Polysulfane antitumor agents from o-benzyne. An odd-even alternation found in the stability of products o-C6H4Sx (x = 1-8)

Benzyne is shown to add elemental sulfur and give rise to a series of polysulfane compounds. A computational and experimental study is presented. Odd-membered o-C6H4Sx rings (x = 1-8), except x = 1, which suffers from ring strain, have enhanced stability compared to even-membered rings. The acquisition of "odd-even" data may shed new light, revealing patterns on polysulfane stability and structure.     

A powerful method to prepare sulfur-rich macrocycles

Various cyclic polysulfanes (up to a 16-membered ring) have been selectively obtained from the corresponding disubstituted trityl-protected polysulfane benzene derivatives upon treatment with elemental iodine in the presence of silica gel. Depending on the position of the sulfur-rich moieties and the presence of a methylene linker between the benzene ring and sulfur atoms, two types of products containing either one or two benzene subunits have been isolated. The scope of the reaction, its selectivity, and mechanism are discussed.     

Theoretical investigations on the conversions of cyclic polysulfides to acyclic polysulfide diradicals and subsequent reactions of biological interest

Sulfur is one of the most necessary biogenic elements in nature that must be assimilated by all organisms; it is an essential macronutrient for living organisms and has multiple roles in plant development. The oxidation of elemental sulfur is a complex process involving the contact of cells with sulfur particles, the oxidation of sulfur to sulfite, and the oxidation of sulfite to sulfate. To provide hypothesis concerning the most probable processes in the early states, we determined, by quantum-chemical calculations, the energies of some allotropic forms containing up to 32–40 sulfur atoms and energetics of their reactions with triplet dioxygen. The most probable reactions occurred with methylpolysulfane anions with an electron transfer to give the superoxide anion radical (and thiyls radicals) and especially the formation of peroxydic polysulfane anions. Calculations confirmed that the triplet diradical is more stable than the singlet one for acyclic polysulfide chains.     

Does the interconversion of polysulfur compounds proceed via hypervalent intermediates? An ab initio MO study

Ab initio MO calculations at the CCSD(T)/6-311++G(2df,p)//MP2/6-311++G** level have been carried out to determine the reaction energies and Gibbs energies of the homolytic dissociation of the S-S bonds in the chainlike sulfanes H2Sn (n = 2-4). Good agreement with the experimental data is observed. At the same level of theory, the formation of the hypothetical sulfuranes H2S(SH)2, H2S(SSH)2, and S(SH)4 from H2S and the mentioned sulfanes has been studied. Species of this type had been proposed as intermediates in the interconversion reactions of polysulfur compounds (e.g., formation of S7 from S8 and vice versa). The three sulfuranes serve here as model compounds. On the basis of the Gibbs energies and activation energies at 298 K, it is shown that the formation of the three sulfuranes from sulfanes requires too much energy and activation energy to successfully compete with homolytic dissociation reactions. In addition, the formation of the methylsubstituted sulfurane S(SMe)4 from the sulfanes Me2S2 and Me2S3 was studied to elucidate the mechanism of the formal exchange of sulfur atoms between polysulfane molecules. However, both the reaction energy of 199 kJ mol(-1) and the activation energy of 287 kJ mol(-1), calculated at the MP2/6-31G* level, are much higher than the homolytic dissociation energy of the S-S bonds in chain- and ringlike polysulfur compounds, such as Me2S4 (140 kJ mol(-1)) and sulfur homocycles (150 kJ mol(-1)). Therefore, it is concluded that the observed interconversion reactions of sulfur rings and of chainlike polysulfanes do not proceed via sulfurane-type intermediates. Instead, these reactions will take place by a radical chain mechanism at high temperatures, while at temperatures below 100 degrees C they are most probably initiated either by traces of nucleophiles that are present as impurities or by the polar surface groups usually present on the walls of the vessels used.     

