Effect of Cholesteric Liquid Crystalline Compounds on the Radical Polymerization of Methyl Methacrylate

Polymerization of methyl methacrylate was carried out at 55 and 65°C using benzoyl peroxide as initiator in the presence of the fol-lowing additives: (a) cholesteric compounds like cholesterol, cho-lesteryl acetate, cholesteryl caprylate, cholesteryl stearate, choles-teryl chloride, cholesteryl laurate, cholesteryl oleyl carbonate, and cholesteryl 2-ethylhexyl carbonate, (b) a nematic liquid crystal, N-(p-methoxy benzylidene)-p-butyl aniline, and (c) rodlike molecules like 2-butynediol and diacetylene diol. The rates of polymerization, activation energies, molecular weights, and tacticities of the poly-mer are discussed in the light of monomer + additive interactions. It is found that monomer-additive complexes affect the polymerization rates.     

CuI/glycerol mediated stereoselective synthesis of 1,2-bis-chalcogen alkenes from terminal alkynes: synthesis of new antioxidants

(E)-1,2-Bis-chalcogen alkenes were stereoselectively prepared in good yields by the addition of diorganyl dichalcogenides to terminal alkynes using CuI/Zn/glycerol as a recyclable catalytic system. The antioxidant activity in vitro of four (E)-1,2-bis-chalcogen alkenes synthesized was evaluated and (E)-1,2-bis-(4-methoxyphenylselanyl)styrene 3b presented excellent activity. The catalytic system used in the synthesis was recovered and used directly up to 5 cycles without loss of activity.     

Electrophoretic separation of reptilian skeletal and cardiac muscle myosin heavy chain isoforms: Dependence on gel format

This report provides a comparison of multiple gel formats to study myosin heavy chain (MHC) isoforms that are expressed in reptilian skeletal and cardiac muscles of five turtle species, water monitor, and prehensile tailed skink. Three gel formats were tested. The results identify one format that is superior, for the overall extent of electrophoretic separation and for the assessment of the number of MHC isoforms in reptilian striated muscles. The same format was shown previously to separate MHC isoforms that are expressed in American alligator. The results also show that another gel format reveals the distinct electrophoretic mobility of MHC isoforms in atrial, ventricular, and jaw adductor samples, compared to those expressed in skeletal muscles in the limbs and elsewhere in the body. In addition, the results reveal that the electrophoretic mobility of specific MHC isoforms, relative to other isoforms, depends on the gel format, as shown previously for mammalian and avian species. The discovery of the expression of masticatory MHC, which is abundantly expressed in jaw adductors of members of Carnivora and several other vertebrate orders, in the homologous muscles of prehensile tailed skink, an herbivore, and the carnivorous water monitor, was made during the course of this study.     

Room temperature synthesis of glycerol carbonate catalyzed by N-heterocyclic carbenes

N-Heterocyclic carbenes were used as efficient organocatalysts for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate. The reaction takes place in a liquid mixture of reactants without solvent at room temperature. It provides glycerol carbonate in high yield using 2.6–4 mol % of catalyst in a reaction period of 20–30 min.     

Role of preparation parameters of Cu–Zn mixed oxide catalyst in solvent free glycerol carbonylation with urea

Solvent-free carbonylation of glycerol with urea to glycerol carbonate (GC) was achieved over heterogeneous Cu–Zn mixed oxide catalyst. Cu–Zn catalysts with different ratios of Cu:Zn were prepared using co-precipitation (CP) and oxalate gel (OG) methods. As compared to CuO–ZnO(2:1) catalyst prepared by oxalate gel (OG) method, much higher conversion of glycerol and highest selectivity towards glycerol carbonate (GC) was achieved with CuO–ZnO_CP(2:1) catalyst. Physicochemical properties of prepared catalysts were investigated by using XRD, FT-IR, BET, TPD of CO₂ and NH₃ and TEM techniques. The effect of stoichiometric ratio of Cu/Zn, calcination temperature of CuO–ZnO catalysts and effect of reaction parameters such as molar ratio of substrates, time and temperature on glycerol conversion to GC were critically studied. Cu/Zn of 2:1 ratio, glycerol–urea 1:1 molar ratio, 145 ​°C reaction temperatures were found to be optimized reaction conditions to achieve highest glycerol conversion of 86% and complete selectivity towards GC. The continuous expel of NH₃ from reaction the mixture avoided formation of ammonia complex with CuO–ZnO catalyst. As a result of this, CuO–ZnO catalyst could be recycled up to three times without losing its initial activity.     

