Stereoselective aldol additions of titanium enolates of N-acetyl-4-isopropyl-thiazolidinethione

The addition of chlorotitanium enolates of N-acetyl isopropyl thiazolidine-2-thione to aldehydes was investigated. The stereoselectivity of the aldol products was controlled by the number of equivalents of base added. The syn aldol product was obtained preferentially when 2 equiv of Lewis acid and 1 equiv of base were employed. The anti aldol product was obtained preferentially when 1 equiv of Lewis acid and 2 equiv of base were employed for unsaturated aldehydes. Unexpected results were found with hindered aldehydes when 2 equiv of base were employed.     

The first mu3-oxalato-bridged copper complex with tridentate Schiff base ligand N-ethyl-N'-salicylidene-1,2-diaminoethane: synthesis,structure, and magnetic properties

The first mu(3)-oxalato-bridged copper(II) complex, [[Cu(3)(L)(3)(mu(3)-C(2)O(4))][Cu(L)(H(2)O)](ClO(4))(2)] x 0.5(H(2)O) x 0.5(CH(3)OH), where HL = N-ethyl-N'-salicylidene-1,2-diaminoethane, has been synthesized and characterized by variable-temperature magnetic susceptibility measurement. The complex exhibits ferromagnetic coupling between the oxalato-bridged copper atoms and antiferromagnetic coupling between the oxygen-bridged copper atoms.     

分解水制氢的KNO3—I2循环之研究：Ⅲ.代替电解反应的一个子循环

本文提出了一个硫酸中间盐子循环用以代替分解水制氢的KNO_3-I_2混合循环中的电解反应,从而使原混合循环变为一个纯热化学循环。     

Influence of pH on electrophoretic behavior of phenothiazines and determination of pKa values by capillary zone electrophoresis

The influence of buffer pH on the electrophoretic behavior of 13 structurally related phenothiazines and determination of pK(a) values by capillary zone electrophoresis (CZE) were investigated. The results indicate that phenothiazines with a piperazine substituent behave quite differently from those with substituents having an aliphatic side chain or a piperidine moiety over the pH range studied. To separate these phenothiazines, it is preferable to select buffer pH in the range of 2.5-3.5. The pK(a) values of phenothiazines with three different types of substituents attached at the 10-position of the phenothiazine ring were determined. The determination of pK(a) values of phenothiazines allows us to rationalize the influence of buffer pH on the migration behavior of these compounds in CZE.     

碳酸氢铵制纯碱的研究

本文对“中间盐”复分解制碱法进行了研究。“中间盐”的加入不能使两个三盐共饱和点在干盐图上发生明显的移动,但能使三盐介稳平衡点的介稳期延长,从而使得用碳酸氢铵和食盐通过复分解制碱成为可能。     

Studies of the Factors Controlling Regioselective Nucleophilic Addition to Dienylium-Iron Complexes

Tricarbonyl(4-alkoxyl-1-alkylcyclohexadienylium)iron complexes (I) react with metal-cation enolate nucleophiles to give in most cases a mixture of products (II) and (III), resulting from attack at the C-1 and C-5 termini of the dienylium ring. Factors that control the regioselectivity of nucleophilic addition, including the steric and electronic effects of the 4-alkoxyl and 1-alkyl substituents, the degree of association between the enolate nucleophiles and their counterions, and the polarity of the solvents, were investigated.     

Adsorption recovery of thorium(IV) by Myrica rubra tannin and larch tannin immobilized onto collagen fibres

Novel adsorbents which can concentrate Th(IV) in aqueous solution were prepared by immobilizingMyrica rubra tannin and larch tannin onto collagen fibre matrices. The adsorption capacities of the immobilized tannins to Th(IV) are related to temperature and pH value of the adsorption process. For example, when the initial concentration of Th(IV) was 116.0 mg·l^-1 and the immobilized tannin was 100 mg, the adsorption capacities of immobilized Myrica rubra tannin and larch tannin were 55.98 mg Th(IV)·g^-1 and 13.19 mg Th(IV)·g^-1, respectively at 303 K, and 73.67 mg Th(IV)·g^-1 and 18.19 mg Th(IV)·g^-1 at 323 K. It was also found that the higher adsorption capacity was obtained at higher pH value. The adsorption equilibrium data of the immobilized tannins for Th(IV) can be well fitted by the Langmuir model and the mechanism of the adsorption was found to be a chemical adsorption. In general, the adsorption capacity of immobilized Myrica rubra tannin to Th(IV) is significantly higher than that of immobilized larch tannin, probably due to the fact that the B ring of Myrica rubra tannin has a pyrogallol structure which has higher reaction activity with metal ions. The breakthrough point of the adsorption column of immobilized Myrica rubra tannin was at 33 bed volumes for the experimental system. The mass transfer coefficient of adsorption column determined by Adams-Bohart equation was 1.61·10^-4 l·mg^-1.min^-1. The adsorption column can be easily regenerated by 0.1 mol·l^-1 HNO₃ solution, showing outstanding ability of concentrating Th(IV). This revised version was published online in July 2006 with corrections to the Cover Date.     

An efficient and general method for resolving cyclopropene carboxylic acids

A general method is described for the resolution of cycloprop-2-ene carboxylic acids via diastereomeric N-acyloxazolidines prepared from enantiomerically pure oxazolidinones. Although a number of oxazolidinones were shown to resolve cyclopropene carboxylic acids, the oxazolidinones of S-phenylalaninol, S-phenylglycine and (1S,2R)-cis-1-amino-2-indanol are optimal in terms of resolving power and cost effectiveness. Separations were performed using simple flash chromatography, and because there is typically a large difference in R_f values it is possible to separate gram quantities of pure diastereomers in a single chromatogram. The cycloprop-2-ene carboxylic acids that can be resolved include those that are substituted at the 1-position by H, Ph, α-naphthyl, CO₂Me, CH₂OMOM, and trans-styryl; alkene substituents include Me, n-alkyl, Ph and tethered alkynes. Remarkably, 2-methyl-3-propylcycloprop-2-ene carboxylic acid can also be resolved with ease. The relative configurations of four diastereomerically pure oxazolidines were determined by X-ray crystallography. Reduction of the N-acyloxazolidinones with LiBH₄ give enantiomerically pure derivatives of 3-hydroxymethylcyclopropene that react with either MeMgCl or vinylMgCl and catalytic CuI to give enantiomerically pure products of syn-addition.     

Synthesis and magnetic properties of trinuclear copper(II) complexes bridged by dimethylglyoximate groups

Summary New three Cu^II-Cu^II-Cu^II homotrinuclear complexes have been synthesized, namely [Cu(dmg)₂{CuL}₂](ClO₄)₂ [L = 5-nitro-1,10-phenanthroline (5-NO₂-phen), 4,4-dimethyl-2,2-bipyridiine (DMbpy), tetramethylenediamine (TMDA) and dimethylglyoximate ion (dmg)^2-]. The magnetic susceptibilities of complexes (1) (L = 5-NO₂-phen) and (2) (L = DMbpy) were measured in the 4.2–300 K range, giving the parameters,J = -335cm^-1 (1) andJ= -327.5cm^-1 (2). The results demonstrate a very strong antiferromagnetic exchange interaction between the adjacent copper(II) ions.