Diethoxy‐azobis(pyridinium) Salt as Photoinitiator for Cationic Polymerization: Towards Wavelength Tunability by Cis–Trans Isomerization

N,N′‐diethoxy‐4,4′‐azobis(pyridinium) hexafluorophosphate (DEAP) has been synthesized by alkylation of the corresponding N‐oxide and characterized. DEAP exhibits UV induced cis–trans isomerization with absorptions at around λ = 459 and 360 nm, respectively. The ability of the DEAP ion to act as a photoinitiator for the cationic polymerization of cyclohexene oxide and N‐vinylcarbazole is demonstrated. The initiation step involves the decay of the excited state of the trans form of the salt with homolytic bond rupture of the nitrogen–oxygen bond. Its potential use as a photoinitiator for free radical polymerization is also demonstrated using methyl methacrylate monomer as the example.

     

Hydrogallierungsreaktionen mit den Monoalkinen H5C6‐C≡C‐SiMe3 und H5C6‐C≡C‐CMe3 – cis/trans‐Isomerie und Substituentenaustausch

Hydrogallation Reactions Involving the Monoalkynes H₅C₆‐C≡C‐SiMe₃ and H₅C₆‐C≡C‐CMe₃ – cis/trans Isomerisation and Substituent Exchange Phenyl‐trimethylsilylethyne, H₅C₆‐C≡C‐SiMe₃, reacted with different dialkylgallium hydrides, R₂Ga‐H (R = Me, Et, nPr, iPr, tBu), by the addition of one Ga‐H bond to its C≡C triple bond (hydrogallation). The gallium atoms attacked selectively those carbon atoms, which were also attached to trimethylsilyl groups. The cis arrangement of Ga and H across the resulting C=C double bonds resulted only for the sterically most shielded di(tert‐butyl)gallium derivative, while in all other cases spontaneous cis/trans rearrangement occurred with the quantitative formation of the trans addition products. The diethyl compound Et₂Ga‐C(SiMe₃)=C(H)‐C₆H₅ ( 2 ) gave by substituent exchange the secondary products EtGa[C(SiMe₃)=C(H)‐C₆H₅]₂ ( 7 , Z,Z) and Ga[C(SiMe₃)=C(H)‐C₆H₅]₃ ( 8 ). Interestingly, compound 8 has two alkenyl groups with a Z configuration, while the third C=C double bond has the cis arrangement of Ga and H (E configuration). The reversibility of the cis/trans isomerisation of hydrogallation products was observed for the first time. tert‐Butyl‐phenylethyne gave the simple addition product, R₂Ga(C₆H₅)=C(H)‐CMe₃ ( 9 ), only with di(n‐propyl)gallium hydride.     

1H,13C NMR spectral data for α-, β-, and γ-lewisites and identification ofcis,trans, trans-γ-lewisite as a new isomer

The¹H and¹³C NMR spectral parameters of α-, β-, and y-lewisites1–5 were obtained and a new isomer,cis,trans,trans-γ-lewisite5, was isolated and identified on the basis of chemical shifts, relative intensities of the signals, and the intra-chain (³ J _hh ,³ J _ch ) and interchain (³ J _casch ) coupling constants. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1833–1835, October, 1993.     

反式-1,4,5,8-四硝基-1,4,5,8-四氮杂萘烷异构体热解机理与稳定性的理论研究

运用密度泛函理论和半经验分子轨道方法,对一系列高能杂环硝胺—反式-1,4,5,8-四硝基-1,4,5,8-四氮杂萘烷异构体的热解机理和稳定性进行了系统地计算研究。在B3LYP/6-31G**和PM3水平上,分别计算了标题物的化学键离解能(BDE)和热解反应活化能(Ea),并根据BDE和Ea数值考察了硝胺取代基对化合物稳定性和热解机理的影响;同时,还详细考察了BDE与Ea、化学键重叠布居数、前线轨道能级以及能隙之间的相关性。结果表明,由BDE、Ea和静态电子结构参数推断的标题物热稳定性和热解机理的结论基本是一致的,N-NO2键均裂是标题物的热解引发步骤,间位取代异构体较对位取代异构体稳定,而邻位取代的异构体稳定性最差。     

Recyclable 1,2‐bis[3,5‐bis(trifluoromethyl)phenyl]diselane‐catalyzed oxidation of cyclohexene with H2O2: a practical access to trans‐1,2‐cyclohexanediol

1,2‐Bis[3,5‐bis(trifluoromethyl)phenyl]diselane‐catalyzed oxidation of cyclohexene by hydrogen peroxide affords a quick, clean and practical access to the important compound trans‐1,2‐cyclohexanediol under mild conditions. The highly atom‐economic properties, clean procedures, high reaction concentration, short reaction time, mild conditions and eco‐friendly, recyclable and low loading catalysts facilitate this methodology for possible future practical industrial production. Copyright © 2014 John Wiley & Sons, Ltd.     

