Sonochemistry and the Acoustic Bubble

Sonochemistry and the Acoustic Bubble provides an introduction to the way ultrasound acts on bubbles in a liquid to cause bubbles to collapse violently, leading to localized 'hot spots' in the liquid with temperatures of 5000° celcius and under pressures of several hundred atmospheres.

These extreme conditions produce events such as the emission of light, sonoluminescence, with a lifetime of less than a nanosecond, and free radicals that can initiate a host of varied chemical reactions (sonochemistry) in the liquid, all at room temperature.

The physics and chemistry behind the phenomena are simply, but comprehensively presented. In addition, potential industrial and medical applications of acoustic cavitation and its chemical effects are described and reviewed.

The book is suitable for graduate students working with ultrasound, and for potential chemists and chemical engineers wanting to understand the basics of how ultrasound acts in a liquid to cause chemical and physical effects.

• Experimental methods on acoustic cavitation and sonochemistry
• Helps users understand how to readily begin experiments in the field
• Provides an understanding of the physics behind the phenomenon
• Contains examples of (possible) industrial applications in chemical engineering and environmental technologies
• Presents the possibilities for adopting the action of acoustic cavitation with respect to industrial applications

• Language: English
• Publisher: Elsevier Science
• Release date: Apr 16, 2015
• ISBN: 9780128017265

Book preview

Sonochemistry and the Acoustic Bubble

Editors

Franz Grieser

School of Chemistry, University of Melbourne, Parkville, VIC, Australia

Pak-Kon Choi

Department of Physics, Meiji University, Kawasaki, Kanagawa, Japan

Naoya Enomoto

Department of Applied Chemistry, Kyushu University, Fukuoka, Japan

Hisashi Harada

Graduate School of Science and Engineering, Meisei University, Hino, Tokyo, Japan

Kenji Okitsu

Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan

Kyuichi Yasui

National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Aichi, Japan

Table of Contents

Cover image

Title page

Copyright

List of Contributors

Preface (English Edition)

Preface (From Japanese Edition)

Chapter 1. What Is Sonochemistry?

1.1. Sonochemistry

1.2. History of Sonochemistry

Chapter 2. Ultrasound Field and Bubbles

2.1. Fundamentals of a Sound Wave

2.2. Sound Propagation in a Bubbly Liquid

Chapter 3. Dynamics of Acoustic Bubbles

3.1. What is Acoustic Cavitation?

3.2. Bubble Dynamics

3.3. Growth or Dissolution of a Bubble

3.4. Interaction with the Surroundings

Chapter 4. Sonoluminescence

4.1. What is Sonoluminescence?

4.2. Single-Bubble Sonoluminescence

4.3. Multibubble Sonoluminescence

Chapter 5. Experimental Methods in Sonochemistry

5.1. Ultrasonic Generators and Sonochemical Reactors

5.2. Sound Field and Ultrasonic Power Measurements

5.3. Chemical Determination Method

5.4. Caution With Regard to Reproducibility of Experiments

Chapter 6. Sonochemical Engineering Processes

6.1. What Is a Sonochemical Engineering Process?

6.2. Solid-Liquid Processes

6.3. Liquid–Liquid Process: Emulsification

6.4. Gas–Liquid Process: Atomization

6.5. Reaction Processes: Polymerization and others

6.6. Development of Sonochemical Reactors: Scale-up and Optimization

Chapter 7. Application of Ultrasound to Organic Synthesis

7.1. Application of Ultrasound to Organic Synthesis

7.2. Sonochemistry in Homogeneous Systems

7.3. Solid–Liquid Phase Reactions

7.4. Liquid–Liquid Heterogeneous Reactions

7.5. Solid–Solid Heterogeneous Reactions

7.6. Synergic Effects with Multiple Forms of Applied Energy

Chapter 8. Application of Ultrasound in Inorganic Synthesis

8.1. Sonochemical Synthesis of Inorganic Materials

8.2. Chemical Synthesis by Acoustic Bubbles

8.3. Physicochemical Synthesis by Acoustic Bubbles

8.4. Film Processing

8.5. Other Sonoprocesses of Inorganic Materials

Chapter 9. Application of Ultrasound in Medicine and Biotechnology

9.1. Implications of Bioeffects of Ultrasound and Applications in Biotechnology

9.2. Application of Ultrasound in Medical Diagnosis

9.3. Therapeutic Applications of Ultrasound

9.4. Industrial Applications

Chapter 10. Application of Ultrasound in Environmental Technologies

10.1. Degradation of Hazardous Organic Chemicals

10.2. Synergy Between Ultrasound Treatment and other Environmental Protection Techniques

10.3. Improving the Environment and Energy Production

Chapter 11. Ultrasound in Heterogeneous Systems and Applications in Food Processing

