MIcrowave Chemistry

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Advances in Microwave
Chemistry


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New Directions in Organic and
­Biological Chemistry
Series Editor
Philip Page 

Dianion Chemistry in Organic Synthesis
Charles M. Thompson
Mannich Bases 
Chemistry and Uses
Maurilio Tramontini and Luigi Angiolini
The Anomeric Effect  
Eusebio Juaristi and Gabriel Cuevas 
C-Glycoside Synthesis 
Maarten Postema
Chirality and the Biological Activity of Drugs 
Roger J. Crossley
Organozinc Reagents in Organic Synthesis 
Ender Erdik
Chemical Approaches to the Synthesis of Peptides and Proteins 
Paul Lloyd-Williams, Fernando Albericio, and Ernest Giralt
Chiral Sulfur Reagents 
M. Mikolajczyk, J. Drabowicz, and P. Kielbasin´ ski

Capillary Electrophoresis 
Theory and Practice
Patrick Camilleri
Concerted Organic and Bio-organic Mechanisms 
Andrew Williams
Modern NMR Techniques for Synthetic Chemistry 
Julie Fisher
Carbocation Chemistry
Applications in Organic Synthesis
Jie Jack Li
Advances in Microwave Chemistry 
Bimal Krishna Banik and Debasish Bandyopadhyay
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Advances in Microwave
Chemistry

Edited by
Bimal Krishna Banik
Debasish Bandyopadhyay


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CRC Press
Taylor & Francis Group

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Contents
Preface......................................................................................................................vii
About the Editors.......................................................................................................ix
List of Contributor.....................................................................................................xi
Chapter 1 Microwave Radiation in Biocatalysis.................................................... 1
David E. Q. Jimenez, Lucas Lima Zanin, Irlon M. Ferreira,
Yara J. K. Araújo, and André L. M. Porto
Chapter 2 Tracking Microwave-Assisted Sample Preparation Through
the Last Years...................................................................................... 27
Mónica B. Alvarez, Anabela Lorenzetti,
Carolina C. Acebal, Adriana G. Lista,
and Claudia E. Domini
Chapter 3 An Insight into Green Microwave-Assisted Techniques:
Degradation and Microextraction..................................................... 119
Natalia A. Gomez, Maite V. Aguinaga, Natalia LLamas,
Mariano Garrido, Carolina Acebal, and Claudia Domini
Chapter 4 Functional Rare Earth-Based Micro/Nanomaterials: Fast
Microwave Preparation and Their Properties................................... 179
Lei Wang and Shengliang Zhong
Chapter 5 Microwave-Assisted Synthesis and Functionalization of
Six-Membered Oxygen Heterocycles................................................ 217
Neha Batra, Rahul Panwar, Ramendra Pratap,
and Mahendra Nath
Chapter 6 Selectivities in the Microwave-Assisted Organic Reactions............. 257
Jiaxi Xu
Chapter 7 Microwave-Assisted Hirao and Kabachnik–Fields Phosphorus–
Carbon Bond Forming Reactions: A Recent Update........................ 293
Goutam Brahmachari

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Contents

Chapter 8 Microwave Synthesis of Materials for Thin-Film Photovoltaic
Absorber Layer Application.............................................................. 327
Raghunandan Seelaboyina, Manoj Kumar,
and Kulvir Singh
Chapter 9 Microwave-Assisted Transition Metal-Catalyzed Synthesis of
Pharmaceutically Important Heterocycles........................................ 343
Dipti Shukla, Priyank Purohit, and Asit K. Chakraborti
Chapter 10 Microwaves in Lactam Chemistry.................................................... 385
Debasish Bandyopadhyay and Bimal Krishna Banik
Chapter 11 Microwave Synthetic Technology: An Eco-friendly
Approach in Organic Synthesis......................................................... 429
Biswa Mohan Sahoo, Bimal Krishna Banik, and
Jnyanaranjan Panda
Chapter 12 Microwave-Assisted Green Chemistry Approach: A Potential
Tool for Drug Synthesis in Medicinal Chemistry............................. 475
Biswa Mohan Sahoo, Bimal Krishna Banik, and
Jnyanaranjan Panda
Index.......................................................................................................................509


