Kinetics of oxidation of iron(II) ions with lipid hydroperoxides

One of the pathways for excessive production of free radicals is the decomposition of lipid hydroperoxides catalyzed by iron. A number of hydroperoxides of unsaturated fatty acids (LOOH), some prepared in our laboratory and others extracted from biological materials, were used to determine the rate constants of Fe²⁺ oxidation by measuring the formation rate of Fe³⁺ ions in the presence of simple unidentate ligands, chloride, and thiocyanate as the [FeCl]²⁺ and [FeNCS]²⁺ complexes, in a deoxygenated dichloromethane:methanol (2:1, v/v) mixture. The rates of Fe²⁺ oxidation with prepared LOOHs via the [FeNCS]²⁺ complex were approximately the same-the average second-order reaction rate constant was 1390 ± 340 dm³ mol⁻¹ s⁻¹; the rate constants of LOOHs from different biological materials were in the same range. The rates measured as the [FeNCS]²⁺ complex were somewhat higher than the rates measured as the [FeCl]²⁺ complex, indicating that ligands could interact in the transition state, thus affecting the disruption of the intermediate complex. Since there were no significant differences in the activation thermodynamic parameters for reactions within the reaction series of studied hydroperoxides, it was assumed that the oxidation proceeded by an inner sphere mechanism, considering that the breakdown of the successor inner sphere complex with the homolytic cleavage of peroxide bonds of hydroperoxides forming reactive alkoxyl radicals was the rate-limiting step. Based on this research, an indirect spectrophotometric method for quantitative determination of LOOH was reestimated. The microprocedure proposed for the lipid hydroperoxide assay could be applied to follow the early stages of lipid peroxidation processes in real biological samples.     

Formation of 4-arylpyridines from pyridinium salts under the action of methylammonium sulfite

Reactions of pyridinium salts or nonquaternized pyridine with 4-methylpyridinium salts in the presence of methylammonium sulfite in aqueous methylamine afford 4-phenylpyridine in 29—57% yields. The probable mechanism of ring transformation in simplest pyridine derivatives under the action of nucleophiles is discussed.     

Thermal studies on the sodium salts of aminosalicylic acids

The effect on the stability of the isomers of aminosalicylic acid of formation of their sodium salts has been studied by use of differential scanning calorimetry and thermogravimetry, coupled with evolved gas analysis by Fourier transform infrared spectroscopy. X-ray powder diffraction and infrared spectroscopy provided complementary information. The DSC curves for the sodium salts of all of the isomers showed complex dehydration/decomposition endotherms. From the initial mass losses of the TG curves, the amounts of water per mole of salt were estimated as 0.5, 2.4 and 1.4 moles for the sodium salts of 3-aminosalicylic acid, 4-aminosalicylic acid and 5-aminosalicylic acid, respectively. TG-FTIR results for the sodium salt of 3-aminosalicylic acid showed the evolution of carbon dioxide in three stages: below 150°C, between 200 and 300°C and continuous formation up to 500°C. This behaviour differs from that of 3-aminosalicylic acid itself, which forms CO₂ between 225 and 290°C. For the sodium salt of 4-aminosalicylic acid, the formation of carbon dioxide starts from 250°C and is still being formed at about 650°C. 4-aminosalicylic acid decarboxylates above 150°C. 5-aminosalicylic acid and its sodium salt showed no evolution of carbon dioxide below 600°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

wo3催化h2o2氧化环己酮合成己二酸

以WO3为催化剂,在无有机溶剂和相转移催化剂的情况下,用H2O2氧化环己酮合成己二酸。探讨了催化剂用量、H2O2用量、反应温度和时间等条件对反应的影响。在优化条件下:n(环己酮)∶n(H2O2)∶n(WO3)=100∶500∶2,反应温度为120℃,反应6 h,己二酸分离收率可达80.3%,纯度为99.8%;催化剂重复使用5次后己二酸收率仍可达70.2%。     

钨化合物催化过氧化氢氧化环己酮合成己二酸

在无相转移催化剂的条件下,用Na2WO4·2H2O 或 H7[P(W2O7)6]·xH2O为催化剂,30% H2O2可以将环己酮高产率地氧化成己二酸.钨催化剂用量、反应液酸度对反应结果有着重要的影响.当钨原子与环己酮的摩尔比为1.5%,反应初始液的pH值为1.0时,己二酸的得率可达82%;而且催化体系具有很好的可循环性.     

