Sonochemistry - The Use of Ultrasonic Waves in Synthetic Organic Chemistry

Abstract

The recent evolution of sonochemistry has led to important improvement of various synthetic processes. The generally accepted theoretical interpretation is based on the phenomenon of cavitation, i.e. the creation of bubbles in a liquid medium, which collapse with the liberation of a considerable energy. Homogeneous reaction mixtures can in some instances give rise to spectacular effect, but the domain of choice of sonochemistry is that of heterogeneous reactions, especially organometallic processes. 1. Introduction 1.1. A Qualitative Approach to the Theoretical Problems of Sonochemistry 2. Homogeneous Sonochemistry 2.1. An Introduction to Sonicated Aqueous Solutions 2.2. Nonaqueous Solutions in Sonochemistry 2.3. Monomolecular Reactions 2.3.1. Organic Compounds 2.3.2. Organometallic Complexes 2.4. Bimolecular Reactions 2.4.1. Oxidations 2.4.2. Hydrolyses and Solvolyses 2.4.3. Additions and Related Reactions 3. Heterogeneous Liquid-Liquid Reactions 3.1. Reactions in the Absence of Added Reagents 3.2. Bimolecular Reactions 3.2.1. Hydrolysis 3.2.2. Substitutions 3.2.3. Additions 4. Non-Organometallic Solid-Liquid Reactions 4.1. Reactions Proceeding by Dispersion of a Friable Solid 4.1.1. Inorganic Solids 4.1.1.1. Hydroxides, Alkoxides and Hydrides 4.1.1.2. Miscellaneous Compounds 4.1.1.3. Transition Metal Complexes 4.1.2. Solid Organic Materials 4.1.2.1. Reactions of Carbohydrates 4.1.2.2. Synthesis of Organoboranes 4.2. Reactions Proceeding on the Surface of Hard Solids 4.2.1. Reactions Proceeding with Consumption of the Solid 4.2.1.1. Oxidations and Reductions 4.2.1.2. Formation of New Bonds 4.2.2. Catalytic Reactions on Solid Surfaces 4.2.2.1 Reactions on Metallic Oxides 4.2.2.2. Sonochemical Hydrogenations on Metallic Catalysts 4.2.2.3. A Novel Sonochemical Hydrogenation Procedure 5. Heterogeneous Reactions Involving Metals 5.1. The Effect of Sonic Waves on Metallic Surfaces 5.1.1. Alkali Metals 5.1.2. Other Metals 5.2. The Effect of Sonic Waves on Single Electron Transfer Processes 5.2.1. Preparation of Organometallics 5.2.1.1. Formation of C-Li or C-Mg Bonds from the Corresponding Halides 5.2.1.2. Preparation of Organolithiurn Compounds by Hydrogen-Metal Exchange 5.2.1.3. Formation of other Organometallics from Halides 5.2.1.4. Wurtz-type Coupling of Organometallics 5.2.1.5. Formation of Heteroatom-Metal Bonds 5.2 2. Single Electron Transfer (SET) in Dissolving Metal Reductions 5.2.2.1. Reduction of Carbonyl Groups 5.2.2.2. Reduction of Aromatic Rings 5.3. Simultaneous Generation and Reaction of Organometallic Species Sonochemical Generalization of the Barbier Procedure 5.3.1. The Barbier Reaction of Carbonyl Compounds 5.3.1.1. The Traditional Barbier Reaction 5.3.1.2. The Barbier Procedure Applied to Amides and Isocyanates 5.3.2. Zinc Metal in the Generalized Barbier Procedure 5.3.2.1. Additions to Carbonyl Groups 5.3.2.2. The Reformatsky Reaction 5.3.2.3. Sonochemical Methylenation of Alkenes and Carbonyl Compounds 5.3.2.4. Reactions Related to the Barbier Procedure with Zinc and Mercury. Cycloadditions 5.3.3.Generalization of the Barbier Reaction to Unusual Media 5.3.3.1. Allylation of Carbonyl Compounds 5.3.3.2. Conjugate Additions to α-Unsaturated Carbonyl Compounds 6. Technical Notes 7. Conclusion