Chiral fluoroacetic acid: synthesis of (R)- and (S)-[2H1]-fluoroacetate in high enantiopurity

A two-step synthesis of (R)- and (S)-[²H₁]-fluoroacetate (sodium salts) in high enantioselectivity is reported. The synthesis is the development of a previous one in which the enantioselectivity has been increased from ～38% ee to >95% ee. The improvement in enantioselectivity applied Bio’s methodology, which involved a deoxyfluorination reaction with DAST on either enantiomer of [²H₁]-benzyl alcohol, adding TMS-morpholine to the reaction. The additive promotes an S_N2 inversion process, and suppresses a competing non-stereospecific S_N1 reaction course, and as a result significantly improves the stereointegrity of the C–F bond formation. The intermediate [²H₁]-benzyl alcohols, [²H₁]-benzyl fluorides and the product [²H₁]-fluoroacetates as their hexyl esters were separately assayed for their stereochemical integrity, using the Courtieu method. This method involved measuring their ²H NMR spectra in a chiral matrix of poly-γ-benzyl l-glutamate. The chiral assay demonstrated that there was no significant loss in stereointegrity during the deoxyfluorination reaction and showed that the enantiomers of [²H₁]-fluoroacetate were generated with high enantiomeric purity (95% ee).     

pH-Metrische Studien an den binären Komplexen von Oxovanadium(IV) mit Hippur- und Anthranilsäure und Pyridin-2-aldoxim

pH-metric studies on the interaction of oxovanadium(IV) with hippuric and anthranilic acids and pyridine-2-aldoxime indicate the formation of monohydroxo derivatives of 1:1 chelates. The equilibrium constants for the reaction, VO²⁺+HA+H₂O?VO(OH)A+2H⁺ have been calculated as 4.47±0.07 and 6.32±0.05 in the 1:1 VO²⁺-hippuric or anthranilic acid systems resp. and for the reaction, VO²⁺+H₂ A ⁺+H₂O?VO(OH)A+3H⁺ as 8.40±0.09 in the 1:1 VO²⁺-pyridine-2-aldoxime hydrochloride system at 30±0.5°C (μ=0.1-KNO₃).     

Reply to comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures

In reply to “Comment on the possible role of reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures” (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) we present an alternative thermodynamic estimation of the reaction rate constant k. Based on the non-symmetric standard state convention we have calculated that the Gibbs energy of reaction Δ_rG=57.26 kJ mol^?1 and the reaction rate constant k=7.23×10^?5 M^?1 s^?1 at ambient temperature. Re-analysis of the thermodynamic estimation (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) showed that the upper limit for the rate constant at 573 K is k=1.75×10⁴ M^?1 s^?1 compared to the value predicted by the diffusion-kinetic modelling (3.18±1.25)×10⁴ M^?1 s^?1 (Swiatla-Wojcik, D., Buxton, G.V., 2005. On the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 74(3–4), 210–219). The presented thermodynamic evaluation of k(573) is based on the assumption that k can be calculated from Δ_rG and the rate constant of the reverse reaction which, as discussed, are both uncertain at high temperatures.     

Gamma-radiolysis of hydrogen—Oxygen-mixtures— Part I. Influences of temperature,vessel wall,pressure and added gases (N2, Ar,H2) on the reactivity of H2/O2-mixtures

