Synthesis of acyclic nucleosides and other C-1 substituted alditols from carbohydrates using a tandem alkoxyl radical β-fragmentation–nucleophilic addition

The oxidative β-fragmentation of alkoxyl radicals generated from easily available carbohydrates is an efficient methodology to obtain acyclic nucleosides and other C-1 substituted alditols. In the reaction conditions an oxycarbenium ion is generated, which can be trapped by a variety of oxygen, carbon and nitrogen nucleophiles, in good yields and stereoselectivities.     

An asymmetric Kharasch reaction mediated by d-xylose: long range diastereocontrol

An asymmetric Kharasch-type atom transfer reaction was studied under 13 different sets of reaction conditions in order to obtain the highest levels of diastereoselection. The highest ratio of 12.5:1 (71%) was observed at low temperatures (−78°C) using the Lewis acid Eu(OTf)₃. Because the new asymmetric center is so distant from the d-xylose, we propose a transition state involving two sugars. The conversion of the major product to a naturally occurring chiral γ-butyrolactone, under basic conditions, is described which also confirmed the diastereoselectivity and absolute stereochemistry of the Kharasch reaction.     

HPLC-ECD检测羟自由基方法的研究

采用高效液相色谱结合库仑阵列多电极检测器体系(HPLC-ECD)建立了一套操作简便、高效、快速测定羟自由基的方法,并探究了检测的灵敏性,浓度和响应因子之间的线性关系,系统的稳定性等.2,3-二羟基苯甲酸(2,3-DHBA)、 2,5-二羟基苯甲酸(2,5-DHBA)以及水杨酸(SA)的相关系数分别为0.9999、 0.9996、 0.9968.2,3-DHBA和2,5-DHBA的检出限都低于0.1 ng/mL,SA的检出限均低于10 ng/mL,各种物质的方法回收率为100.5%～102.9%.     

5,6-苯并-2-亚甲基-1,3-二氧环庚烷的活性自由基开环聚合反应

活性 (或称可控 )自由基聚合研究是目前高分子科学的研究热点之一[1～ 8] .活性自由基聚合制备的聚合物具有分子量随转化率提高而线性增加、分子量分布窄和聚合反应为一级反应动力学等特点 .自由基开环聚合所得产物体积收缩小 ,某些含有不饱和双键的螺环单体发生双开环聚合时甚至发生体积膨胀 ;开环聚合还可在聚合物主链上引入各种官能团 ,如酯基、碳酸酯基、酮基等 [9～ 12 ] .因此 ,用活性聚合的方法对自由基开环聚合的分子量和分子量分布进行控制 ,可以制备出具有各种不同结构和性能的新聚合物 . Wei等 [13] 报道了利用稳定自由基法实现…     

自由基引发剂对重油加氢裂化的影响研究

在高压釜式反应器中考察了添加过氧化特二丁基(DTBP)、偶氮二异丁腈(AIBN)和单质碘(I2)三种自由基引发剂对克拉玛依蜡油、孤岛减压渣油加氢裂化反应的影响。在氢气初始压力7.0 MPa,反应1 h的条件下,对引发剂用量、催化剂用量、反应温度等影响因素进行了考察。结果表明,添加自由基引发剂后,重油的加氢裂化转化率,轻质油收率以及HDS、HDN都明显增加。添加质量分数5 000×10-6或10 000×10-6引发剂后,蜡油和减压渣油加氢裂化的轻质油收率最大可增加10%、13%,HDS和HDN最大可增加11%和7%左右。采用较少的催化剂用量或较低的反应温度即可以实现较高的重油转化率和轻质油收率。相对而言,DTBP和I2的促进作用优于AIBN。添加引发剂前后的加氢裂化的产物分布对比说明,引发剂的加入有利于蜡油或渣油原料一次裂化产物的生成。     

自由基引发剂用于渣油减黏裂化的研究

基于热裂化按照自由基反应机理进行的特点,在高压釜式反应器中分别添加四种自由基引发剂偶氮二异丁腈(AIBN)、过氧化特二丁基(DTBP)、单质硫(S)和单质碘(I2),考察引发剂在390℃～410℃,引发剂添加量0～3000×10-6条件下对三种减压渣油减黏裂化的影响。通过测定减黏前后渣油的运动黏度和四组分的变化,对引发剂的作用机理进行了初步研究。结果表明,自由基引发剂对不同基属的减压渣油减黏裂化反应均有明显的促进作用,大小依次为:LHVR≥GDVRDQVR,并且这种促进作用在较低的反应温度下更加明显,促进效果由渣油本身的物理化学性质所决定。在同等条件下,I2和S促进渣油减黏的效果是AIBN和DTBP降黏率的两倍,这与S和I2形成氢化物的"活性原子"可以多次循环发生作用有关。与S相比,单质I2减黏促进作用更为明显。     

Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4‐(2‐bromo‐2‐methylpropionyloxy)‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Br‐TEMPO), was synthesized by the reaction of 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy with 2‐bromo‐2‐methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br‐TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ω‐end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468–2475, 2006     

Simulation and analysis of free radical branching copolymerization kinetics

Iｔｉｓｄｉｆｆｉｃｕｌｔａｎｄｅｖｅｎｉｍｐｏｓｓｉｂｌｅｔｏｄｅｔｅｒｍｉｎｅｂｙｒｅｇｕｌａｒｋｉｎｅｔｉｃｓｍｅｔｈｏｄｓｓｏｍｅｋｉｎｅｔｉｃｓｐａｒａｍｅｔｅｒｓｏｆｓｏｍｅｃｏｍｐｌｅｘｃｈｅｍｉｃａｌｒｅａｃｔｉｏｎｓ,ｅｓｐｅｃｉａｌｌｙｐｏｌｙｍｅｒｉｚａｔｉｏｎｒｅａｃｔｉｏｎｓｗｈｏｓｅｍｅｃｈａｎｉｓｍｓｈａｖｅｎｏｔｂｅｅｎｋｎｏｗｎ.Ｗｅｈａｖｅｔｒｉｅｄｔｏｓｏｌｖｅｔｈｉｓｐｒｏｂｌｅｍｂｙｔｈｅｍｅｔｈｏｄｏｆｒｅｇｒｅｓｓｉｏｎａｎｄｓｉｍｕｌａｔｉｏｎｏｆｃ…     

Free radical exit in emulsion polymerization. I. Theoretical model

The exit or desorption of free radicals from latex particles is an important kinetic process in an emulsion polymerization. This article unites a successful theory of radical absorption (i.e., initiator efficiency), based on propagation in the aqueous phase being the rate determining step for entry of charged free radicals, with a detailed model of radical desorption. The result is a kinetic scheme applicable to true “zero-one” systems (i.e., where entry of a radical into a latex particle already containing a radical results in instantaneous termination), which is still, with a number of generally applicable assumptions, relatively simple. Indeed, in many physically reasonable limits, the kinetic representation reduces to a single rate equation. Specific experimental techniques of particular significance and methods of analysis of kinetic data are detailed and discussed. A methodology for both assessing the applicability of the model and its more probable limits, via use of known rate coefficients and theoretical predictions, is outlined and then applied to the representative monomers, styrene and methyl methacrylate. A detailed application of the theory and illustration of the methodology of model discrimination via experiment is contained in the second article of this series. © 1994 John Wiley & Sons, Inc.     

Investigation of the free radical polymerization of styrene in the presence of several 1,1-disubstituted ethylenes

A variety of 1,1-disubstituted ethylenes, having an electron-withdrawing (capto) and an electron-donor (dative) substituent on the same carbon, were synthesized and added to styrene polymerizations. The dative substituents investigated were alkoxy or alkylcarbonate. After the addition of a polystyryl radical to a disubstituted ethylene, the resulting alkoxy or carbonate radicals could potentially fragment, resulting in chain termination and the formation of alkyl radicals. This process is called addition-fragmentation chain transfer (AFCT). The polymers produced during this study were examined for evidence of copolymerization and AFCT. The relative stability of the radicals generated by the fragmentation process appears to be the predominant factor controlling the ratio of copolymerization versus AFCT. © 1993 John Wiley & Sons, Inc.     

Free radical dispersion polymerization of styrene in a mixture of 2-propanol and tetrahydrofuran

Free radical dispersion polymerization of styrene in a mixture of 2-propanol and tetrahydrofuran was carried out at 70°C up to high conversions. The influence of the change of the critical chain length on the evolution of the insoluble polymer component was examined. Monomer conversion and the formation of the insoluble polymer component were measured in order to test a mathematical model presented in our previous article. The critical polymer chain length i₀, the initiation rate constant k_d, and the ratio k_p/k, where k_p and k_t are propagation and termination rate constants, respectively, have been obtained and compared with those reported in the literature. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2757–2761, 1998     

Synthesis of AB2 miktoarm star-shaped copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with two initiating groups for atom transfer radical polymerization (ATRP), 4-(2,2-bis-(methyl 2-bromo isobutyrate)-propionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br₂-TEMPO), was synthesized by reacting 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2,2-bis-(methyl 2-bromo isobutyrate) propanoic acid. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br₂-TEMPO. The obtained polystyrene had two active bromine atoms for ATRP at the ω-end of the chain and was further used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare AB₂-type miktoarm star-shaped copolymers. The molecular weights of the resulting miktoarm star-shaped copolymers at different monomer conversions shifted to higher molecular weights without any trace of the macroinitiator, and increased with monomer conversion.     

