共查询到20条相似文献,搜索用时 62 毫秒
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黄宁红 《广东微量元素科学》2006,13(1):63-66
研究了应用微波技术从金银花(Lonicera japonicaThunb)中提取黄色素的新工艺,并确定了最佳工艺条件:提取剂为无水乙醇,原料用量(g)与提取剂用量(mL)比为1∶60,提取时间为50 s,微波功率为560 W,提取次数为3次。最佳工艺条件下的色素提取率为83.40%,产品pH值为6。与溶剂浸提法相比,微波法提取金银花黄色素的每次提取时间由1 h减少到50 s,提取率从52.21%增加到83.40%,效果明显优于常规的溶剂浸提法。 相似文献
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“测定I3-=I-+I2平衡常数”是大学无机化学实验课的实验之一,该实验中使用了较多的碘,分散振荡时间较长,导致残留的碘挥发到空气中给环境和人体带来危害。为此对该实验进行了改进,利用超声波辅助分散减少分散时间,用微量代替常量减少试剂用量。经过多次重复实验,在超声波辅助分散5 min,降低试剂用量90%的情况下,测得平衡常数为1.54×10-3,相对误差为2.67%,证明该方法完全可以替代现有的实验方法。 相似文献
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目前样品中氮的测定主要采用蒸馏法(包括常量、半微量、微量法),其次还有室温抽气吸收法(常量法)、扩散法(微量法)、仪器分析法(碳氮自动分析法、氨气敏电极法)等。作者设计制作了一套定氮装置,采用加热抽气吸收法测定氮的含量。本法具有蒸馏法和室温抽气吸收法的优点,整套装置装配简单,操作方便,测定快速,只需10min左右便可完成氮的整个蒸 相似文献
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以乙醇为溶剂用微波辐射溶剂回流提取法提取苦参中生物碱,经蒸发除去乙醇后提取物残渣用稀盐酸溶解,所得溶液用氯仿萃取除去其中的杂质,所得水相经碱化后再次用氯仿萃取使生物碱溶入氯仿中.蒸发除去萃取液中氯仿,残留物溶于一定量的甲醇中,用作气相色谱-质谱分析.应用此方法分离并测定了苦参中7种生物碱.结果表明:常规的溶剂回流提法(即不用微波辐射)相比较,微波辐射溶剂回流提取法的提取率明显提高. 相似文献
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《化学研究与应用》2021,33(6)
在单因素试验的基础上,利用星点设计-响应面法来优化酶提取法提取麦冬总黄酮的提取工艺,同时利用DPPH法和Fenton法测定总黄酮提取液清除1,1-二苯基-2-三硝基苯肼自由基和羟基自由基的能力。结果表明麦冬总黄酮酶提取法的最佳提取工艺条件:酶用量为46.61 mg,酶解时间为4.14 h,酶解温度为55.56℃,提取率为0.283%。在此条件下,麦冬总黄酮提取液对DPPH自由基和羟基自由基有较强的清除作用,随着总黄酮浓度的升高,其抗氧化能力逐渐增强,其IC_(50)分别为7.33 mg·L~(-1)和14.08 mg·L~(-1)。该工艺稳定可行,可为麦冬黄酮类化合物的开发利用提供参考。 相似文献
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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%. 相似文献
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Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction
Laurent Gavara Thomas Boisse Jean-Pierre Hénichart Adam Daïch Philippe Gautret 《Tetrahedron》2010,66(38):7544-5571
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. 相似文献
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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. 相似文献
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Rebecca J. Burton Mandy L. CrowtherNeal J. Fazakerley Shaun M. FilleryBarry M. Hayter Jason G. KettleCaroline A. McMillan Paula PerkinsPeter Robins Peter M. SmithEmma J. Williams Gail L. Wrigley 《Tetrahedron letters》2013
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. 相似文献
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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. 相似文献
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N. A. Nedolya 《Chemistry of Heterocyclic Compounds》2008,44(10):1165-1219
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. 相似文献
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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. 相似文献
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《Tetrahedron》2014,70(21):3377-3384
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. 相似文献
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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. 相似文献