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Preface

Modern technology that facilitates the development of new science in a number of
ways is the topic of current interest. Highly expeditious preparation and testing of
new molecules have been demonstrated in recent years. For example, microwaveassisted reactions have been used extensively for the synthesis of privileged molecules with known and unknown structures. In many experiments, the superiority
of microwave-assisted chemistry over the conventional heating method has been
observed and proved. A few authors have attempted to explain the cause of the acceleration rates, stereoselectivity of the products, cleaner synthesis, increased yields,
and the environmentally benign nature of these reactions that are associated with
domestic and automated microwave-induced reactions. It has been argued that the
reactants absorb energy, thereby permitting them to activate at the molecular level
and helping to form a non-equilibrium situation, allowing molecules to transfer
heat into other components. The cause of acceleration of numerous reactions by the
microwave-induced method has expanded this field. However, both thermal and nonthermal microwave effects are proposed for rapid reactions that are observed under
microwave-induced methods compared to conventional heating. The synthesis of
molecules under microwave irradiation is one of the most attractive areas of current
research in chemistry, both academic and industrial. In many instances, the molecules synthesized by microwave-induced reactions have demonstrated reasonable
pharmacological activities.
Microwave-induced methods are not restricted to chemistry. Their relevance has
expanded to other areas of science: medicine, biotechnology, biology, and engineering. Significant progress has been made in these areas using microwave technology.
Some of the methods described herein are new and, therefore, the scope in these
areas is unlimited.
The diversity of microwave-assisted chemistry as presented in this book is exceptionally high. The chapters are not organized based upon a specific subject matter.
Rather, they are numbered in the order of acceptance date. Authors from Argentina,
Brazil, China, India, and the United States have contributed chapters in this book.
Each of the twelve chapters presented in this book aimed to provide the contemporary aspects of advances in microwave-mediated science.
In Chapter 1, Jimenez, Zanin, Ferreira, Araú jo, and Porto described recent applications of microwave radiation in biocatalysis. The synergism of the microwave
radiation microbial cells, and enzymes is claimed to produce molecules that are of
interest to chemistry, biology, and natural products, as well as the biodegradation of
recalcitrant xenobiotic compounds. In Chapter 2, Alvarez, Lorenzetti, Acebal, Lista,
and Domini demonstrated microwave-assisted sample preparation. In Chapter 3,
Gomez, Aguinaga, LLmas, Garrido, Acebal, and Domini reported green microwavemediated processes for degradation and microextraction. In Chapter 4, Wang and
Zhong advanced the preparation and application of functional rare earth (RE)-based

micro/nanomaterials using the microwave. In Chapter 5, Batra, Panwar, Pratap, and
Nath described microwave-accelerated synthesis and functionalization of numerous
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Preface

oxygen-containing six-membered heterocyclic compounds: benzopyrans, 1, 3-dioxanes, 4H -pyrans, spiropyrans, chromones, xanthenes, and coumarins as well as
some fused six-membered oxygen heterocycles. In Chapter 6, Xu investigated the
origin of selectivities in the microwave-mediated organic reactions. Diverse selectivities, including chemoselectivity, regioselectivity, diastereoselectivity, and enantioselectivity in organic reactions were discussed under the microwave-assisted and
conventional heating conditions. In Chapter 7, Brahmachari reported and updated
microwave-induced Hirao and Kabachnik-Fields phosphorus-carbon bond forming
reactions. Various examples of unusual carbon-phosphorous compounds were shown
for the first time. In Chapter 8, Seelaboyina, Kumar, and Singh studied the microwaveinduced synthesis of absorber layer materials for thin film photovoltaic application.
Recent progress in the microwave-assisted synthesis of size and composition defined
CIS, CIGS, and CZTS nanopowder for the absorber layer in TFPV application is
reported. In Chapter 9, Shukla, Purohit, and Chakraborti studied microwave-assisted
transition metal-catalyzed synthesis of pharmaceutically important heterocycles.
Examples were provided where different heterocyclic scaffolds are obtained in the
presence of a transition metal-based catalyst under microwave heating compared to
that obtained by conventional heating. In Chapter 10, Bandyopadhyay and Banik discussed the microwave-induced synthesis of versatile important lactams. In Chapter 11,
Sahoo, Banik, and Panda demonstrated the use of microwave technology in synthesizing various organic compounds following an eco-friendly route. In Chapter 12,
Sahoo, Banik, and Panda investigated a green chemistry approach for the synthesis
of drugs and drug candidates.
After reading this book, one may become convinced that the microwave has no
boundary in science: it can be applied to almost all types of discoveries. In conclusion, this book provides an exploratory, as well as a concise and critical understanding of the significances in microwave research. Therefore, this book will be useful
for scientists particularly for chemists, biologists, biotechnologists, and engineers

who are working in diverse and specific new research areas.
We take the opportunity to thank the authors for their highly significant and exceptional contributions. Thanks are also due to Ms. Hilary Lafoe and Taylor & Francis
who have realized that such a book on microwave chemistry will be extremely useful
for researchers around the world.
Bimal Krishna Banik 
Debasish Bandyopadhyay 
 


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About the Editors
Dr. Bimal Krishna Banik  is the Vice President of Research and Education
Development of Community Health Systems of South Texas. He was a Tenured Full
Professor and First President’ s Endowed Professor at the University of Texas-Pan
American and an Assistant Professor of University of Texas M. D. Anderson Cancer
Center for many years. He was awarded a Bachelor of Science Honors Degree in
Chemistry from Itachuna Bejoy Narayan College and a Master of Science Degree
in Chemistry from Burdwan University. He obtained his Ph.D. degree based upon
his thesis work performed at the Indian Association for the Cultivation of Science,
Jadavpur. Dr. Banik was a Postdoctoral Fellow at Case Western Reserve University
(Ohio) and Stevens Institute of Technology (New Jersey). He is a Fellow (FRSC)
and Chartered Chemist (CChem) of the Royal Society of Chemistry. Dr. Banik has
been involved in organic, medicinal chemistry, and biomedical research for many
years. As Principal Investigator, he has been awarded $7.25 million USD grants
from National Institutes of Health, National Cancer Institute, Kleberg Foundation,
University of Texas M. D. Anderson Cancer Center, University of Texas Health
Science Center and University of Texas-Pan American (UTPA). 
Dr. Debasish Bandyopadhyay  studied chemistry at the Chandernagore Government College and the University of Burdwan (India). He received his Ph.D. in 2004
from the University of Calcutta (India), the oldest university in South-East Asia.

