THE USE OF NAFION-H® AS AN EFFICIENT CATALYST FOR THE DEPROTECTION OF TRIMETHYLSILYL ETHERS TO THEIR CORRESPONDING ALCOHOLS UNDER MILD AND HETEROGENEOUS CONDITIONS

Trimethylsilyl ethers were converted to their corresponding alcohols in the presence Nafion-H® and wet SiO ₂ with good-to-excellent yields under mild and heterogeneous conditions.     

Compressed sensing in random access networks with applications to underwater monitoring

For networks that are deployed for long-term monitoring of environmental phenomena, it is of crucial importance to design an efficient data gathering scheme that prolongs the life-time of the network. To this end, we consider a Random Access Compressed Sensing (RACS) scheme that considerably reduces the power and bandwidth usage of a large network. Motivated by underwater applications, we propose a continuous-time RACS that eliminates the need for synchronization and scheduling which are difficult to achieve in a distributed acoustic network. We provide an analytical framework for system design that ensures fast recovery and power-efficiency. Through analysis and examples, we demonstrate that recovery of the field can be attained using only a fraction of the resources used by a conventional TDMA network, while employing a scheme which is simple to implement.     

Solvent‐Free Preparation of 1,1‐Diacetates from Aldehydes Mediated by Zirconium Hydrogen Sulfate at Room Temperature

A mild and efficient method has been developed for the preparation of acylals in good yields through a reaction of aldehydes with acetic anhydride using Zr(HSO₄)₄ as catalyst at room temperature and under solvent‐free conditions.     

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.