Halobismuth(III) salts with substituted aminopyridinium cations

The crystal structures of six halobismuth(III) salts of variously substituted aminopyridinium cations display discrete mononuclear [BiCl₆]^3? and dinuclear [Bi₂X₁₀]^4? anions (X = Cl or Br), and polymeric cis‐double‐halo‐bridged [Bi_nX_4n]^n? anionic chains (X = Br or I). Bis(2‐amino‐3‐ammoniopyridinium) hexachloridobismuth(III) chloride monohydrate, (C₅H₉N₃)₂[BiCl₆]Cl·H₂O, (1), contains discrete mononuclear [BiCl₆]^3? and chloride anions. Tetrakis(2‐amino‐3‐methylpyridinium) di‐μ‐chlorido‐bis[tetrachloridobismuth(III)], (C₆H₉N₂)₄[Bi₂Cl₁₀], (2), tetrakis(2‐amino‐3‐methylpyridinium) di‐μ‐bromido‐bis[tetrabromidobismuth(III)], (C₆H₉N₂)₄[Bi₂Br₁₀], (3), and bis(4‐amino‐3‐ammoniopyridinium) di‐μ‐chlorido‐bis[tetrachloridobismuth(III)] dihydrate, (C₅H₉N₃)₂[Bi₂Cl₁₀]·2H₂O, (4), incorporate discrete [Bi₂X₁₀]^4? anions (X = Cl or Br), while catena‐poly[2,6‐diaminopyridinium [[cis‐diiodidobismuth(III)]‐di‐μ‐iodido]], {(C₅H₈N₃)[BiI₄]}_n, (5), and catena‐poly[2,6‐diaminopyridinium [[cis‐dibromidobismuth(III)]‐di‐μ‐bromido]], {(C₅H₇N₂)[BiBr₄]}_n, (6), include [Bi_nX_4n]^n? anionic chains (X = Br or I). Structures (2) and (3) are isostructural, while that of (5) is a pseudomerohedral twin. There is no discernible correlation between the type of anionic species obtained and the cation or halide ligand used. The Bi^III centres always have a slightly distorted octahedral geometry and there is a correlation between the Bi—X bond lengths and the number of classic N—H…X hydrogen bonds that the X ligand accepts, with a greater number of interactions corresponding with slightly longer Bi—X distances. The supramolecular networks formed by classic N—H…X hydrogen bonds include ladders, bilayers and three‐dimensional frameworks.     

过氧杂多酸(盐)在催化有机反应中的应用

含活性氧的过氧杂多酸(盐)是由杂多酸(盐)与过量H2O2反应而生成的,其具有高效的催化活性,可以用于催化氧化不同的物质,是一类性能优异的绿色催化剂,其在有机合成中有十分广阔的发展前景。本文介绍了过氧杂多酸(盐)的结构、性质和催化作用,并综述了近年来其在催化有机反应中的研究进展。     

钛硅分子筛催化环己酮液相氨肟化固定床工艺

采用固定床模式,研究了钛硅分子筛催化环己酮制环己酮肟液相氨肟化反应.结果表明,该工艺模式具有可行性与普适性.优化的反应条件为:温度333K,体系氨浓度>2%,酮/H₂O₂摩尔比=5,H₂O₂空速0.083h^-1.此时环己酮转化率、环己酮肟选择性、H₂O₂转化率及其有效利用率分别达18.7%,99.5%,94.7%和98.7%.进一步研究了H₂O₂在该过程中的反应行为,发现固定床工艺模式能有效提高H₂O₂的有效利用率,其主要原因是该模式有利于羟胺的生成及其进一步与酮反应生成肟.适当的空速与氨和酮的浓度是实现H₂O₂高效利用的关键因素.     

Catalytic ring opening of acetylcyclopropane by water and alcohols under the action of copper or palladium salts

The possibility of the cleavage of the C—C bond in acetylcyclopropane (ACP) under the action of water or alcohols in the presence of copper or palladium salts was demonstrated for the first time. At 175—180 °C, the reactions proceeded regioselectively with the cleavage of the C(1)—C(2) bond in the cyclopropane ring. The reaction of ACP with water afforded 5-hydroxypentan-2-one, bis(3-acetylpropyl) ether, and furan compounds, whereas the reactions with alcohols proceeded selectively to form 5-alkoxypentan-2-ones. The yields of the latter depend on the nature and structure of the alcohol, the maximum values (98%) being achieved in the case of primary alcohols.     

Unexpected high oxidation of cyclohexane by Fe salts and dihydrogen peroxide in acetonitrile

The reaction of cyclohexane (CyH) with 1.5 equivalent of dihydrogen peroxide (30% aqueous solution) in the presence of 1 mol% of an iron(II) or iron(III) salt (without added ligand), at 50 °C in acetonitrile, produces cyclohexanol (CyOH) and cyclohexanone (CyO) in high yields (up to 87% of CyH is converted to CyOH + CyO). Remarkably, CyH is totally converted within 2 h in the presence of Fe(ClO₄)₂ as catalyst under argon, producing 45% of CyOH and 42% of CyO. The addition of a tridentate Schiff-base ligand, namely 2,6-bis-[1-(benzylimino)ethyl]pyridine (dapb), leads to a clear increase of the selectivity towards CyOH + CyO, which are obtained with an overall yield of 93% (and even 100% selectivity to CyOH and CyO) in the case of the [Fe(ClO₄)₃/dapb] catalytic system.     