The influence of pressure, temperature, of “matrix gases” N₂, Ar, H₂ and of the pretreatment of the vessel wall on the rate of reaction from ⁶⁰Co γ-radiolysis of hydrogen—oxygen-mixtures, in the region of slow reaction, was investigated. The G(-H₂)-value2 of H₂/O₂-mixtures (H₂:O₂ = 1:9−2:1) ranges from 1 to 14 with only slight dependence on pressure, temperature, H₂/O₂-ratio, and surface/volume ratio (S/V). The temperature has little influence (35–210°C). Replacing most of the O₂ in the H₂:O₂ (1:9)-mixtures with N₂, Ar or excess H₂ at higher temperature, causes the G(-H₂)-values to increase. The influence of these matrix gases increases with increasing temperature (35–210°C) and decreasing S/V ratio (0.59 and 3.8 cm^-1) of the reaction vessel; it depends also on the pretreatment of the wall surface. Varying the total pressure, the G(-H₂)-values show a temperature and gas mixture dependent maximum between about 20 and 200 mb. At higher temperature (210°C) we observed an influence of dose for 50 mb H₂/air-mixtures, whereas at 1 b and 35–90°C no influence of the dose on the rate of reaction of such mixtures was found.The activation by N₂, Ar, H₂ is discussed on the base of the H₂/O₂-reaction being a radical-chain reaction, built up by at least 38 coupled elementary steps (Ref⁽¹⁾ or see part 2). O₂ reacts with H₂, at increased rates of conversions (> 25%), in the expected stoichiometric ratio of 2:1. Oxygen may however also be converted in non-stiochiometric amounts under certain conditions.     

Elucidation of methyl tert-butyl ether degradation with Fe/H2O2 by purge-and-trap gas chromatography-mass spectrometry

Degradation of methyl tert-butyl ether (MTBE) with Fe²⁺/H₂O₂ was studied by purge-and-trap gas chromatography-mass spectrometry. MTBE was degraded 99% within 120 min under optimum conditions. MTBE was firstly degraded rapidly based on a Fe²⁺/H₂O₂ reaction and then relatively slower based on a Fe³⁺/H₂O₂ reaction. The dissolved oxygen decreased rapidly in the Fe²⁺/H₂O₂ reaction stage, but showed a slow increase in the Fe³⁺/H₂O₂ reaction stage. tert-Butyl formate, tert-butyl alcohol, methyl acetate and acetone were identified as primary degradation products by mass spectrometry. A preliminary reaction mechanism involving two different pathways for the degradation of MTBE with Fe²⁺/H₂O₂ was proposed. This study suggests that degradation of MTBE can be achieved using the Fe²⁺/H₂O₂ process.     

Chemistry of 2-mercaptophenol (H2mp) . Part iii. One dimensional arrays of binuclear anions of Mo (VI) linked by bis (2-hydroxyphenyl) disulfide via hydrogen bondings

The reaction of (Bu₄N) ₄ [Mo₈O₂₆] with a suitable amount of 2-mercaptophenol (H₂mp) in MeOH in the presence of equimolar Et₃N gave the complex (Bu₄N) ₂ [{MoO₂ (2-SC₆H₄O) }₂ (μ-O) ] (2 2′-HOC₆H₄SSC₆H₄OH) 2H₂O (1) with a one-dimensional chain network formed via hydrogen bondings (average OH OMo distance 2655 Å) of the hydroxyl groups in the spacer 2 2′-HOC₆H₄SSC₆H₄OH with the terminal oxo groups of the dimolybdenum anions 2 2′-HOC₆H₄SSC₆H₄OH was obtained by oxidation of H₂mp in the presence of molybdenum when the reaction was run in air The characteristic cis-MoO₂² absorptions appear at 913 and 864 cm^{−1 1} H NMR and ¹ H–¹ H COSY spectra characterized the phenyl protons of the mercaptophenol groups in the anion and in 22′-HOC₆H₄SSC₆H₄OH in the ranges of 6700–6270 and 7368–6799 ppmrespectivelywith ³J and ⁴J coupling constants of 8 and 1 Hz respectively.     

The reaction between [η5-C5H5M(CO)3]2, η5-C5H5M(CO)3I (M  Mo,W) and isonitriles

The reaction between η⁵-C₅H₅M(CO)₃I (M  Mo, W) and isonitriles, RNC, (RNC  PhCH₂NC, t-BuNC and 2,6-dimethylphenylisocyanide (XyNC)) is catalysed by the dimer [η⁵-C₅H₅M(CO)₃]₂ (M = Mo, W) to yield η⁵-C₅H₅M(CO)_3?n(RNC)_nI (n = 1–3) and [η⁵-C₅H₅Mo(RNC)₄]I. The complexes (η⁵-C₅H₅)₂Mo₂(CO)₆?n(RNC)_n (n = 1, RNC = MeNC, PhCH₂NC, XyNC, t-BuNC; n = 2, RNC = t-BuNC) have been prepared in moderate yield from the direct reaction between [η⁵-C₅H₅Mo(CO)₃]₂ and RNC, and also catalyse the above reaction. A reaction pathway involving a fast non-chain radical mechanism and a slower chain radical mechanism is proposed to account for the catalysed reaction.     

