Determination of the concentration of hydroxyl groups on aerosil surfaces

The concentration of the hydroxyl groups on Aerosil surfaces was estimated by chemical analysis and IR spectroscopy. The temperature ranges for thermal stability of the OH groups and for their reactivity in surface chemical reactions were established. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1757–1760, October, 1997.     

Chemical modification of the polymeric sorbent containing hydroxyl functional groups

Summary Dimethyldichlorosilane and stearic acid chloride were used for deactivation of hydroxyl functional groups present in the skeleton of the methacrylic ester ofp,p′-dihydroxydiphenylpropane diglycidyl ether-divinylbenzene, porous copolymer used as HPLC packing. The influence of chemical modification on the chromatographic behaviour of the copolymer was studied. To characterize selectivity of the packings, retention indices of five homologous series and test compounds were determined. The data obtained suggest that modification with stearic acid chloride affects both the chemical and porous structure of the copolymer while modification with dimethydichlorosilane changes only the chemical character of the packing.     

The assignment of IR absorption bands due to free hydroxyl groups in cellulose

Interpretation of the IR hydroxyl absorption bands in cellulose has been limited to the inter- and intramolecularly hydrogen-bonded hydroxyl groups in the crystalline form. This paper attempts to assign IR frequencies due to ‘free‘ or non-hydrogen bonded hydroxyl groups by using a curve fitting method. The almost completely methylated cellulose derivatives of tritylcellulose (previously used in related studies) exhibited small IR bands due to hydroxyl groups. The IR bands were assumed to appear under stereohindered conditions and thus resulted in a mixture of bands which included the contribution of free hydroxyl groups. The curve fitting method deconvoluted the IR bands into three bands in the OH stretching region: they were interpreted in terms of free or hydrogen bonded hydroxyl groups. The assignments were confirmed by comparison of an almost completely methylated derivative with partially methylated derivatives having different degrees of substitution. In addition, intramolecular hydrogen bonds involving OH at the C-3, C-2 and C-6 positions were shown to be easily formed, even between extremely small numbers of unsubstituted hydroxyl groups present, and thus cause perturbation of the specific deconvoluted band. This revised version was published online in August 2006 with corrections to the Cover Date.     

A new colorimetric test for detection of hydroxyl groups in solid-phase synthesis

A new colorimetric test (methyl red-DIC test) for monitoring the presence of hydroxyl groups on resins for use in solid-phase synthesis was developed. The resin became orange-red when the carboxyl group of methyl red formed ester linkages with the resin’s hydroxyl groups. This new test can be used not only for qualitative analysis but also quantitative analysis by using pictures of the relationship between color depth and hydroxy loading rates.     

原子转移自由基聚合法合成含羟基星状共聚物

以２－溴异丁酸季戊四醇四酯为引发剂在ＣｕＢｒ／ｂｐｙ催化下实施苯乙烯和丙烯酸β－羟丙酯原子转移自由基共聚合,结果表明聚合物的分子量与理论分子量接近,聚合反应具有活性聚合的特征。进一步对聚合产物进行ＧＰＣ,Ｈ－ＮＭＲ,ＩＲ和羟值滴定分析,表明合成的星状共聚合物中同时具有苯乙烯和丙烯酸β－羟丙酯结构单元,而且羟基在聚合物中近似均匀分布。     

Gold-catalyzed chemo- and site-selective direct C-H functionalization of phenols with diazo compounds

<正>Phenols motifs are used as common versatile synthons in organic synthesis due to their wide availability and low cost.Thus, C-H functionalization of phenols is highly attractive to the community of synthetic chemistry. In the past decade, many methods have been developed via installing a protective group on the hydroxyl to allow for ortho/meta/para functionalization of phenols. One of the most effective methods for direct C-H functionalization is the carbene     

The site-selective functionalization of halogen-bearing phenols: an exercise in diversity-oriented organometallic synthesis

The organometallic approach to diversity-oriented organic synthesis was subjected to a further test, this time in the phenol series. The model compounds selected were 2,3,6-trifluorophenol, the three isomers of (trifluoromethoxy)phenol and the three isomers of chlorophenol. A combination of optionally site selective metalations and protective group-controlled metalations enabled the selective generation of several isomeric intermediates in each case and their subsequent conversion into functionalized derivatives, in particular hydroxybenzoic acids.     