The effect of diallyl polysulfanes on cellular signaling cascades

Diallyl polysulfanes, such as diallyl trisulfide and diallyl tetrasulfide, are regarded as a group of potential chemopreventive compounds as they have been proven to be effective inhibitors of cancer cells. These agents have been implicated in signal transductions, including the generation of Reactive Oxygen Species (ROS), Endoplasmic Reticulum (ER) stress, mitogen-activated protein kinase (MAPK) signaling, regulation of cell cycle progression, and induction of apoptosis. Nonetheless, certain aspects of the diallyl polysulfane triggered inhibitory effects on cancer cells are still not clear. Understanding the targeted signaling pathways may help to develop new strategies to treat cancer and other diseases. This review is therefore aimed at addressing the targeting of specific intracellular signal transduction cascades by these diallyl polysulfanes in order to shed some light on possible mechanisms of action of these compounds.     

SOME REACTIONS OF ALIPHATIC AMIDES WITH SULFUR AND SODIUM POLYSULFIDES

Abstract

Some reactions of the aliphatic amides, CH₃CONH₂, CH₃CONHCH₃, CH₃CON(CH₃)₂ and CH₃CON(C₂H₅)₂ with elemental S and sodium sulfides, Na₂S _n , n ≥ 1, have been studied. The initial reaction product with elemental sulfur appears to be a substituted polysulfane, CH₃COS _n NR, formed by the insertion of the sulfur chain into the C[sbnd]N bond. This product decomposes on further heating, forming COS as the major gas product. In solutions of Na₂S _n in the amides, the reactive material appears to be elemental S, present in equilibrium with S _n ^?2. In the N-dialkyl substituted amides, CH₃CON(CH₃)₂ and CH₃CON(C₂H₅)₂, the tetrasulfide is uniquely stabilized by solvent coordination so that solutions of Na₂S₄ in these amides are stable for long periods of time at 130°C.     

Regiochemistry of the photostimulated reaction of the phthalimide anion with 1-iodoadamantane and tert-butylmercury chloride by the S(RN)1 mechanism

The photostimulated reaction of the phthalimide anion (1) with 1-iodoadamantane (2) gave 3-(1-adamantyl) phthalimide (3) (12%) and 4-(1-adamantyl) phthalimide (4) (45%), together with the reduction product adamantane (AdH) (21%). The lack of reaction in the dark and inhibition of the photoinduced reaction by p-dinitrobenzene, 1,4-cyclohexadiene, and di-tert-butylnitroxide indicated that 1 reacts with 2 by an S(RN)1 mechanism. Formation of products 3 and 4 occurs with distonic radical anions as intermediates. The photoinduced reaction of anion 1 with tert-butylmercury chloride (10) affords 4-tert-butylphthalimide (11) as a unique product. By competition experiments toward 1, 1-iodoadamantane was found to be ca. 10 times more reactive than tert-butylmercury chloride.     

Reactions of SO3 with the O/H radical pool under combustion conditions

The reactions of SO3 with H, O, and OH radicals have been investigated by ab initio calculations. For the SO3 + H reaction (1), the lowest energy pathway involves initial formation of HSO3 and rearrangement to HOSO2, followed by dissociation to OH + SO2. The reaction is fast, with k(1) = 8.4 x 10(9)T(1.22) exp(-13.9 kJ mol(-1)/RT) cm(3) mol(-1) s(-1) (700-2000 K). The SO3 + O --> SO2 + O2 reaction (2) may proceed on both the triplet and singlet surfaces, but due to a high barrier the reaction is predicted to be slow. The rate constant can be described as k(2) = 2.8 x 10(4)T(2.57) exp(-122.3 kJ mol(-1)/RT) cm(3) mol(-1) s(-1) for T > 1000 K. The SO3 + OH reaction to form SO2 + HO2 (3) proceeds by direct abstraction but is comparatively slow, with k(3) = 4.8 x 10(4)T(2.46) exp(-114.1 kJ mol(-) 1/RT) cm(3) mol(-1) s(-1) (800-2000 K). The revised rate constants and detailed reaction mechanism are consistent with experimental data from batch reactors, flow reactors, and laminar flames on oxidation of SO2 to SO3. The SO3 + O reaction is found to be insignificant during most conditions of interest; even in lean flames, SO3 + H is the major consumption reaction for SO3.     

