Enantioselective synthesis of unsymmetrical benzoins from (S)-mandelic acid enolate and aromatic aldehydes

The reaction of the lithium enolate of the 1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with aromatic aldehydes proceeds readily to give the corresponding aldol products in good yields and diastereoselectivities. Subsequent hydroxyl protection, basic hydrolysis of the dioxolanone, oxidative decarboxylation of the α-hydroxyacid moiety, and hydroxyl deprotection provides chiral unsymmetrical benzoins with high enantiomeric excesses.     

Biodegradation of poly(lactic acid) powders proposed as the reference test materials for the international standard of biodegradation evaluation methods

The methods for producing reference test materials for biodegradation evaluation tests have been studied. Mechanical crushing at low temperature of polymer pellets using dry ice was selected for the method of producing polymer powder of poly(lactic acid) (PLA). The powders were fractionated using 60 mesh (250 μm) and 120 mesh (125 μm) sieves. The size distributions were then measured. The average diameter of the PLA particles obtained by this method was 214.2 μm. The biodegradation speeds of these PLA polymer powders were evaluated by two methods based on the international standard and one in vitro method based on the enzymatic degradation. First, the degree of biodegradation for this PLA powder was 91% for 35 days in a controlled compost determined by a method based on ISO 14855-1 (JIS K6953) at 58 °C managed by the Mitsui Chemical Analysis and Consulting Service, Inc. (Japan). Second, these polymer powders were measured for biodegradation by the Microbial Oxidative Degradation Analyzer (MODA) in a controlled compost at 58 °C and 70 °C based on ISO/DIS 14855-2 under many conditions. The degree of biodegradation for this PLA powder was approximately 80% for 50 days. In addition, the polymer powders were biodegraded by Proteinase K which is a PLA degradation enzyme. This polymer powder was suitable as a reference material for the evaluation methods of biodegradation.     

Cu-Nanoparticles: efficient catalysts for the oxidative cyclization of Schiffs’ bases

Cu-Nanoparticles provide an efficient catalysis for the synthesis of 2-arylbenzoxazoles by the coupling of aromatic or heteroaromatic aldehydes with 2-aminophenol though the oxidative cyclization of the Schiffs’ bases using 10 mol % of the Cu-nanoparticles in the presence of K₂CO₃ in MeOH. This method avoids the use of metal oxide or organic oxidizing agents, namely, DDQ or strong acids such as polyphosphoric acid or boric acid.     

甲烷在BaPrO3上的氧化偶联

以碱土金属Ba、Sr代替碱金属与氧化能力较强的Pr、Ce相匹配,可以得到稳定性、活性都更好的催化剂。对于Ba-Pr二元体系,组成为BaPrO_3者C_2的收率及选择性可达极大值,在1083 K及CH_4:O_2=5:1条件下,经100 h反应考察,始终保持恒定的反应性能:甲烷转化率为20％,C_2选择性可达57％。催化剂的反应性能与催化剂组成的关系表明,碱性与氧化能力之间有协同作用。XRD结果表明,Ba和Sr离子分别进入了PrO(1.8)和CeO_2的晶格,抑制其燃烧性能。动力学研究结果支持了这种推测:甲烷氧化偶联反应的控制步骤是甲烷分子在PrO_(1.8)相上的C-H键断裂。     

Influence of isomerism of difluorobenzophenone on the synthesis and properties of poly(arylene ether ketones)

The influence of isomerism of difluorobenzophenone on the efficiency of polycondensation and the properties of homo- and copoly(arylene ether ketones) was studied. The latter were prepared by the reaction of 2,4"- and 4,4"-difluorobenzophenone with potassium diphenolates of bisphenol À and phenolphthalein in N,N-dimethylacetamide. A high content of an admixture of the 2,4"-isomer in 4,4"-difluorobenzophenone decreases the molecular weight of related poly(arylene ether ketones) and has no substantial effect on their glass transition temperature.     

An electrochemical interpretation of the mechanism of the chemical decarboxylation of 6-carboxyperhydropyrimidin-4-ones

The present work analyzes the anodic oxidation of the tetrabutylammonium salt of 1-benzoyl-2(S)-tert-butyl-6(S)-carboxyperhydropyrimidin-4-one, which is a useful starting material in the synthesis of enantiopure α-substituted β-amino acids. It was demonstrated that in CH₂Cl₂ solvent, the anodic oxidation reaction results in fast and complete decarboxylation, followed by proton elimination thereby leading to the same product of chemical (diacetoxyiodobenzene) oxidative decarboxylation. The electrochemical mechanism involves two electron transfer steps, but appears as a monoelectronic process owing to the release of one proton from the key acyliminium carbocation intermediate. The relative stability of this intermediate and the suppression of any solvolysis reaction in CH₂Cl₂ allow for the detection of the acyliminium intermediate by means of cyclic voltammetry experiments. By contrast, in the presence of a nucleophilic solvent such as acetonitrile, the acyliminium intermediate is trapped in a typical Ritter reaction.     

