method and applied to the conversion of soybean oil to biodiesel via transesterification. For that, the statistical analysis of the catalyst amount and temperature, factors that influence the process, was evaluated by means of central composite design 2². MoO₃ was characterized in terms of structure by X-ray diffraction (XRD), textural characterization Brunauer-Emmett-Teller (BET), density by helium pycnometry (DE), particle size analysis (DG) and acidity tests by temperature-programmed desorption of ammonia (NH₃-TPD), chemical analysis by X-ray fluorescence (EDX), morphology by scanning electron microscopy (SEM) and catalytic properties. The transesterification products were characterized by gas chromatography (GC), acidity index (AI) and kinematic viscosity (KV). The results indicate the catalyst formation with a surface area of 1.36 m²g^?1, and density of 4.5 g/cm³ which consists of a single crystalline phase of orthorhombic configuration, with total NH₃ acidity of 33.61 μ.mol/g. Morphological characterization revealed that the catalyst is formed by irregular plates of various sizes and shapes, with a wide sizes range of agglomerated particles. In the soybean oil transesterification reactions, the catalyst was active showing 96.9% conversion to ethyl esters. The experimental design was meaningful and predictive, with a reliability level of 95%. The statistical analysis identified temperature as a significant variable for the adopted planning. To conclude, a new single-phase catalyst (α-MoO₃) has been developed and successfully applied to the biodiesel Synthesis from soybean oil. These results have a positive and promising impact for biodiesel production by transesterification of soybean oil against ethanol.     

Synthesis of environmental benign biolubricant from wild castor seed by reactive extraction and optimization

Castor oil alkyl esters are a possible biolubricant since they contain 90% hydroxyl fatty acid, which improves the oil's lubricity. Due to the limitations of the conventional approach, castor oil propyl ester (COPE) from wild castor seed was synthesized by reactive extraction. The factors influencing yield of reaction was optimised by response surface methodology to obtain a high yield. The influence of amount of catalyst, propanol to oil proportion, temperature, and rotating speed on castor oil propyl ester yield was investigated using a central composite design.The optimised reaction condition is propanol to oil molar proportion of 275: 1 with 1.5 wt% of catalyst loading at 90 °C and rotating speed of 450 rpm with COPE yield of 78.6% in 3hrs. Physico-chemical properties of alkyl esters were determined. COPE can be employed as a bioadditive to ultra-low sulphur diesel fuels due to its high lubricity.     

The use of sulfated tin oxide as solid superacid catalyst for heterogeneous transesterification of <Emphasis Type="Italic">Jatropha curcas</Emphasis> oil

This work presents the use of sulfated tin oxide enhanced with SiO₂ (SO₄²⁻/SnO₂-SiO₂) as a superacid solid catalyst to produce methyl esters from Jatropha curcas oil. The study was conducted using the design of experiment (DoE), specifically a response surface methodology based on a threevariable central composite design (CCD) with α = 2. The reaction parameters in the parametric study were: reaction temperature (60°C to 180°C), reaction period (1 h to 3 h), and methanol to oil mole ratio (1: 6 to 1: 24). Production of the esters was conducted using an autoclave nitrogen pressurized reactor equipped with a thermocouple and a magnetic stirrer. The maximum methyl esters yield of 97 mass % was obtained at the reaction conditions: temperature of 180°C, reaction period of 2 h, and methanol to oil mole ratio of 1: 15. The catalyst amount and agitation speed were fixed to 3 mass % and 350–360 min⁻¹, respectively. Properties of the methyl esters obtained fell within the recommended biodiesel standards such as ASTM D6751 (ASTM, 2003).     

扫帚状氧化铈制备及其对Pt基阳极催化剂催化性能的影响

采用水热合成法,合成了比表面积为175 m²·g^-1,孔径在2~4nm范围内的扫帚状CeO₂。通过微波辅助乙二醇还原氯铂酸法制备了Pt-CeO₂/RGO催化剂,探究扫帚状CeO₂的添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪（XRD）、扫描电镜（SEM）、N₂吸附-脱附、X射线光电子能谱（XPS）对所制备的CeO₂及催化剂进行表征。利用电化学工作站对催化剂进行电化学性能测试。结果表明,催化剂中CeO₂保持原有扫帚状,Pt纳米粒子均匀分布于石墨烯载体表面;当m_RGO∶m_CeO2=1∶2时,添加了扫帚状CeO₂的Pt-CeO₂/RGO催化剂的电催化性能最优,电化学活性表面积为102.83 m²·g^-1,对乙醇氧化的峰值电流密度为757.17 A·g^-1,1 000 s的稳态电流密度为108.17 A·g^-1,对乙醇催化氧化反应的电荷转移电阻最小,活化能最低。     

