Lack of Linear Free Energy Relationships in the p-Toluenesulfonic Acid Mediated Chromium(VI) Oxidation of Organic Sulfides

Summary.  The oxidation of methylphenyl sulfide by imidazolium dichromate in acetonitrile mediated by p-toluenesulfonic acid is first order in IDC and TsOH and zero order in MeSPh in the concentration range studied. The IDC oxidation of 14 para-, meta-, and ortho-substituted phenylmethylsulfides at 20–45°C conforms to the isokinetic relationship but not to any of the linear free energy relationships; the isokinetic temperature lies within the experimental temperature range. Received April 18, 2000. Accepted (revised) July 12, 2000     

配位化学中的直线自由能关系(XIX)

前文[1]曾报导了侧基二氧四胺大环配体的合成及表征．与普通配合物相比，大环多胺配合物具有较高的稳定性及惰性和奇特的空间构型，其过渡金属配合物具有特殊的性质和用途，如作酶的模型、氧的载体等．铜（Ⅱ）配合物可作超氧歧化酶（SOD）的模型，超氧离子是人体内的氧代谢产物，它在体内过量积累会引起多种疾病，超氧歧化酶对超氧离子起催化歧化作用，以维持机体的正常运行间，故这种大环多胺Cu（Ⅱ）配合物具有重要的生物功能及广阔的应用前景．本文研究了四种带侧基二氧四胺大环配体-5-取代邻菲罗啉（5－Xphen；L1）铜（Ⅱ）三元配合…     

Selective Oxidation of Sulfides to Sulfoxides using H2O2 Catalyzed by p-Toluenesulfonic Acid (p-TsOH) Under Solvent-Free Conditions

Abstract

An efficient, chemoselective, and environmental friendly procedure for the oxidation of sulfides to sulfoxides is described. Various types of aromatic and aliphatic sulfides are selectively oxidized to sulfoxides in good to excellent yields using 30% H₂O₂ in the presence of catalytic amounts of a p-TsOH under solvent-free conditions at room temperature.     

Kinetic Studies on the Oxidation of Organic Sulfides with Percarbonate in Acetic Acid

Oxidation of organic sulfides by anhydrous H₂O₂using percarbonate in glacial acetic acid is a second order reaction and is independent of the acidity of the medium. The oxidation conforms to the isokinetic and Hammett relationships.     

Kinetics of the Effect of Some Bidentate Amino Acid Ligands in the Oxidation of Lactic Acid by Chromium(VI)1

The oxidation of lactic acid by Cr(VI) under acidic conditions is catalyzed by bidentate amino acid ligands such as glycine, alanine, aspartic acid and hydroxyproline. Catalysis is a function of [L]/[Cr(VI)] ratio and acidity. Pyruvic acid and acetaldehyde in a ratio of 2 : 1 are obtained as oxidation products in both uncatalyzed and catalyzed oxidation. This supports the previous understanding of the oxidation of -substituted carboxylic acids. Cromium(V) and chromium(VI) behave similarly in a C–H bond rupture (Rocek, J. and Radkowsky, A.E., J. Am. Chem. Soc., 1973, vol. 95, p. 7123), whereas Cr(IV) is responsible for C–C bond cleavage products (Wiberg, K.B. and Schafer, H., J. Am. Chem. Soc., 1969, vol. 91, p. 927).     

Effect of Added Pyridine Bases on the Electron Transfer Reaction of Chromium(VI) with Organic Sulfides. Spectral Evidence for the Formation of a Chromium(V) Intermediate

The electron transfer reaction of Cr(VI) with organic sulfides is facilitated by added pyridine bases 2,2′-bipyridine, 1,10-phenanthroline, picolinic acid and pyridine 2,6-dicarboxylic acid. The added base forms a Cr(VI)-base adduct carrying positive charge which acts as a more reactive oxidant compared to Cr(VI). UV–Visible spectrophotometric study provides evidence for the formation of Cr(V) as the intermediate. The reactions in the absence and presence of pyridine bases follow the reactivity–selectivity principle.     