Kinetic study of the daytime atmospheric fate of (z)-3-hexenal

Rate coefficients for three daytime atmospheric reactions of (Z)-3-hexenal (3HA)-photolysis (J(1)), reaction with OH radicals (k(2)), and reaction with ozone (k(3))-were measured at 760 Torr and 298 K using a 6 m(3) photochemical reaction chamber. The UV absorption cross sections (σ(3HA)(λ)) were obtained in the wavelength range 240-350 nm. The photodissociation rate of 3HA relative to that of NO(2) was measured by a solar simulator at 760 Torr and was determined to be J(1)/J(NO2) = (4.7 ± 0.4) × 10(-3). Using the obtained σ(3HA)(λ) and J(1)/J(NO2), the effective photodissociation quantum yield was calculated to be Φ(3HA) = 0.25 ± 0.06. The rate coefficient for the reaction with OH radicals was measured by the relative rate method with three reference compounds and was determined to be k(2) = (6.9 ± 0.9) × 10(-11) cm(3) molecule(-1) s(-1). The rate coefficient for the reaction with ozone was measured by an absolute method and was determined to be k(3) = (3.5 ± 0.2) × 10(-17) cm(3) molecule(-1) s(-1). Using the obtained rate coefficients, the daytime atmospheric lifetime of 3HA was estimated.     

无添加剂条件下文石型碳酸钙晶须制备及影响因素研究

在不加任何结晶控制剂或模板条件下,以CaCl2和Na2CO3为原料,利用复分解反应法制备了具有较好形貌和高长径比,且分布均一的文石型碳酸钙晶须,并利用扫描电镜(SEM)、X-射线粉末衍射(PXRD)和傅里叶转换红外光谱图(FT-IR)等手段对其进行了表征。研究了浓度、滴加速度、反应温度、搅拌速度以及滴加方式等因素对碳酸钙晶须的影响。结果表明最佳制备工艺为:CaC12溶液与Na2CO3溶液的浓度为0.05 mol.L-1,溶液滴加速度为1 mL.min-1,反应体系温度为80℃,搅拌速度为250 r.min-1。     

Sequence of Reactant Combination Alters the Course of the Staudinger Reaction of Azides with Acyl Derivatives. Bimanes. 30

The Staudinger reaction of azides has now been followed by NMR and other spectroscopic techniques. syn-(Azidomethyl,methyl)(methyl,methyl)bimane (1) and Ph(3)P form a triazaphosphadiene intermediate 2 and then the bimane P-triphenyliminophosphorane 3. The iminophosphorane reacts with an acyl chloride to yield an iminophosphonium salt 4 which then forms the oxazaphosphetane 13. The latter undergoes an electrocyclic reversion to form the phosphine oxide and the chloroimines 7E and 7Z, the last being hydrolyzed to the (acylamido)bimane 6. This set of reactions constitutes the "iminophosphorane pathway". A significant diversion of the reaction path to an (N-alkylamino)phosphonium chloride 8 occurs through reaction of 4 with H(2)O present in the CDCl(3) and through reaction of 3 with HCl. A different azide (alpha-azido-o-xylene 1b) produces the (acylamido)-o-xylene as the sole product. A less sterically hindered phosphine (tri-2-furylphosphine) reacts more slowly to form the iminophosphorane 3a from the azidobimane 1. Reaction of the bimane P-tri-2-furyliminophosphorane with acyl chloride gives only the (acylamido)bimane 6. If the acyl chloride is mixed with 1, followed by addition of the Ph(3)P, the triazaphosphadiene adduct 5 is formed via the triazaphosphadiene. The adduct 5 is converted rapidly into a six-membered cyclic compound 11. The latter either loses nitrogen to yield 6 via 7Z and 7E and the phosphine oxide or loses chloride 10 through a novel chloride-induced elimination reaction from its protonated form. The change in procedure thus results in a dramatic change in the reaction pathway, a reaction set that constitutes the "triazaphosphadiene adduct pathway". In the case of alpha-azido-o-xylene, alpha-chloro-o-xylene (10b) is the only product. The reactions of the azides 1 or 1b with tri-2-furylphosphine also produce chlorides as the major products accompanied by some acetamido derivatives. The nucleophile-induced reaction explains a "surprising result" (formation of ester rather than amide) reported by Sahlberg et al. (Sahlberg, C.; Jackson, A. M.; Claesson, A. Acta Chem. Scand. 1988, B42, 556-562). The intramolecular "aza-Wittig" reaction may depend on the nucleophilicity of the triazaphosphadiene. A comprehensive mechanistic scheme for the Staudinger reaction of azides is conveniently divided into the following: (A) formation of the triazaphosphadiene (Scheme 1), (B) reactions of the triazaphosphadiene (Scheme 2), and (C) reactions via the iminophosphorane (Scheme 3). Some approximate kinetic parameters are reported for some of the reactions.     

