The structure and dynamics of the copper(II)—l-proline 1:2 complex in solution

The ¹³C relaxation times (T₁ and T₂) and isotropic contact shifts (Δω) of a one molar aqueous solution of l-proline at pH = 11 (or pD = 11.4) containing ca 10^?4 M copper(II) perchlorate are measured at 62.86 MHz over a temperature range of 26–70°C. The purely dipolar longitudinal relaxation of carbon-13 nuclei contrasting with purely scalar transverse relaxation allowed us to extract carbon-to-metal distances (through T₁ measurements) and hyperfine coupling constants and dynamic parameters (from T₂ and Δω measurements). The structure of the complex in solution is found closely similar to that in the solid state. Curve-fitting procedures allowed us to derive the hyperfine electron—carbon coupling constants A_c = ?1.95, + 0.42, + 1.90 and ?1.70 MHz for carbons α, β, γ, δ, of the pyrrolidinic ring, the reorientation correlation time of the complex, τ_R (25°C) = 1.15 × 10^?10 sec, the l-proline exchange rate, k_M (25°C) = 4.0 × 10⁵ sec^?1 (and the corresponding activation parameters ΔH^≠ = 9.0 kcal mol^?1 and ΔS^≠ = ?0.7 e.u.), and the electronic relaxation time, T_1e = 1.13 × 10^?8 sec (at 25°C). The latter value was found in agreement with the one computed from ESR data and the above τ_R value, showing the predominant contributions of spin—rotation interaction and, to a lesser extent, of the effect of g-tensor anisotropy to the electronic relaxation rate.     

Influence of the preparation history of α-Fe2O3 on its reactivity for hydrogen reduction

TG experiments on the hydrogen reduction of α-Fe₂O₃ were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe₂O₃ samples were prepared by the thermal decomposition of seven iron salts in a stream of oxygen, air or nitrogen at temperatures of 500–1200°C for 1 h. Thirteen metal ions such as Cu²⁺, Ni²⁺, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature (T_i. α-Fe₂O₃ prepared at lower temperatures showed lower T_i values and the reduction proceeded stepwise (Fe₂O₃ → Fe₃O₄ → Fe). T_i values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe₂O₃ → Fe₃O₄ → Fe) proceed simultaneously. the preparation in oxygen gave higher T_i than that in air or nitrogen. The doping by metal ions, except Ti⁴⁺, lowered the T_i of α-Fe₂O₃. The Cu²⁺ ion showed the lowest T_i, while Ti⁴⁺ showed the highest T_i and the inhibition effect.The reduction process was expressed by two equations; Avrami—Erofeev's equation for α-Fe₂O₃ → Fe₃O₄ and Mampel's equation for Fe₃O₄ → Fe.     

Stereoselective synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-ol and its propionate,the sex pheromones of pine sawflies

The stereoselective synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-ol (diprionol) and its propionate, the sex pheromones of pine sawflies (Neodiprion sp. and other), in high enantiomeric purity was achieved from (1R,3S)-2,2-dichloro-3-methylcyclopropanecarboxylic acid. The carbon skeleton of diprionol was formed via copper-catalyzed cross-coupling reactions and diastereoselective methylation of the intermediate chiral α-methylbranched aldehyde with MeTi(Oi-Pr)₃ in the presence of [(R,R)-TADDOL]Ti(Oi-Pr)₂. The latter transformation leads to a syn-adduct with high stereoselectivity, which depends on the presence and configuration of the α-stereogenic center in the aldehyde. The diastereomeric purity of (2S,3S,7S)-diprionol can be substantially increased via crystallization of its 3,5-dinitrobenzoate.     