He performed his first postdoctoral research at the same university with Professor
Asima Chatterjee and Professor Julie Banerji. In 2007, he joined the University
of Texas-Pan American as a NIH/NCI postdoctoral fellow with Professor Bimal
Krishna Banik in the Department of Chemistry. In 2011, he was appointed as
Assistant Professor of Research in the same department. His research foci include,
but are not limited to, the development of greener methodologies to synthesize
novel pharmacophores; design, in silico validation and synthesis of anticancer
compounds; extraction, purification, structure elucidation, and chemical modification of plant natural products targeting pharmacologically active molecules. He
has authored 67 international patent/book chapter/journal articles. He is currently
engaged as Associate Editor with two internationally reputed journals and Editorial Board Member of eight international journals.

ix


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List of Contributor
Carolina C. Acebal
INQUISUR, Departamento de Química
Universidad Nacional del Sur
Bahía Blanca, Argentina
Maite V. Aguinaga
INQUISUR, Departamento de Química
Universidad Nacional del Sur
Bahía Blanca, Argentina
Mónica B. Alvarez
INQUISUR, Departamento

de Qmica
Universidad Nacional del Sur
Bahía Blanca, Argentina
Yara J. K. Araújo
Institute of Chemistry of São Carlos
University of São Paulo
São Paulo, Brazil
Debasish Bandyopadhyay
Department of Chemistry
University of Texas
Edinburg, Texas
Bimal Krishna Banik
Community Health Systems of South
Texas
Edinburg, Texas

Asit K. Chakraborti
Department of Medicinal Chemistry
National Institute of Pharmaceutical
Education and Research (NIPER)
S.A.S Nagar, India
Claudia E. Domini
INQUISUR, Departamento de Química
Universidad Nacional del Sur
Bahía Blanca, Argentina
Irlon M. Ferreira
Institute of Chemistry of São Carlos
University of São Paulo
São Paulo, Brazil
Mariano Garrido

INQUISUR, Departamento de Química
Universidad Nacional del Sur
Bahía Blanca, Argentina
Natalia A. Gomez
INQUISUR, Departamento de Química
Universidad Nacional del Sur
Bahía Blanca, Argentina
David E. Q. Jimenez
Department of Chemistry
Federal University of Amapá
Amapá, Brazil

Neha Batra
Department of Chemistry
University of Delhi
Delhi, India

Manoj Kumar
Centre for Nanotechnology
Bharat Heavy Electricals Limited
(BHEL) Corporate R & D,
Vikasnagar, India

Goutam Brahmachari
Department of Chemistry
Visva-Bharati University
Santiniketan, India

Adriana G. Lista
INQUISUR, Departamento de Química

Universidad Nacional del Sur
Bahía Blanca, Argentina
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xii

List of Contributor

Natalia Llamas
INQUISUR, Departamento de Química
Universidad Nacional del Sur
Bahía Blanca, Argentina

Biswa Mohan Sahoo
Department of Pharmacy
Vikas Group of Institutions
Andhra Pradesh, India

Anabela Lorenzetti
INQUISUR, Departamento de Química
Universidad Nacional del Sur
Bahía Blanca, Argentina

Raghunandan Seelaboyina
Centre for Nanotechnology
Bharat Heavy Electricals Limited
(BHEL) Corporate R & D,
Vikasnagar, India

Mahendra Nath
Department of Chemistry
University of Delhi
Delhi, India

Dipti Shukla
Department of Medicinal Chemistry
National Institute of Pharmaceutical
Education and Research (NIPER)
S.A.S Nagar, India

Jnyanaranjan Panda
Department of Pharmaceutical
Chemistry
Roland Institute of Pharmaceutical
Sciences
Berhampur, India
Rahul Panwar
Department of Chemistry
University of Delhi
Delhi, India
André L. M. Porto
Institute of Chemistry of São Carlos
University of São Paulo
São Paulo, Brazil
Ramendra Pratap
Department of Chemistry
University of Delhi
Delhi, India

Priyank Purohit
Department of Medicinal Chemistry
National Institute of
Pharmaceutical Education
and Research (NIPER)
S.A.S Nagar, India

Kulvir Singh
Centre for Nanotechnology
Bharat Heavy Electricals Limited
(BHEL) Corporate R & D,
Vikasnagar, India
Lei Wang
College of Chemistry and Chemical
Engineering
Jiangxi Normal University
Nanchang, China
Jiaxi Xu
Department of Organic Chemistry
Beijing University of Chemical
Technology
Beijing, China
Lucas Lima Zanin
Institute of Chemistry of São Carlos
University of São Paulo
São Paulo, Brazil
Shengliang Zhong
College of Chemistry and Chemical
Engineering
Jiangxi Normal University

Nanchang, China


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1

Microwave Radiation
in Biocatalysis
David E. Q. Jimenez, Lucas Lima Zanin,
Irlon M. Ferreira, Yara J. K. Araújo,
and André L. M. Porto

CONTENTS
1.1Introduction....................................................................................................... 1
1.1.1 Principles of Microwave Radiation.......................................................2
1.1.2 Influence of Microwave Radiation on Enzymes.................................... 6
1.2 Application of Microwave Radiation in Biocatalysis........................................ 8
1.2.1 Use of Isolated Enzymes in Biocatalysis under Microwave
Radiation and Conventional Heating..................................................... 8
1.2.2 Biocatalytic Reactions Using Whole Cells of Microorganisms
under MW............................................................................................ 19
1.3 Conclusions and Perspectives..........................................................................20
Acknowledgments..................................................................................................... 22
References................................................................................................................. 22