盐酸普拉克索的合成工艺改进

以(S)-2,6-二氨基-4,5,6,7-四氢苯并噻唑（3）为原料,经缩合、还原反应制得普拉克索（2）; 2与盐酸成盐后制得盐酸普拉克索一水合物（1）,其结构经¹H NMR, ¹³C NMR, IR和MS（ESI）确证。研究了溶剂、反应温度、投料比γ［n(3) : n(正丙醛)］、析晶终止温度和精制降温速度对1收率的影响。结果表明：在最佳反应条件（无水甲醇为溶剂,γ=1.0 : 1.8,于-15~-20 ℃反应,析晶终止温度为-5~-10 ℃）下,最高收率可达61.5%。     

Nature of the chain propagation in the photostimulated reaction of 1-bromonaphthalene with sulfur-centered nucleophiles

The reactivity of -SC(NH)NH2 (1), MeCOS- (2), and PhCOS- (3) toward 1-naphthyl radicals was studied in DMSO. The photostimulated reaction of anions 1, 2, and 3 with 1-bromonaphthalene (4) after quenching with MeI renders 1-(methylthio)naphthalene (6) as a main product together with bis(1-naphthyl) sulfide (7) and naphthalene (5). The thioacetate ion (2) and thiobenzoate ion (3) were unreactive toward 4 as electron-donor under photostimulation; however, in the presence of potassium tert-butoxide anion (entrainment conditions), they gave the mentioned products 5, 6, and 7, after the addition of MeI. Quenching of the triplet state of 4 was assigned as the photoinduced initiation step, with a rate constant value of (4.6+/-0.5)x10(8) M-1 s-1 for tert-butoxide anion and a rough estimated value of (8+/-7)x10(7) M-1 s-1 for anion 1. By using hydrogen abstraction from DMSO as the competitive reaction, the absolute rate constants for the addition of anions 1, 2, and 3 to 1-naphthyl radicals have been determined to be 1.0x10(9), 1.2x10(9), and 3.5x10(9) M-1 s-1, respectively. This reactivity order is in agreement with the stability of the resulting radical anions (ArNu)*- (10-12)*-. The inhibition experiments of the photoinduced substitution reaction in the presence of radical scavengers and the global quantum yield higher than the unity are evidence of a radical chain mechanism for these substitution reactions by anions 1 and 2. Anion 3 adds to the 1-naphthyl radical, but is neither able to initiate nor to keep the propagation cycle. Evaluation of the electron-transfer driving forces for the reaction between (ArNu)*- and 4 together with the absence of a chain reaction for the anion 3 indicate that the propagation in the proposed mechanism is given by an acid-base reaction between the radical .C(O)Me or .C(NH)NH2 (13) and a base.     

Kinetics and mechanism of the C6H5 + CH3CHO reaction: experimental measurement and theoretical prediction of the reactivity toward four molecular sites.