气-液半间歇反应器中甘油氯化:用于生产氯代醇的新型催化剂(英)

Glycerol from biodiesel production can be an important industrial feedstock for chemical commodities as it can be used in the food,cosmetic,pharmaceutical and tobacco industries.However,crude glycerol derived from biodiesel production has a low value because of impurities.The purification of this glycerol into a high grade involves high costs and is not economically feasible for small and medium size plants.The glycerol conversion into chlorohydrins was studied using new homogeneous catalysts and hydrochloric acid as chlorination agent.This is an interesting alternative route to epichlorohydrin and then to epoxy resins.The behavior of two series of homologous catalysts,glycolic acid series(glycolic acid,di-glycolic acid and thio-glycolic acid) and amminoacid series(glutamic acid,aspartic acid and cysteine),were investigated for their activity and selectivity.Glycolic acids were more active than amminoacids.The pK_a values had a strong influence on selectivity(mono-chlorohydrins/di-chlorohydrins) for the amminoacid series,which was not observed for the glycolic acids.A kinetic model and reaction mechanism developed in a previous work were used for interpreting the kinetic runs.     

活性炭担载的铂催化剂在碱性条件下选择性氧化甘油制备乳酸

生物柴油是一种环境友好的燃料,随着其生产及应用的快速增长,其生产过程中重要的副产物甘油将会大量过剩.因此,将甘油转化为高附加值的化学品对于提高生物柴油整体竞争力具有重大意义.乳酸是重要的化工原料,可用于制备生物兼容和可降解的聚乳酸塑料,广泛应用于食品和医药等领域.近年来,由甘油制乳酸的研究受到格外关注,相对于水热反应和氢解反应等,催化选择氧化反应因温和的反应条件而更具竞争力.
　　目前,甘油催化选择氧化制乳酸一般需加入较高比例的NaOH,而碱的类型对反应性能的影响鲜有报道.另外,催化剂常采用TiO2和CeO2等氧化物载体,而炭载体具有比表面积较大、在酸碱溶液中稳定及贵金属易于回收等优点,在催化领域有着广泛应用.因此,本文研究了活性炭(AC)担载的Pt催化剂在甘油催化选择氧化制乳酸反应中的催化性能.
　　首先研究了Pt/AC催化剂和碱在甘油催化选择氧化制乳酸过程中的催化作用.实验发现, Pt/AC和碱协同作用才能得到乳酸. Pt/AC催化剂在甘油脱氢生成中间产物(甘油醛和二羟基丙酮)的过程中起主导作用,碱的存在能够促进甘油羟基脱氢;中间产物实验证实,中间产物生成乳酸过程中碱起主导作用,它促进甘油醛和二羟基丙酮脱水反应和坎尼扎罗重排反应获得乳酸.进一步研究发现,中间产物二羟基丙酮比甘油醛更有利于乳酸生成,而Pt/AC催化剂有利于中间产物氧化为甘油酸.
　　进一步研究了不同类型的碱对反应性能的影响.结果表明,碱金属氢氧化物(LiOH, NaOH, KOH)比碱土金属氢氧化物(Ba(OH)2)更有利于提高甘油转化率和乳酸选择性.在加入碱金属氢氧化物条件下,甘油转化率与其离子半径呈正相关,而乳酸选择性则呈相反趋势.在LiOH存在下,乳酸选择性明显高于NaOH和KOH条件.当LiOH：甘油摩尔比为1.5时,甘油转化率和乳酸选择性均最高.在较低的LiOH与甘油摩尔比时,随着反应的消耗,溶液中的OH–减少,其促进甘油脱氢的作用变弱,并且不利于中间产物进行坎尼扎罗反应,故反应活性和乳酸选择性较差;而当LiOH比例过高时,会导致溶解氧浓度迅速降低,从而使甘油转化率和乳酸选择性下降,同时副产物甘油酸的选择性有所提高.这可能是因为较高比例的碱会促进中间产物甘油醛生成,该中间产物在Pt/AC催化作用下发生进一步氧化反应生成甘油酸.
　　研究了反应时间对催化性能的影响.结果表明,反应6 h后,甘油已经完全转化,乳酸选择性最高,达到69.3%;进一步延长反应时间,乳酸选择性有所下降,而副产物乙酸选择性略有增加,这可能是部分乳酸分解所致. Pt/AC催化剂经5次循环使用后仍保持了较高的甘油转化率和乳酸选择性.     