手性席夫碱及其金属配合物作为手性催化剂的某些应用

简要介绍和评述了近15年来手性Schiff碱及其金属配合物作为手性催化剂, 在不对称氢化、不对称氢转移、不对称氢硅化、不对称硅氰化和不对称氢氰化等反应中的应用研究进展.     

神奇的手性螺环配体

过渡金属参与的不对称催化反应是有机合成化学研究的前沿和热点. 寻找和发现新颖配体骨架并开展新型高效的手性配体及催化剂的设计合成是不对称催化反应研究的核心内容. 从20世纪90年代,特别是进入21世纪以来,螺环骨架手性配体受到了广泛的关注,并逐渐发展成为特色鲜明的手性配体类别. 手性螺环配体的骨架已由多手性的螺[4.4]壬烷骨架发展到只具有单一手性的螺二氢茚和螺[4.4]壬二烯等螺环骨架类型,形成了包括手性螺环单磷配体、双膦配体、膦氮配体、双氮配体等丰富的手性配体库. 这些手性螺环配体及其催化剂不仅在不对称催化氢化、不对称碳―碳键形成、不对称碳―杂原子键形成等多种类型的不对称催化反应中均表现出优异的催化活性和对映选择性,且使得许多原先难以控制对映选择性的不对称催化反应变得可能. 而今,手性螺环结构已成为“优势结构”,相应的手性螺环配体及其催化剂已被国内外同行广泛采用. 手性螺环配体的兴起为手性催化剂研究增加了活力,极大地促进了不对称合成化学的发展. 今后,手性螺环配体的研究除了将向新型、高效、高选择性手性配体及催化剂方向发展外,将其应用于新的不对称催化反应的对映选择性控制、以及应用于手性天然产物和药物的高效不对称合成将成为新的研究热点.     

Role of surface hydroxyl groups in promoting room temperature CO sensing by Pd-modified nanocrystalline SnO2

SnO₂/Pd nanocomposites were synthesized via sol-gel method followed by variable processing procedures. The materials are sensitive to CO gas in the concentration range 2-100 ppm at room operating temperature. It was shown that modification of nanocrystalline tin dioxide by Pd changes the temperature dependence of sensor response, decreasing the temperature of maximal signal. To understand the mechanism of room temperature CO sensitivity, a number of SnO₂/Pd materials were characterized by XRD, TEM, BET, XPS and TPR techniques. From the results of FTIR, impedance and sensing measurements under variable ambient conditions it was concluded that improvement in CO sensitivity for Pd-modified SnO₂ is due to alteration of CO oxidation pathway. The reaction of CO with surface OH-groups at room temperature was proposed, the latter being more reactive than oxygen species due to the possible chain character of the reactions. It was proposed that Pd additive may initiate chain processes at room temperature.     

Functionalized Chiral Ionic Liquids: A New Type of Asymmetric Organocatalysts and Nonclassical Chiral Ligands

By judiciously anchoring functional groups onto chiral ionic liquids, functionalized chiral ionic liquids (FCILs) are emerging as a new type of asymmetric organocatalysts and nonclassical chiral ligands. This Focus Review highlights the applications of FCILs from the viewpoint of asymmetric catalysis. We focus mainly on the de novo designed and synthesized FCILs which likely still maintain the typical ionic liquids properties, and in a few cases relevant ionic liquid immobilized chiral catalysts are briefly discussed.     

Novel polyurethane networks based on hybrid inorganic/organic phosphazene‐containing nanotubes with surface active hydroxyl groups

Recently, our group reported a novel preparation of poly(cyclotriphosphazene‐co‐4,4′‐sulfonyldiphenol) nanotubes (PZSNTs), which could be conveniently prepared in a one‐pot process at room temperature without any surfactant or other compatibilizing agent. PZSNTs were a new kind of phosphazene‐containing crosslinked polymers which attracted considerable interest for their outstanding biocompatibility, thermal stability, and flame‐retardant property. Moreover, PZSNTs which possessed inherent surface active hydroxyl groups could be directly used as a crosslinking agent to prepare polyurethane hybrid networks. PZSNTs were homogeneously dispersed in the polyurethane matrix. Tensile tests indicated that the nanocomposites were significantly reinforced by crosslinking of PZSNTs. The tensile strength was enhanced from 11.4 to 21.5 MPa while the elongation at break was almost invariable (460–430%). The storage moduli of the nanocomposites were significantly higher than that of the pure polyurethane. In terms of thermogravimetric analysis (TGA), the nanocomposites displayed an improved thermal stability. Copyright © 2010 John Wiley & Sons, Ltd.     