11.1. Introduction

11.2. Formation of Emulsions

11.3. Dispersions

11.4. Ultrasonic Cleaning

11.5. Surface Modifications

11.6. Ultrasound in Food Modifications/Processing

Index

Copyright

Elsevier

Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands

The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK

225 Wyman Street, Waltham, MA 02451, USA

Copyright © 2015 Elsevier Inc. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

ISBN: 978-0-12-801530-8

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication Data

A catalog record for this book is available from the Library of Congress

For Information on all Elsevier publications visit our website at http://store.elsevier.com/

Transferred to Digital Printing in 2015

On the Cover: Photos of sonoluminescence (SL) and sonochemiluminescence (SCL) obtained in different aqueous systems under various conditions: Left to right: (1) SL from water using a horn-type transducer at 24 kHz, (2) SL from water in a cylindrical reactor using a plate-type transducer at 151kHz, (3) SL from an aqueous NaCl solution in a cylindrical reactor using a plate-type transducer at 138 kHz, (4) SCL from an aqueous luminol solution in a rectangular reactor. Ultrasonic fields are superposed by using dual transducers of 472 kHz (from the left side) and 422 kHz (from the bottom). (5) SL from an aqueous NaCl solution using a horn-type transducer at 24 kHz, and (6) SCL from an aqueous luminol solution using 422 kHz ultrasound propagating from the bottom upward to the liquid surface. Images (4) and (6) are reprinted with permission from K. Yasuda, T. Torii, K.Yasui, Y. Iida, T. Tuziuti, M. Nakamura, and Y. Asakura, Ultrason. Sonochem. 14 (2007) 699. Copyright 2007 Elsevier Publishing. (See Chapters 4 and 6 for details).

List of Contributors

Yoshiyuki Asakura,     Honda Electronics Co., Ltd., Toyohashi, Aichi, Japan

Pak-Kon Choi,     Department of Physics, Meiji University, Kawasaki, Kanagawa, Japan

Naoya Enomoto,     Department of Applied Chemistry, Kyushu University, Fukuoka, Japan

Franz Grieser,     School of Chemistry, University of Melbourne, Parkville, VIC, Australia

Hisashi Harada,     Graduate School of Science and Engineering, Meisei University, Hino, Tokyo, Japan

Takahide Kimura,     Department of Chemistry, Shiga University of Medical Science, Otsu, Shiga, Japan

Takashi Kondo,     Department of Radiological Sciences, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama

Shinobu Koda,     Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Aichi, Japan

Hiroyasu Nomura,     Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Aichi, Japan

Kenji Okitsu,     Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka, Japan

Shigemi Saito,     School of Marine Science and Technology, Tokai University, Shizuoka, Japan

Keiji Yasuda,     Department of Chemical Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Aichi, Japan

Kyuichi Yasui,     National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Aichi, Japan

Preface (English Edition)

This book has been written to provide a comprehensive but basic overview of how ultrasound can be used to initiate, enhance, and, in general, act on chemical reactions and systems. It aims to provide coverage of the field of sonochemistry at an introductory level more broadly than found in specialist monographs. As ultrasound reactors are widely used in both the laboratory and in commercial processes, the book provides a useful fundamental understanding on what lies behind the application in play.

The book is a carefully structured beginner's guide to acoustic cavitation phenomena, i.e., the formation and subsequent collapse of micro-bubbles in a liquid exposed to ultrasound. It sets out to consolidate what is known about how ultrasound acts on bubbles, and the chemical and physical consequences of its exposure to a broad range of systems. Ultrasound's chemical effects (sonochemistry) are caused by the radicals formed inside bubbles during their collapse (implosion) as a consequence of the extreme temperatures and pressures created within such bubbles. These free radicals are the basis of many chemical reactions, including electron transfer reactions, new stable compound formation, initiation of polymerization processes, as well as oxidation reactions leading to molecular degradation. The implosion of micro-bubbles also generates physical effects that come from fluid flow in the form of microstreaming, microjets of fluid, and flow from the shock waves produced.

