Alkylation of p-cresol with tert-butanol catalyzed by heteropoly acid supported on zirconia catalyst

Butylation of p-cresol by tert-butanol was catalyzed by 12-tungstophosphoric acid supported on zirconia (TPA/ZrO₂) under flow conditions. Catalysts prepared with different TPA loading (5–30 wt.%) were calcined at 1023 K and acidity was estimated by temperature programmed desorption (TPD) of NH₃. Fifteen percent TPA/ZrO₂ showed the highest acidity and found to be the most active catalyst in butylation of p-cresol. The effects of temperature, space velocity (LHSV) and molar ratio of the reactants on the conversion of p-cresol and products selectivities were optimized and the optimum reaction conditions evaluated were 403 K, tert-butanol/p-cresol (Bu/Cr) molar ratio 3 and LHSV 4 h⁻¹. Under the optimized conditions, conversion of p-cresol was found to be 61 mol% with product selectivity for 2-tert-butyl-p-cresol (TBC) 81.4%, 2,6-di-tert-butyl-p-cresol (DTBC) 18.1% and tert-butyl-p-tolyl ether (ether) 0.5%. Study of time on stream (TOS) performed as a function of time for 100 h showed that the loss in activity in terms of conversion of p-cresol was 6%.     

新疆牛至挥发油化学成分的分析

气相色谱 -质谱技术对新疆牛至花和茎的挥发油化学成分进行分析研究。从牛至茎和花中分别鉴定了 4 2和 37种成分 ,占挥发油总量的 95 %以上 ,茎和花的挥发油化学成分相差很大     

镁基储氢合金的表面处理和表面催化

表面处理作为储氢合金性能改善的有效手段，近年来得到了很好的发展和应用，本文简要介绍了镁基储氢合金表面处理的主要方法及其对合金性能的影响。     

Energies des premiers états électroniques du radial NO3 dans l'approximation Hartree-Fock

Ab initio Hartree-Fock calculations on NO₃ using a Gaussian basis give the lowest electronic states in the order ²A₂, ²E and ²E, with a near degeneracy of ²A₂ and ²E.

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Groupe de Recherches du C.N.R.S. associé à la Faculté des Sciences d'Orsay.

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Remerciements. Les auteurs remercient W. Fink pour avoir mis à leur disposition son programme et les avoir aider par ses suggestions. Ils remercient également J. Horsley pour les avoir initier à l'exploitation du programme.     

原子转移自由基聚合法合成磺胺类片段印迹聚合物及其表征

采用原子转移自由基聚合与片段印迹技术相结合的方法,以磺胺类物质的结构类似物4,6-二氯嘧啶为模板合成印迹聚合物。以4,6-二氯嘧啶(模板)︰甲基丙烯酸缩水甘油酯(功能单体)︰2,2'-联吡啶(配体)的摩尔比为10︰180︰1合成印迹聚合物。控制反应温度为60℃,反应时间为5 h。印迹聚合物的吸附量为1.48 mg/g,非印迹聚合物的吸附量为0.73 mg/g。以合成的聚合物为新型材料,对样品中的兽药残留进行选择性分离、富集,结果表明印迹聚合物的选择吸附能力明显优于非印迹聚合物。通过电镜扫描对聚合物的表面形态进行了表征。     

Phenomenological analysis of the phase transitions sequence in the ferroelectric crystal (CH3NH3)5Bi2Cl11 (PMACB)

A phenomenological model is proposed to describe the sequence of phase transitions in Pentakis (methylammonium) Undecachlorodibismuthate (111), (CH₃NH₃)₅Bi₂Cl₁₁ (PMACB) crystal on the basis of the recent structural data. The ferroelectric phase transition at 307 K is attributed to the ordering in a sublattice of the methylammonium cations CH₃NH ₃ ⁺ } placed in centrosymmetric sites in the paraelectric phase, whereas the isomorphous anomaly at about 180 K is related to a variation of the order in the sublattice of the remaining CH₃NH ₃ ⁺ } cations. The phenomenological thermodynamic potential is constructed for this system of two nonequivalent sublattices and the numerical values of its coefficients are then estimated from the dielectric, pyroelectric and calorimetric data. The sublattices are found to be weakly coupled near the ferroelectric phase transition. The anomaly at 180 K is interpreted as a continuous trace of a first order phase transition in a field created by the cations already ordered in the ferroelectric phase transition. This is analogous to a cusp A₊₃ in the catastrophes theory. The comparison of the Curie constants with the saturation values of the spontaneous polarization suggests that the sublattices cannot be treated as consisting of simple two-states pseudospins.     

