The Mitsunobu Reaction: Origin,Mechanism, Improvements,and Applications

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation–reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.     

Synthesis and characterization of well-defined poly(methyl methacrylate)/CaCO3/SiO2 three-component composite particles via reverse atom transfer radical polymerization

The attempt to prepare structurally well-defined polymer/inorganic composite particles, i.e., poly(methyl methacrylate) (PMMA)/CaCO₃/SiO₂ three-component composite particles, via reverse atom transfer radical polymerization (ATRP), using 2-2′-azo-bis-isobutyronitrile as initiator and Cu(II) bromide as catalyst was reported. CaCO₃/SiO₂ two-component composite particles were first obtained through sol–gel method, and their morphology and surface element information were determined by transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. The results indicate that the CaCO₃ was encapsulated by the obtained SiO₂. After being modified by silane coupling agent, the CaCO₃/SiO₂ composite particles copolymerized with methyl methacrylate (MMA) under standard reverse ATRP conditions to produce PMMA/CaCO₃/SiO₂ three-component composite particles. In the case concerned, first-order kinetic plots and linear increase of molecular weight (Mn) vs conversion and narrow molecular weight distribution for the graft polymer samples were observed. Furthermore, the gel permeation chromatography results illustrated that both the free PMMA chains from the solvent and the graft PMMA chains from the surface of CaCO₃/SiO₂ two-component composite particles were growing at the same rate. Characterizations of the PMMA-grafted CaCO₃/SiO₂ composite particles were done by Fourier transform infrared and thermogravimetric analysis. The results showed that the surface of the modified inorganic particles was grafted by the MMA and that the grafting percentage was about 8.7%.     

Temperature Dependence of the Solubility of Acetaminophen in Propylene Glycol + Ethanol Mixtures

The thermodynamic functions Gibbs energy, enthalpy and entropy of solution, mixing and solvation of acetaminophen in propylene glycol (PG) + ethanol (EtOH) cosolvent mixtures were evaluated from solubility data measured at several temperatures, using the van't Hoff and Gibbs equations. The solubility was greater at 50% m/m of PG at 20.0^C, while it was greater at 80% of PG at 40.0 ^C where m/m refers to mass percent. The solvation of this drug is appreciably greater in the mixtures than in the pure solvents. By means of an enthalpy–entropy compensation analysis, complex behavior was found for the solution. From 0 up to 20% of PG and from 60 up to 100% of PG the solution process is enthalpy driven, whereas from 20 up to 60% of PG it is entropy driven. These facts can be explained in terms of a decrease in the energy required for cavity formation in the solvent for mixtures containing 20–60% of PG.     

Propene polymerization using homogeneous MAO-activated metallocene catalysts: Me2Si(Benz[e]Indenyl)2ZrCl2/MAO vs. Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2/MAO

Propene was polymerized at 40°C and 2-bar propene in toluene using methylalumoxane (MAO) activated rac-Me₂Si(Benz[e]Indenyl)₂ZrCl₂ ( BI ) and rac-Me₂Si(2-Me-Benz[e]Indenyl)₂ZrCl₂ ( MBI ). Catalyst BI /MAO polymerizes propene with high activity to afford low molecular weight polypropylene, whereas MBI /MAO is less active and produces high molecular weight polypropylene. Variation of reaction conditions such as propene concentration, temperature, concentration of catalyst components, and addition of hydrogen reveals that the lower molecular weight polypropylene produced with BI /MAO results from chain transfer to propene monomer following a 2,1-insertion. A large fraction of both metallocene catalyst systems is deactivated upon 2,1-insertion. Such dormant sites can be reactivated by H₂-addition, which affords active metallocene hydrides. This effect of H₂-addition is reflected by a decreasing content of head-to-head enchainment and the formation of polypropylene with n-butyl end groups. Both catalysts show a strong dependence of activity on propene concentration that indicates a formal reaction order of 1.7 with respect to propene. MBI /MAO shows a much higher dependence of the activity on temperature than BI /MAO. At elevated temperatures, MBI /MAO polymerizes propene faster than BI /MAO. © 1995 John Wiley & Sons, Inc.     

Compartmentalized polymerization initiated by oil-soluble initiators. Calculation of average number of radicals per particle

Expressions for calculating the stationary state distribution of radicals in compartmentalized systems with a constant number of reaction loci containing an oil-soluble initiator are given. Besides pairwise formation of radicals in the particles, desorption and reabsorption, water phase termination, solubility of the initiator in the aqueous phase, and the possibility of formation of a single radical species are taken into consideration. The calculation is based on a probabilistic analysis leading to a third-order recurrence relation solved using confluent, hypergeometric Kummer functions. Some calculated curves illustrating the de-pendence of the average number of radicals per particle on various relevant parameters are included. © 1995 John Wiley & Sons, Inc.     