1.1 INTRODUCTION
Although microwave ovens manufactured for homes have been used since the 1970s,
the first report that these energy sources were appropriately being used to accelerate
organic reactions was in 1986. In their pioneering studies, Gedye [1] and Guiguere

[2] used the domestic microwave as a tool for conducting organic reactions. In these
studies, the authors described the results obtained in esterification reactions and
cycloaddition with a domestic microwave apparatus [3].
The risk associated with the flammability of organic solvents and the lack of available systems to control temperature and pressure were the main reasons for using
microwave reactors developed especially for organic synthesis. Today, this device
is safe and allows the synthetic organic chemist control over all reaction parameters
(temperature, pressure and power), thus achieving greater reproducibility and safety
in the experiments [3, 4].
In the last decade, microwave radiation has been used to simplify and improve the
reaction conditions of many classic organic reactions. Reactions carried out under
microwave radiation are generally faster and cleaner and have better yields than
reactions performed under conventional heating in similar conditions [5, 6]. The
microwave methods provide an efficient and safe technology, according to the principles of “Green Chemistry” [7], because this technique enables solvent-free reactions
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Advances in Microwave Chemistry

to be performed, decreasing the number of competing side reactions, increasing the
yield and reducing the reaction time [8–10].
More recently, microwave radiation became an important tool for performing biocatalytic reactions. The potential of this technique has been exploited, particularly in
the resolution of racemates to obtain enantiomerically pure compounds using immobilized lipases [11–14].
The organic synthesis presents a great contribution to obtain molecules with biological activities. Thus, the development of methodologies that apply the principles of
Green Chemistry in the synthesis of new selective products with chemo-, regio- and
enantio-selective and environmentally benign characteristics is required. Therefore,
the use of microwave radiation in synthetic protocols has been very advantageous
because the reactions are performed in a very short time in the absence of organic

solvents and with a low consumption of energy [15].

1.1.1 Principles of Microwave Radiation
Microwaves are electromagnetic waves like energy carriers; these are located in the
region of the electromagnetic spectrum between infrared light and radio waves in the
frequency range between 300 and 300,000 MHz (Figure 1.1) [3, 7].
Domestic microwave ovens operate at a frequency of 2450 MHz (wavelength
of 12.24 cm) to avoid interference with frequency telecommunications and mobile
phones. According to the Federal Communications Commission (www.fcc.gov), only
four frequencies are reserved for Industrial, Scientific and Medical (ISM) purposes:
915 ± 25, 2450 ± 13, 5800 ± 75 and 22,125 ± 125 MHz, with the most commonly used
frequencies being 915 and 2450 MHz.
Microwave ovens that can process a frequency change of 0.9 to 18 GHz have been
developed for the transformation of materials [16–18].
The microwave is a type of non-ionizing radiation capable of causing molecular
motion in dipolar polarization and ionic conduction, but not changes in the molecular structure of molecules [11]. Since the energy of a microwave photon in this
X Rays

10–10

10–9

Ultraviolet

10–8

Visible

10–7

10–6

Infrared

10–5

10–4

Radio
Wave

Microwave

10–3

10–2

10–1

1

Wave length (m)

3x1012

3x108

3x1010

3x106

3x104

3x102

Frequency (MHz)

Electrons of
valence layer

Molecular vibrations

Molecular rotation

FIGURE 1.1  Illustration of electromagnetic spectrum. (Adapted from Young DD, Nichols J,
Kelly RM, Deiters A (2008) Microwave activation of enzymatic catalysis. Journal of the
American Chemical Society 130: 10048–10049.)


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Microwave Radiation in Biocatalysis

3

frequency region is 0.037 kcal.mol−1, very low energy is needed to break a chemical
bond, which is generally of the order of 80–120 kcal.mol−1 [19].
The conventional heating process is fundamentally different to microwave heating upon radiation. In conventional heating an external power source reaches the
walls of the flask and heat is transferred from the flask surface into the solution
(reagents and solvents); through the driving process, such heating can often cause
a convection current in solution. In contrast, with heating under microwave radiation, the energy is transferred directly to the substances by molecular interaction

with the ions dissolved in the solution and/or the solvent; thus localized overheating
of the substance absorbs the microwave (Figure 1.2) [16, 17]. This type of heating
will depend on the ability of that particular material, reagent or solvent to absorb the
microwave energy and convert it into heat [19].
Microwave heating, also called dielectric heating, converts electromagnetic
energy into heat by two main mechanisms: dipolar polarization and ionic conduction [3]. The mechanism of dipolar polarization associated with the alignment of the
molecules has permanent or induced dipoles with the applied electric field. When
the field is removed the molecules return to a disordered state, and the energy that
was absorbed into this guidance, these dipoles, is dissipated as heat, causing the
molecules to be quickly heated in the system (Figure 1.3) [18, 20].
The ionic conduction process consists of an electromagnetic migration of ions when
an electric field is applied in the solution. The friction generated between these ions in
solution, due to the migratory movement, causes heating of the solution through friction losses. These losses depend on the size, charge and conductivity of dissolved ions
and their interaction with the solvent. The applied electric field alternates quickly, about
5 billion times per second to the applied frequency 2450 MHz [20, 21]. This oscillation causes considerable intermolecular friction resulting in the generation of heat. A
schematic representation is shown in Figure 1.4 for the driving ionic mechanism [20].
When the power microwave focuses on the material (or substance), there are three
possibilities regarding the penetration of an electromagnetic wave: reflection, transparency and absorption (Figure 1.5). Materials such as metals reflect the microwave
without being affected by it due to the high dielectric loss factor (εʺ) and intensity of penetration of the electromagnetic wave close to zero. When the microwave

FIGURE 1.2  Illustration of conventional and microwave heating processes. (From Kingston
HM, Jassie LB. Introduction to microwave sample preparation: theory and practice.
American Chemical Society, ACS professional reference book, Washington DC, 1998. With
permission.)