预处理温度对甘油氢解双金属Ir-Re催化剂性能的影响

在生物柴油生产过程中大量副产的甘油是重要的生物质转化平台化合物.通过甘油氢解制备高附加值的1,3-丙二醇是甘油的资源化利用的重要途径,能够显著提高生物柴油产业的经济效益,同时也是探究更复杂的糖醇类化合物氢解的模型反应.因此,甘油氢解制备1,3-丙二醇成为当前学术界的研究热点.通常,以Re或W为助剂修饰的贵金属催化剂是有效的甘油选择性氢解制1,3-丙二醇的催化剂,其中,双金属Ir-Re催化剂是目前最高效的催化剂之一.甘油氢解反应是典型的结构敏感性反应,它的催化性能依赖于双金属催化剂的结构,而后者受制备工艺条件如热处理方式及条件的影响.最近,我们报道了以直接还原法(即浸渍-还原法)制备的Ir-Re催化剂为合金结构,在甘油氢解中表现出更为优越的反应活性及目前报道中最高的1,3-丙二醇生成速率,并提出了可能的双功能反应机理,即催化剂表面的Re-OH酸性位和Ir均为甘油氢解的活性位.本文采用直接还原法制备KIT-6(具有三维有序介孔孔道结构的SiO2)负载的双金属Ir-Re催化剂,进一步研究还原温度对Ir-Re/KIT-6的结构及其催化性能的影响,揭示催化剂表面酸性在甘油氢解反应中的重要作用并阐明其构-效关系.结果显示不同还原温度(400–700 oC)制备的催化剂的比表面积、孔体积及孔径数据基本一致,表明还原温度对Ir-Re/KIT-6的织构性质的影响很小.根据程序升温还原和透射电镜-能量散射点扫描结果可知,不同温度还原后的催化剂表面Ir和Re均以金属态形式存在,同时两者存在直接的相互作用,形成了Ir-Re合金;而漫反射红外图谱上CO吸附峰的红移以及峰形的显著变化也印证了Ir-Re合金结构的形成. TEM结果显示,在400–700oC还原后得到的Ir-Re合金纳米粒子均匀分布于KIT-6上,尺寸基本一致(2.5–2.8 nm),与CO化学吸附结果一致.此外, NH3-程序升温脱附结果表明催化剂的酸量随着还原温度的升高而逐渐增大,但酸强度没有明显变化,这可能是由于高温还原进一步促进了Ir和Re的相互作用,在原子尺度上混合更为均匀所致. Ir-Re催化剂上甘油氢解反应结果显示,随着还原温度由400提高到600 oC,所制催化剂的活性先增加而后趋于稳定.由此可以认为Ir-Re催化性能的差异与Ir分散度和酸强度的关联较小,主要是由于催化剂表面酸量所致.直接关联酸量与反应活性(以反应时间内的平均1,3-丙二醇生成速率表示)可以看到,反应活性随着酸量的增加而线性增大,表明Ir-Re/KIT-6的表面酸量直接影响了甘油氢解反应速率的快慢,即酸位Re-OH直接参与了催化反应.众所周知, Re金属活化H2的能力很弱,而金属Ir在反应中起到催化加氢的作用.实验结果很好地印证了Ir-Re合金催化甘油氢解反应的双功能反应机理,即酸位Re-OH与金属Ir协同参与氢解反应,分别作为甘油吸附位和H2活化中心,因此提高催化剂的表面Re-OH的数量将是进一步提高催化活性的途径之一.总的来说,在400–700 oC还原得到的Ir-Re/KIT-6催化剂具有Ir-Re合金结构.还原温度对催化剂的织构性质、金属纳米粒子的尺寸、Ir的分散度及表面酸强度的影响不大,但还原温度的升高有利于Ir和Re的相互作用,显著提高了催化剂的表面酸量,因而提高催化活性.此外,表面酸量和反应活性的线性关系表明酸位Re-OH参与Ir-Re合金催化甘油氢解反应,印证了双功能反应机理.     

基于第一性原理方法研究ReOx在ReOx-Rh/ZrO2和ReOx-Ir/ZrO2催化的甘油氢解反应中的作用机制

采用密度泛函理论研究了ZrO₂负载的Ru基、Rh基以及Re改性的Rh基、Ir基催化剂上甘油氢解生成1,2-丙二醇和1,3-丙二醇的热力学过程, 重点考察了ReO_x调变催化剂活性和选择性的作用机制. 结果表明, Ru/ZrO₂和Rh/ZrO₂催化剂上甘油分解经由脱水-加氢反应途径, 1,2-丙二醇的生成是热力学有利过程, 其中Ru基催化剂活性更高. 在Re修饰的Rh基和Ir基催化剂上, 反应遵循直接氢解机理, 其中金属表面解离的氢原子进攻ReO_x团簇上与醇盐紧邻的C-O键是催化甘油转化为丙二醇最核心的步骤. ReO_x-Rh/ZrO₂催化剂上1,2-丙二醇为主要产物, 并伴随1,3-丙二醇的生成, ReO_x的修饰则显著提高了Ir/ZrO₂催化剂上1,3-丙二醇选择性. 与单金属催化剂上发生的间接氢解机理相比, 修饰催化剂上1,3-丙二醇选择性的提高可主要归因于Rh(Ir)-Re协同催化的直接氢解反应过程, 其中羟基化铼官能团有利于末端醇盐中间体的生成. ReO_x-Ir/ZrO₂催化剂上较大的Ir-Re团簇使得末端金属醇盐的立体优选性比次级醇盐更为突出, 从而具有最高的1,3-丙二醇选择性.     

利用甘油废水Pt/TiO2光催化制氢

研究了以甘油为电子给体在Pt/TiO2上光催化生成氢的反应.结果表明甘油能显著地提高光催化放氢效率,并且其自身的降解活性也很好.研究了反应时间、甘油起始浓度、溶液pH值、甘油废水中共存物对光催化放氢的影响.甘油光催化降解最终产物是H2O和CO2,检测到了甘油醛、羟基乙醛、羟基乙酸、甲醛等中间产物.探讨了可能的反应机理.