Enthalpy of formation of aqueous tungstate ion and of crystalline tungstic acid (H2WO4)

Calorimetric measurements of the enthalpy of reaction of WO₃(c) with excess OH^?(aq) have been made at 85°C. Similar measurements have been made with MoO₃(c) at both 85 and 25°C, to permit estimation of ΔH°=?13.4 kcal mol^?1 for the reaction WO₃(c)+2OH^?(aq)=WO^2?₄(aq)+H₂O(liq) at 25°C. Combination of this ΔH° with ΔH°_f for WO₃(c) leads to ΔH°_f=?256.5 kcal mol^?1 for WO^2?₄(aq). We also obtain ΔH°_f=?269.5 kcal mol^?1 for H₂WO₄(c). Both of these values are discussed in relation to several earlier investigations.     

Oxidomolybdenum(VI) complexes with atrane-type [O3N] ligands

Dioxomolybdenum(VI) complex [MoO₂Cl₂(dmso)₂] reacts with a series of tetradentate O₃N-type aminoalcohol–bisphenol ligands to form oxomolybdenum(VI) complexes of type [MoOCl(Lⁿ)]. The reaction of H₃L¹ produces [MoOCl(L¹)] as two separable isomers, whereas the reaction of H₃L² or H₃L³ yields a single product. The X-ray analyses of cis- and trans-[MoOCl(L¹)] reveal that the complexes are formed of monomeric molecules. The ligands have tetradentate coordination through three oxygen donors and one nitrogen donor, which is located trans to the terminal oxo group. The sixth coordination site is occupied by a chloro ligand.     

Preparation of LiZnPO4·H2O via a novel modified method and its non-isothermal kinetics and thermodynamics of thermal decomposition

The single phase ??-LiZnPO₄·H₂O was directly synthesized via solid-state reaction at room temperature using LiH₂PO₄·H₂O, ZnSO₄·7H₂O, and Na₂CO₃ as raw materials. XRD analysis showed that ??-LiZnPO₄·H₂O was a compound with orthorhombic structure. The thermal process of ??-LiZnPO₄·H₂O experienced two steps, which involved the dehydration of one crystal water molecule at first, and then the crystallization of LiZnPO₄. The DTA curve had the one endothermic peak and one exothermic peak, respectively, corresponding to dehydration of ??-LiZnPO₄·H₂O and crystallization of LiZnPO₄. Based on the iterative iso-conversional procedure, the average values of the activation energies associated with the thermal dehydration of ??-LiZnPO₄·H₂O, was determined to be 86.59?kJ?mol^?1. Dehydration of the crystal water molecule of ??-LiZnPO₄·H₂O is single-step reaction mechanism. A method of multiple rate iso-temperature was used to define the most probable mechanism g(??) of the dehydration step. The dehydration step is contracting cylinder model (g(??)?=?1?(1???)^1/2) and is controlled by phase boundary reaction mechanism. The pre-exponential factor A was obtained on the basis of E _a and g(??). Besides, the thermodynamic parameters (??S ^??, ??H ^??, and ??G ^??) of the dehydration reaction of ??-LiZnPO₄·H₂O were determined.     