The subject matter has been approached from an introductory basis but the reader would benefit most if they had a basic knowledge of physics and chemistry. Irrespective of this, many examples of ultrasound-driven effects and practical applications are described. Included are problems (and solutions) to help the interested reader comprehend/digest some of the material presented. Each chapter has a collection of references, both to specialist studies and to reviews, for further reading in those areas of particular interest.

The book is substantively a translation of the Japanese book entitled The Acoustic Bubble and Sonochemistry edited by Pak-Kon Choi, Naoya Enomoto, Hisashi Harada, and Kenji Okitsu, a monograph of the Acoustical Science Series, edited by the Acoustical Society of Japan and published by Corona Publishing Co., Ltd, Tokyo in 2012. In this English edition, Chapter 11 has been newly added, and some refinements made in the other chapters, such as the addition of Questions and Answers.

We believe there is a need for a textbook on the fundamental principles and experimental methods of the field, as well as an informative evaluation of its (potential) applications in chemical engineering, organic and inorganic synthesis, and medical, environmental, and food processing technologies. The book should be a useful resource and instructional platform to the field for a broad range of researchers, engineers, and as well as serve as a textbook for students. This has been the reason for adapting the original Japanese version of this book into English. We hope that many nonspecialists in the area will find the book an enlightening introduction to the constantly developing field of sonochemistry.

The Editors, November, 2014.

Preface (From Japanese Edition)

Two broad categories exist in the application of ultrasound. One application area lies in communications, and the other with high-power implementations. Ultrasound is used widely and popularly in the field of communications, where the velocity and transit time of ultrasonic waves are measured to determine the position and size of a substance or a void in a sound medium. Such signal applications of ultrasound reach pervasively into our daily lives, such as in medical diagnosis, nondestructive testing, sonar, and surface acoustic wave (SAW) filters in cellular phones. The other important application domain of ultrasound is with high-power (energetic) uses such as ultrasonic cleaning, cell disruption, emulsification, and humidification (water atomization). In these applications, high-intensity ultrasound brings about physical, chemical, biological effects, as well as their combined actions, with respect to chemical reactions and physical interactions among the various materials and substances exposed to ultrasound.

In the authoritative book on ultrasonics in Japan, Ultrasonics Handbook (Cho-onpa Gijutsu Binran) (Ed. Saneyoshi et al., Nikkan Kogyo Shinbun, 1978), it is stated that the high-power use of ultrasound is less advanced than the signal use because high-intensity sonicators are expensive. Even in the revised version of the handbook (Cho-onpa Binran, Maruzen 1999) published two decades later, the segment concerning the application of high-power ultrasound is still less than 10%, in spite of the great reduction in the cost of equipment over the intervening time. The main reason for this is not merely cost but also that the fundamentals behind high-power ultrasound are established to a lesser extent than those of communications ultrasound.

What are the essential difficulties and problems in the science and technology of high-power ultrasound? Most of the high-power applications deal with a liquid medium. In ultrasonic cleaning, for instance, we place items that we want to clean in an ultrasound-activated water bath. Then, tiny bubbles created by the ultrasonic irradiation wash out the contaminant material. Since the bubbles (or cavities) are formed by the action of sound waves, we call this phenomenon acoustic cavitation (or ultrasonic cavitation), and the created bubbles are called acoustic bubbles (or acoustic cavitation bubbles). Note that the origin and behavior of such bubbles are highly complicated; we have been gradually shedding light upon them over the last ∼10  years. In order to effectively use high-power ultrasound in practice, we require a detailed understanding of the behavior of acoustic bubbles and how to control them.

Another issue inherent with acoustic cavitation is that it requires diverse knowledge and various techniques in many fields of science and technology. That is, not only fundamental physics, such as acoustics, fluid mechanics, and thermodynamics, but also chemistry, biology, and medical science needs to be grasped as well, depending on the application field. As few fundamental and standard textbooks on high-power applications of ultrasound have been published so far, it may not be easy for specialists in ultrasonics to handle living cells, or it may be inconvenient for organochemical specialists to modify a commercially available sonicator suitable for their specific application.

In order to break down such walls among the various fields of application, we attempt to explain the basic points and the various applications of high-power ultrasound in the present textbook, assuming that the reader is a basic beginner in any field. (The title of the book Sonochemistry implies that not only chemical but also biological and medical applications are included.) The overall contents are as follows,

Chapter 1: Brief history of sonochemistry

Chapters 2–5: Basics of ultrasound, acoustic bubbles, and sonoluminescence

Chapters 6–10: Applications in various fields.

