过硫酸盐与吡咯烷体系引发丙烯酰胺聚合反应机理的研究

我们曾经报道过硫酸盐和脂肪族六元环胺可以组成氧化还原引发体系用于烯类单体水溶液聚合,并且证实环仲胺如吗啉(MP)和哌啶(PD)被氧化后生成氮自由基参与了引发反应。本文对过硫酸盐和五元环胺吡咯烷(PyD)组成的引发体系进行了研究。 1 实验部分     

过硫酸盐和脂肪二元叔胺体系引发烯类聚合的反应与机理的研究

本文研究了过硫酸盐和脂肪二元叔胺体系引发丙烯酰胺水溶液聚合的反应和机理。发现脂肪二元叔胺具有很高的促进聚合活性。测定了聚合反应表观活化能和动力学方程。端基分析表明聚合物中含有胺端基。用自由基捕捉技术和ESR波谱方法研究了脂肪二元叔胺与过硫酸盐体系的初级自由基,证实脂肪二元叔胺参与了引发烯类聚合的反应。提出了引发反应机理。     

α-全氟烷基吡咯的合成及性质

前文已报道了全氟碘代烷在连二亚硫酸钠的引发下,对烯烃、富电子芳环的反应,并认为反应是自由基历程。本文报道应用这个反应合成α-全氟烷基吡咯。 Waksclman报道N-甲基吡咯与R_FI在自     

N-[ω-(三丁基锡甲氧基)烷基]邻苯二甲酰亚胺的合成及其光环化反应

烷基二醇与三丁基锡碘甲烷反应得三丁基锡甲氧基烷基醇(2a~2 e);2(或其衍生物)与邻苯二甲酰亚胺反应合成了N-[ω-(三丁基锡甲氧基)烷基]邻苯二甲酰亚胺(5a~5 e),其结构经NMR和MS表征。5在光诱导下,由单电子转移引发,经分子内自由基偶合,高产率(85%~99%)地获得可控制反应位置的大环化合物。     

胺存在下自由基聚合与活性自由基聚合

综述了胺存在下自由基聚合,包括含胺的过氧化二酰与芳叔胺氧化还原体系、有机过氧化氢物与芳叔胺或脂肪叔胺氧化还原体系、过硫酸盐与脂肪胺氧化还啄体系和极性单体的胺光诱导电荷转移引发自由基聚合,以及活性／控制自由基聚合,主要为原子转移自由基研究的成果。     

对-二氮杂萘 N,N′-二氧化物光解产物的 ESR 研究

芳香 N-氧化物在光激发下发生脱氧、重排、环扩大和环缩小等反应.但 N-氧化物的初级光化学反应是否涉及自由基中间体的过程却未见文献报道.本文利用电子自旋共振技术研究两种对-二氮杂萘 N,N′-二氧化物(1,2)在光解过程中所生成的自由基中间体.     

镍催化环丁酮肟酯与芳基锌试剂的Negishi偶联反应

发展了一种镍催化环丁酮肟酯和芳基锌试剂之间Negishi偶联的方法.镍既作为亚胺自由基的引发剂,也作为芳基锌试剂与烷基自由基偶联反应的催化剂在反应中起作用.本方法可避免使用剧毒的氰化物,且具有很广的底物适应性和官能团兼容性,因此可能是一种具有潜在吸引力的高效合成烷基腈类化合物的新策略.初步的机理研究显示,该反应极可能经历自由基历程.     

氟烷基化和氟烷氧基化的研究2.在铜存在下氟烷基碘与芳烃的反应

氟烷基碘(RfI)在铜存在下与芳烃,C6H5Y(Y=烷基,OCH5,CF3,F,Cl,Br,I)在乙酐中反应得到相应的氟烷基化芳烃(RfC6H4Y)混合物,转化率和产率与所用铜粉量和芳烃上的电子密度有关,带有供电子基的芳烃转化率和产率都较高;反之则低,反应可能是自由基机理,氟烷基自由基能被环己烯和异丙苯所捕获。引发苯乙烯聚合生成含氟聚合物。芳环上的定位效应似乎也支持这一机理。若用DMSO为溶剂则可能是通过氟烷基铜中间体。     

某些新的N-苯乙烯基脲及N-苄基硫脲衍生物的合成

用苯乙烯基异氰酸脂与脂肪胺反应合成了6个新的N-苯乙烯基脲化合物,产品收率多在90%以上。通过α-甲基苄基和对氯α-甲基苄基异硫氰酸脂与脂肪胺反应制备了12个新的N-苄基衍生物。     

镍催化环丁酮肟酯与芳基锌试剂的Negishi偶联反应（英文）

发展了一种镍催化环丁酮肟酯和芳基锌试剂之间Negishi偶联的方法.镍既作为亚胺自由基的引发剂,也作为芳基锌试剂与烷基自由基偶联反应的催化剂在反应中起作用.本方法可避免使用剧毒的氰化物,且具有很广的底物适应性和官能团兼容性,因此可能是一种具有潜在吸引力的高效合成烷基腈类化合物的新策略.初步的机理研究显示,该反应极可能经历自由基历程.     