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Advances in Microwave Chemistry

H
O
H

+

H
O
H

H
O
H

H
O
H
H
H
O
O
H
H

-

E

(a)

O
H

H

H
H

H

H O

O

O H
H

H

O

H

H
O H

(b)

FIGURE 1.3  Illustration for molecular behavior in the presence of an electromagnetic field.
(a) Polarized molecules aligned with the electromagnetic field. (b) Thermally induced disorder

when the electromagnetic field changes occur. E = electric field. (From Souza GB, Nogueira
ARA, Rassini JB. Circular Técnica da Embrapa, 33: 1–9, 2002. With permission.)

FIGURE 1.4  Illustration of ionic conduction in the presence of an electromagnetic field.
E = electric field. (From Sanseverino AM. “Micro-ondas em síntese orgânica.” Química Nova
25: 660–667, 2002. With permission.)

FIGURE 1.5  Relationship between the dielectric loss factor and ability to absorb microwave power for some materials. (From Thostenson ET, Chou TW. “Microwave processing:
fundamentals and applications.” Composites Part A. Applied Science and Manufacturing 30:
1055–1071, 1999. With permission.) (License Number: 3614930551491.)


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Microwave Radiation in Biocatalysis

5

passes through the material without causing any effect, this material is transparent
to microwave. When a material absorbs the microwave, there is an interaction of the
electromagnetic wave with the electric dipole of the molecule at the molecular level
[17]. Physico-chemical properties such as concentration, heat capacity, molecular
structure and dielectric constant affect the absorption of energy [20].
The heat amount of a material under microwave radiation will depend on its
dielectric properties, i.e., the ability of this specific substance to convert electromagnetic energy into heat at a given temperature and frequency. This is determined by
the dissipation factor (tan δ) which is measured by the ratio of the dielectric loss factor (εʺ) and the dielectric constant (εʹ) of the substance (tan δ = εʺ/εʹ). The dielectric
loss factor measures the efficiency of electromagnetic energy conversion into heat.
Thus, the higher the dissipation factor, the greater the substances will be heated
under microwave [18, 19]. Polar molecules and ionic solutions can strongly absorb
microwave energy to present a permanent dipole moment, and nonpolar solvents,
such as hexane, do not heat under microwave radiation [18]. Another important factor is the dielectric constant, which is a measure of molecular polarity.

When polar solvents are used in a microwave over a high dissipation factor, they
can still be rapidly overheated to temperatures above the boiling point; in this case
it is necessary to use the microwave reactor vials sealed with the “closed vessel”,
enhancing the efficiency and speed of the reaction. This rapid increase in the temperature can be further enhanced for extreme solvents using dissipation factors such
as ionic liquid [22]. Obviously, a particular solvent with a low dissipation factor may
heat up significantly in the presence of polar compounds, such as salts or ionic liquid.
Table 1.1 presents the physical parameters, such as dielectric constant and dissipation factor, for some solvents [18].
The chemical reactions carried out in the presence of microwave radiation have
several advantages including: reduction of competitive reactions, shorter reaction
time, increased productivity and better reproducibility [23]. These effects can be
rationalized by three principles: thermal effects, specific effects of microwave and
non-thermal effects of microwave. The thermal effects can be understood as a direct
result of the high reaction temperatures, which can be obtained when the reactants
and polar solvents are irradiated by microwave. The decrease in reaction time at
elevated temperatures may be evidenced by the implementation of the Arrhenius
Law [24].
The specific effects of microwave can be defined as acceleration rates, which
cannot be achieved by conventional heating, for example, overheating of solvents
at atmospheric pressure, the selective heating of the reactants and the formation
of “hot spots” (high-temperature isolated points in the reaction medium). Mainly,
although these effects are produced exclusively in the presence of microwave radiation, observed results are due to the increase in reaction temperature [8, 25].
The non-thermal effects of microwave result from a direct interaction between
the electric field and the species present in the reaction medium [9, 26]. The presence of an electric field affects the dipolar orientation in some types of reactions by
increasing the factor of the pre-exponential Arrhenius equation and decreasing the
∆G activation of the transition state. The first is based on the increased probability of intermolecular shocks due to subsequent changes in the orientation of polar


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Advances in Microwave Chemistry

TABLE 1.1
Data of Dielectric Constant (εʹ), Dielectric Loss (εʺ), tan δ and
Boiling Point (p.f.) for Some Organic Solvents
Solvent

εʹ

εʺ

tan δ

Hexane

1.89

b.p. (°C)

b.p.*

0.038

0.020

69

N.a.

