A simple and efficient biphasic method for the preparation of 4-nitrophenyl N-methyl- and N-alkylcarbamates

Treatment of 4-nitrophenyl chloroformate with alkylammonium hydrochloride salts and solid anhydrous Na₂CO₃ in either CH₂Cl₂ or CH₃CN gave 4-nitrophenyl N-methylcarbamate and other N-alkylcarbamate analogues in excellent yields. Of particular interest is the observation that 4-nitrophenyl N-methylcarbamate, a safer alternative to the highly toxic methyl isocyanate, is obtained in quantitative yield (?95% pure as determined by ¹H NMR) after simple filtration and solvent evaporation.     

The Constituents of Cynanchum Taiwanianum

The isolation and identification of eleven crystalline components from the aerial part of Cynanchum taiwanianum Yamazaki (Asclepiadaceae) are described. Their structures were determined on the basis of spectral evidence and chemical transformation. Besides caffeic acid, β-amyrin, and methyl phaeophorbide a, the isolated flavonoid components are classified into two groups, i.e. kaempferol derivatives (kaempferol, astragalin, afzelin, trifolin) and quercetin derivatives (quercetin, isoquercitrin, quercitrin, hyperin).     

(Liquid + liquid) equilibria of (water + propionic acid + methyl isoamyl ketone or diisobutyl ketone or ethyl isoamyl keton) at T = 298.2 K

(Liquid + liquid) equilibrium (LLE) data for (water + propionic acid + solvent) were measured at T = 298.2 K and atmospheric pressure. The solvents were methyl isoamyl ketone (5-methyl-2-hexanone), ethyl isoamyl ketone (5-methyl-3-heptanone) and diisobutyl ketone. The tie-line data were correlated by means of the NRTL and UNIQUAC equation, and compared with results predicted by the UNIFAC method. A comparison of the extracting capabilities of the solvents was made with respect to distribution coefficients, separation factors, and solvent free selectivity bases.     

Polymerization of methyl methacrylate in the presence of iron(II) complex with tetradentate nitrogen ligands under conditions of atom transfer radical polymerization

Four tetradentate nitrogen ligands, viz. dichloro{[N,N^′-diphenyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (1), {[N,N^′-dioctyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (2), {[N,N^′-dibenzyl-N,N^′-di(quinoline-2-methyl)]-1,2-ethylene diamine} (3), and (1R,2R)-(−)-N,N^′-di(quinoline-2-methyl) di-iminocyclohexane (4), were investigated as novel complexing ligands in iron-mediated atom transfer radical polymerization (ATRP) of methyl methacrylate where ethyl-2-bromoisobutyrate was the initiator in o-xylene at 90 °C. With ligands 1 and 2 the experimental molecular weights increased gradually with monomer conversion. High to moderate conversions (87%, 43%) were obtained in relatively short times (90 min for 1 and 30 min for 2), which indicates an efficient catalyst system, but after these times a dramatic increase in viscosity of the polymerization medium led to loss of control. It is noteworthy that polymerization proceeded in a controlled manner with ligand 1, which has two rather bulky substituents on the N-atom. Such bulky ligands did not work for a copper-based system, where they led to excessive terminations or other side reactions. When the bulkiness of the substituents was significantly increased, as in ligand 3, a decrease in polymerization rate and loss of control occurred. Ligand 4 was less efficient than the other ligands, probably because the ethylene bridge was replaced by cyclohexane bridge.     

Multiple bonds between main group elements and transition metals, 155. (Hexamethylphosphoramide) methyl(oxo) bis(η-peroxo)rhenium(VII), the first example of an anhydrous rhenium peroxo complex: crystal structure and catalytic properties

Methyl(oxo)bis(η²-peroxo)rhenium(VII)1, the active species of the system CH₃ReO₃/H₂O₂ in the catalytic oxidation of different organic and organometallic compounds, is stabilized by a water molecule attached to the rhenium center. This water molecule can be removed and substituted by hexamethylphosphoramide (HMPA) to yield (hexamethylphosphoramide)methyl(oxo)bis(η²-peroxo rhenium(VII) (3). The synthesis, crystal structure (X-ray difraction study), and catalytic properties of which compound are reported. Crystal data are as follows: monoclinic, space group P2₁/n, A = 900.76(7) pm, B = 1229.80(11) pm, C = 1318.57(11) pm, β = 90.251(7)°, R_w = 0.034 for 1878 reflections. The catalytic properties of compound 3 in the oxidation of olefins with H₂O₂ are similar to those of 1.     