Ionization of cyclic aromatic amines by free electron transfer: products are governed by molecule flexibility

The bimolecular electron transfer from secondary aromatic amines to parent radical cations of nonpolar solvents such as alkanes and alkyl chlorides results in the synchronous formation of amine radical cations as well as aminyl radicals, in comparable amounts. If as for cyclic aromatic amines (c-Ar(2)NH) the intramolecular bending motion around the amine group is restricted in varying degrees (acridane, phenothiazine) or completely prevented (carbazole), then this picture is modified. In the free electron transfer, the completely rigid carbazole yields exclusively amine radical cations. Acridane exhibits preferred radical cations, but phenothiazine with the more flexible six-membered ring involving sulfur as a further heteroatom follows the common two-product rule; see above. The phenomenon is reasoned by a peculiarity in the bimolecular free electron transfer where after diffusional approach the actual electron jump proceeds in the ultrashort time range. Therefore, it reflects femtosecond molecular motions which, in the case of free mobility, continuously pass through different molecule conformers, combined with fluctuation of the electrons of the responsible molecular n-orbitals. The rigid systems, however, do not show this effect because of a nonexistent bending motion.     

Free Radical Studies at Low Temperatures

Free radicals can be produced in the gas phase and then condensed together with the molecules of an inert gas; they can also be generated and trapped in isolated sites in rigid solids. IR and ESR spectra of trapped radicals provide information concerning their structure and chemical properties. The techniques employed for producing and studying radicals are reviewed and a number of recent IR and ESR investigations of trapped radicals are discussed. The last part of the article deals exclusively with the applications of the rotating cryostat to the study of the ESR spectra and reactions of trapped radicals at low temperatures.     

Electron spin resonance studies of propagating radicals in polymerization. I. Methacrylate propagating radicals

Ferric chloride-photosensitized free-radical initiation was used to generate propagating radicals in polymerization of methacrylic acid (MAA), allyl methacrylate (AMA), methyl methacrylate (MMA), 1,3-butylene dimethacrylate (1,3-BDMA), hydroxypropyl methacrylate (HPMA), lauryl methacrylate (LMA), hexyl methacrylate (HMA), and methacrylamide (MA) in rigid glasses of methanol or acetone at near liquid nitrogen temperatures. The formation and conformational changes of these propagating radicals at different temperatures were studied by electron spin resonance (ESR) spectroscopy. When methanol was the rigid glass, ·CH₂OH radicals were formed initially and were stable below ?160°C. As the temperature of the rigid glass was increased, the ·CH₂OH radicals reacted with monomer to yield propagating radicals. With the exception of the propagating radical for methacrylamide, the propagating radicals of the methacrylates examined initially generated five-line ESR spectra which gradually changed to nine-line spectra, as temperature of the rigid glass was increased. It was concluded that one type of propagating radical was formed in all cases. However, when the temperature of the rigid glass was increased, the single structural conformation that initially allowed one of the methylene hydrogens and methyl group to interact with the unpaired electron to generate only a five-line spectrum was changed to yield a second conformation that allowed interaction to generate an additional four-line spectrum. Finally, a mixture of the propagating radical for methacrylate monomer in two structural conformations was obtained, and an ESR spectrum consisting of nine lines (5 + 4 lines) was generated. In the case of the propagating radical for methacrylamide this change to yield two structural conformations evidently was hindered, so that only an ESR spectrum consisting of five lines was generated.     

Nature of mechanoradical formation of substituted celluloses as studied by electron spin resonance

Mechanically induced free radical (mechanoradical) formation of several substituted celluloses such as carboxylmethyl cellulose, chitin, and chitosan was studied based on electron-spin resonance (ESR) in comparison with those of plasma-induced radicals. Room temperature ESR spectra had multicomponent spectra and were different in pattern from each other. The mechanoradical concentration gradually decreased after reaching the maximum value in each substituted polysaccharide, accompanied by a decrease in molecular weight in the course of vibratory milling. One of the most intriguing facts is that the component radicals are all glucose-based radicals as in the case of plasma irradiation, although it is known that mechanoradicals are formed by 1,4-glucosidic bond cleavage of polysaccharides.     

