A Non-Parametric Approach to Model Evaluation

All existing tests and criteria for model evaluation are based on the sum of squared residuals. These measures do not evaluate the performance of a model in predicting turning points in the variable of interest. Here, three tests are proposed to evaluate models on the basis of their ability to predict turning points and to give an unbiased prediction of the relative order of magnitude of changes. Five models are evaluated using the proposed tests. Results indicate that the tests expose facets of models that R² and sum of squared residuals are unable to highlight. Hence, the tests are suggested to complement existing model evaluation techniques.     

An NMR study of the decomposition of a 2,2-disubstituted thiazolidine. Kinetic evidence for a schiff base intermediate

The pH-rate profile for the decomposition of 2,2,5,5-tetramethyl-4-thiazolidinecarboxylic acid is used to identify the presence of a Schiff base intermediate. Activation parameters for the reaction are reported at various pH's and in particular the negative values of entropy support the presence of a carbinolamine in the rate-determining step.     

Catastrophic phase inversion of abnormal emulsions in the vicinity of the locus of transitional inversion

This paper deals with the phase behaviour of model abnormal emulsions of cyclohexane/water/polyethoxylated surfactant in the vicinity of the locus of transitional inversion (optimum formulation). Abnormal emulsions are formed under dynamic conditions if the phase containing the soluble surfactant becomes the dispersed phase. Phase maps have been suggested in the literature that define the boundaries of emulsion morphologies. On these maps, only one transformation can be observed for any formulation scan. Furthermore, the morphology of emulsions in the vicinity of the locus of transitional inversion is rather vague. One might assume that by changing the HLB of the surfactant used in an abnormal emulsion to favour the continuous phase, that abnormal emulsion will gradually transform to a normal emulsion of the same type. A new experimental procedure was adopted in which emulsification was started with abnormal emulsions. To transform the abnormal emulsions to the normal emulsion of the same type, they were exposed to variations in temperature, the surfactant HLB, or water–oil phase ratio. As the optimum formulation was approached, the abnormal emulsions became so unstable that could not exist anymore in the un-favoured morphology and inverted to the normal emulsion of the opposite type. Further variation in the formulation along the route led to a transitional inversion to the normal emulsion of the original type. The result indicates an important finding that the transformation of abnormal emulsions to normal ones of the same type occurred via two successive inversions of catastrophic and transitional nature. It appears that the boundaries of catastrophic inversion correspond to the emulsions with the finest drop size. A modification to the phase behaviour maps, to include the locus of catastrophic phase inversion in the vicinity of the transitional inversion, was thus suggested.     

Wells-Dawson Type Heteropolyacid Catalyzed Synthesis of Quinoxaline Derivatives at Room Temperature

Summary. Wells-Dawson heteropolyacid (H₆P₂W₁₈O₆₂ · 24H₂O) was used as an effective catalyst for the synthesis of biologically active quinoxaline derivatives from the condensation of o-phenylenediamines with 1,2-dicarbonyl compounds at room temperature in excellent yields.     

A green protocol for chemoselective O-acylation in the presence of zinc oxide as a heterogeneous, reusable and eco-friendly catalyst

The solvent-free acylation of alcohols and phenols with acyl chlorides using ZnO as a catalyst is described. The remarkable selectivity under mild and neutral conditions, and recyclability of the catalyst, are advantages.     

Synthesis of trans-(3S,4S)-dibenzyloxycyclopentanone

The 1-cyano-1-thiophenylcyclopentone derivative $\text{1}$, obtained from (R,R)-(+)-tartaric acid, has been converted into a number of derivatives including the important $\text{trans}$-(3S,4S)-dibenzyloxycyclopentanone $\text{2}$ in 45% overall yield.     

高效和可重复使用的Zr-MCM-41催化剂催化Strecker反应合成氨基腈类化合物(英文)

The synthesis and characterization of Zr-MCM-41 nanoreactors and their catalytic activity in the synthesis of new amino nitrile derivatives by the Strecker reaction in high yields and in short reaction times is reported.     

Catalytic oxidation of urazoles and bis-urazoles to their corresponding triazolinediones using aluminium nitrate and a catalytic amount of silica sulfuric acid

Abstract  

A simple and efficient catalytic oxidation of urazoles and a bis-urazole to the corresponding triazolinediones by treatment with Al(NO₃)₃.9H₂O in the presence of a catalytic amount of silica sulfuric acid is described. A good range of urazole derivatives was selectively oxidized in CH₂Cl₂ at room temperature in good to excellent yields.     

H2SO4/Silicagel: Highly Efficient Catalyst for the Synthesis of α-Aminonitriles Using Trimethysilyl Cyanide

Summary. The multicomponent Strecker reaction using trimethylsilyl cyanide was performed at room temperature and α-aminonitriles were prepared in excellent yields in the presence of a catalytic amount of H₂SO₄ adsorbed on silica gel.     

Interaction of dimethyltin(IV) dichloride with 5′‐IMP and 5′‐UMP

The formation constants of the species formed in the systems H⁺ + dimethyltin(IV) + 5′‐IMP and 5′‐UMP, H⁺ + 5′‐IMP and H⁺ + 5′‐UMP have been determined in aqueous solution in the pH range 1.5–9.5 at constant temperature (25 °C) and constant ionic strength (0.1 mol dm⁻³ NaClO₄), using spectrophotometric and potentiometric techniques. ¹H and ³¹P NMR investigations in aqueous solution confirmed the species formation. The precipitated complexes of IMP and UMP by Me₂Sn(IV)²⁺ at low pH values were characterized by elemental analysis and FTIR spectroscopy methods, the bonding sites of the ligands were determined and ruled out purine and pyrimidine moieties (N‐7 and N‐1 in IMP and N‐3 in UMP, respectively) while a bidentated coordination of the phosphate group is concluded in both cases. Finally, the experiments revealed the existence of complexes with trigonal bipyramidal structures that is in agreement with similar systems resulted previously. Copyright © 2008 John Wiley & Sons, Ltd.