The kinetics and mechanism of the reaction of C6H5 with CH3CHO have been investigated experimentally and theoretically. The total rate constant for the reaction has been measured by means of the cavity ring-down spectrometry (CRDS) in the temperature range 299-501 K at pressures covering 20-75 Torr. The overall bimolecular rate constant can be represented by the expression k = (2.8 +/- 0.2) x 10(11) exp[-(700 +/- 30)/T] cm3 mol-1 s-1, which is slightly faster than for the analogous C6H5 + CH2O reaction determined with the same method in the same temperature range. The reaction mechanism for the C6H5 + CH3CHO reaction was also explored with quantum-chemical calculations at various hybrid density functional theories (DFTs) and using ab initio high-level composite methods. The theories predict that the reaction may occur by two hydrogen-abstraction and two addition channels with the aldehydic hydrogen-abstraction reaction being dominant. The rate constant calculated by the transition state theory for the aldehydic hydrogen-abstraction reaction is in good agreement with the experimental result after a very small adjustment of the predicted reaction barrier (+0.3 kcal mol-1). Contributions from other product channels are negligible under our experimental conditions. For combustion applications, we have calculated the rate constants for key product channels in the temperature range of 298-2500 K under atmospheric-pressure conditions; they can be represented by the following expressions in units of cm 3mol-1 s-1: k1,cho = 8.8 x 10(3)T2.6 exp(-90/T), k2,ch3 = 6.0 x 10(1)T3.3 exp(-950/T), k3a(C6H5COCH3 + H) = 4.2 x 10(5)T0.6 exp(-410/T) and k3b(C6H5CHO + CH3) = 6.6 x 10(9)T-0.5 exp(-310/T).     

A synthesis of chiral 1,1,3-trisubstituted 1,2,3,4-tetrahydro-beta-carbolines by the Pictet-Spengler reaction of tryptophan and ketones: conversion of (1R,3S)-diastereomers into their (1S,3S)-counterparts by scission of the C(1)-N(2) bond

The Pictet-Spengler cyclization of the imines (3) prepared by the condensation of L-tryptophan methyl ester (1) and aryl methyl ketones (2), using titanium(IV) isopropoxide as an iminating reagent, quantitatively proceeded, when treated with trifluoroacetic acid (TFA) or formic acid, to provide two diastereomers, that is (1S,3S)-1-aryl-3-isopropoxycarbonyl-1-methyl-1,2,3,4-tetrahydro-beta-carbolines (4) and their (1R,3S)-diastereomers (5), of which the diastereomer ratios varied from 1 to 5 depending on the reaction conditions. The (1R,3S)-diastereomers (5) are thermodynamically more stable than their (1S,3S)-congeners (4), as shown by equilibration experiments in TFA. The conversion of 4 to 5 (also 5 to 4) should occur under acidic conditions by cleavage of the C(1)-N(2) bond with complete retention of configuration at the C-3 chiral center. The low diastereo-selectivity observed in the Pictet-Spengler reaction of 1 and 2 is concluded to be a stereochemical outcome under conditions of kinetic control (lower temperature, shorter reaction time), while the high diastereo selectivity with preferential formation of the more stable isomer (5) is the result of thermodynamically controlled experiments (higher temperature, longer reaction time).     

(5-氨基-[1,3,4]噻二唑-2-基)-丙酸乙酯的合成工艺改进

以丁二酸酐为起始原料,经醇解和酰化反应制得丁二酸单乙酯酰氯(3);3经甲烷磺酸催化与氨基硫脲环合合成了重要药物中间体——(5-氨基-[1,3,4]噻二唑-2-基)-丙酸乙酯,其结构经~1H NMR,IR和MS确证。运用正交试验对环合反应条件进行优化。最优反应条件为:3 132 mmol,n(氨基硫脲)∶n(3)∶n(甲烷磺酸)=1∶3∶3,于110℃反应3 h,总收率51.3%。     

S-oxygenation of thiocarbamides. 3. Nonlinear kinetics in the oxidation of trimethylthiourea by acidic bromate

