Imidazolium salts as phase transfer catalysts for the dialkylation and cycloalkylation of active methylene compounds

The dialkylation and cycloalkylation reactions of active methylene compounds in the presence of readily available imidazolium salts (ionic liquids) as phase transfer catalysts were performed to afford the respective dialkylated or cycloalkylated products. This method is very efficient for the synthesis of 1,1-disubstituted derivatives and cyclopropane and cyclopentane ring systems in a facile manner.     

Comparison of 1300 nm quantum well lasers using different material systems

The band structure and material gain are calculated for 1300-nm band quantum well lasers of GaInNAs, AlGaInAs and GaInAsP material systems. The material compositions for each system are carefully chosen for comparison. The calculated results show that the peak gain is around the same in spite of the difference in band structures for the three systems.     

Determination of Complexation Selectivity of Aromatic Phosphonic Acids by Ammonium and Potassium Cations Using CE

Benzyl phosphonic acid, meta and para xylene diphosphonic acid and mesytilene triphosphonic acid were previously synthesized. Now we wanted to evaluate the ability of these compounds to complex selectively potassium and ammonium cations. We based our work on two different strategies. First we used Capillary Electrophoresis for calculating the binding constants. They enabled us to calculate the preferential binding energy, in other words the thermodynamic selectivity of complexation. Secondly, we used molecular mechanics to evaluate the difference of stability of the complexes. The results obtained in Capillary Electrophoresis appeared consistent with those obtained in molecular mechanics and, consequently, we demonstrated that mesytilene triphosphonic acid leads to the best selectivity of complexation towards ammonium and potassium cations. This complexation selectivity was shown, as an example, through the separation of four monovalent cations obtained in capillary zone electrophoresis. The evolution of complexing properties was discussed by referring to the structure of the studied phosphonic acids.     

季按盐体系N263一 HCl萃取色层分离富集金的研究

本文以季铁盐Nz6:一附载在硅球上作为固定相，用原子吸收法研究了Nzb,-HCl体系分离富集金的性能.静态试验了酸度对吸附金的影响，测定了N,6,-Si0:的吸附容量、与金的反应速率常数k值为7.3 x 10-'sec-1，其等温吸附线符合Freundlich经验等温吸附方程:Q=KC里/:在动态法试验的基础上，测定了金废水和金样的金含量，回收率测试结果满意     

Partial molal enthalpies,excess partial molal heat capacities,and structural effects ofn-Am4NBr in the water-dioxane system

Integral heats of solution of tetra-n-pentylammonium bromide, n-Am₄NBr, in aqueous binary mixtures of dioxane are reported at 25° and 35°C from 0.0 to 0.3 mole fraction of dioxane. The excess partial molal heat capacity c _p ^° at 30°C is derived from the integral heats of solution at infinite dilution at 25° and 35°C. The partial molal enthalpies of n-Am₄NBr exhibit a rather flat maxima at 0.2 mole fraction dioxane. The c _p ^° values suggest a structure-breaking role for dioxane. The results obtained in this study are compared with those obtained with n-Bu₄NBr in the same system in an earlier study.     

合成试剂及反应XI X一硝酸铈铵催化下溴酸钠对酰肼的氧化裂解

在硝酸铈铵催化下,酰肼可被溴酸钠氧化成羧酸。本方法具有试剂价廉、反应迅速、操作简便、产率较高的特点。     

Quantum Efficiency of Photooxidation of Porphyrins by Halomethanes in Solutions

The quantum yields of photooxidation of porphyrins, chlorophyll a, and –carotene in diethyl ether in the presence of different concentrations of CCl₄ in irradiation into the S ₀ S ₁ absorption bands are determined. The quantum yields for deoxygenated solutions are in the range (0.001–4.200)·10^–3. In the presence of oxygen, the quantum yield is increased by more than an order of magnitude and is related to the formation of the peroxyl radical CCl₃O₂ . It is shown that in the initial stage of the photochemical reaction, an electron from the excited molecules of tetrapyrrole pigments in the S ₁ state is transferred to the molecules of halogen derivatives of methane.     

Unimolecular reactivity of strong metal-cation complexes in the gas phase: ethylenediamine-Cu(+)

The gas-phase reactions between ethylenediamine (en) and Cu(+) have been investigated by means of mass spectrometry techniques. The MIKE spectrum reveals that the adduct ions [Cu(+)(H(2)NCH(2)CH(2)NH(2))] spontaneously decompose by loosing H(2), NH(3) and HCu, the loss of hydrogen being clearly dominant. The spectra of the fully C-deuterated species show the loss of HD, NH(3) and CuD but no losses of H(2), D(2), NH(2)D, NHD(2), ND(3) or CuH are observed. This clearly excludes hydrogen exchange between the methylene and the amino groups as possible mechanisms for the loss of ammonia. Conversely, methylene hydrogen atoms are clearly involved in the loss of molecular hydrogen. The structures and bonding characteristics of the Cu(+)(en) complexes as well as the different stationary points of the corresponding potential energy surface (PES) have been theoretically studied by DFT calculations carried out at B3LYP/6-311+G(2df,2p)//B3LYP/6-311G(d,p) level. Based on the topology of this PES the most plausible mechanisms for the aforementioned unimolecular fragmentations are proposed. Our theoretical estimates indicate that Cu(+) strongly binds to en, by forming a chelated structure in which Cu(+) is bridging between both amino groups. The binding energy is quite high (84 kcal mol(-1)), but also the products of the unimolecular decomposition of Cu(+)(en) complexes are strongly bound Cu(+)-complexes.     

Solvation effects on cation–π interactions: a test study involving the quaternary ammonium ion

Water solvation effects on theoretical binding energies of the tetramethylammonium cation with benzene, phenol and indole have been analyzed as a prototype of biological cation– interactions. Solvent effects were introduced in the quantum chemical computations either by considering molecules belonging to the first solvation of the tetramethylammonium or by a polarizable continuum model. Our results show that the calculated binding energies are reduced by about three quarters with respect to the corresponding gas-phase results, but the sequence benzene<phenol<indole is preserved, in accordance with the concept of cation– interactions. Similar results are obtained for the interaction of tetramethylammonium with the benzene–indole pair.Contribution to the Jacopo Tomasi Honorary Issue