Mechanism of the reaction of N-p-tosylsulphilimine and related compounds with thiophenolate ion

The reaction of alkyl aryl N-p-tosylsulphilimines with thiophenolate ion was found to afford quantitatively the sulphide that arises by an S_N2 like reaction on the carbon atom adjacent to the tri-valent sulphur atom. This reaction was also found to proceed smoothly with such compounds as sulphoxides and sulphones and sulphoxmanes. The kinetic study on the reaction between aryl methyl N-p-tosylsulphilimine with thiophenolate ion in DMF reveals that the reaction is of second order, namely, first order with respect to each thiophenolate ion and the sulphilimine. The enthalpy and entropy of activation for the reaction are ΔH^≠ = ?17· kcal/mol and ΔS^≠ = ?5·7 eu respectively. The effect of substituents in the reaction, p-XC₆H₄⁺(^?SO₂C₆H₄Y-p)CH₃ + p-ZC₆H₄SK is nicely correl with Hammett σ values giving ?_x = + 2·4, ?_y = + 1·2 and ?_z = ?1·8 respectively. Meanwhile, a marked steric retardation by a bulky alkyl group in alkyl phenyl N-p-tosylsulphilimine is observed. Furthermore, from the stereochemical study of the reaction using an optically active sec-octyl phenyl N-p-tosylsulphilimine with thiophenolate ion it is concluded that the reaction proceeds via a typical S_N2 process on α-carbon atom attached to the tri-valent sulphur atom.     

Säureinduzierte carbin-acylumwandlung

The reaction of dicarbonyl- and carbonyl(trimethylphosphine)(cyclopentadienyl)-carbyne complexes of molybdenum and tungsten η⁵-C₅H₅(CO)_2−n(PMe₃)_nMCR (n = 0, 1; M = Mo, W; R = CH₃, C₆H₅, C₆H₄CH₃, C₃H₅) with protic nucleophiles HX (X = Cl, CF₃COO, CCl₃COO) leads, through a combined protonation/carbon-carbon coupling reaction, to η²-acyl complexes η⁵-C₅H₅(CO)_1−nX₂(PMe₃)_n-M(η²-COCH₂R). The reaction conditions, the results of the spectroscopic measurements and the X-ray structure of η⁵-C₅H₅(CO)(Cl₂)W(η²-COCH₂CH₃) are reported.     

Efficient synthesis of functionalized spiro-2,5-dihydro-1,2-λ-oxaphospholes

The reaction of ethyl propiolate with triphenylphosphine (Ph₃P) in the presence of N-alkylisatins led to ethyl 2,2,2-triphenyl-2,5-dihydro-1,2-λ⁵-oxaphosphole-4-carboxylate-spiro-1-alkyl-1,3-dihydro-2H-indol-2-ones in good yield. The reaction of dialkyl acetylenedicarboxylates with Ph₃P in the presence of N-alkylisatins led to dialkyl 2,2,2-triphenyl-2,5-dihydro-1,2-λ⁵-oxaphosphole-3,4-dicarboxylate-spiro-1-alkyl-1,3-dihydro-2H-indol-2-ones and alkyl 4-(alkoxy)-5-oxo-2,5-dihydro-3-furancarboxylate-spiro-1-alkyl-1,3-dihydro-2H-indol-2-ones.     

Experimental study of the D + H2(ν = 1) reaction

The D + H₂(ν = 1) reaction, D + H₂(ν = 1) → K_a HD(ν = 1) + H, → K_n HD(ν = 0) + H, → K_r D + H₂(ν = 0) has been studied. The measurements were made in a flow-tube apparatus at 300 K. Vibrationally excited H₂ was generated in a furnace and D atoms in a microwave discharge. EPR and thermometric techniques were used for the detection of D and H atoms and H₂(ν = 1). The product branching rate constants (in CM³/Molecule s) were found to be K_a = (10.7 ± 4.1) × 10^?13. K_n = (5.4 ± 2.7) × 10^?13, K_r, < 2.7 × 10^?13.     

Ion—molecule reactions in GeH4/SiH4 systems studied by ion trap mass spectrometry

Gas phase ion—molecule reactions occurring in GeH₄/SiH₄ systems under different partial pressures and their mechanisms have been investigated by ion trap mass spectrometry (ITMS). SiH⁺_n (n=0–3) and GeH⁺_n (n = 0–3) are the main ionic species at zero reaction time when the GeH₄: SiH₄ ratio is in the range 1:1 to 1:12. Self-condensation sequences are observed at increasing reaction times. Moreover, formation of ions containing GeSi bonds, such as GeSiH⁺_n (in = 2–5) and GeSi₂H⁺_n (n = 4, 5), occurs by reactions of Si₂H⁺_n (n = 2–5) and Si₃H⁺_n (n = 4, 5) with GeH₄. At longer reaction times, further substitution of silicon with germanium in GeSiH⁺_n (n = 2–5) ions has been observed, to give Ge₂H⁺_n (n = 2–5).     