XRD and Si MAS-NMR spectroscopy across the β-Lu2Si2O7-β-Y2Si2O7 solid solution

Samples in the system Lu_2−xY_xSi₂O₇ (0?x?2) have been synthesized following the sol-gel method and calcined to 1300 °C, a temperature at which the β-polymorph is known to be the stable phase for the end-members Lu₂Si₂O₇ and Y₂Si₂O₇. The XRD patterns of all the compositions studied are compatible with the structure of the β-polymorph. Unit cell parameters are calculated as a function of composition from XRD patterns. They show a linear change with increasing Y content, which indicates a solid solubility of β-Y₂Si₂O₇ in β-Lu₂Si₂O₇ at 1300 °C. ²⁹Si MAS NMR spectra of the different members of the system agree with the XRD results, showing a linear decrease of the ²⁹Si chemical shift with increasing Y content. Finally, a correlation reported in the literature to predict ²⁹Si chemical shifts in silicates is applied here to obtain the theoretical variation in ²⁹Si chemical shift values in the system Lu₂Si₂O₇-Y₂Si₂O₇ and the results compare favorably with the values obtained experimentally.     

Densities and Excess Molar Volumes of Binary and Ternary Mixtures of Aqueous Solutions of 2,2,2-Trifluoroethanol with Acetone and Alcohols at the Temperature of 298.15 K and Pressure of 101 kPa

Excess molar volumes V_m^E of the binary mixtures of (trifluoroethanol + 1-propanol), (trifluoroethanol + 2-propanol), (acetone + water), (methanol + water), (ethanol + water), (1-propanol + water), (2-propanol + water), and the ternary mixtures of (trifluoroethanol + methanol + water), (trifluoroethanol + ethanol + water), (trifluoroethanol~+ 1-propanol + water), (trifluoroethanol + 2-propanol + water) and (trifluoroethanol + acetone + water) were measured with a vibrating tube densimeter at the temperature of 298.15 K and the pressure 101 kPa. The extrema in V_m^E of trifluoroethanol mixtures occur at –0.690 cm³-mol^–1 for (trifluoroethanol + 1-propanol), at –0.990~cm³-mol^–1 for (trifluoroethanol + 2-propanol); at 0.562 and –0.973 cm³-mol^–1 for (trifluoroethanol + methanol + water), at 0.629 and –0.973 cm³-mol^–1 for (trifluoroethanol + ethanol + water), at 1.082 and –0.659 cm³-mol^–1 for (trifluoroethanol~+ 1-propanol + water), at 0.998 and –0.991 cm³-mol^–1 for (trifluoroethanol~+ 2-propanol + water), and at 0.515 and –1.472 cm³-mol^–1 for (trifluoroethanol + acetone + water). The experimental ternary V_m^E values were predicted by empirical expressions using binary solution data.     

INVESTIGATION OF THE ATRP OF n-BUTYL METHACRYLATE USING THE Cu（I）／N,N,N＇ N＂ N＂-PENTAMETHYLDIETHYLENETRIAMINE CATALYST SYSTEM

The polymerization of n-butyl methacrylate was investigated using the Atom Transfer Radical Polymerization technique with CuBr and CuCl/N,N,N‘,N“,N“-pentamethyldiethylenetriamine catalytic systems. Various combinations of catalyst systems and initiators were utilized in order to optimize the polymerization conditions and to obtain well-defined polymers (i.e. controlled molecular weights and low polydispersities). It has been found that the optimal initiator for this system is a chlorine-based initiator, when the catalyst used is a Cu(I) salt in conjunction with the N,N,N‘,N“,N“-pentamethyldiethylenetriamine ligand. Bromine-based initiators tend to result in large amounts of initial termination, leading to polymers with less than ideal chain end functionality, even if CuCI is used as the Cu(I) species to invoke the halogen exchange. Additionally, the effects of the polymerization temperature, copper(I) species and the initiator structure were determined.     

2-巯基噻唑[5，4-d]并嘧啶类化合物及其衍生物的合成

由邻硝基氯代嘧啶（3）为原料料，与多硫化钠和二硫化碳共煮，经一步反应 获得了2-巯基噻唑[5，4-d]并嘧啶（4）。由4出发，合成了一系列2位取代的衍生 物5，4和5的结构均通过了~1H NMR及元素分析确让。并对少数化合物的生物活性进 行了测试。     

Radiation polymerization of thermo-sensitive poly (N-vinylcaprolactam)

Temperature-sensitive poly (N-vinylcaprolactam) both in water-soluble state and in gel was prepared by γ-radiation polymerization. The effects of radiation dose, radiation dose rate and monomer concentration on polymerization and the low critical solution temperature characteristics of the polymer were studied. The results show that the polymer prepared within certain radiation dose (beyond 2 kGy) and dose rate range (2–14 Gy/min) has good temperature sensitivity and uniformity.