DABCO-catalyzed reactions of hydrazones with activated olefins

This paper describes several highly efficient DABCO-catalyzed aza-Michael addition reactions of hydrazones to activated olefins. In most cases, these aza-Michael addition reactions gave the corresponding products in high yields under mild conditions. The plausible reaction mechanism is discussed on the basis of deuterium labeling experiments. Upon treatment with HCl, the corresponding cyclized products can be obtained in high yields from the Michael addition products.     

氧化-还原低温引发甲基丙烯酸甲酯/丙烯酸丁酯超浓乳液聚合研究

以乳化剂十二烷基硫酸钠 (SDS)和共乳化剂十六烷醇 (HD)作为复合乳化体系 ,过氧化二苯甲酰(BPO)和N ,N 二甲基苯胺 (DMA)作为氧化还原引发体系 ,甲基丙烯酸甲酯 丙烯酸丁酯 (MMA BA)作为混合单体 ,制备了分散相占 83 %以上的稳定的超浓乳液 ,然后在低温下引发聚合 .探讨了引发剂浓度、氧化剂与还原剂的摩尔比、乳化剂的浓度、液膜增强剂的种类、聚合温度等因素对聚合稳定性和聚合速率的影响 ,测定并计算得到了聚合速率的公式 ;用激光散射粒度分布仪测定了聚合物乳胶粒子的大小及粒径分布 ,用透射电子显微镜观察了聚合物乳胶粒的形态 ,讨论了乳化剂浓度、聚合温度等对乳胶粒形态、大小的影响     

A characteristic CH band in VCD of methyl glycosidic carbohydrates

Novel vibrational circular dichroism (VCD) studies in the CH region of a series of methyl glycosidic carbohydrates were examined. The specific CH stretching VCD band predicts absolute stereochemistries of their anomeric positions. The C-1 chiral information was extracted to the methoxy substituent as a probe. The concept of the vibrational chirality probe from a single chiral center in the presence of numerous such centers might be useful in determining the absolute configuration, when a multiplicity of chiral centers is present in a molecule such as a carbohydrate.     

The structure of diluted binary solutions of amides according to the heat capacity data

The specific heat capacities of hexamethylphosphoric triamide, diethylpropionamide, their aqueous solutions, and mixtures of hexamethylphosphoric triamide with formamide were measured in the temperature range from 288.15 to 318.15 K. The dependences of the partial molar heat capacity of aqueous solutions of amides on the composition of the mixture have maxima in the region of 0.02–0.04 molar fractions of amide. The maximum on a similar dependence for solutions of hexamethylphosphoric triamide corresponds to the concentration of 0.01 molar fractions. The conclusion on the formation of solvates (hydrates) in the systems studied was made. The heat capacity coefficients of pair and triple interactions were calculated in terms of the McMillan-Mayer theory. A change in the heat capacity characteristics with the temperature change was analyzed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2479–2483, December, 1998.     

Phase equilibria for binary systems of octane boosters with 2,2,4-trimethylpentane

Isobaric vapor–liquid equilibrium data at 95.96 kPa for the three binary systems of 2,2,4-trimethylpentane with methyl tert-butyl ether, di-isopropyl ether and dimethoxymethane are determined. A Swietoslawski type ebulliometer is used for the measurements. The experimental T–x data are used to estimate Wilson parameters and the parameters, in turn, are used to calculate vapor phase compositions and activity coefficients. All the systems studied here do not exhibit azeotropes and behave like non-ideal solutions.