Effect of ultrasound on heterogeneous systems

Examples of sonochemical reactions occuring under heterogeneous conditions are discussed with respect to their mechanism. The activation of a metal surface involves complex phenomena, in which parameters of importance seem to be the hardness and the adhesion of the passivating layer. Some considerations are given on the probable link between sonochemistry and tribochemistry.     

Activation de reactions par les polyoxydes d′ethylene III : Reductions par l′eutectique sodium-potassium

Polyethylene oxides are efficient phase transfer catalysts which promote the reduction of CC, CC bonds as well as aromatic substrates by the Na-k eutectic. Yields and general conditions of the reaction give it a generally useful synthetic value.     

Sonochemically prepared organozinc reagents1. conjugate additions to α-β unsaturated aldehydes

Organozinc reagents, prepared by sonication from organic halides, lithium and zinc bromide, add conjugatively to α-enals in the presence of nickel acetylacetonate. Satisfactory yields are obtained from arylbromides.     

Polyethylene Oxides as Organic Reactions Activators II.1 An Easy Generation of Dihalocarbenes

Polyethylene oxides are shown to promote an efficient dihalocarbene formation from bromo — and chloroform and solid potassium hydroxide — Adducts with olefins are obtained in High yields.     

An Improvement in the Wittig-Horner Synthesis of Allenyl Sulfones and Allenes Carboxanilides Under Sonochemical Conditions

A significant improvement in the Wittig-Horner synthesis of allenyl sulfones and allene carboxanilides is described under ultrasonic irradiation in a homogeneous phase.     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Zeros of the Whittaker function associated to Coulomb waves

The zeros in the complex z plane of the Whittaker function W_c/z,µ(z),closely related to spherical waves in the quantum-mechanicalCoulomb problem, are investigated for varying real values ofthe parameters c and µ     

A theoretical study of the barbier reaction

Semiempirical MO calculations are shown to provide a more detailed picture of the radical ion mechanism of the Barbier reaction in the general case. Calculated electron affinities give a clue for its extension to other cases.