扫帚状氧化铈制备及其对Pt基阳极催化剂催化性能的影响

采用水热合成法,合成了比表面积为175 m~2·g~(-1),孔径在2~4nm范围内的扫帚状CeO_2。通过微波辅助乙二醇还原氯铂酸法制备了Pt-CeO_2/RGO催化剂,探究扫帚状CeO_2的添加对Pt基催化剂电催化性能的影响。利用X射线衍射仪(XRD)、扫描电镜(SEM)、N_2吸附-脱附、X射线光电子能谱(XPS)对所制备的CeO_2及催化剂进行表征。利用电化学工作站对催化剂进行电化学性能测试。结果表明,催化剂中CeO_2保持原有扫帚状,Pt纳米粒子均匀分布于石墨烯载体表面;当m_(RGO)∶m_(CeO2)=1∶2时,添加了扫帚状CeO_2的Pt-CeO_2/RGO催化剂的电催化性能最优,电化学活性表面积为102.83 m~2·g~(-1),对乙醇氧化的峰值电流密度为757.17A·g~(-1),1 000 s的稳态电流密度为108.17 A·g~(-1),对乙醇催化氧化反应的电荷转移电阻最小,活化能最低。     

Structure of liquid-crystalline phases formed by N-acetyl-L-glutamic acid oligomeric benzyl esters –2H NMR study

A series of N-acetyl-L-glutamic acid oligopeptide benzyl esters with exact residue numbers 4, 6, and 12 has been synthesized by a stepwise procedure. For these oligopeptide–dioxane binary systems, the behavior of the liquid-crystalline phases has been examined␣by the use of ²H NMR, and the results indicate that highly ordered aggregates formed by these oligopeptides in dioxane are in an alignment similar to that in a nematic mesophase. Received: 27 February 2001 Accepted: 8 May 2001     

One-pot esterification and amidation of phenolic acids

We developed a new one-pot reaction of phenolic acids to afford the corresponding esters and amides through acyl-protected and activated phenolic acid intermediates. The simultaneous protection/activation of phenolic acids with alkylchloroformates proceeded readily in the presence of DMAP at room temperature; subsequent addition of alcohols or amines afforded the corresponding esters or amides. The use of iso-butyloxycarbonyl as the protecting and activating group in the one-pot reactions afforded phenolic esters or amides in 91% average yield. As a practical example of this convenient synthesis, caffeic acid phenethyl ester (CAPE) was readily synthesized from commercially available caffeic acid and phenethyl alcohol in 95% yield, and an isotopomer of CAPE, [3,10-¹³C₂]CAPE, was synthesized in 91% yield from [3-¹³C]caffeic acid and 2-[1-¹³C]phenethyl alcohol. This method may be useful for the convenient esterification and amidation of diverse phenolic acids.     

Hydrolysis of phosphate esters with polymer-supported catalysts containing cyclodextrin pendant group

Polymer-supported catalysts of several kinds, including-cyclodextrin (P-CD),-cyclodextrin-diethylenetriamine (P-CD-DETA), and-cyclodextrin-N-methylhydroxamate (P-CD-NMHA)-containing polymers, as well as their corresponding metal complexes, were synthesized and examined as catalysts for the hydrolysis of phosphate esters. The kinetic measurements were performed in a phosphate buffer (0.05 M, pH 8.2) at a temperature of 25.0±0.1 °C. Each kinetic run was initiated on introducing ester stock solution (0.13 ml) containing diphenylp-nitrophenyl phosphate (DPPNPP) in dioxane (0.010 M). The rate of hydrolysis of DPPNPP was evaluated by measuring the absorbance of liberatedp-nitrophenol at 402 nm. The dissociation constants between DPPNPP and the polymers P-CD, P-CD-DETA and P-CD-NMHA obtained from Eadie-type plots were 16.8, 16.4 and 8.0 (×10^–3 M) and the acceleration factors were 1.5, 2.8 and 8.6 respectively. Hence P-CD-NMHA is the most promising catalyst. The activation parameters, preexponential factor (A) and activation energy using P-CD-NMHA as catalyst, areA=1.2×10⁹ min^–1 andE _a=43 kJ/mol respectively; the latter was about 12 kJ/mol lower than the activation energy of spontaneous hydrolysis. The results indicate that the catalytic power of P-CD-NMHA may reflect the combined behavior of molecular recognition and nucleophilicity.     

Cyclization of allyl α-halocarboxylates in the presence of metallocomplex initiators

Allyl trichloroacetate and allyl 2,2-dichloropropionate, unlike allyl bromoacetate and allyl 2-bromopropionate, undergo cyclization into γ-lactones in the presence of a Fe(CO)₅— amide system. All these esters undergo reductive dehalogenation under the action of the Bu ⁿ ₃SnH-AIBN system. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 796–799, April, 1997.     

Electrochemical synthesis of phosphorus esters from white phosphorus in the presence of copper complexes and ethanol

In the presence of white phosphorus the redox potentials of the copper ions change and the potential of the reduction wave of Cu^I/Cu⁰ shifts noticeably toward more positive values. The Cu^I—P₄ complex is characterized by a lower value of the electrochemical gap, that is, higher polarizability and reactivity compared to those of the free Cu^I cation. Phosphorus esters can be synthesized from P₄ and ethanol. The latter is in the composition of the copper(ii) complexes, which act as a catalyst-charge mediator.     