Free radical reactions of carbohydrate derivatives in the synthesis of carbocyclic compounds

The benzyloxy group at C(4) of the pyranose ring in 3,4-disubstituted and 3-deoxy carbohydrate derivatives affects the direction of intramolecular free-radical C(2)-C(6) cyclization. A possible mechanism of the formation of the tetrahydrofuran ring was proposed.For Part 3, see Ref. 1.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 767–773, April, 1995.The present work was partially supported by the Russian Foundation for Basic Research (project No. 93-03-5834) and the International Science Foundation (Project No. MOM 000).     

Fundamental studies of grafting reactions in free radical copolymerization. I. A detailed kinetic model for solution polymerization

Graft site initiation occurs by primary radical and/ or polymeric radical attack on the back-bone polymer. The controlling mechanism is determined by the structure of the backbone and the activity of the free radicals. The efficiency of incorporating monomer into the graft chains depends upon the graft site initiation mechanism and the mode of polymer chain termination (recombination or disproportionation). A kinetic analysis results a series of uniquely different expressions describing the graft efficiency, ? corresponding to different combinations of graft site initiation and chain termination mechanisms. The dependency of ? upon monomer, initiator, and backbone concentrations is different from case to case. The complete kinetic model is capable of predicting reaction rate, graft efficiency, graft frequency, graft ratio, and molecular weight averages and distributions. Simulations are provided to compare predicted results with experimental data for two different systems which show contrasting mechanisms of graft site initiation and mode of termination. © 1995 John Wiley & Sons, Inc.     

Synthesis and radical polymerization properties of thermal radical initiators based on o‐imino‐isourea: The effect of the alkyl side chain on the radical initiation temperature

Four types of thermal radical initiators (TRIs) that are based on o‐imino‐isourea with cyclohexyl and isopropyl groups were successfully synthesized, namely, C‐HexDCC, DiiprDCC, C‐HexDIC, and DiiprDIC. The free radical polymerization and thermal properties of those synthesized TRIs were determined via differential scanning calorimetry (DSC) (using n‐butyl acrylate) and thermogravimetric analysis (TGA), respectively. The TRI derivatives showed peak temperatures (T_max) from 89 to 97 °C in n‐butyl acrylate, and DiiprDIC, with isopropyl groups on both sides of the N O group, showed the lowest peak temperatures. The rates of N O bond homolysis (k_d) of all the TRIs were calculated from their half‐lives determined using real‐time nuclear magnetic resonance (NMR) spectroscopy, and their theoretical bond dissociation energies (BDEs) were calculated using density functional theory (DFT) calculations. The free radical polymerization of n‐butyl acrylate using each TRI was efficiently determined from T_peak of the DSC curves; conversions depending on polymerization temperature (80, 90, and 100 °C) were monitored to observe kinetic information of TRIs during polymerization. Furthermore, to investigate the use of TRIs in curing, we applied them to an automotive clear coating system and monitored the real‐time evolution of the elastic modulus (G′) during thermal curing using a rheometer for representative DiiprDIC. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1749–1756     

Activity of the furfuryl ring in the free radical polymerization of acrylic monomers

The effect and the participation of the furfuryl ring, in particular the hydrogen at position C-5 in the free radical polymerization are analyzed following the polymerization of furfuryl acrylate (FA) and furfuryl methacrylate (FM) initiated by AIBN under photochemical activation. The results obtained indicate that the polymerization of FA deviates from the classical free radical kinetic scheme, giving rise to crosslinked polymers even at a degree of conversion lower than 7%. This behavior is well explained taking into consideration the participation of the furfuryl ring which acts as a degradative transfer agent. This was demonstrated by the kinetic analysis of the free radical polymerization of MMA initiated by the thermal decomposition of AIBN in the presence of different concentrations of furfuryl acetate. © 1996 John Wiley & Sons, Inc.     

Kinetics of radical polymerization of dimethylphenyl methacrylates

The kinetics of free radical polymerization of all six existing isomeric dimethylphenyl methacrylates were studied in bulk at 60°C, initiated by dilauroyl peroxide, using dilatometry. The different polymerization rates observed, resulting from the different monomer structures, are discussed in terms of steric and other effects, considering also the previous results for tolyl methacrylates. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of well‐defined ABC‐type triblock copolymers via atom transfer radical polymerization and stable free‐radical polymerization

An asymmetric difunctional initiator 2‐phenyl‐2‐[(2,2,6,6 tetramethylpiperidino)oxy] ethyl 2‐bromo propanoate ( 1 ) was used for the synthesis of ABC‐type methyl methacrylate (MMA)‐tert‐butylacrylate (tBA)‐styrene (St) triblock copolymers via a combination of atom transfer radical polymerization (ATRP) and stable free‐radical polymerization (SFRP). The ATRP‐ATRP‐SFRP or SFRP‐ATRP‐ATRP route led to ABC‐type triblock copolymers with controlled molecular weight and moderate polydispersity (M_w/M_n < 1.35). The block copolymers were characterized by gel permeation chromatography and ¹H NMR. The retaining chain‐end functionality and the applying halide exchange afforded high blocking efficiency as well as maintained control over entire routes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2025–2032, 2002