High‐performance liquid chromatography separation of unsaturated organic compounds by a monolithic silica column embedded with silver nanoparticles

The optimization of a porous structure to ensure good separation performances is always a significant issue in high‐performance liquid chromatography column design. Recently we reported the homogeneous embedment of Ag nanoparticles in periodic mesoporous silica monolith and the application of such Ag nanoparticles embedded silica monolith for the high‐performance liquid chromatography separation of polyaromatic hydrocarbons. However, the separation performance remains to be improved and the retention mechanism as compared with the Ag ion high‐performance liquid chromatography technique still needs to be clarified. In this research, Ag nanoparticles were introduced into a macro/mesoporous silica monolith with optimized pore parameters for high‐performance liquid chromatography separations. Baseline separation of benzene, naphthalene, anthracene, and pyrene was achieved with the theoretical plate number for analyte naphthalene as 36 000 m^?1. Its separation function was further extended to cis/trans isomers of aromatic compounds where cis/trans stilbenes were chosen as a benchmark. Good separation of cis/trans‐stilbene with separation factor as 7 and theoretical plate number as 76 000 m^?1 for cis‐stilbene was obtained. The trans isomer, however, is retained more strongly, which contradicts the long‐ established retention rule of Ag ion chromatography. Such behavior of Ag nanoparticles embedded in a silica column can be attributed to the differences in the molecular geometric configuration of cis/trans stilbenes.     

Precision Chain‐Walking Polymerization of trans‐4‐Octene Catalyzed by α‐Diimine Nickel(II) Catalysts Bearing ortho‐sec‐Phenethyl Groups

α‐Diimine nickel complexes bearing bulky ortho‐sec‐phenethyl groups (bis{[N,N′‐(4‐methyl‐2,6‐di‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel ( 1 ), bis{[N,N′‐(4,6‐dimethyl‐2‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel ( 2 ), bis{[N,N′‐(4‐methyl‐2‐sec‐phenethylphenyl)imino]‐1,2‐dimethylethane}dibromonickel ( 3 )) and {bis[N,N′‐(2,4,6‐trimethylphenyl)imino]‐1,2‐dimethylethane}dibromidonickel ( 4 ) are used as a precatalyst for the polymerization of trans‐4‐octene upon activation with modified methylaluminoxane. These catalysts conduct chain‐walking polymerization of trans‐4‐octene to give polymers possessing propyl and butyl branches with high molecular weight and narrow molecular weight distribution. The branching structure depends on the nickel complex as well as the polymerization temperature, and the ratio of propyl branch was increased with increasing the bulkiness of the ligand and decreasing the polymerization temperature. Consequently, the most bulky 1 among the complexes used is found to polymerize trans‐4‐octene with high 1,5‐regioselectivity at −20 °C to give poly(1‐propylpentan‐1,5‐diyl).

     

A high‐performance liquid chromatographic analysis and preliminary pharmacokinetic characterization of 3′‐hydroxypterostilbene in rats

A high‐performance liquid chromatographic method was developed for the analysis of 3'‐hydroxypterostilbene. This method involves the use of a Luna^® C₁₈ column with ultraviolet detection at 325 nm. The mobile phase consisted of acetonitrile, water and formic acid (50:50:0.01, v/v/v) with a flow rate of 0.8 mL/min. The calibration curves were linear over the range 0.5–100.0 µg/mL. The mean extraction efficiency was between 97.40 and 111.16%. The precision of the assay was 0.196–14.39% (RSD%), and within 15% at the limit of quantitation (0.5 µg/mL). The bias of the assay was <16% and within 15% at the limit of quantitation. This assay was successfully applied to pre‐clinical pharmacokinetic samples from rat urine and serum. Copyright © 2009 John Wiley & Sons, Ltd.