Micellar Effect on Chromium(VI) Oxidation of Ethanol and Propan-1-ol in Aqueous Acid Media

Cetylpyridinium chloride (CPC) inhibits the Cr(VI) oxidation of ethanol and propan-1-ol while sodium dodecyl sulfate (SDS) catalyzes the title reactions. At higher values of the [surfactant], the rate attains a limiting value. The micellar effect has been explained by considering the preferential partitioning of the reactants in terms of the suggested mechanism. Applicability of the Menger-Portnoy model and Piszkiewicz model to explain the observed micellar effect has been examined. This revised version was published online in June 2006 with corrections to the Cover Date.     

配位化合物中的线性热力学函数关系II.离子选择电极研究α-氨基酸与铜(II)配合物在混合溶剂中的线性热力学函数

用铜离子选择电极测定五种α-氨基酸(对氟苯丙氨酸、丝氨酸、缬氨酸、丙氨酸及α-氨基异丁酸)的铜(Ⅱ)配合物在25.0±0.1、35.0±0.1和45.0±0.1 ℃, μ=0.16 mol L~(-1)KNO_3时于水中及30%(V/V)和50%(V/V)的乙醇-水中的稳定常数. 用pH电位法测定了各配体在混合溶剂中的离解常数. 实验表明用铜离子选择电极研究上述配合物在混合溶剂中的线性自由能、线性焓和线性熵关系, 得到了较好的结果.     

The Controlled Oxidation of Organic Sulfides to Sulfoxides with the Help of O-Iodosylbenzoic Acid

The oxidation procedure plus a simple preparation of oiodosylbenzoic acid are described.     

Carcinogenic Chromium(VI) Compounds Formed by Intracellular Oxidation of Chromium(III) Dietary Supplements by Adipocytes

Chromium(III) nutritional supplements are widely consumed for their purported antidiabetic activities. X‐ray fluorescence microscopy (XFM) and X‐ray absorption near‐edge structure (XANES) studies have now shown that non‐toxic doses of [Cr₃O(OCOEt)₆(OH₂)₃]⁺ ( A ), a prospective antidiabetic drug that undergoes similar H₂O₂ induced oxidation reactions in the blood as other Cr supplements, was also oxidized to carcinogenic Cr^VI and Cr^V in living cells. Single adipocytes treated with A had approximately 1 μm large Cr hotspots containing Cr^III, Cr^V, and Cr^VI (primarily Cr^VI thiolates) species. These results strongly support the hypothesis that the antidiabetic activity of Cr^III and the carcinogenicity of Cr^VI compounds arise from similar mechanisms involving highly reactive Cr^VI and Cr^V intermediates, and highlight concerns over the safety of Cr^III nutritional supplements.     

Fast Oxidation of Organic Sulfides by Hydrogen Peroxide by In Situ Generated Peroxynitrous Acid

A powerful oxidant and an unstable isomer of HNO₃, peroxynitrous acid ONOOH is generated by the fast reaction of H₂O₂ with HNO₂ in acidic medium [Eq. (1)]. If sulfides R₂S are present, ONOOH sulfoxidizes them in minutes. This reaction occurs faster than the decay of ONOOH to HNO₃ and allows the fast preparation of sulfoxides with H₂O₂. (1)     

Spectrophotometric Determination of Trace Chromium(VI) in Mass Chromium(III)

There is little conclusive evidence of the toxic effects of Cr(III) so far, but Cr(VI) has carcinogenic activity, so the analysis of the chromine ions is very important in environmental research and the quality control of industry products. Usually Cr(III) and Cr(VI) interfere with each other in the species analysis, the measurement of Cr(VI) of numerous previous papers is related to the Cr(VI) samples, which contain a little Cr(III). When the amount of trivalent chromine exceeds ten …     

酸性磷型萃取剂萃取稀土的线性自由能关系

用线性回归分析探讨了各种类型和结构的一元酸性磷型萃取剂萃取稀土的表观萃取平衡常数 (lgKex)与萃取剂分子中取代基的电子效应参数 (ΣσΦ)和空间效应参数 (Συ )之间的相关关系。结果表明 ,对于这类萃取体系 ,线性自由能关系式lgKex=ρΣσΦ ψΣυ h 普遍成立。据此讨论了萃取剂结构与萃取性能之间的定量关系 ,可用于初步预测一定结构的这类萃取剂萃取稀土的lgKex值。     

Bistriphenylsilanol-Assisted Oxidation Catalyzed by Chromium(VI) Oxide of Activated Trimethylsilyl Ethers with tert-Butyl Hydroperoxide

Secondary benzylic or allylic trimethylsilyl ethers are oxidized at room temperature to the corresponding ketones in good yields using aqueous 70% t-BuOOH and catalytic amounts of a mixture of Ph₃SiOH and CrO₃.     