Oxidative and Photochemical Stability of Ionomers for Fuel‐Cell Membranes

To predict hydroxyl‐radical‐initiated degradation of new proton‐conducting polymer membranes based on sulfonated polyetherketones (PEK) and polysulfones (PSU), three nonfluorinated aromatics are chosen as model compounds for EPR experiments, aiming at the identification of products of HO^.‐radical reactions with these monomers. Photolysis of H₂O₂ was chosen as the source of HO^. radicals. To distinguish HO^.‐radical attack from direct photolysis of the monomers, experiments were carried out in the presence and absence of H₂O₂. A detailed investigation of the pH dependence was performed for 4,4′‐sulfonylbis[phenol] ( SBP ), bisphenol A (= 4,4′‐isopropylidenebis[phenol]; BPA ), and [1,1′‐biphenyl]‐4,4′‐diol ( BPD ). At pH ≥ pK_A of HO^. and H₂O₂, reactions between the model compounds and O₂^.? or ¹O₂ are the most probable ways to the phenoxy and ‘semiquinone’ radicals observed in this pH range in our EPR spectra. A large number of new radicals give evidence of multiple hydroxylation of the aromatic rings. Investigations at low pH are particularly relevant for understanding degradation in polymer‐electrolyte fuel cells (PEFCs). However, the chemistry depends strongly on pH, a fact that is highly significant in view of possible pH inhomogeneities in fuel cells at high currents. It is shown that also direct photolysis of the monomers leads to ‘semiquinone’‐type radicals. For SBP and BPA , this involves cleavage of a C? C bond.     

Application of stress induces ascorbate peroxidases of S. polyrhiza for green-synthesis Cu nanoparticles

The objective of this study was to assess the effects of stress on physiology/biochemical component of S. polyrhiza and its impact on CuNPs synthesis and bioethanol production. NaCl with RV5 provokes oxidative stress in S. polyrhiza and significantly increase MAD, Proline, H₂O₂, ROS, SOD and APX activity compare to control condition. Starch accumulation in S. polyrhiza was found 354% higher and correspond 4.4 times higher ethanol yield under stress condition compare to control. CuNPs were synthesized with an average size of 23–26 nm by purified fraction of APX having 37 KDa MW, 1.44 IU specific activity. Synthesized CuNPs were stable up to 15 consecutive cycles and potency against wide range of reactive dyes. The maximum remedial efficiency of synthesized CuNPs for COD and BOD was 55263.3 ± 3298.5 mg/m³min. and 30560.3 ± 1987.5 mg/m³min. respectively for RV5 wastewater. 0.072 mg/g of bioethanol was produced from the wet pulp remaining after nanoparticles synthesis. High efficiency of CuNPs and significant production of Ethanol, indicate that the feasibility for circular model for continuous industrial wastewater treatment.     

1,2-Thiazole durch Ringtransformation von 2H-Thiopyran-2-thionen

Summary Aminolyses of 4-dialkylamino-2-methylthiothiopyranes halides with ammonia leads to 4-amino-2-dialkylaminothiopyranylium halides. On treatment with alkali these products are hydrolyzed to N,N-dialkyl-3-amino-2,4-hexadienthioamides, which react with peroxide under oxidative cyclization to 5-dialkylamino-1,2-thiazoles. In order to determine the structures of the unsaturated thioamides and isothiazoles¹³C-NMR-spectroscopic analysis and a single crystal X-ray structure analysis of 5-dimethylamino-3-(2-methyl-1-propenyl)-1,2-thiazole (6 a) at 100K were carried out: C₉H₁₄N₂S,M _r=182.28, monoclinic, P 2₁/a,a=11.622(2),b=6.303 (1),c=13.678(2), =104.49(3)°,V=970.1(3)ų,Z=4,d _x=1.248 g/cm³, =27.0 mm^–1,R=4.93%,R _w=4.84% (1 672 observations, 157 parameters).

Herrn Prof. Dr. G. Zigeuner zum 70. Geburtstag gewidmet     

Manganese(III) acetate based oxidative cyclizations of 3-oxopropanenitriles with conjugated alkenes and synthesis of 4,5-dihydrofuran-3-carbonitriles containing heterocycles

4,5-Dihydrofuran-3-carbonitriles 3a-i were obtained through oxidative cyclizations of 3-oxo-3-phenylpropanenitrile 1a, 3-oxo-3-thien-2-ylpropanenitrile 1b, 3-(2-furyl)-3-oxopropanenitirle 1c, 3-(1-benzofuran-2-yl)-3-oxopropanenitrile 1d, and 4,4-dimethyl-3-oxopropanenitrile 1e mediated manganese(III) acetate with 1,1-diphenyl-1-butene 2a and 1,2-diphenyl-1-pentene 2b. The treatments of these 3-oxopropanenitriles with 2-thienyl substituted alkenes such as 2-[(E)-2-phenylvinyl]thiophene 2c, 2-[(E)-1-methyl-2-phenylvinyl]thiophene 2d, and 2-(1-phenylvinyl)thiophene 2e formed 5-(2-thienyl)-4,5-dihydrofuran-3-carbonitriles 3j-r in good yields (45-93%). As a result, 2-thienyl substituted alkenes formed products in higher yields than phenyl substituted derivatives.