Hydrogen atom abstraction reactions from tertiary amines by benzyloxyl and cumyloxyl radicals: influence of structure on the rate-determining formation of a hydrogen-bonded prereaction complex

A time-resolved kinetic study on the hydrogen atom abstraction reactions from a series of tertiary amines by the cumyloxyl (CumO(?)) and benzyloxyl (BnO(?)) radicals was carried out. With the sterically hindered triisobutylamine, comparable hydrogen atom abstraction rate constants (k(H)) were measured for the two radicals (k(H)(BnO(?))/k(H)(CumO(?)) = 2.8), and the reactions were described as direct hydrogen atom abstractions. With the other amines, increases in k(H)(BnO(?))/k(H)(CumO(?)) ratios of 13 to 2027 times were observed. k(H) approaches the diffusion limit in the reactions between BnO(?) and unhindered cyclic and bicyiclic amines, whereas a decrease in reactivity is observed with acyclic amines and with the hindered cyclic amine 1,2,2,6,6-pentamethylpiperidine. These results provide additional support to our hypothesis that the reaction proceeds through the rate-determining formation of a C-H/N hydrogen-bonded prereaction complex between the benzyloxyl α-C-H and the nitrogen lone pair wherein hydrogen atom abstraction occurs, and demonstrate the important role of amine structure on the overall reaction mechanism. Additional mechanistic information in support of this picture is obtained from the study of the reactions of the amines with a deuterated benzyloxyl radical (PhCD(2)O(?), BnO(?)-d(2)) and the 3,5-di-tert-butylbenzyloxyl radical.     

L-tryptophan radical cation electron spin resonance studies: connecting solution-derived hyperfine coupling constants with protein spectral interpretations

Fast-flow electron spin resonance (ESR) spectroscopy has been used to detect a free radical formed from the reaction of l-tryptophan with Ce (4+) in an acidic aqueous environment. Computer simulations of the ESR spectra from l-tryptophan and several isotopically modified forms strongly support the conclusion that the l-tryptophan radical cation has been detected by ESR for the first time. The hyperfine coupling constants (HFCs) determined from the well-resolved isotropic ESR spectra support experimental and computational efforts to understand l-tryptophan's role in protein catalysis of oxidation-reduction processes. l-Tryptophan HFCs facilitated the simulation of fast-flow ESR spectra of free radicals from two related compounds, tryptamine and 3-methylindole. Analysis of these three compounds' beta-methylene hydrogen HFC data along with equivalent l-tyrosine data has led to a new computational method that can distinguish between these two amino acid free radicals in proteins without dependence on isotope labeling, electron-nuclear double resonance, or high-field ESR. This approach also produces geometric parameters (dihedral angles for the beta-methylene hydrogens) that should facilitate protein site assignment of observed l-tryptophan radicals as has been done for l-tyrosine radicals.     

毛细管柱GC/MS/ESR 联用研究自由基PBN加合物

采用硅烷化方法，并用石英毛细管柱气相色谱与双聚焦质谱仪组成的ＧＣ／ＭＳ联用系统，首次成功地分析鉴别了六种自由基的ＰＢＮ加合物，总结了这些自旋加合物的断裂规律。实验结果表明，硅烷化结合ＧＣ／ＭＳ和自旋捕捉ＥＳＲ联用技术是确定活泼自由基的一种有效方法。     

ESR STUDY OF PLASMA-TREATED POLYTETRAFLUOROETHYLENE FILMS

The plasma treatment of polytetrafluoroethylene (PTFE) films was carried out in a capacitively coupled reactor with external electrodes. The free radicals generated in the process of treatment were detected by ESR techniques. The ESR spectra tended to indicate that the free radicals of the pLasma-treated PTFE film sample were turned into peroxy radicals on exposure to air. The extrema separation (W) of the ESR spectrum of the peroxy radical increased with the lowering temperature and underwent a sudden change within the temperature range of 170 to 190K. The ESR spectrum observed at 77K was quite different from that observed at room temperature. Finally, the effects of treatment time, input power and system pressure on radical concentration of the treated samples were studied. The attenuation of the peroxy radical at room temperature was also investigated.     

Azulene-substituted aromatic amines. synthesis and amphoteric redox behavior of N,N-Di(6-azulenyl)-p-toluidine and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine and their derivatives

[reaction: see text] N,N-Di(6-azulenyl)-p-toluidine (1a) and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine (2a) and their derivatives with 1,3-bis(ethoxycarbonyl) substituents on each 6-azulenyl group (1b and 2b) were prepared by Pd-catalyzed amine azulenylation and characterized as a study into new aromatic amines for multistage amphoteric redox materials. The redox behavior of each compound was characterized by cyclic voltammetry. These compounds undergo facile reduction to stable anion radicals and dianion diradicals owing to the resonance stabilization between the 6-azulenyl groups and exhibit electrochemical oxidation depending on the amine subunits. The ESR measurement of anion radicals and a dianion diradical generated by the electrochemical reduction of amine 1b and diamine 2b revealed that the unpaired electron of these radicals delocalizes over the entire azulene ring including the central nitrogen atoms. UV-vis spectral analysis of amines 1a,b and diamines 2a,b, taken during the electrochemical reduction, exhibited a gradual decrease of the absorption bands of the neutral species along with an increase of the new absorption maxima at 625, 605, 640, and 610 nm, respectively, with the development of well-defined isosbestic points at 502, 562, 478, and 545 nm, respectively. As indicated by a combined ESR and UV-vis spectral study, the species giving rise to the new absorption maxima are concluded to be the generation of anion radicals and dianion diradicals of aromatic amines and diamines with high thermodynamic stability.