Solid‐state NMR studies of cis‐1,4‐polyisoprene crosslinked with dicumyl peroxide in the presence of triallyl cyanurate

The network of dicumyl peroxide (DCP)/triallyl cyanurate (TAC) crosslinked cis‐1,4‐polyisoprene was studied by solid‐state NMR techniques such as direct‐polarization (DP), cross‐polarization (CP), and proton T₂ experiments. Line broadening and cis/trans isomerization of mobile carbons were observed in the DP experiments. The information on rigid carbons of network structures was observed with the CP technique. Motional heterogeneity was examined by proton T₂ relaxation experiments. Decreases in long T₂ (T_2L) values from the mobile non‐network structures and short T₂ (T_2S) values from the rigid network structures were observed with an increase in peroxide or coagent concentration. The percentage of T_2S in T₂ relaxation, which is related to network density, was observed to increase with peroxide and coagent addition. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1417–1423, 2000     

Über die bestimmung von isomerisierungsenthalpien und -entropien mit der IR-intensitätsmethode

Among the many sources of error which may affect the results for the enthalpy ΔH and entropy ΔS of isomerization determined by the IR-intensity method, the influence of the temperature dependence of the absorptivities of the reference bands, α_g(T) and α_t(T), is studied theoretically. Based on the general case I, the following three special cases II–IV are examined, in which increasingly stronger constraints are imposed on the compound-specific functions α_g(T) and α_T(T): II. Constant ratio α_g(T)/α_T(T), III. α_g(T) and α_T(T) both temperature independent and different, IV. α_g(T) and α_T(T) both temperature independent and equal. For each case the formulae for the evaluation of ΔH and ΔS as well as the kind and the number of the quantities to be measured are given. Moreover, in the cases I and II new methods for the analysis of the measured data are suggested. In each case the plots of the normalized band intensities $\text{A}{}_{\mathrm{g}}$ and $\text{A}{}_{\mathrm{t}}$ and the temperature T versus each other in different two-dimensional diagrams have been examined to find out whether one of the simpler special cases is applicable for the respective pair of reference bands. It is shown that these plots are not a suitable tool because of the relatively poor accuracy and reproducibility of measured IR-band intensities obtainable up to now.     

Synthesis and resolution of an α-phenyl substituted ortho-palladated matrix

A novel ortho-palladated benzylaminate matrix bearing phenyl substituent at the α-carbon stereocenter was prepared in the racemic state by direct intramolecular palladation of tertiary diphenylmethylamine with palladium(II) acetate; its structure and palladacycle conformation were determined by ¹H NMR studies of the mononuclear triphenylphosphine adduct. The resolution of the dimeric complex was performed via recrystallization of its diastereomeric (S)-prolinate derivatives. The absolute configuration (R_C,R_C) of the enantiopure dimer thus obtained was determined by an X-ray diffraction investigation of the less soluble (R_C,S_CS_N)-diastereomer of its (S)-prolinate adduct.     

Simultaneous determination of the activation energy and the reaction kinetic model from the analysis of a single curve obtained by a novel method

It has been demonstrated that a single plot of the values of Δlnα^1/2/Δln(1-α) (taken from a single α?T curve obtained under a controlled linear increase of the reaction rate) as a function of the corresponding values of Δ(1/T)/Δln(1?α) permits the simultaneous determination of both the activation energy and the kinetic model in accordance with a solid state reaction.     

Synthesis of both RP and SP enantiomers of unsymmetrical methylphosphonates based on a new approach utilizing a P-ester bond with α-hydroxyacids

Condensation of methyl methylphosphonochloridate with the dilithium salt of 2-methyllactic acid gave P-racemic methylphosphonates which unexpectedly contained two units of α-hydroxyacid linked via carboxylic ester bond. The racemic mixture was chromatographically separated via diastereomeric salts with quinine or cinchonine to give, based on the X-ray analysis, pure (R_P)-(+) and (S_P)-(−) enantiomers. Both enantiomers were immobilized on the ArgoGel^®–OH solid support. Condensation of methyl methylphosphonochloridate with α-hydroxyacid methyl esters [2-methyllactate, (S_C)-(−)-lactate, methyl (S_C)-(+) and (R_C)-(−)-mandelates] gave chromatographically inseparable 1:1 mixtures of diastereomers in 63–69% yields. A basic hydrolysis of the latter resulted in a selective and unexpected cleavage of the P–OMe group in a quantitative yield [(S_C)-(+) and (R_C)-(−)-mandelates, (S_C)-(−)-lactate] or simultaneous cleavages of P–OMe and C(O)OMe groups (2-methyllactate).     