Toluene

Dichloromethane
THF
Acetone
Ethyl acetate
Acetonitrile
Nitromethane
Chloroform
Chlorobenzene
Water
1,2-Dichloroethane
Methanol
2-Propanol

2.4
9.1
7.4
20.7
6.0
37.5
36.0
4.8
2.6
78.3
10.4
32.6
19.9

0.096
0.382
0.348

1.118
0.354
2.325
2.034
0.437
0.263
9.889
1.321
21.483
14.622

0.040
0.042
0.047
0.054
0.054
0.062
0.064
0.091
0.101
0.123
0.127
0.659
0.799

111
40
66
56
77

82
101
61
132
100
83
65
82

N.a.
N.a.
N.a.
164
N.a.
194
N.a.
N.a.
N.a.
N.a.
N.a.
151
145

Ethanol

24.3

22.866

0.941

78

164

N.a. = not appropriate to use in closed vessel; b.p. = boiling point; b.p.* = point temperature in closed vessel.
Source: Eskilsson CS, Bjorklund E, 2000. “Analytical-scale microwave-assisted
extraction.” Journal of Chromatography A 902: 227-250.

molecules as a function of the electric field oscillation. The second suggests that the
mechanisms of formation of polar charged species in the transition state must be favored
by microwave radiation due to the interaction with the electric field generated [24, 25].

1.1.2 Influence of Microwave Radiation on Enzymes
The effects of microwave radiation in terms of the rate and selectivity of the enzymatic reactions have not been fully clarified; however, there are some studies that
suggest explanations for the observed effects.
Yadav and Lathi carried out a study of transesterification reactions of methyl acetate with different alcohols using Novozyme 435® lipase as a catalyst under microwave radiation. The authors found full conversion and the reaction rate was higher
under microwave radiation than conventional heating. However, after checking the
kinetic model based on the initial rates, they found no change in the ping-pong Bi-Bi
mechanism using lipase. The authors suggest that the enzyme seems to become
slightly different when heated under microwave radiation [27].
Rejasse et al. analyzed a lot of biocatalytic reactions in the presence of microwave
radiation and concluded that in aqueous media the properties of irradiated enzymes
are identical to those obtained under conventional heating. In non-aqueous media


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Microwave Radiation in Biocatalysis

7

activity, selectivity and stability of enzymes can be improved under microwave heating, which occurs through absorption of electromagnetic energy polar species [28].
Some conformational changes can occur with enzymes in the presence of microwave. In a study with β-glucosidase from Pyrococcus furiosus in the presence of
microwave radiation, Young et al. (2008) showed an increased molecular mobility of
the enzyme structure by rapidly induced dipole alignment of the peptide bond with
the oscillating electric field. This structural change can lead to an increased activity
or even inactivation of the enzyme compared with conventional heating [11].
An interesting observation of the effect of electromagnetic fields on biological
structures was reported by Laurence et al. (2000) that showed that the energy of the
microwave was sufficient to induce a conformational change in some proteins. The
water molecules that are around the proteins form hydrogen bonds with the hydrophilic regions of the protein and are essential to maintaining their structure of the
same. Upon increasing temperature, these bonds are disrupted and alter the conformation of the protein [29].
The influence of non-thermal effects on the reactivity and selectivity of reactions
was described by Loupy et al. (2001). They showed that in polar mechanisms the
transition state is more polar than the ground state, resulting in an increase of the
reactivity by decreasing the activation energy. This study suggests that stabilization
of the transition state can occur in two types of mechanisms: (a) neutral species reactions leading to a transition state dipole; (b) loaded nucleophilic reactions leading to
the dissociated ion pairs in the transition state [30].
The research of Loupy et al. (2001) showed that the transition state for biocatalytic
reactions under microwave radiation involves the formation of tetrahedral enzymesubstrate complexes that have dipole characteristics and the reaction occurs quickly
(Figure 1.6) [30, 31]. Figure 1.7 shows the relative stabilization of a more polar transition state when compared to the ground state [32].
Finally, although the influence of microwave on the mechanism of enzymatic
reactions has been studied for more than two decades, there is still no consensus on
the real effects of electromagnetic radiation on the structure and activity of proteins.

FIGURE 1.6  Possible tetrahedral enzyme-substrate complex presenting dipolar characteristics for ester hydrolysis catalyzed using Candida rugosa lipase. (Adapted from Cygler M,
Grochulski P, Kazlauskas JK, Schrag JD, Bouthillier F, Rubin B, Serreqi AN, Gupta AK,
1994. A structural basis for the chiral preferences of lipases. Journal of American Chemical
Society 116: 3180-3186.)

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FIGURE 1.7  Relative stabilization of more polar transition state when compared to ground
state. (From Fransson L. Molecular modeling: understanding and prediction of enzyme selectivity. Licentiate thesis. Royal Institute of Technology School of Biotechnology, AlbaNova
University Center SE-106 91 Stockholm, Sweden, 2009. With permission.)

1.2 APPLICATION OF MICROWAVE RADIATION IN BIOCATALYSIS
Microwave radiation has been used for increasing the yield and selectivity in biocatalytic reactions and decreasing the reaction times. Lipases are used as versatile
biocatalysts in biological and chemical process, such as modification fats and lipids,
kinetic resolutions of alcohols and amines, hydrolysis, and esterification and interesterification reactions [33, 34].