Dihydrogen activation promoted by homonuclear ion pairs involving cobalt(II) and cobalt(−I)

Acyltetracarbonyls have been shown to be formed from the reaction of hexene with CO/H₂ (1/1) mixtures (P(CO) = P(H₂) = 300 mmHg) in THF/H₂O at room temperature catalysed by homonuclear Co_II, Co^?I ion pairs.     

Green synthesis of 4,6-bisarylpyrimidin-2(1H)-ones and azo-linked 4-arylpyrimidin-2(1H)-ones using NiFe2O4@SiO2nPr@glucose amine as a mild nano catalyst

The clean, environmentally benign and effective synthesis of novel azo-linked 4-arylpyrimidin-2(1H)-one derivatives and 4,6-bisarylpyrimidin-2(1H)-ones via three-component reaction of various aldehydes or synthetized azo-linked aldehydes, urea, and acetophenone promoted by NiFe₂O₄@SiO₂ⁿPr@glucose amine at room temperature (25 °C) was reported. NiFe₂O₄@SiO₂ⁿPr@glucose amine were synthesized and characterized by transmission electron microscope (TEM), fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM), X-ray powder diffraction (XRD) and X-ray spectroscopy (EDX). These compounds were obtained in high yields and short reaction times. The catalyst could be easily recovered and reused for six cycles with almost consistent activity. The structures of the synthesized 4,6-bisarylpyrimidin-2(1H)-one compounds were confirmed by ¹H NMR, ¹³C NMR and FTIR spectral data and elemental analyses.     

Understanding E2 versus SN2 Competition under Acidic and Basic Conditions

Our purpose is to understand the mechanism through which pH affects the competition between base-induced elimination and substitution. To this end, we have quantum chemically investigated the competition between elimination and substitution pathways in H₂O+C₂H₅OH₂⁺ and OH⁻+C₂H₅OH, that is, two related model systems that represent, in a generic manner, the same reaction under acidic and basic conditions, respectively. We find that substitution is favored in the acidic case while elimination prevails under basic conditions. Activation-strain analyses of the reaction profiles reveal that the switch in preferred reactivity from substitution to elimination, if one goes from acidic to basic catalysis, is related to (1) the higher basicity of the deprotonated base, and (2) the change in character of the substrates LUMO from C^β−H bonding in C₂H₅OH₂⁺ to C^β−H antibonding in C₂H₅OH.     

An unusual oxidation-dealkylation of 3,4-dihydropyrimidin-2(1H)-ones mediated by Co(NO3)2·6H2O/K2S2O8 in aqueous acetonitrile

4-Aryl-6-methyl-3,4-dihydropyrimidin-2(1H)-one (DHPM) scaffolds of Biginelli type were oxidized using Co(II)/S₂O₈²⁻ and the reaction afforded 6-unsubstituted pyrimidin-2(1H)-ones through an unprecedented dealkylation process. 4-Alkyl DHPMs under similar conditions afforded yet another unusual product, ethyl tetrahydropyrimidin-2,4(1H,3H)-dione-5-carboxylate.     

Synthesis of substituted tetrahydron-1H-carbazol-1-one and analogs via PhI(OCOCF3)2-mediated oxidative C–C bond formation

A variety of tetrahydro-1H-carbazol-1-ones and analogs were conveniently synthesized from the reaction of the corresponding 2-(phenylamino)cyclohex-2-enone with hypervalent iodine reagent PhI(OCOCF₃)₂ (PIFA), through a direct intramolecular oxidative C(sp²)–C(sp²) bond formation. This approach realized the construction of the biologically important tetrahydro-1H-carbazol-1-one and tetrahydrocyclohepta[b]indol-6(5H)-one skeletons. The mechanism of the process was proposed and briefly discussed.