For further study in each field, each chapter provides the original references through which we encourage the readers to deepen their knowledge.

Finally, we thank the Acoustical Society of Japan (since 1936) and the Japan Society of Sonochemistry (since 1992, 20th Anniversary Publication) for their generous contributions to the publication of this book.

September 2012

The Editors, Japan

Chapter 1

What Is Sonochemistry?

Hiroyasu Nomura,  and Shinobu Koda     Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Nagoya, Aichi, Japan

Abstract

The authors present a general introduction to the scientific discipline of sonochemistry and the history of sonochemistry. The origin of sonochemistry is explained in terms of rarefaction and collapse of bubbles caused with ultrasound. Sonochemistry deals with physical phenomena and chemical reactions caused by acoustic cavitation, by which high pressure and temperature conditions, called the hot spot, are created. The history of sonochemistry, starting from the achievement reported by Wood and Loomis in 1927, is reviewed, and, in particular, the epochs of sonochemistry are presented.

Keywords

Bubble collapse; Cavitation; Historical developments; Hot spot; Plasma; Sonochemistry; Sonoluminescence

Chapter Outline

1.1 Sonochemistry 1

1.2 History of Sonochemistry 2

References 7

1.1. Sonochemistry

Ultrasound is defined as sound above the frequency of 20  kHz, which human beings cannot hear. In nature, dolphins and bats, for example, transmit and receive ultrasound below around 100  kHz. In 1917, Langevin, using the piezoelectric effect discovered by Curie, created a Langevin transducer made of a quartz oscillator sandwiched between two pieces of thick iron plates that enabled the generation of artificial ultrasound with high output power. The work of Langevin significantly stimulated research dealing with ultrasound, and this led to the extension of applications of ultrasound into a variety of areas, such as physical acoustics, sonar, fishfinder, and medical diagnostics, among others.

The first report on the physical and biological effects of ultrasound was published by Wood and Loomis in 1927 [1]. This article is widely considered to be the one that gave birth to the discipline of sonochemistry; the term sonochemistry first appeared in the title of an article by Weissler in 1953 [2]. Nowadays, sonochemistry is recognized as an academic term and is commonly used. Sonochemistry is a field in chemistry and physics that deals with the short-lived, localized field of high pressure and high temperature produced through ultrasonic cavitation. In 1964, El'piner published the first monograph on sonochemistry titled Ultrasound: Physical, Chemical, and Biological Effects, which was translated from Russian by Sinclar [3].

Ultrasonic cavitation may be produced by irradiating high-power ultrasound, with a frequency of 20  kHz to several MHz, into water and many other liquids. The phenomenon can be readily observed in an ultrasonic cleaner. Figure 1.1 displays the growth and implosion of small bubbles induced by ultrasound. The bubbles generated by ultrasound reach a critical size over a few acoustic cycles and, following the growth of these bubbles, they rapidly implode. There is almost no heat transfer between the inside of bubbles and the surrounding liquid during the rapid inertial collapse of the bubbles. Under the assumption that the compression process is adiabatic, the temperature and pressure within the core of bubbles undergoing contraction reach thousands of degrees Kelvin and several hundred atmospheres, respectively. This localized field with high temperature and high pressure is called the hot spot, which is the source of the chemical and physical effects induced by acoustic cavitation. This localized high-temperature condition subsequently delivers heat rapidly to the surrounding liquid, which is at ambient temperature, and consequently creates a rapidly cooling temperature gradient in the vicinity of bubbles at a rate of the order of 10⁹  K/s. The pressure at some point distant from the bubbles is made up of the sum of hydrostatic pressure and acoustic pressure and ranges from 1  atm to several atmospheres. Therefore, under conditions where large differences exist between the high pressures inside and outside a bubble, the relief of such a situation generates shock waves.

Figure 1.1  Scheme of bubble growth and collapse on ultrasound.

In essence, sonochemistry is a field of science that deals with phenomena and reactions induced by shock waves generated by rapidly released localized pressure and by radicals formed in and/or around bubbles from the thermal decomposition of molecules in the system, both of which originate from ultrasonic cavitation. In the chemical industry, processes using ultrasound are referred to as sonochemical processes and will be described in detail in Chapter 6.