聚合物负载的手性催化剂和手性试剂和合成及应用

近年来,用聚合物负载的手性催化剂和手性试剂完成的不对称合成反应主要集中在潜手性酮的不对称还原反应;烯烃的不对称双羟基化反应;烯烃的不对称环氧化反应;不对称Ｄｉｅｌｓ－Ａｌｄｅｒ反应和饱和碳原子上的不对称取代反应。就近十年来聚合物负载手性催化剂和手性试剂的合成及应用进行了讨论。     

One-pot synthesis of fluorinated terphenyls by site-selective Suzuki-Miyaura reactions of 1,4-dibromo-2-fluorobenzene

The Suzuki-Miyaura reaction of 1,4-dibromo-2-fluorobenzene with two equivalents of arylboronic acids gave fluorinated para-terphenyls. The reaction with 1 equiv of arylboronic acid resulted in site-selective formation of biphenyls. The one-pot reaction of 1,4-dibromo-2-fluorobenzene with two different arylboronic acids afforded fluorinated para-terphenyls containing two different terminal aryl groups.     

不对称催化反应在手性农药不对称合成中的一些应用

近十多年来，不对称催化反应在单一手性农药研发中的应用渐渐引起人们的关 注，结合自己的研究对这一领域的不对称催化反应及手性催化剂的发展进行了归纳 总结。     

使用手性相转移催化剂合成D-苯丙氨酸

目前,氨基酸不对称合成方法甚多,但是使用手性相转移催化剂未见有报道。本文报道在同位素标记氨基酸不对称合成研究中,用非标记甘氨酸进行模型试验的初步结果:使用(-)-氯化-N-苄基辛可尼丁鎓作催化剂,可获得近90%光学纯度的 D-苯丙氨酸,化学产率61.6%。     

果糖衍生手性酮催化剂的合成

以D 果糖为原料,经缩酮化、氧化、选择性水解和酯化等反应合成了果糖衍生手性酮催化剂,总收率68%,其结构经¹H NMR确证。     

Facile functionalization of isotactic polypropylene by azide and alkyne groups for click chemistry application

This paper presents two facile methods to achieve functionalization of isotactic polypropylene (i‐PP) by azide and alkyne groups. One method comprises metallocene‐catalyzed isospecific propylene polymerization with dialkylzinc as chain transfer agent to produce iodo‐terminated i‐PP, which can be transformed to azide‐terminated i‐PP. The other utilizes hydroxyl‐grafted i‐PP as a raw material to react with bis (trichloromethyl)carbonate and propargyl amine, generating grafted alkyne groups. Both approaches are effective, controllable and safe. The azide‐terminated and alkyne‐grafted i‐PP are readily applicable to click chemistry for construction of new i‐PP architecture, e.g. long‐chain branched i‐PP. Copyright © 2011 John Wiley & Sons, Ltd.     

高分子支载的手性催化剂在不对称有机反应中的应用进展

本文评述了近年来高分子支载的手性催化剂在不对称氢化、不对称还原、不对称烷基化、不对称Ｄｉｅｌｓ－Ａｌｄｅｒ加成以及不对称二羟基化等有机反应中的应用进展。     

Hydroxyl chain‐end functionalization of polymeric organolithium compounds with oxetane

Hydroxyl chain‐end functionalizations of polymeric organolithium compounds with oxetane (trimethylene oxide) were studied in benzene at 25 °C. Functionalizations of poly(styryl)lithium and polystyrene‐oligo‐butadienyllithium proceed efficiently to form the corresponding ω‐hydroxypropyl‐functionalized polymers in 98 and 97% isolated yields, respectively. No nonfunctional polymer (≤1–2%) was detected by thin layer chromatography (TLC) analysis for either polymer. All functionalized polymers were characterized by ¹³C and ¹H NMR analyses; no evidence for oxetane oligomerization at the chain end was observed. The MALDI‐TOF mass spectrum of ω‐hydroxypropylpolystyrene was consistent with the expected structure without any detectable oligomerization of oxetane. A small, but detectable series of peaks corresponding to nonfunctional polystyrene was also observed in the MALDI‐TOF mass spectrum. The functionalization of the adduct of 1,1‐diphenylethylene and PSLi produced the corresponding ω‐hydroxypropyl‐functionalized polymer in only 86% isolated yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2684–2693, 2006