The oxidation of trimethylthiourea (TMTU) by acidic bromate has been studied. The reaction mimics the dynamics observed in the oxidation of unsubstituted thiourea by bromate with an induction period before formation of bromine. The stoichiometry of the reaction was determined to be 4:3, thus 4BrO(3)- + 3R(1)R(2)C=S+ 3H(2)O --> 4Br- + 3R(1)R(2)C=O + 3SO(4)(2-) + 6H+. This substituted thiourea is oxidized at a much faster rate than the unsubstituted thiourea. The oxidation mechanism of TMTU involves initial oxidations through sulfenic and sulfinic acids. At the sulfinic acid stage, the major oxidation pathway is through the cleavage of the C-S bond to form a reducing sulfur leaving group, which is easily oxidized to sulfate. The minor pathway through the sulfonic acid produces a very stable intermediate that is oxidized only very slowly to urea and sulfate. The direct reaction of aqueous bromine with TMTU was faster than reactions that form bromine, with a bimolecular rate constant of (1.50 +/- 0.04) x 10(2) M(-1) s(-1). This rapid reaction ensured that no oligooscillatory bromine formation was observed. The oxidation of TMTU was modeled by a simple reaction scheme containing 20 reactions.     

Kinetics and mechanism of the oxidation of amaranth with hypochlorite

The reaction mechanism of the oxidation of Amaranth dye (2-hydroxy-1-(4-sulfonato-1-naphthylazo) naphthalene-3,6-disulfonate) with hypochlorite under varied pH conditions was elucidated by a kinetic approach. Under excess concentration of oxidant, the reaction followed pseudo-first-order kinetics with respect to Amaranth, and the oxidation was found to occur through two competitive reactions, initiated by hypochlorite and hypochlorous acid. The reaction order with respect to both OCl(-) ion and HOCl was unity. While the latter reaction was fast, the significance of the oxidation paths depended on the relative concentration of the two oxidizing species, which was dictated by the reaction pH. The role of the H(+) ion in the reaction was established. For the hypochlorite ion and hypochlorous acid facilitated reactions, the second-order rate coefficients were 1.9 and 23.2 M(-1) s(-1), respectively. The energy parameters were E(a) = 33.7 kJ mol(-1), ΔH(?) = 31.2 kJ mol(-1) and ΔS(?) = -190.6 J K(-1) mol(-1) for the OCl(-) ion-driven oxidation, and E(a) = 26.9 kJ mol(-1), ΔH(?) = 24.3 kJ mol(-1) and ΔS(?) = -222.8 J K(-1) mol(-1) for the reaction with HOCl-initiated oxidation. The major oxidation products for both the pathways were 3,4-dihydroxy naphthalene-2,7-disulfonic sodium salt (P(1)), dichloro-1,4-naphthoquione (P(2)) and naphtha(2,3)oxirene-2, 3-dione (P(3)). On the basis of the primary salt effect and other kinetic data, the rate law for the overall reaction and probable reaction mechanism was elucidated. The proposed mechanism was validated by simulations using Simkine-2.     

DFT Studies on the Isomerization of Butene Double Bond Catalyzed by 1-Butyl-3-methyl-imidazolium in Ionic Liquid

1 INTRODUCTION Butene and its isomers are important petroleum raw materials. Isomerization reaction of butene plays a key role in the course of C4 alkylation and its reaction mechanism has captured the attention of chemists all along[1, 2]. As a green so…     

一种以三聚氯氰为桥基的新型小分子功能活性染料的合成

以对氨基苯甲酸甲酯和水合肼为原料,经酰胺化反应制得对氨基苯甲酸甲酰胺,进一步与水杨醛通过还原氨化反应生成席夫(1）;以罗丹明B和水合肼为原料,1经闭环反应制得罗丹明B酰肼（2）; 2在四氢呋喃溶剂中与三聚氯氰经缩合取代反应生成一缩产物（3）; 3进一步在四氢呋喃中与1于45~50 ℃回流6 h,经取代反应生成二缩产物,其结构经¹H NMR, MS, IR和元素分析表征。