1.2. History of Sonochemistry

The article of Wood and Loomis has become a landmark report in the field and must not be forgotten in detailing the history of sonochemistry. Wood and Loomis investigated the effects of ultrasound on various phenomena, using ultrasound of 100–700  kHz frequency and a 2-kW oscillator based on a quartz plate (7–14  mm thickness) [1]. The sonochemistry described in their report included emulsion preparation, atomization, particle aggregation, the acceleration of chemical reactions, crystal segregation and growth, the dispersion of colloidal soil, effects on bactericidal activity, and other actions. Although they presented a preliminary survey of the effects of ultrasound, the results had a strong influence on the subsequent development of sonochemistry.

In 1929, Schmitt et al. published a report on the chemical oxidation effects of ultrasound [4]. Further, in 1935, Frenzel and Schultes irradiated a photographic plate that was set in water with acoustic waves and found that the plate had been exposed to light. The phenomenon opened the way to sonoluminescence and sonochemiluminescence research, conducted even to the present day [5]. In 1935, as the first study of the effects of ultrasound on electrochemistry, Claus and Hall reported that microparticles of silver and mercury synthesized in an electrode reaction under ultrasonic irradiation are fine and have a high dispersibility [6]. In 1938, Porter and Young reported that ultrasonic waves induce the rearrangement of molecules and accelerate phenyl isocyanate generation from benzamide (C6H5CON3) [7]. Although a detailed investigation was not reported, it can still be said that this was the first research undertaken on the application of ultrasound in organic chemistry.

In 1932, Oyama (Electric Engineering, Tohoku Imperial University, Japan) repeated the experiments of Wood and Loomis with a high-power ultrasound generator, and the work marked the beginning of basic research on applications of high-power ultrasound in Japan. In 1933, Oyama presented On the Intense Supersonics and its Applications, in which the author reported not only on the measurements of acoustic pressure and the coefficient of sound absorption but also on the acceleration of the precipitation rate of iron powder in aqueous copper sulfate solutions [8]. It was the first report to deal with the acceleration of chemical changes by ultrasound. Oyama also reported on ultrasound-driven emulsification, colloidal gold aggregation and dispersion, protein aggregation, and change in the solution pH.

In 1993, Moriguchi presented a series of reports titled Influence of Ultrasound on Chemical Phenomenon and found that ultrasound accelerated gas-evolving reactions in a hetero phase system consisting of zinc and hydrochloric acid or sulfuric acid [9]. Sata studied ultrasonic degradation of macromolecules and the effects of ultrasound on colloidal dispersions [10]. In 1936, Kusano investigated the ultrasound induced decomposition of KI and H2O2 in aqueous solutions [11]. Studies on chemical reactions by ultrasonic irradiation have steadily progressed over the years since the pioneering experiments by Wood and Loomis.

In the late 1930s, the now famous studies on polymer degradation were reported from the laboratories of Schmid and Weissler. Schmid et al. reported the decrease of molecular weight and viscosity of polystyrene solutions with increasing sonication time [12]. Weissler found not only a decrease of viscosity with sonication time but also an abrupt decrease of viscosity above a certain ultrasonic intensity in toluene solutions containing polystyrene and in aqueous solutions of hydroxyethyl cellulose [13]. This suggested a certain level of ultrasonic intensity is required in order to generate cavitation, which is the cavitation threshold.

Many academic research fields remained stagnant during the period of World War II, from 1939 to 1945. There are few reports on sonochemistry from those days. A book (in Japanese, Otokagaku to Otokousitugaku) [14] was published after the war in 1948 and was a very impressive contribution from the authors. The title of the Japanese book translates to Sonochemistry and Its Application to Colloid Chemistry. In the 1940s, the group of Kasahara conducted medical applications of ultrasound and investigated the microbicidal mechanisms of pathogens under ultrasound. Bactericidal effects were divided into three categories: chemical effects (oxidation), mechanical effects, and combined effects. Effects of Ultrasound on Bacteria–Virus was summarized in the Handbook of Ultrasonic Technology (in Japanese, Cho-onnpa Gijutsu Binnran) [15].

In 1950, Weissler reported the chemical effects of ultrasound on the oxidation of KI in aqueous carbon tetrachloride solutions [16]. In 1950, Ostroski and Stambauch obtained a high reaction rate and enhanced efficiency for the emulsion polymerization of styrene under sonication with frequencies of 15 and 500  kHz [17]. In the same year, Renaud succeeded in preparing Grignard reagents in ether solution by using ultrasound [18]. However, back in those days not enough attention was paid to these advances, and consequently the development of organic sonochemistry was delayed by about 20  years. At that time, Miyagawa first pointed out the utilization of ultrasound on synthetic organic chemistry in Japan [19]. And in 1959, in the review titled Ultrasound and Organic Compounds [20], Tsukida introduced the report by Zechmeistra and Magoon [21] that was published in celebrating the 70th birthday of Prof. Arthur Stoll.