Thermodynamic studies of (R)-BINOL-menthyl dicarbonates

The (R)-BINOL-menthyl dicarbonates, one of the most important compounds in catalytic asymmetric synthesis, was synthesized by a convenient method. The molar heat capacities C _p,m of the compound were measured over the temperature range from 80 to 378 K with a small sample automated adiabatic calorimeter. Thermodynamic functions [H _T–H _298.15] and [S _T–S _298.15] were derived in the above temperature range with a temperature interval of 5 K. The thermal stability of the substance was investigated by differential scanning calorimeter (DSC) and a thermogravimetric (TG) technique.     

Asymmetric synthesis of the allocolchicinoid natural product N-acetylcolchinol methyl ether (suhailamine), solid state and solution phase conformational analysis

An asymmetric synthesis of the allocolchicinoid N-acetylcolchinol methyl ether (NCME) from 3-methoxybenzaldehyde is reported. Comparison of ¹H and ¹³C NMR spectroscopic data obtained for this sample of NCME provide further evidence for the assertion that this compound is congruous with the natural product that has been dubbed suhailamine, establishing NCME as a naturally-occurring allocolchicinoid. The single crystal X-ray diffraction structure of NCME is also reported for the first time, revealing a preference for adoption of the (7S,R_a,Z) form—i.e., describing the orientation of the biaryl axis and the amide N–CO bond as well as the configuration of the stereocenic centre—in the solid state. A preference for the same form in DMSO-d₆ solution is revealed upon analysis by a range of NMR spectroscopic techniques, whilst an interconverting 69:24:7 mixture of the (7S,R_a,Z), (7S,S_a,Z) and (7S,R_a,E) forms is observed in CDCl₃.     

Enantioselective, (−)-sparteine-mediated deprotonation of geranyl and neryl N,N-diisopropylcarbamate: configurational stability of the intermediate lithium compounds

(E)/(Z)-Isomeric allylic carbamate esters were deprotonated by n-butyllithium/(−)-sparteine in toluene. Trapping experiments with chlorotrimethylsilane afforded the α-substitution products, with (R)-configuration, revealing that the pro-S proton is removed predominantly to form the corresponding (S)-lithium·(−)-sparteine derivatives; k_S/k_R>15:1 and >7:1, respectively. A slow (S)→(R)-epimerization occurs at −78 °C (T_1/2>60 min). The allylic double bond is stable to (Z)-(E) isomerization under these conditions.     

Fe对胜利褐煤焦结构和气化反应性能的影响

酸洗褐煤负载不同含量的Fe催化剂在固定床反应器上进行热解,然后采用FT-IR、Raman spectra、TPD和TG研究Fe催化剂对煤焦官能团、碳微晶结构、表面活性位和气化反应性的影响。FT-IR结果表明,催化热解作用下煤焦中-OH、-CH₃、-CH₂活性官能团数量增加。Raman光谱测试结果显示,随着Fe含量的增加,I_G/I_all由0.095减少到0.087,I_D3/I_all由0.090增加至0.097,表明在Fe催化作用下部分大芳香环结构转变为小芳香环结构。TPD实验结果表明,活性位数量随着煤焦中Fe含量升高而不断增加。在3%含Fe量时煤焦活性位数量随着吸附温度的升高而增加,800 ℃后煤焦表面活性位数量开始降低。750 ℃条件下CO₂吸附量随着吸附时间的延长而增加,45 min后煤焦达到饱和吸附状态。煤焦-水蒸气等温气化实验表明,煤焦气化反应性与活性位数量有密切的关系,Fe催化剂主要通过增加煤焦表面活性位数量提高煤焦气化反应性。     

Measurement of triplet extinction coefficients of organic compounds by McClure's method

