阻抑动力学光度法测定痕量铌(Ⅴ)

研究发现,在硫酸介质中,痕量铌(Ⅴ)能灵敏地阻抑溴酸钾氧化二甲基黄褪色。研究了该阻抑褪色反应的最佳条件及动力学参数,建立了一种测定痕量铌(Ⅴ)的新方法。该法测定线性范围为0~30 ng/10mL,检出限为4.21×10-11 g/ mL。方法用于矿石中铌的测定,结果满意。     

近场激光热透镜光谱分析法测定铌

采用氦-氖激光器(632．8nm)观测了铌(V)与2-(5-溴-2-吡啶偶氮)-5-二乙氨基苯酚(5-Br-PADAP)和酒石酸所形成的紫蓝色三元配合物的激光热透镜效应，建立了近场激光热透镜光谱分析法测定铌的新方法。铌(V)质量浓度在0-500ng/mL范围内与热透镜信号强度呈良好的线性关系，检出限为5ng/mL。该方法已应用于钢样及铌矿样中铌的测定。     

偶氮胭脂红B光度法测定痕量铌

铌的测定常采用络合光度法,但络合光度法的灵敏度不高,一般在2~10μg/10 mL[1~4],难以达到痕量铌的分析要求,催化动力学光度法灵敏度高,目前以催化动力学光度法测定铌的报道较少,灵敏度能达到μg·L-1[5~7]。本文研究发现在硫酸中铌对溴酸钾氧化偶氮胭脂红B反应的影响作用,且铌量不同,其对反应的影响不同,据此在一定范围内建立了测定痕量铌的新方法。1试验部分1.1主要仪器与试剂723型分光光度计,CS501型超级恒温槽。铌标准溶液:100 mg·L-1,称取Nb2O50.143 0 g于瓷坩埚中,加焦硫酸钾5 g,缓慢加热熔融至清,冷却,用500 g·L-1柠檬酸溶液浸…     

催化动力学光度法测定痕量铌

在稀硫酸介质中，铌（Ⅴ）灵敏催化溴酸钾氧化氯磺酚Ｓ褪色反应，据此建立了催化动力学光度法测定铌的新方法。线性范围为０．００５￣０．１ｍｇ／Ｌ，检测限２．９μｇ／Ｌ。本法准确、灵敏、简便，已用于合金钢中微量铌的测定。     

溴酸钾二甲酚橙体系-顺序注射-催化光度法测定痕量钒

在酸性介质条件下,钒(Ⅳ)能显著催化溴酸钾对二甲酚橙的氧化褪色反应。据此建立了测定痕量钒(Ⅳ)的顺序注射催化光度法。方法的线性范围为0.5⁵0ng/mL、检出限为0.4ng/mL。对10ng/mL的钒(Ⅳ)连续11次测定的相对标准偏差为1.1%。用于环境水样中痕量钒(Ⅳ)的测定,加标回收率为91%50ng/mL、检出限为0.4ng/mL。对10ng/mL的钒(Ⅳ)连续11次测定的相对标准偏差为1.1%。用于环境水样中痕量钒(Ⅳ)的测定,加标回收率为91%¹08%。     

溴酸钾-二甲酚橙体系-顺序注射-催化光度法测定痕量钒

在酸性介质条件下,钒(Ⅳ)能显著催化溴酸钾对二甲酚橙的氧化褪色反应。据此建立了测定痕量钒(Ⅳ)的顺序注射催化光度法。方法的线性范围为0.5~50ng/mL、检出限为0.4ng/mL。对10ng/mL的钒(Ⅳ)连续11次测定的相对标准偏差为1.1%。用于环境水样中痕量钒(Ⅳ)的测定,加标回收率为91%~108%。     

示波导数催化极谱测定矿石中微量铌

微量铌的催化极谱测定已有报导。我们以二苯基乙醇酸代替文献中采用的苦杏仁酸,並应用示波导数极谱法在氯酸钾-二苯基乙醇酸-四甲基溴化铵底液中测定铌,使分析速度和灵敏度有所提高。本文对铌的测定条件、干扰元素及其分离、催化波的性质进行了     

微乳液介质-二甲氧基羟基苯基荧光酮催化光度法测定合金中铌

1 引言 研究了以非离子微乳液介质，在稀硫酸体系中，用氨三乙酸作活化剂，铌催化溟酸钾氧化二甲氧基羟基苯基荧光酮褪色的新指示反应，据此建立了催化动力学光度法测定铌的新方法。非离子型微乳液有明显提高了体系的灵敏度和稳定性，检出限达到0．15μg/L。该方法应用于样品中痕量铌的测定，其相对标准偏差小于6．8％。     

纸上层析分离-ICP-AES测定稀有金属矿中的铌钽

采用HF、HNO_3溶解样品,纸上层析分离富集铌、钽,焦硫酸钾分解铌钽氧化物,酒石酸浸取,ICP-AES测定稀有金属矿中铌钽。研究了溶样用酸、色层分离展开剂比例及展开温度、焦硫酸钾用量、酒石酸浓度等对测定结果的影响,结果表明,采用纸上层析法可使铌钽与其他干扰元素彻底分离,焦硫酸钾熔融后,用酒石酸浸取使铌、钽完全进入溶液,以电感耦合等离子体光谱仪(ICP-AES)进行测定。在20 g/L的酒石酸介质中,ICP-AES测定铌钽的线性范围为0~50μg/mL,检出限为铌0.14μg/mL,钽0.16μg/mL;相对误差小于8%,精密度(RSD)小于6%,可测定矿石中0.001%~40%的Nb_2O_5,Ta_2O_5。该方法可同时测定稀有金属矿中铌钽原矿、精矿及尾矿中铌钽的含量,适合基体复杂、含量差别大的批量样品的检测。     

电感耦合等离子体发射光谱法测定γ-钛铝铌合金中铝、铌、钨、硼

建立电感耦合等离子体原子发射光谱法测定γ-钛铝铌合金中铝、铌、钨、硼的分析方法。采用10 mL盐酸+2 mL氢氟酸+1 mL硝酸消解γ-钛铝铌合金，以基体匹配法建立系列校准曲线，选择铝394.401 nm、铌269.706 nm、钨207.912 nm、硼249.772 nm为分析线，采用左右两点离峰背景扣除方法校正背景光谱的重叠干扰和漂移干扰，各元素质量分数的线性范围分别为：铝30%～40%，铌10%～25%，钨0.015%～1.0%，硼0.003%～0.10%。测定结果的相对标准偏差均不大于4%(n=10)，加标回收率为93%～108%。该方法能够满足Ti-(30～40)Al-(15～20)Nb-x W-y B中主量铝、铌和微量钨、硼的同时、快速检测需求。     

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.