A report by Noltingk and Neppiras in 1951 had a great impact on the understanding of the dynamics of acoustic bubbles [22]. Assuming that the compression of the contents for a bubble on collapse is adiabatic, they predicted the temperature inside a bubble attains a value of around 10,000  K. The localized volume at the extreme temperatures in the core of a bubble, initiated by ultrasound, is called the hot spot, and the ensuing chemistry from the chemical effects of ultrasound was termed hot spot chemistry by Fitzgerald et al. [23]. As mentioned earlier, the term sonochemistry first appeared in 1953, and it has been widely used ever since 1970.

A number of publications in the 1960s considered the frequency dependence of the cavitation threshold. Iernetti summarized earlier work and indicated that the cavitation threshold remained almost constant until about 100  kHz, and above that frequency increases with frequency [24]. From the 1960s to the late 1970s, to the authors' knowledge, it is not known exactly why so little research on the chemical effects of ultrasound was conducted. In 1961, Negishi confirmed the appearance of subharmonics in acoustic pressure by the observation of cavitation noise spectra [25], although the subharmonics f0/2 and f0/3, where f0 refers to the fundamental frequency, were already observed by Esche [26] and Bohn [27], respectively. Negishi succeeded in visualizing a considerable amount of significant acoustic-generated phenomena, including the observation that sonoluminescence from water occurs during the final stage of bubble collapse. In 1962, Yoshioka and Omura attached a magnetostrictive oscillator to the bottom of a 36-cm-diameter spherical flask that was driven with the second harmonic in moving radius mode that produced a spherically symmetric acoustic field with a 16.0- to 16.2-kHz resonant frequency. They then observed the image of bubbles near the center of the flask and the frequency spectrum on a Braun tube. The two images were simultaneously recorded on 16-mm film [28]. They were frequently able to observe bubbles that emitted light. The diameters of those bubbles were from 1  mm to a few millimeters in size, and the bubbles appeared to be static at the center of the flask. The bubbles that emitted light were not stable, but clearly single bubble sonoluminescence (SBSL) could be observed. It was considered to be the forefront of research in the field in the world at that time.

From a standpoint somewhat different from sonochemistry, acoustic cavitation attracted the attention of many researchers. After the investigations by Noltingk and Neppiras, active research world-wide was carried out, and in 1972 a review article by Nomoto summarized this work [29]. The article mainly referred to acoustic physics, and sonoluminescence was also discussed.

Nearly 30  years after Renaud reported on the preparation method of organometallic compounds by ultrasound [18], Luche and Damino showed that the Barbier reaction, of an alkyl halide and a carbonyl group with a lithium organometallic reagent, effectively progressed under ultrasonic irradiation (60  W, 50  kHz) [30]. Referring to the results of Luche and Damino, Kitazume and Ishikawa synthesized trifluorotrimethyl carboninols in high yield by trifluoromethylation of carbonyl compounds with trifluoromethylzinc iodide under sonication (35-W, 32-kHz, 30-min irradiation) [31]. This research can be seen as pioneering work in the study of sonochemistry for the purposes of organic synthesis. Ando et al. found for the case of solid–liquid two-phase reactions that under stirring conditions, acetylation between benzyl bromide and toluene in an anhydrous solvent proceeds in the form of a Friedel–Crafts reaction, whereas under ultrasonic irradiation, the aromatic electrophilic substitution of benzyl bromide and cyanides in aromatic solvents changes to a nucleophilic one. In other words, the reaction pathway switches under ultrasonic irradiation [32]. They concluded that radical reactions effectively proceed under ultrasonic irradiation when ionic reactions coexist with radical ones in a conventional reaction system. This change in reaction path due to ultrasonic irradiation of the reaction system was termed sonochemical switching [33]. In 1984, The Chemical Society of Japan published a series titled Special Articles on the Progress of Generating Active Species in Chemistry. Kitazume and Ishikawa [34], Ando et al. [33], Makino et al. [35], and Suga et al. [36] contributed to the series. Of special note, in 1982, Makino et al. were the first to identify ·H and OH radicals in the sonolysis of aqueous solutions by electron spin resonance measurements [37].

In 1983, Suslick and Schubert synthesized a