亚临界水萃取在分析化学中的应用

亚临界水的介电常数ε随温度增加而减少,在250℃时ε值只有27（介于甲醇与乙醇之间）,比常温常压下下水的介电常数ε＝80下降了许多。亚临界水极性的减弱,使它对中极性和非极性有机化合物的溶解度大大增加,可以定量萃取出固体试样中的多环芳烃和多氯联苯化合物。另外,亚临界水也可以作为反相高效液体色谱的洗脱液。     

利用亚临界丁烷分离茶树鲜叶中的阿维菌素

以茶树鲜叶为原料,利用亚临界丁烷流体分离鲜叶表面残留的阿维菌素.在料溶比为1∶10(m/V)的条件下,利用响应面法(RSM)的Box-Benhnken Design(BBD)设计实验,考察不同温度、时间、分离次数等条件对多酚氧化酶活性的影响,同时分析亚临界丁烷处理对茶树鲜叶生理特性的影响.结果表明,亚临界丁烷流体在保持茶叶物理结构和多酚氧化酶活性基本不变的情况下,可有效分离茶叶中的阿维菌素;通过Design Expert软件分析,得出分离阿维菌素的最优工艺参数为温度45℃,时间30 min,分离次数1次,料液比为1∶10(m/V),分离效率大于91%,多酚氧化酶相对活性为25.73%.通过扫描电镜观察,茶树鲜叶结构在丁烷处理前后无明显变化.本研究结果表明,亚临界丁烷流体可有效分离茶叶中的农药残留,为亚临界流体在去除天然植物农残的应用中提供了实验依据和技术支持.     

蔬果中12种残留农药的亚临界水萃取研究

利用亚临界水可以定量萃取基质中绝大部分化合物的特点,借助加速溶剂萃取仪(ASE)将亚临界水萃取与固相吸附联用,通过在ASE萃取池中填加C18吸附层的方式改进了萃取吸附模式,优化了萃取温度,研究了亚临界水在萝卜、香瓜、苹果和白菜等蔬果基质中对异稻瘟净等12种农药的萃取效果,用气相色谱-串联质谱法(GC-MS/MS)进行检...     

氨基酸合成方法研究(Ⅲ)——相转移催化下N-(乙氧基羰基亚甲基)亚氨酸酯的烷基化反应

在氨基酸的合成方法中,利用甘氨酸衍生物合成高级氨基酸,是引人注目的研究课题。我们考虑到N-(乙氧基羰基亚甲基)苯甲亚氨酸乙酯1a和N-(乙氧基羰基亚甲基)乙亚氨酸乙酯1b可以方便地由腈和甘氨酸酯制备,特别是由乙腈制备的1b具有原料价廉易得等优点,为此研究了固-液相转移催化条件下,1a和1b的烷基化反应,合成了一系列碳链增长的α-氨基酸。     

亚临界水脱除煤中硫的实验研究

近年来,超临界流体以其独特的性质作为溶剂或反应介质在众多领域得到应用。对于煤在超临界及亚临界水中的行为研究也越来越受到国内外学者的重视,如Kashimura等、Hu等和Cheng等对褐煤在亚临界及超临界水中的降解行为进行了研究。Timpe等报道了水热处理对年轻煤中有机硫及微量元素的脱除行为。     

纤维素超/亚临界水水解研究进展

纤维素作为天然可再生资源,由于其水解糖化技术的可行性和水解产物的重要性而受到人们的广泛关注。目前多种生物和化学技术应用于纤维素水解糖化的研究,其中超、亚临界水是纤维素水解的绿色新型水解技术之一,具有反应快、转化率高等特点。本文比较了纤维素在超、亚临界水中不同的水解机理和产物分布,归纳了反应温度、压力和时间以及催化剂和纤维素结构对超、亚临界水水解反应的影响,并且介绍了超、亚临界水水解技术联用在纤维素水解中的应用。     

秸秆超(亚)临界水预处理与水解技术

秸秆的资源化特别是乙醇化技术由于其技术可行性和产物高值化受到了广泛关注。预处理与水解是乙醇化的关键过程。目前针对秸秆的转化已经开展了多种化学或生物技术的研究,其中超（亚）临界技术与传统技术相比显示了独特的优势,如更高的反应速率、不需催化剂、无产物抑制等。本文在总结秸秆传统预处理与水解技术的基础上,对秸秆超（亚）临界水预处理与水解的过程和机理,特别是超临界亚临界组合技术的研究现状、工艺及其相关研究的进展进行了综述和分析,并阐述了超临界亚临界组合技术首先在超临界水中打破纤维结构进行初级水解,再通过亚临界反应将初级水解产物低聚糖进一步水解为葡萄糖的基本原理。最后对超（亚）临界技术在秸秆资源化领域的研究和应用前景进行了展望。     

东北泥炭亚临界—超临界萃取研究

在半连续装置上进行了中国东北几种泥炭非等温亚临界-超临界萃取研究。以甲苯作溶剂时最佳条件是:压力10MPa,温度330—350℃;以甲醇、乙醇作溶剂时最佳条件是:压力10MPa,温度300—320℃。萃取结果表明,生成萃取物的温度范围宽(180—420℃),主要集中在250—320℃温度区。选用灰分低、(H+N-O)/C原子比高的泥炭对萃取有利。动力学处理表明,主要萃取过程可用三级动力学方程描述,表观活化能为50—185KJ/mol。     

亚临界水萃取-酶抑制法快速检测蔬菜中的灭多威农药

本文研究了蔬菜中灭多威农药的亚临界水萃取-酶抑制法快速检测技术.研究表明,在萃取温度70℃,萃取时间5 min,提取液的pH为8.0,提取液体积为5 mL的条件下,灭多威有最高萃取效率.将本法分别应用于测定模拟样品和实际样品,结果表明亚临界水萃取的萃取效率和精密度都要高于国家标准方法中的手摇振荡萃取.     

亚临界流体挤出法复合诱导EPDM废胶粉脱硫化及动态交联热塑性弹性体制备

在三元乙丙废胶粉(W-EPDM)与未硫化的三元乙丙橡胶(EPDM)熔融挤出过程中,采用注入亚临界流体和提高双螺杆挤出机螺杆转速的方法,研究了亚临界流体品种(水,乙醇/水混合物,丙醇)、螺杆转速、脱硫促进剂品种(烷基酚多硫化物450、二烯丙基二硫醚)对脱硫共混物(DGTR/EPDM)凝胶含量、门尼粘度、溶胶红外吸收光谱及脱硫共混物共混PP动态交联热塑性弹性体((DEPDM/EPDM)/PP)力学性能的影响,对动态交联热塑性弹性体材料的试样断面形貌也进行了SEM观察。实验结果表明:亚临界乙醇/水混合物(7/3)或亚临界丙醇条件对脱硫反应中S—S键的断裂具有较好的选择性,可引起废胶粉交联网络中S—S交联键断裂反应增加,而主链断裂反应下降,所得脱硫产物制备的动态交联热塑性弹性体材料中未熔融的凝胶颗粒尺寸较小,材料的力学性能明显增大;脱硫促进剂烷基酚多硫化物450具明显的促进脱硫反应的作用。在亚临界正丙醇的最佳挤出反应条件下(220℃,600rpm,促进剂450),所得脱硫共混物(DEPDM/EPDM)制备的动态交联热塑性弹性体材料(DEPDM/EPDM)/PP的拉伸强度和断裂伸长率分别达到17.1MPa和443%,其力学性能和断面形貌结构明显优于以传统罐式脱硫法所得的相应材料。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.