Mild Oxidative Bromination of Alkenes and Alkynes with Zinc Bromide and Lead Tetraacetate

Abstract

Zinc bromide and lead tetraacetate is a practical and safe source of bromine. The combined reagents are used to brominate a variety of alkenes to vicinal dibromoalkanes. Similarly, alkynes can be converted into dibromoalkenes in high yields. The reagents are also capable of tetrabromination of alkynes.     

Synthesis of peptidomimetic-spirostane hybrids via Ugi reaction: a versatile approach for the formation of peptide-steroid conjugates

A general approach towards the preparation of peptide-steroid conjugates has been addressed. Utilizing the Ugi reaction, five peptidomimetic-steroid hybrids were achieved in good to excellent yields from carboxy- and amino-spirostanes and mono-protected α-amino acids. Diverse synthetic routes, specially focused on the formation of secosteroids, were implemented to introduce Ugi-type functionalities at different positions of the steroidal nucleus. This versatile approach is suitable for the formation of stable conjugates of steroids with other biologically relevant molecules.     

Lead Tetraacetate Oxidation on Caryachine,A Phenolic Pavine

Lead tetraacetate oxidation on caryachine, a pavine alkaloid possessing a phenolic group at the position para to the N-methine, in dichloromethane yielded four products — 10-acetoxy-O-acetyl-caryachine, 10-acetoxycaryachine, 7-acetoxy-O-acetylcaryachine and (6S, 11R, 12R)-11-acetoxy-O-acetyl-caryachine. The reaction took place via adoption of an acetoxy group at a position majorly ortho to the phenolic group, but very minorly at the desired benzylic position para to the phenolic group.     

On the lead tetraacetate oxidation of 4-amino-1,2,4-triazoles, 1-amino- and 2-amino-1,2,3-triazoles

Lead tetraacetate oxidation of 4-amino-1,2,4-triazoles, 1-amino- and 2-amino-1,2,3-triazoles affords mainly fragmentation to nitriles or acetylenes, even in the presence of intramolecularly attached double bonds.

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Über die Bleitetraacetatoxidation von 4-Amino-1,2,4-triazolen, 1-Amino- und 2-Amino-1,2,3-triazolen (Kurze Mitteilung)

Zusammenfassung Bei der Oxidation von 4-Amino-1,2,4-triazolen, 1-Amino- und 2-Amino-1,2,3-triazolen mit Bleitetraacetat entstanden hauptsächlich Nitrile bzw. Acetylene durch Fragmentierung — trotz der Gegenwart von intramolekularen Doppelbindungen.

     

Graphene Mediates Charge Transfer between Lead Chromate and a Cobalt Cubane Cocatalyst for Photocatalytic Water Oxidation

The interfacial barrier of charge transfer from semiconductors to cocatalysts means that the photogenerated charges cannot be fully utilized, especially for the challenging water oxidation reaction. Using cobalt cubane molecules (Co₄O₄) as water oxidation cocatalysts, we rationally assembled partially oxidized graphene (pGO), acting as a charge-transfer mediator, on the hole-accumulating {−101} facets of lead chromate (PbCrO₄) crystal. The assembled pGO enables preferable immobilization of Co₄O₄ molecules on the {−101} facets of the PbCrO₄ crystal, which is favorable for the photogenerated holes transferring from PbCrO₄ to Co₄O₄ molecules. The surface charge-transfer efficiency of PbCrO₄ was boosted by selective assembly of pGO between PbCrO₄ and Co₄O₄ molecules. An apparent quantum efficiency for photocatalytic water oxidation on the Co₄O₄/pGO/PbCrO₄ photocatalyst exceeded 10 % at 500 nm. This strategy of rationally assembling charge-transfer mediator provides a feasible method for acceleration of charge transfer and utilization in semiconductor photocatalysis.     

A Novel Oxidative N-Demethylation of 12-Membered Macrolide with Lead Tetraacetate

Erythromycin has been extensively used in the treatment of bacterial infections for over 50 years1. In addition to the antimicrobial effect, the quite unique antiinflammatory activity of the erythromycin derivatives has attracted much attention as new the…     

无隔膜电解槽中四醋酸铅间接电有机合成研究

醋酸铅可以在Pt电极上被氧化生成四醋酸铅, 循环伏安法和计时电流法研究表明其初始动力学过程存在三维连续成核机理. 在该醋酸电解液中加入一定量的苯, 控制一定的电流密度、温度等条件可以阻化铅在对电极上的析出, 实现了无隔膜电解槽中四醋酸铅的电解生成, 并应用于间接有机电合成. 本工作分别将其应用于苯乙酮和苯乙烯的间接有机电氧化反应, 得到苯乙酮的乙酰氧基化产率为68.2%以及苯乙烯的氧化产率为35.6%.     

Lead(IV) acetate oxidative ring-opening of 2,3-epoxy primary alcohols: a new entry to optically active α-hydroxy carbonyl compounds

The treatment of 2,3-epoxy primary alcohols with lead(IV) acetate (LTA) leads to α-acetoxy aldehydes or α-acetoxy ketones, through the nucleophilic ring-opening of an intermediate oxonium and the subsequent carbon-carbon bond cleavage. This reaction represents a new route to optically active α-hydroxy carbonyl compounds.     