We tested McClure's method for measuring the triplet extinction coefficients ε_T of organic compounds on anthracene and pyrene, using the u.v. lines from a krypton ion cw laser as a steady-state excitation source. Our values for anthracene ε_T = 82 × 10³1/mole cm at 426 nm and pyrene ε_T = 37 × 10³l/mole cm at 413 nm agree well with values obtained by other methods. McClure derived his linear relationship from kinetic considerations. One simply measures triplet optical densities (OD_T) at a fixed wavelength (e.g. at a triplet absorption maximum) as functions of different cw laser excitation intensities (powers) I_ex. A plot of 1/OD_T against 1/I_ex yields a straight line. Extrapolating to the intersection of the ordinate (1/I_ex = 0, or I_ex = ∞) yields 1/OD^∞_T. Since, at infinite excitation intensity I_ex, the concentration of the triplet state molecules N_T is equal to the original concentration N_S of the ground state concentration, ε_T can be easily calculated from ε_T = OD^∞_T/N_Sd where OD^∞_T is the triplet optical density at infinite excitation intensity, N _S is the original concentration of molecules (at ground state), and d is the thickness of the sample. The success of this method requires the production of high concentrations of triplet state molecules N_T, as well as steady-state excitation. CW lasers fulfill all these requirements. We discuss the spectroscopic equipment employed for measuring triplet optical densities in some detail. Methods for reducing heat gradients (noise) in liquid nitrogen, laser excitation spot sizes, reduction of spherical aberrations, etc., are reviewed. We varied the cw laser illumination density (laser power/area) by setting the focusing lens at different distances from the sample, and measured 1/OD_T as a function of 1/I_ex. As long as the size of the excitation area was not below a critical size, all the straight lines obtained at different lens settings converged well into only one value of 1/OD^∞_T. Measurements were also performed at different concentrations of the solutes.     

Acid-catalyzed rearrangement of α-hydroxytrialkylsilanes

Cationic rearrangement of several α-hydroxysilanes is described. Treatment of both (1R,1′R,2′S)-α-hydroxycyclopropylsilane syn-9 and (1S,1′R,2′S)-anti-9 under aqueous H₂SO₄ underwent rearrangement via a common α-silyl cation intermediate A to give a mixture of the ring-opened (R)-vinylsilane 13, the tandem [1,2]-CC bond migration product (1R,2S,1′R)-14, and its 1′S isomer 15. On the other hand, the acidic treatment of (R,E)-α-hydroxyalkenylsilane 8 or (R,Z)-8 was each accompanied with partial racemization to give an enantiomeric isomer of allylic alcohol 23 via a preferential syn-facial S_N2′ reaction, respectively. Both α-hydroxyalkynylsilane 6 and α-hydroxyalkylsilane 12 were inert to the acidic conditions; however, treatment of (R)-α-mesyloxyalkynylsilane 26 under aqueous H₂SO₄ gave a mixture of the optically active rearranged allene 27, α,β-unsaturated ketone 28, and (S)-α-hydroxyalkynylsilane 6 with partial racemization. Comparisons of the reactivities of these α-hydroxysilanes under acidic conditions are also disclosed.     

Thermal decomposition of biodiesel fuels produced from rapeseed, jatropha, and coffee oils with different alcohols

Thermal behaviors and the effects of various alcohols on biodiesel fuel (BDF) derived from edible oil such as rapeseed oil and inedible oils such as coffee oil and jatropha oil, were studied. TG curves in air and N₂ of rapeseed BDF, jatropha BDF, drip coffee, and BDF espresso coffee BDF synthesized from the methanol presented similar results which exhibited only one mass loss step, which is attributed to vaporization or combustion of the methyl esters. The decomposition temperature (T _d) of rapeseed, jatropha and coffee Bt-BDF were high by about 30 °C compared with the standard, Me-BDF. The amount of decomposition residue at 400 °C was found to be related to the number of carbon atoms in the alcohol, with the residue becoming greater with more carbons in the alcohol. The oxidation stability of rapeseed BDF depended on the carbon chain of the alcohol. However, coffee and jatropha BDFs were stable in spite of the long chain alcohol.     

