Large scale Biginelli reaction via water-based biphasic media: a green chemistry strategy

An important stage in process development is kilo scale preparation of the target compound. For this reason, a procedure involving water-based biphasic reaction media has been developed for conducting some exothermic reactions on a large scale. This protocol is illustrated by the energy-efficient and rapid preparation of dihydropyrimidinones by a solvent-free, green chemistry procedure applied to the Biginelli reaction using p-toluenesulfonic acid as catalyst.     

Non-linear bifurcation analysis of non-gradient systems

The post-divergence behaviour of non-gradient systems is studied through a perturbation approach, attention being restricted to equilibrium paths in the neighbourhood of a critical point. Simple and coincident critical points are treated separately. Various characteristic phenomena are explored in general terms by identifying certain distinct properties of the Jacobian matrix in a state-space formulation. It is demonstrated that the well-known asymmetric and symmetric points of bifurcation can also arise in non-gradient systems and the conditions giving rise to each of these phenomena are discussed. An illustrative example is presented.     

The effect of symmetry on the imperfection-sensitivity of coincident critical points

Summary The imperfection sensitivity of an N-degree-of-freedom symmetric system exhibiting a two-fold coincident critical point is studied. Symmetry in one as well as in both the critical coordinates is considered. The concepts of general and special critical points, associated with smooth and improper equilibrium surfaces respectively, are used to explore all the relevant stability properties of the system without resorting to formal stability considerations. An illustrative example concerning a column on elastic foundation is analyzed.

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Übersicht Es wird die Parameter-Empfindlichkeit eines Systems von N Freiheitsgraden untersucht, das zwei zusammenfallende kritische Punkte besitzt. Dabei wird sowohl in einer als auch in beiden kritischen Koordinaten Symmetrie vorausgesetzt. Die Begriffe der allgemeinen und der speziellen kritischen Punkte, abgeleitet von den Eigenschaften der Gleichgewichtsoberflächen, werden dazu verwendet, alle wichtigen Stabilitätseigenschaften zu untersuchen, ohne daß die üblichen Stabilitätsbetrachtungen angestellt werden müssen. Als Beispiel wird eine Säule auf nachgiebiger Unterlage untersucht.

     

On the imperfection sensitivity of compound branching

Summary The effect of small imperfections on the stability behaviour of an N-degree-of-freedom system exhibiting 2-fold coincident critical points is investigated. The analysis is based on equilibrium surfaces and the multiple-parameter perturbation technique. The relationship between certain forms of the equilibrium surface and the Catastrophe theory is discussed. An illustrative structural model is analyzed.

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Übersicht Es wird der Einfluß kleiner Abweichungen auf die Stabilität von Systemen mit N Freiheitsgraden mit einem zweifachen kritischen Punkt untersucht. Die Analyse beruht auf der Betrachtung von Gleichgewichtsflächen und auf der Störungsrechnung für mehrere Parameter. Die Beziehungen zwischen den auftretenden Gleichgewichtsflächen und der Katastrophentheorie werden erörtert. An einem Strukturmodell wird die Vorgehensweise erläutert.

     

Water-based biphasic media for exothermic reactions: green chemistry strategy for the large scale preparation of clofibric acid and analogues

A water-based biphasic reaction process has been developed for conducting exothermic reactions without organic solvents. This procedure is rapid, simple, and suitable for small scale synthesis as well as larger (multi-molar) scale reactions. The preparation of several hundred grams of clofibric acid and analogues by this eco-friendly and energy-efficient procedure is described. Smaller amounts of these compounds were prepared by the friction-activated ‘Grindstone Chemistry’ method described previously.