Nuclear magnetic resonance spectroscopic study on ionic liquids of 1-alkyl-3-methylimidazolium salts

Chemical shifts of ¹H and ¹³C NMR of series of methylimidazolium salts (MIM⁺, X=Br⁻, BF₄⁻ and PF₆⁻) function on the length of alkyl groups on the ring, type of solvents and the concentration. The bromides series demonstrate more chemical shift variation on H2 upon the change of solvents and concentration. Unexpected H-D exchange reactions were also observed in the MIM⁺Br⁻ by using CD₃OD and D₂O. The exchange rates strongly depend on the length of the alkyl group, which could cause more steric factor to reduce the interaction between deuterium atom from solvent and C2 of the ring.     

Synthesis and tautomeric transformations of 2-(tert-butyl)-1,2,4-benzotriazine-3(2H)-thiones

Treatment of 2-(tert-butyl)-1,2,3,4-benzotetrazinium tetrafluoroborates with sodium thiocyanate afforded 2-(tert-butylazo)phenyl isothiocyanates 3, which exist in equilibrium with 2-(tert-butyl)-1,2,4-benzotriazine-3(2H)-thiones 3′. The equilibrium depends on the substituents R in the benzene ring: the percentage of the open isomer 3 is about 20% for R = H or Me; for R = Cl or Br, the equilibrium is completely shifted to cyclic isomer 3′. The equilibrium is slow on the time scale of the ¹H and ¹³C NMR experiments. For compounds 3a/3′a (R = H), the spectra at 24 °C show two sets of signals, while those at 0 °C contain only signals for isomer 3′a. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1192–1195, July, 2006.     

The aggregation of sodium dehydrocholate in water

 We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10⁻⁴ mol dm⁻³ there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10⁻⁴ and (5.2 ± 2.2) × 10⁻³ mol dm⁻³, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration. At =(2.20 ± 0.85) × 10⁻² mol dm⁻³ the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes. These aggregates increase in size with concentration and change their shape at 8 × 10⁻² mol dm⁻³, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for substances with similar structure, such as bile salts. Received: 14 May 2001 Accepted: 10 August 2001     

Second crystal modification of 1,10-diazonia-18-crown-6 dichloride

The second crystal modification (II) of 1,10-diazonia-18-crown-6 dichloride [H₂DA18C6]²⁺·2Cl^?, where [H₂DA18C6]²⁺ is the 1,10-diaza-18-crown-6 dication (DA18C6) with two protonated nitrogen atoms, was investigated by XRD. The monoclinic modification (II) (space group P2₁/n, a = 9.600 Å, b = 5.689 Å, c = 15.749 Å, β = 91.03°, Z = 2) was solved by direct methods and refined by full-matrix least squares analysis in an anisotropic approximation to R = 0.032 for all 2494 independent reflections collected (CAD-4 automatic diffractometer, λMoK _α). In modification II, the conformation of the DA18C6 dication and the ion packing differ from those in triclinic modification I investigated previously.     

γ辐照引发无皂乳液聚合法一步合成Ag-聚4-乙烯基吡啶杂化微凝胶

无机-聚合物纳米复合材料是将聚合物与一种或多种无机纳米粒子复合而成的一种材料,它同时具有无机纳米粒子和聚合物的优良特性,在许多重要技术领域具有广泛的应用前景.近20年来,无机-聚合物纳米复合材料的制备及应用备受关注[1~6].包括杂化微凝胶在内的纳米复合微球是无机-聚合     

Copper(I)-catalysed homo-coupling of aryldiazonium salts: synthesis of symmetrical biaryls

Copper(I) triflate acts as an efficient stoichiometric reagent for the homo-coupling of aryldiazonium salts bearing electron-withdrawing group(s), to yield symmetrical biaryls in acetonitrile under mild reaction conditions. Aryldiazonium salts bearing electron-donating groups undergo the reaction by using catalytic amounts of a copper complex prepared in situ from copper(II) triflate and 2,2′-bipyridine with metallic copper as an ultimate reductant.     

Ring opening of 2-(cyanomethyl)aziridines by acid chlorides: synthesis of novel 4-amino-2-butenenitrile derivatives through intermediate aziridinium salts

1-Arylmethyl-2-(cyanomethyl)aziridines were transformed into novel N-arylmethyl-N-(2-chloro-3-cyanopropyl)amides as the major reaction products upon treatment with acid chlorides in CH₂Cl₂ through the ring opening of intermediate aziridinium salts. Subsequently, N-arylmethyl-N-(2-chloro-3-cyanopropyl)amides were converted into stable N-arylmethyl-N-(3-cyano-2-propenyl)amides for the first time by means of a dehydrochlorination mediated by Et₃N in CH₂Cl₂.     

Di-μ-hydroxy-bis(N,N,N′,N′-tetramethylenediamine)-copper(II) chloride [Cu(OH)·TMEDA]2Cl2: an efficient, practical catalyst for benzylation and allylation of amides

An efficient protocol for the benzylation or allylation of amides using the corresponding benzyl or allyl chlorides as electrophiles under basic conditions with commercially available 5 mol % of [Cu(OH)TMEDA]₂Cl₂ as catalyst was developed. Under these conditions, unprotected amino acids were benzylated without any racemization.     

Multistate/multifunctional behaviour of 4'-hydroxy-6-nitroflavylium: a write-lock/read/unlock/enable-erase/erase cycle driven by light and pH stimulation

We have investigated the network of reactions observed for the photochromic 4'-hydroxy-6-nitroflavylium compound in aqueous solutions upon pH changes (including pH jump and stopped flow experiments) and light excitation. The changes observed in the NMR and UV/Vis spectra allowed identification of ten different forms in which this compound can be transformed depending on the experimental conditions. Equilibrium and kinetic constants have been determined. Compared with other members of the flavylium family, 4'-hydroxy-6-nitroflavylium is characterized by a large cis-->trans isomerization barrier, and a very efficient hydration reaction. These peculiar features allow writing, reading, storing and erasing photonic information on 4'-hydroxy-6-nitroflavylium by a novel cyclic process that involves the following steps: write-lock/read/unlock/enable-erase/erase.     

Seawater—A test of multicomponent electrolyte solution theories. II. Enthalpy of mixing and dilution of the major sea salts

In a continuing effort to predict the physicochemical properties of seawater from the properties of single aqueous electrolyte solutions, the pairwise heats of mixing at constant molal ionic strength,I=1.0 ional, have been determined for the six possible pairs of salts from the set (NaCl, Na₂SO₄, MgCl₂, MgSO₄) at 30°C. In addition, heats of dilution for two aqueous solutions formed from these salts and havingI=1.0 ional have been determined at 30°C. In order to present the most thermodynamically consistent results, it was found necessary to apply a correction term to the relative apparent equivalent enthalpies given in the literature at 30°C. These correction terms derived from a consideration of published results on heats of dilution at very low concentrations. Further, in order to make predictions for seawater at 25°C, it was deemed desirable to refit existing heat-capacity data. The heats relative apparent equivalent enthalpies for the two mixtures mentioned as well as for seawater. The estimates are based on the theoretical equation of Reilly and Wood for charge-asymmetric mixtures which derives from the work of Friedman. In the most applicable cases, the estimates agree with experimental relative apparent equivalent enthalpies to within 5%. In general, the results substantiate the theoretical equation.Taken in part from the Ph.D. dissertation of W. H. Leung, University of Miami, Miami, Florida 33149.