Thermal behavior and thermodynamic properties of berberine hydrochloride

The low-temperature heat capacities of berberine hydrochloride were measured over the temperature range from 78 to 350 K by an adiabatic calorimeter. The thermodynamic functions H _T ? H _298.15 and S _T ? S _298.15 were derived from the heat capacity data. The results showed that the structure of berberine hydrochloride was stable over the temperature range from 78 to 350 K. The thermal stability of the compound was further tested by DSC and TG measurements. The results were in agreement with those obtained from adiabatic calorimetry experiment. The standard molar enthalpy of formation in the crystalline state of berberine hydrochloride was obtained from the standard molar energies of combustion in oxygen at T = 298.15 K, measured by a rotating-bomb combustion calorimeter.     

Enantioselective reduction of ketophosphonates using chiral acid adducts with sodium borohydride

A method for asymmetric reduction of α-and β-ketophosphonates using a chiral complex prepared from sodium borohydride and D-or L-tartaric acid is developed. Reduction of α-or β-ketophosphonates by these reagents led to formation of corresponding (S)-or (R)-hydroxyphosphonates. Reduction of chiral di(1R,2S,5R)-menthylketophosphonates by the chiral complex NaBH₄/(R,R)-tartaric acid due to the dual compliant asymmetric induction resulted in increased stereoselectivity of the reaction and led to formation of the hydroxyphosphonates with ee 90% or higher. On the other hand, reduction of di(1R,2S,5R)-methylketophosphonates by the chiral complex NaBH₄/(S,S)-tartaric acid proceeded as non-compliant dual asymmetric induction and resulted in decreased reaction stereoselectivity leading to formation of hydroxyphosphonates with ～45–60% ee. The developed methodology was applied to the synthesis of (R)-phosphocarnitine in multigram amounts.     

An investigation of the activity of carbon blacks recovered from elastomer composites

The activity of carbon blacks recovered from elastomer systems is determined by use of a temperature jump technique imposed on the carbon blacks in air using a TG unit. The elastomer composites were composed of styrene-butadiene rubber (SRR), fillers, activators, accelerators together with a number of different carbon blacks. The organic content was pyrolyzed away by heating in nitrogen, the atmosphere was changed to air and the activity of the carbons was assessed by the temperature jump method. This enables the Arrhenius parameters to be established for the gasification of the carbons in air. This data was compared with the oxidation rates of carbons before they were introduced into the elastomer system. Nitrogen adsorption surface areas based on a BET analysis showed that the surface area of the carbons was similar before and after incorporation into the composite. The kinetic parameters of the carbons were however somewhat altered by incorporation into the elastomer systems, but their order of activity towards the gasification process as assessed by their relative rate of gasification remained the same. This is explained by postulating that the higher rates of oxidation is associated with the present of edge carbon atoms at the surface compared to the much slower oxidation rates of the “basel” plane carbon atoms. It appears that this surface structure is largely retained in the composite carbon-elastomer system. This enables some speculation regarding the reinforcing action of certain carbon blacks in the composite system.     

Development of master curves for discriminating the mechanism of solid state reactions from experimental data obtained by using the cyclic and controlled rate thermal analysis

The cyclic and Controlled Rate Thermal Analysis method (CRTA) has been used. The two rates automatically selected in the cyclic curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction. Thus, the activation energy can be calculated without previous knowledge of the actual reaction mechanism. Provided that the activation energy,E, is known, a procedure has been developed for determining the kinetic law obeyed by the reaction by means of master curves that represent the values of the reacted fraction, α, as a function of?E/R(1/T-1/T _0.5),T _0.5 being the temperature at which α=0.5. This procedure has been tested by studying the thermal decomposition reaction of BaCO₃.     

Thermodynamic functions of α-halonaphthalenes from 0.25 to 16 atmospheres

Real gas thermodynamic functions, C_F, S, (H  H_o)/T, and ? (F  H_o)/T, have been calculated for α-halonaphthalenes (C₁₀H₇X, where X  F, Cl, Br, I) from 0.25 to 16 atm within the temperature range of 273.15 to 1200 K correcting the thermodynamic property ideal gas values by means of the Berthelot equation of state.