NaY型沸石分子筛催化环己胺氧化制备环己酮肟

考察了系列氧化剂、催化剂和溶剂对环己胺液相氧化制备环己酮肟的影响,发现以乙腈为溶剂,过氧化氢为氧化剂,NaY型沸石分子筛对该反应具有优良的催化性能。 对该反应体系进行了五因素四水平的正交实验,确定了适宜的催化剂用量、溶剂用量、反应时间、反应温度和氧化剂用量,比较分析了各因素对环己胺转化率和环己酮肟选择性的影响。 确定了环己胺液相氧化反应的最佳工艺条件为：环己胺为3 mL,催化剂为03 g,环己胺、溶剂和氧化剂的体积比为1∶3∶3,65 ℃反应2 h。 讨论了环己胺液相催化氧化的反应机理。     

Deuterium isotope effect on 13C chemical shifts of tetrabutylammonium salts of Schiff bases amino acids

Deuterium isotope effects on 13C chemical shift of tetrabutylammonium salts of Schiff bases, derivatives of amino acids (glycine, L-alanine, L-phenylalanine, L-valine, L-leucine, L-isoleucine and L-methionine) and various ortho-hydroxyaldehydes in CDCl3 have been measured. The results have shown that the tetrabutylammonium salts of the Schiff bases amino acids, being derivatives of 2-hydroxynaphthaldehyde and 3,5-dibromosalicylaldehyde, exist in the NH-form, while in the derivatives of salicylaldehyde and 5-bromosalicylaldehyde a proton transfer takes place. The interactions between COO- and NH groups stabilize the proton-transferred form through a bifurcated intramolecular hydrogen bond.     

Dehydrogenation of 1,4-dihydropyridine derivatives by the action of hydroperoxides in the presence of metal salts

Conclusions Molybdenum, tungsten, vanadium, and other metal salt-catalyzed hydroperoxide oxidation is a convenient preparative method for the dehydrogenation of 1,4-dihydropyridines to pyridine bases.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 670–671, March, 1972.     

Functionallization of the δ-carbon atom by the ferrous ion induced decomposition of alkyl hydroperoxides in the presence of cupric salts

In the ferrous ion induced decomposition of alkyl hydroperoxides in the presence of cupric halides or pseudohalides, intramolecular functionalization, with ligand transfer from cupric salts to δ-carbon atom, is achieved.     

HRGC separation of hydroperoxides formed during the photosensitized oxidation of (R)—(+)-Limonene

(R)—(+)-Limonene was photooxidized in the presence of Rose Bengal as catalyst. After TLC isolation, the hydroperoxides formed were separated directly by HRGC and analyzed by MS (El; Cl). Each hydroperoxide isomer was then isolated by HPLC for structure determination which after reduction of the HOO group with sodium borohydride was performed by ¹H-NMR and ¹³C-NMR. Six hydroperoxide isomers formed by oxidation of the endocyclic double bond were identified. The compounds eluted from the HRGC column in the following order (proportions are given in brackets) I (40.1%) (1S, 4R)-p-mentha-2, 8-diene 1-hydroperoxide; II (5.8%) (1R, 4R)-p-mentha-2, 8-diene 1-hydroperoxide; III (20.6%) (2R, 4R)-p-mentha-[1(7), 8]-diene 2-hydroperoxide; IV (8.5%) (2R, 4R)-p-mentha-6, 8-diene 2-hydroperoxide; V (4%) (2S, 4R)-p-mentha-6, 8-diene 2-hydroperoxide; and VI (21.0%) (2S, 4R)-p-mentha-[1(7), 8]-diene 2-hydroperoxide. Direct HRGC separation of the limonene hydroperoxides offers, inter alia, the possibility of determining their flavor qualities by HRGC/effluent sniffing.     

环己酮氨肟化反应中TS-1催化剂的积炭失活

 采用连续淤浆反应器,在环己酮质量空速为6 h-1和温度为70 ℃的条件下,对 TS-1 催化剂上环己酮氨肟化制环己酮肟反应过程中的活性变化规律进行了考察,并用热重-差热分析、程序升温脱附、 N2物理吸附、程序升温氧化和傅里叶变换红外光谱等测试手段对不同运转时间及再生后的催化剂进行了表征. 结果表明,催化剂运转时间在60 h以内时活性稳定,然后迅速下降; 积炭是引起催化剂失活的主要原因. 催化剂表面的积炭主要沉积在 TS-1 的微孔内,含碳物种有两种类型: 易除炭存在于Ti中心附近,可在350 ℃下氧化除去; 难除炭沉积于强酸中心 Si-OH 处,需在700 ℃下才能除去. 催化剂失活前后的骨架结构未发生显著变化,经烧炭再生后活性可恢复到新鲜催化剂的水平.