Microwave-assisted Organic Synthesis

One Hundred Reaction Procedures

D. Bogdal

• Publisher: Elsevier Science
• Year: 2006
• eBook ISBN: 9780080518732
• Topic: Biological Sciences
• Subtopic: Science Research & Methodology
• Index: Biological Sciences

Microwave-assisted Organic Synthesis: One Hundred Reaction Procedures provides readers with a broad overview of microwave assisted Organic Synthesis, enabling students and researchers alike to produce more efficient and high yield syntheses while saving time and resources. The work addresses key problems faced by chemistry laboratories in academia and in industry, that of an ever increasing need for procedures which are low-waste, energy efficient, high yield, occur over a short reaction period, and use environmentally friendly solvents. All these factors play an important role in the development of Green Chemistry methods, and in this, Microwave-assisted Organic Synthesis: One Hundred Reaction Procedures is an excellent resource for any library. - Provides a broad overview of microwave enhanced chemistry - Extensive references to the source of each procedure, including equipment used, full operating procedure, and associated hazards - Includes exercises and worked problems which can support more independent study

Chapter 1

Interaction of microwaves with different materials

Microwaves are electromagnetic radiation placed between infrared radiation and radio frequencies, with wavelengths of 1 mm to 1 m, which corresponds to the frequencies of 300 GHz to 300 MHz, respectively. The extensive application of microwaves in the field of telecommunications means that only specially assigned frequencies are allowed to be allocated for industrial, scientific or medical applications (e.g., most of wavelength of the range between 1 and 25 cm is used for mobile phones, radar and radio-line transmissions). Currently, in order not to cause interference with telecommunication devices, household and industrial microwave ovens (applicators) are operated at either 12.2 cm (2.45 GHz) or 32.7 cm (915 MHz). However, some other frequencies are also available for heating [1]. Most common domestic microwave ovens utilize the frequency of 2.45 GHz, and this may be a reason that all commercially available microwave reactors for chemical use operate

Heating in microwave cavities is based upon the ability of some liquids and solids to absorb and transform electromagnetic energy into heat. In general, during the interaction of microwaves with materials three different behaviors of a material can be observed depending whether the material is counted among:

• electrical conductors (e.g, metals, graphite - Fig.1.2a)

Figure 1.2 Interaction of microwaves with different materials: (a) - electrical conductor, (b) - isulator, (c) - lossy dielectric.

• insulators, which are considered as materials with good dielectric properties (extremly poor conductors)(e.g., quartz glass, porcelain, ceramics, Teflon - Fig. 1.2b)

• lossy dielectrics, which are materials that exhibit so called dielectric losses, which in turn results in heat generation in an oscillating electromagnetic field (e.g., water - Fig. 1.2c)

When a strongly conducting material (e.g., a metal) is exposed to microwave radiation, microwaves are largely reflected from its surface (Fig. 1.2a). However, the material is not effectively heated by microwaves, in response to the electric field of microwave radiation, electrons move freely on the surface of the material, and the flow of electrons can heat the material through a resistive (ohmic) heating mechanism. In opposite, in the case of insulators (e.g., porcelain), microwaves can penetrate through the material...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Dedication
• Preface
• Acknowledgements
• Chapter 1: Interaction of microwaves with different materials
• Chapter 2: Microwave effect vs. thermal effect
• Chapter 3: Microwave equipment
• Chapter 4: Reaction vessels and glassware
• Chapter 5: Techniques for conducting chemical reactions under microwave irradiation
• Chapter 6: Safety precautions on the application of microwaves in laboratory
• Chapter 7: Reactions under microwave conditions
• Appendix
• References
• Index