Mechanistic studies of hydrogen-peroxide-mediated anthocyanin oxidation

The oxidation of cyanidin-3-O-glucoside by hydrogen peroxide was investigated in a range of solvents. The reaction products had chemical structures identical to those formed by the reaction of this compound with the alkylperoxyl radical 2,2?-azobis(2,4-dimethyl)valeronitrile. A plausible oxidation mechanism was proposed based on the obtained reaction products, and this mechanism was confirmed by HPLC–MS experiments using ¹⁸O-labeled reagents. Further, the reaction conditions were found to influence both the reaction rate and the products formed during the transformation, which validated the proposed mechanism.     

汽油铅与血铅的关系

论述了汽油铅对人体血铅水平的影响，主要内容包括：血铅水平与大气铅水平的关系，大气铅水平与加铅汽油耗量的关系，汽油铅耗量与居民血铅水平的关系。     

重视陶瓷食具容器铅浸出量的问题

陶瓷食具是盛放食物的容器，与人体健康休戚相关。但在陶瓷坯表面上有一层极薄的釉，制釉原料中含有铅的化合物，若在陶瓷餐具中放置果汁，醋等酸性食物，游离铅便会溶入食物中进入体内。     

营养性驱铅饮料的研究

研究了营养性驱铅饮料的动物和人群试验，动物试验：饮料与铅动物组间比较，饮料组动物的尿，粪排铅量高，分别是对照组的１．５倍和１．１倍，血，肝，肾中含量低，体内Ｚｎ，Ｃｕ，Ｆｅ等微量元素基本稳定，其体重增长与对照组相一致，人群试验；试验组尿铅排出明显，试验末（２月后）仅为试验初的２１．７％，血铅平均减少０．３９μｍｏｌ／Ｌ，血中Ｈｂ，δ－ＡＬＡＤ和尿中δ－ＡＬＡ等均恢复良好；不影响体内ＺｎＣｕ等微量元     

测定有害元素铅在药品检验中的意义

近年来铅污染的危害，已起人们的广泛关注和重视。药品中铅的有效控制尤为重要，本文探讨了中国药典中铅的限量检测方法以及测定西药和中药材中铅的意义。     

天然大蒜精油对人体的排铅作用

本文探讨了天然大蒜精油的排铅功能。研究中采用石墨炉原子吸收光谱法分析测定志愿者血液中铅含量,检测方法按照国家卫生标准(WS/T20-1996)进行,其线性回归方程为:A=0.00158+0.00152c,相关系数为r=0.9997,并采用国家标准物质(GBW09139)进行验证,结果符合要求。志愿者服用大蒜精油胶囊4周后,68.7%参试人员排铅率达50%以上,21.9%参试人员排铅率为25%~50%。该研究验证了天然大蒜精油具有显著的排铅功能,作为一种安全的食源性添加剂,可帮助人们通过正常的食物摄取降低乃至消除铅中毒的潜在风险。     

Lead in Hair of Children Exposed to Gross Environmental Pollution

Abstract

In the context of a cross-sectional study, concentrations of lead in hair (PbH) were determined by atomic absorption analysis among 263 children aged 1 to 9 years, living less than 900m from a lead smelter in Santo Amaro City, Bahia, Brazil. PbH levels ranged from 20 to 4933 ppm; the median was 349 and the geometric mean was 313 ppm. The mean PbH level was increased among individuals with the following characteristics: female; younger age; shorter distance between residence and smelter; longer residence time in the area; racial group Dark; curly hair; being a child of a lead worker; high lead content in peridomiciliar area. The mean PbH level did not vary markedly according to the child's nutritional status, iron status and the habit of pica. The marked variations in pbH levels point out the feasibility of its use as an epidemiological index in situations of heavy environment pollution.     

铅的生物富集效应

铅以微量元素的含量水平，广泛分布于动、植物的人体中。对比大量的动植物种群及各种年龄组的人群，似乎铅在一定的分子组态，特别是生物有机铅，不一定都是有害物质。相反可起一定的新陈代谢调节作用。或者可称为新陈代谢调节剂。特别是在动物、植物、人体中铅为微量、超微量状态时，铅更显现调节作用。     

铅的大气环境及北大园区大气中铅的测定

简述了大气中铅污染的主要来源，铅的毒性及其在人发，血液及尿中的参考值，采和双膜法收集了大气样品，并用阳极溶出伏安法测定北大园区内铅的水平，结果表明，大气中铅主要存在于〈１０μｍ的细粒子中，北大校园内大气中铅的浓度低于国家规定的Ⅱ级地区标准。     

慢性铅中毒一例

详细问诊，为诊断慢性铅中毒提供了重要依据。     

微波消解样品-电感耦合等离子体原子发射光谱法测定铅精矿中铅、砷、镉、汞

采用微波消解样品-电感耦合等离子体原子发射光谱法同时测定铅精矿中主体元素铅及有毒有害元素砷、镉、汞的含量。0.20g试样置于消解罐中,先后加入硝酸9mL、盐酸3mL、氟硼酸2mL及过氧化氢2.5mL,密闭罐盖按设定的微波消解程序进行消解。试验选择铅、砷、镉和汞的分析线分别为220.351,189.042,228.802,184.950nm以消除基体干扰。铅、砷、镉、汞的检出限分别为16.0,2.2,0.4,0.8μg.g-1。方法用于铅精矿标准样品(GBW 07617)和铅精矿实际样品分析,此方法的测定值与认定值及原子吸收光谱法或原子荧光光谱法的测定值相一致。方法的相对标准偏差(n=10)在0.15%～3.9%之间。