1.2.1 Use of Isolated Enzymes in Biocatalysis under
Microwave Radiation and Conventional Heating
Enzymes can be used in synergism between biocatalytic processes with microwave
radiation. In general, immobilized enzymes and thermophilic enzymes are certainly
more stable under microwaves.
Enzymatic hydrolysis of nitrophenoate indicated that hyperthermophilic enzymes
can be activated at temperatures far below their optimum, presumably by microwave-induced conformational flexibility. This finding offers the prospect of using
hyperthermophilic enzymes at ambient temperatures to catalyze reactions with thermally labile substrates. In addition, microwave could be used to regulate biocatalytic
rates at very low temperatures for enzymes from less thermophilic sources [11].
When using microwave radiation, enzymatic reactions can occur in minutes and
with high yields and selectivities [12]. This important technological tool is consistent
with the principles of Green Chemistry and so it has been widely used in organic
reactions and more recently in reactions catalyzed by enzymes [10, 22, 35].
Ribeiro et al. (2012) researched the Enzymatic Kinetic Resolution (EKR) of
(±)-mandelonitrile by Candida antarctica lipase (CALB) under microwave radiation

and conventional heating in toluene. The ethyl (S)-mandelonitrile was obtained with
an enantiomeric excess of 92% and isolated yield of 35% at 8 h of reaction under


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Microwave Radiation in Biocatalysis
OH

OH
CALB
vinyl acetate

CN
(±)-2-hydroxy-2-phenyl
acetonitrile

OAc

CN

80 °C, 8 h
MW

(R)-2-hydroxy-2-phenyl
acetonitrile

CN
(S)-cyano(phenyl)methyl

acetate
yield = 35%
e.e.p = 92%

SCHEME 1.1  EKR of (±)-mandelonitrile under MW.

microwave radiation (Scheme 1.1). The transesterification of (±)-mandelonitrile conducted under conventional heating yielded the (R)-mandelonitrile with 51% enantiomeric excess and the (S)-mandelonitrile with 98% enantiomeric excess after 184 h [13].
In another study, Ribeiro et al. (2013) carried out enzymatic resolution on a number of fluoroaromatic compounds using CALB in toluene and vinyl acetate as an
acylating agent. The reactions showed shorter reaction times (4–14 h), higher enantiomeric excesses for the (S)- or (R)-acetates and better yields under microwave radiation in comparison with conventional heating (48–144 h) (Scheme 1.2) [36].
Yu et al. (2007) conducted the kinetic resolution of (±)-2-octanol catalyzed by
CALB using vinyl acetate under microwave radiation at 60°C for 2 h to yield the (S)-2octanol with 50.5% conversion and enantiomeric excess of 99% (Scheme 1.3). Reaction
under microwave radiation afforded 50% conversion of acetylated (R)-enantiomer
(3 h) and conventional heating was required for 12 h at 40°C [37]. In addition, Yu et al.
(2012) investigated the enzymatic resolution of (±)-2-octanol under microwave radiation in the ionic liquid. In this study, the reaction under microwave radiation afforded
better results than in solvent-free systems under conventional heating [22].
Souza et al. (2009) reported the kinetic resolution of (±)-1-phenylethanol with
vinyl acetate as acyl donor and cyclohexane as solvent under microwave heating
and conventional heating. In this study, the authors concluded about the existence
of non-thermal microwave effects in the kinetic resolution of a secondary alcohol
with five immobilized lipases. This study showed that lipases do not differ when
heating in an oil bath or microwave radiation using (±)-1-phenylethanol as substrate
(Scheme 1.4) [38].
OH

R5
R4

CR13
R3

R2

CALB
vinyl acetate
toluene
MW

OH

R5
R4

CR13
R3

R2

(R) or (S)

OAc

R5
R4

CR13
R3

R2

(S) or (R)

R1 = F, R2 R3 = R4 = R5 = H (e.e.p = 99%, S)
R1 = F, R2 = R4 = R5 = H, R3 = Br (e.e.p = 78%, S)
R1 = F, R2 = R3 = R5= H, R4 = Br (e.e.p = 98%, S)
R1 = H, R2 = R4 = R5 = F, R3 = H (e.e.p = 99%, R)

SCHEME 1.2  EKR of fluoroaromatic compounds under MW.


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Yadav and Devendran (2012) investigated the EKR of (±)-1-(1-naphthyl)ethanol
under microwave radiation and conventional heating. Three different lipases were
used: Novozyme 435® (Candida antarctica), Lipozyme RMIM (Rhizomucor miehei)
and Lipozyme TLIM (Thermomyces lanuginosus). The Novozyme 435® was the best
biocatalyst, giving a conversion of 48% and 90% e.e.p for (R)-acetylated product at
60°C for 3 h (Scheme 1.5). By conventional heating, the product was obtained after
5 h with 40% conversion and 64% e.e.p [5].
Devendran and Yadav (2014) researched the kinetic resolution of (±)-1-phenyl2-propyn-1-ol through transesterification reaction with acyl acetate to evaluation of
synergism between microwave radiation and enzymatic catalysis. Lipases from different microbial origins were employed in this study (Novozyme 435®, Lipozyme
RM-IM and Lipozyme TL IM). The Candida antarctica lipase B, immobilized
on acrylic resin was the best catalyst in n-hexane with vinyl acetate as acyl donor.
Under optimum conditions, maximum conversion (48.78%) and high enantiomeric
excess (93.25%) were obtained in 2 h at 60°C under MW in synergism with CALB
(Scheme 1.6) [39].