对甲苯磺酸催化三吲哚烷基化合物的合成

室温下,吲哚与3-吲哚甲醛在对甲苯磺酸的催化下高收率得到三吲哚烷基化合物,所有产物的结构经1H NMR,IR和HR-MS表征。     

Micellar Effect on the Reaction of Chromium(VI) Oxidation of L‐Sorbose in the Presence and Absence of Picolinic Acid in Aqueous Acid Media: A Kinetic Study

The kinetics and mechanism of chromic acid oxidation of L‐sorbose in the presence and absence of picolinic acid (PA) have been studied under the conditions, [L‐sorbose]_T » [PA]_T » [Cr(VI)]_T, at different temperatures. In the absence of PA, the monomeric chromic acid undergoes esterification with the substrate followed by the acid catalysed redox decomposition of the Cr(VI)‐substrate ester through glycol splitting to formaldehyde and the lactone of C₅‐aldonic acid and Cr(IV) which subsequently participates in the faster reactions. In the presence of PA, the Cr(VI)‐PA complex produced in a pre‐equilibrium step experiences a nucleophilic attack by the substrate to produce a ternary complex which decomposes through glycol splitting giving rise to the organic products and Cr(IV)‐PA complex. Both the uncatalysed and PA‐catalysed paths show the first‐order dependence on [L‐sorbose]_T and [Cr(VI)]_T. The PA‐catalysed path is first‐order in [PA]_T and it shows a fractional order in [H⁺]. The uncatalysed path shows a second‐order dependence on [H⁺]. In the presence of the surfactants like N‐cetylpyridinium chloride (CPC, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic sulfate), the reaction orders remain unchanged. CPC has been found to inhibit both the uncatalysed and PA‐catalysed paths while SDS shows the rate accelerating effect for both the uncatalysed and PA‐catalysed paths. The observed micellar effects have been rationalised by considering the distribution of the reactants between the micellar and aqueous phases in terms of the proposed reaction mechanism.     

Bimetallic Oxidation Catalysts: Oxidations with Tert Butylhydroperoxide Mediated by Bis-(Tributyltin Oxide) Dioxochromium (VI)

At 40–80°C, t.BuOOH in conjunction with catalytic amounts of (n.Bu₃ SnO)₂ CrO₂ 1 oxidizes benzylic alcohols, methylenes in α-position of aryl, ethylenic or acetylenic groups into ketones, anthracene into anthraquinone, adamantane into adamantan-1-ol and 2-one. Except for propargylic oxidations, yields are generally superior to those obtained when CrO₃ is used as catalyst instead of 1.     

Linear Free Energy Relationships in SNAr Reactions of Aryl and Diaryl N-Anions with Aryl Halides

A good correlation has been established between the Brønsted coefficients _{N u c} and _{o x} for reactions of aryl-containing N-anions with various aryl halides. This correlation reflects the dependence of the internal barrier of aromatic nucleophilic substitution on the oxidation potentials of nucleophiles.     

Rates of Chromium(VI)-Oxidation of Benzocyclenols

The oxidation rate of benzocyclobutenol ( 6 ) and of the homologous alcohols up to 1-benzocyclo-octenol ( 7 ) with chromium (VI) has been determined in 90% acetic acid. The rate profile for the oxidation reaction is similar to that obtained for the solvolysis of the corresponding chlorides, and clearly shows a low reactivity for the benzocyclobutenyl skeleton, for reactions in which the hybridization changes from sp³ to sp². On the other hand, semicarbazone formation occurs faster with benzocyclobutenone ( 6a ) than with the homologous ketones. The implication of these results for the oxidation mechanism is discussed.