Dinuclear complexes of chiral tetradentate pyridylimine ligands: diastereoselectivity, positive cooperativity, anion selectivity, ligand self-sorting based on chirality, and magnetism

The synthesis and coordination chemistry of two chiral tetradentate pyridylimine Schiff base ligands are reported. The ligands were prepared by the nucleophilic displacement of both bromides of 1,3-bis(bromomethyl)benzene (2) or 3,5-bis(bromomethyl)toluene (3) by the anion of (S)-valinol, followed by capping of both amine groups with pyridine-2-carboxaldehyde. Both ligands react with CoCl(2) and NiCl(2) to give [M(2)L(2)Cl(2)](2+) complexes. Remarkably, neither fluoride nor bromide ions can act as bridging ligands. The formation of [Co(2)((S)-3)(2)Cl(2)](2+) is highly diastereoselective, and X-ray crystallography shows that both metal centers in the [Co(2)((S)-3)(2)Cl(2)](CoCl(4)) complex adopt the lambda configuration (crystal data: [Co(2)(C(31)H(40)N(4)O(2))(2)Cl(2)](CoCl(4)).(CH(3)CN)(3), monoclinic, P2(1), a = 11.595(2) A, b = 22.246(4) A, c = 15.350(2) A, V = 3705(1) A(3), beta = 110.643(3) degrees, Z = 2). Structurally, the dinuclear complex can be viewed as a helicate with the helical axis running perpendicular to the [Co(2)Cl(2)] plane. The reaction of racemic 2 with CoCl(2) was shown by (1)H NMR spectroscopy to yield a racemic mixture of Lambda,Lambda-[Co(2)((S)-2)(2)Cl(2)](2+) and delta,delta-[Co(2)((R)-2)(2)Cl(2)](2+) complexes; that is, a homochiral recognition process takes place. Spectrophotometric titrations were performed by titrating (S)-3 with Co(ClO(4))(2) followed by Bu(4)NCl, and the global stability constants of [Co((S)-3)](2+) (log beta(110) = 5.7), [Co((S)-3)(2)](2+) (log beta(120) = 11.6), and [Co(2)((S)-3)(2)Cl(2)](2+) (log beta(110) = 23.8) were calculated. The results revealed a strong positive cooperativity in the formation of [Co(2)((S)-3)(2)Cl(2)](2+). Variable-temperature magnetic susceptibility curves for [Co(2)((S)-2)(2)Cl(2)](BPh(4))(2) and [Co(2)((S)-3)(2)Cl(2)](BPh(4))(2) are very similar and indicate that there are no significant magnetic interactions between the cobalt(II) centers.     

The harmonic Floquet oscillator

The harmonic oscillator interacting with a monochromatic electromagnetic field is one of the few soluble models in the application of Floquet theory. After recalling the form of the Floquet wave functions and eigenenergies we show how they can be derived as a limiting case of the solution for two oscillators with a bilinear coupling. We also derive a solution in the acceleration frame and examine the high-frequency regime. Finally, the model offers an opportunity to test the performances of a coupled-channel formulation of Floquet theory.     

_f-A_aD_d氢键体系的统计特征

基于氢键的形成和缩聚反应机理在统计意义下的相似性,利用高分子反应统计理论和反应动力学理论对氢键溶液的一个模型体系进行了相关讨论.给出了体系的溶胶分数和发生溶胶-凝胶相变的条件,指出质子受体基团间的竞争作用对溶胶凝胶相变点的影响,进而讨论了体系的数量分布函数和相关问题.