Solvent-free 1,6-conjugate arylation of para-quinone methides: A greener approach to unsymmetrical triarylmethanes

A highly efficient arylation of para-quinone methides (p-QMs) with N,N-dimethylaniline under solvent free condition has been developed, which proceeded via a para-toluenesulfonic acid (TsOH)-promoted 1,6-conjugated addition pathway. This methodology provided a green and sustainable methodology to construct various novel unsymmetrical triarylmethanes (TAMs) with the advantages of good functional group tolerance, scalability, and regioselectivity.     

Halogenation of ketones with N-halosuccinimides under solvent-free reaction conditions

Several aryl substituted ketones, cyclic ketones, 1,3-diketones and a β-ketoamide were halogenated with N-halosuccinimides under solvent-free reaction conditions (SFRC) at various temperatures (20-80 °C), whereas less enolized ketones required the presence of an acid catalyst (p-toluenesulfonic acid, PTSA). Bromination of substituted acetophenones obeys first order kinetics v=k_Br[ketone] and the following correlation with the keto-enol equilibrium constant: log k_Br=0.3pK_E+C₁, less enolized substrates being more reactive; the moderate positive charge developed in the rate determining step was confirmed by the Hammett correlation (ρ=−0.5). On the other hand, in cyclic ketones an opposite relation was observed: log k_Br=−0.6pK_E+C₂, indicating higher reactivity of substrates with higher enolization constant (K_E). The important role of the nature of the solvent (MeCN, MeOH) in preorganization of the ketone-NBS-PTSA mixture prior to SFRC bromination was found.     

Iron-catalyzed three-component coupling of aldehyde, alkyne, and amine under neat conditions in air

Various iron-salts (and complexes) and especially iron(III) chloride catalyzed the three-component coupling of aldehyde, alkyne, and amine to generate propargylic amines with high efficiency under neat conditions in air. The iron-catalyzed reaction is particularly effective for reactions involving aliphatic aldehydes. The reaction is not sensitive to and occurs smoothly in water and in air. No additional co-catalyst or activator is required.     

Synthesis of sulfides under solvent- and catalyst-free conditions

Abstract  A simple, highly efficient, and green protocol has been developed for preparation of sulfides from alkyl or aryl thiols and benzyl-, allyl-, t-butyl, and adamantyl halides under solvent- and catalyst-free conditions. Graphical abstract        

One-pot reductive amination of aldehydes and ketones with α-picoline-borane in methanol, in water, and in neat conditions

A one-pot reductive amination of aldehydes and ketones with amines using α-picoline-borane as a reducing agent is described. The reaction has been carried out in MeOH, in H₂O, and in neat conditions in the presence of small amounts of AcOH. This is a highly efficient and mild procedure that is applicable for a wide variety of substrates. In particular, this is the first successful demonstration that this type of reaction can be carried out in water and in neat conditions.     

Initial Steps in Thermal Degradation of Fractions of PVC with Different Tacticities

PVC samples were prepared in bulk by using AIBN and UV radiation as the initiator system. The polymerization temperatures were 40, 0, -25, and -50oC. The samples were fractionated by means of successive extractions with dioxane, tetrahydro-furan, and cyclohexanone, and two fractions of each sample were characterized in order to study their thermal degradation. This was carried out by conductivity measurements with the use of a differential conductimetry cell for degradations up to 0.1% and a single cell for degradations up to 0.4%. From the UV-visible spectra of equally degraded samples it is concluded that the higher the tacticity of PVC, the higher the proportion of long polyene sequences is; this behavior is independent of the conversion. The degraded samples were ozonized in order to measure the number of scissions per chain. This number was found to be low for syndiotactic samples and high for atactic samples, which is accounted for by the increased clustering of double bonds to form long polyene sequences in the more syndiotactic polymers. Previous results suggesting increased ease of propagation along syndiotactic sequences are therefore confirmed more quantitatively.     

On characterizations of atomistic lattices

In the present paper we characterize atomistic lattices. These characterizations are given in terms of concepts related to pure elements (cf. [4], [6]) and neat elements (cf. [3]).     

Termination Rates in Free Radical Copolymerizations

The rates of free radical copolymerizations at given rates of initiation can be analyzed ideally in terms of monomer feed concentrations and reactivity ratios, propagation rate constants for homopolymerizations of the particular monomers, and an overall rate constant for termination during copolymerization. This model, which is due to Atherton and North, can account for the effects of initiator concentration and viscosity of the polymerization medium on copolymerization rates.

This article reports an empirical formulation for the overall termination rate constant in terms of monomer concentrations and reactivity ratios and a cross-termination factor. The new model accounts for experimental data in the styrene-methyl methacrylate system in which polarity differences between unlike radicals may result in enhanced termination rates. It also predicts observed copolymerization rates of methyl methacrylate-vinyl acetate and styrene-α-methylstyrene mixtures in which polarity effects are absent. The cross-termination factor may be approximated from reactivity ratio data for predictive purposes.     

《光谱实验室》投稿须知(2002)

《光谱实验室》是中国科学院主管，中国科学院化工冶金研究所等单位联合主办，科学出版社出版的中国科学核心期刊之一，是自主经营，自负盈亏的刊物，编委要有献身本专业科技出版事业的精神，来稿必须符合国家关于出版物的政治和技术标准，出版正常周期为2－6个月，“保质，高效”是本刊的主要特色。