60 °C, 2 h

MW

(±)-2-octanol

OAc

OH

CALB
vinyl acetate

OH

(S)-octan-2-ol

(R)-octan-2-yl acetate
c = 50.5 %
e.e. p = 99%

SCHEME 1.3  EKR of (±)-2-octanol under MW.
O
OH

CALB
vinyl acetate

O

OH
+

MW
(R)-1-phenylethyl acetate
c = 50%
e.e.p = > 99%, E > 200

(±)-1-phenylethanol

SCHEME 1.4  EKR of (±)-1-phenylethanol under MW.
H 3C

OH

H 3C

OH

H 3C

OAc

CALB
vinyl acetate

(±)-1-(naphthalen-1-yl)
ethan-1-ol

60 °C, 3 h
MW

(R)-1-(naphthalen-1-yl)
ethan-1-ol

SCHEME 1.5  EKR of (±)-1-(1-naphthyl) ethanol under MW.

(S)-1-(naphthalen-1-yl)
ethyl acetate
c = 48%
e.e.p = 90%


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Microwave Radiation in Biocatalysis
O
OH

(±)-1-phenylpropargyl
alcohol

CALB
vinyl acetate
n-hexane
60 ° C, 2 h
MW

OH

O

CH3

+

(S)-1-phenylpropargyl (R)-1-phenylpropargyl
acetate
alcohol
c = 48.78 %
e.e.p = 93.25 %

SCHEME 1.6  EKR of (±)-1-phenylpropargyl alcohol under MW.

Rouillard et al. (2014) reported the use of lipases under microwave radiation on
the kinetic resolution of homochiral (±)-(Z)-cyclooct-5-ene-1,2-diol and (±)-(Z)-2acetoxycyclooct-4-enyl acetate. In order to best achieve the kinetic resolution, different
parameters were studied including the type of lipase, temperature and the impact of
microwave power compared to conventional heating for kinetic resolution of (±)-(Z)cyclooct-5-ene-1,2-diol. Optimization of the reaction parameters led to highly enriched
mono and diacetylated products in a clean, efficient and safe way (Scheme 1.7) [40].
EKR of secondary alcohols was performed using CALB in toluene at 60°C under
microwave radiation and conventional heating. The conversions under microwave
radiation were obtained between 30–50% and 43–99% e.e.p. However, conventional
heating obtained conversions of 6–36% and 6–99% e.e.p (Scheme 1.8) [23].
The regioselective esterification of isoquercitrin and floridzine with different
saturated (oleic, stearic, linoleic, linolenic, eicosapentaenoic and docosahexaenoic
acid), monounsaturated and polyunsaturated fatty acids was performed under three
different reaction conditions: (i) by conventional heating; ii) by microwave radiation
in acetone; and iii) by microwave radiation in the absence of solvent. When lipase
Novozyme 435® was used as a biocatalyst at temperatures of 45–60°C, the reaction
times varied from 18 to 24 h, giving yields of 81–97% for conventional heating. The
reaction under microwave radiation in acetone gave the monoacetylated isoquercitrin

in 120 s with 98% yield (stearic acid) and the floridzine acetylated in 160 s with 98%
yield (linolenic acid) (Scheme 1.9). The most effective method for the reaction without solvent yielded 98% for acetylated isoquercitrin and 85% for acetylated floridzine with reaction times of 75 and 105 s, respectively [6]. The enzymatic acetylation
OH

+

OH
(1R,2R)

(1S,2S)

(±)-cyclooct-5-ene-1,2-diol
Power: 5-300 W

OH

CALB
vinyl acetate

OAc

OH

THF, 14 h
MW

OH

+

monoacetylated
yield = 32-58%
e.e.p = 45-67%

OAc
OAc
diacetylated
yield = 2-37%
e.e.p = 94-> 99%

SCHEME 1.7  Chemoenzymatic acetylation of (±)-diols using immobilized CALB
under MW.


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OH

CALB
4-chlorophenyl acetate

R2

1R

toluene, 60 ºC
MW

(±)-alcohols
1

R and R2:

+

R2

1R

1R
R2
c = 30-50%
e.e.p = 43-99%

OMe

Br

Br
OH

OAc

OH

OH

OH

OH

OMe

OH

O

OH

O

O
MeO

OH

SCHEME 1.8  EKR of (±)-secondary alcohols under MW.
OH

OH

OH

OH

CALB
stearic acid
MW

O
OH

O

HO

O

HO

O
HO

O

O
OH

OH

HO

O
HO

O
C17H35

O

HO

O

OH

OH

isoquercetrin monoacetylated
yield = 98%

isoquercetrin

OH

OH
HO

CALB

OH
HO
HO

HO

OH

O

O

O
OH
floridzine

linolenic acid
MW

OH

OH
HO
HO

O
O
O

O

O
C17H29

floridzine monoacetylated
yield = 94%

SCHEME 1.9  Regioselective esterification of isoquercetin and floridzine using CALB

under MW.

of these compounds occurred with regioselectivity, which is an advantage compared
to non-enzymatic methods, which generally have very low regioselectivity [41–45].
Yadav and Devendran (2012) researched the synthesis of isoamyl myristate in a
solvent-free reaction using CALB under microwave radiation through the esterification of myristic acid and isoamyl alcohol. In 60 min, the reaction gave 96% conversion