稀土掺杂Lu3Al5O12荧光粉的发光特性及能量传递

采用高温固相法制备了Ce、Sm共掺Lu_3Al_5O_(12)荧光粉。通过X射线衍射分析、荧光光谱分析研究了样品的结构、发光特性,并通过理论计算研究了能量传递效率、能量传递的临界距离以及能量传递方式。X射线衍射分析表明所制备的荧光粉具有单一的石榴石结构;荧光光谱分析表明,在464 nm蓝光激发下,Sm~(3+)的引入可增加Lu_3Al_5O_(12)∶Ce,Sm发射光谱中红光成分,并且随着Sm~(3+)浓度的增加,Ce~(3+)发光强度逐渐减弱。计算出Ce~(3+)、Sm~(3+)之间的能量传递效率高达77.42%,确定了Ce~(3+)、Sm~(3+)之间的能量传递机制为偶极-偶极相互作用。     

An Air- and Water-Stable Hydrogen-Bond-Donor Catalyst for the Enantioselective Generation of Quaternary Carbon Stereocenters by Additions of Substituted Cyanoacetate Esters to Acetylenic Esters

The chiral enantiopure cobalt(III) complex Δ-[Co((S,S)-dpen)₃]³⁺ 2Cl⁻B(C₆F₅)₄⁻ (Δ-(S,S)- 2 ³⁺ 2Cl⁻B(C₆F₅)₄⁻; dpen=1,2-diphenylethylenediamine) is an effective catalyst, together with pyridine (10 mol % each), for enantioselective additions of substituted cyanoacetate esters NCCH(R)CO₂R′ to acetylenic esters R′′C≡CCO₂R′′′. In the resulting adducts NC(R′O₂C)C(R)CR′′C=CHCO₂R′′′, C=C isomers in which the CO₂R′′′ moiety is trans to the new carbon–carbon bond dominate (avg. ratio 98:2). These are obtained in 70–98 % ee (avg. 86 %; data for optimum R′ and R′′′), as determined by ¹H NMR with the chiral solvating agent Λ-(S,S)- 2 ³⁺ 2I⁻B(3,5-C₆H₃(CF₃)₂)₄⁻. NMR experiments show that the cyanoacetate and acetylenic esters and pyridine can hydrogen bond to certain NH groups of the catalyst. Rates are zero order in the cyanoacetate and acetylenic esters as well as the catalyst, and implications are discussed.     

A convenient synthesis and structural analysis of novel 4,5,6,7-tetrahydro-1H-indazoles

A new series of t-4-aryl-3,c-6-dihydroxy-6-methyl-4,5,6,7-tetrahydro-1H-indazole-r-5-carboxylic acid isopropyl esters has been synthesized by adopting a conventional method from cyclic β-keto esters. ¹H, ¹³C NMR, and IR spectra for all the compounds were investigated. HMBC, HSQC, COSY, and NOESY spectra of the representative compounds were studied. The stereochemistry of a six-membered ring of the fused indazoles resembled that of keto esters. From the HMBC correlations the indazole structure was confirmed as 1H-indazole.     

Modified Coumarins. 18. Synthesis of Angular Dihydropyranocoumarins Containing Amino Acids and Peptides

Angular dihydropyranocoumarins containing natural and synthetic amino acids and dipeptides were synthesized using activated esters. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 422–427, September–October, 2005.     

Preparation and characterization of cellulose β-ketoesters prepared by homogeneous reaction with alkylketene dimers: comparison with cellulose/fatty acid esters

Cellulose was dissolved in lithium chloride/1,3-dimethyl-2-imidazolidinone (LiCl/DMI), and reacted with alkylketene dimers (AKDs) under non-aqueous and homogeneous conditions to prepare cellulose/AKD β-ketoesters with high degrees of substitution (DS). Six AKDs synthesized from octanoic, decanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids via their fatty acid chlorides were used in this study. The cellulose/AKD β-ketoesters obtained were gummy solid at room temperature, and had DS values ranging from 1.9 to 2.9. Cellulose/fatty acid esters with DS 2.5–2.9 were also prepared as references. ¹³C-NMR spectra of the cellulose/AKD β-ketoesters showed that cellulose carbons and substituent carbons close to cellulose chains were restricted in motion and behaved like solid in solutions. In contrast, the cellulose/fatty acid esters did not demonstrate such anomalous ¹³C-NMR spectra. The unique ¹³C-NMR patterns are characteristic for the cellulose/AKD β-ketoesters, which have long and branched alkyl substituents in each anhydroglucose unit. Size-exclusion chromatography furnished with multi-angle laser light scattering (SEC-MALLS) revealed, on the other hand, that all cellulose/AKD β-ketoesters and cellulose/fatty acid esters prepared had flexible or random-coil conformations in tetrahydrofuran (THF). There were no clear differences in conformation or stiffness of cellulose chains between cellulose/AKD β-ketoesters and cellulose/fatty acid esters.