Milestones in Microwave Chemistry

117 Pages·2016·8.26 MB·English

by  György Keglevich (eds.)

SPRINGER BRIEFS IN MOLECULAR SCIENCE
GREEN CHEMISTRY FOR SUSTAINABILITY
György Keglevich Editor
Milestones
in Microwave
Chemistry
123
SpringerBriefs in Molecular Science
Green Chemistry for Sustainability
Series editor
Sanjay K. Sharma, Jaipur, India
More information about this series at http://www.springer.com/series/10045
ö
Gy rgy Keglevich
Editor
Milestones in Microwave
Chemistry
123
Editor
György Keglevich
BudapestUniversity of Technologyand
Economics
Budapest
Hungary
ISSN 2191-5407 ISSN 2191-5415 (electronic)
SpringerBriefs inMolecular Science
ISSN 2212-9898
SpringerBriefs inGreen Chemistry for Sustainability
ISBN978-3-319-30630-8 ISBN978-3-319-30632-2 (eBook)
DOI 10.1007/978-3-319-30632-2
LibraryofCongressControlNumber:2016933216
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Contents
1 The Spread of the Application of the Microwave Technique
in Organic Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Erika Bálint and György Keglevich
2 Microwave-Assisted Syntheses in Organic Chemistry. . . . . . . . . . . . 11
Nóra Zs. Kiss, Erika Bálint and György Keglevich
3 The Use of MW in Organophosphorus Chemistry. . . . . . . . . . . . . . 47
György Keglevich, Erika Bálint and Nóra Zs. Kiss
4 Interpretation of the Effects of Microwaves. . . . . . . . . . . . . . . . . . . 77
Péter Bana and István Greiner
v
Contributors
Péter Bana Department of Organic Chemistry and Technology, Budapest
University of Technology and Economics, Budapest, Hungary
Erika Bálint MTA-BME Research Group for Organic Chemical Technology,
Budapest University of Technology and Economics, Budapest, Hungary
István Greiner Gedeon Richter Plc, Budapest, Hungary
György Keglevich Department of Organic Chemistry and Technology, Budapest
University of Technology and Economics, Budapest, Hungary
Nóra Zs. Kiss Department of Organic Chemistry and Technology, Budapest
University of Technology and Economics, Budapest, Hungary
vii
Introduction
These days microwave (MW)-assisted chemistry has become an integrant part of
environmentally-friendly (“green”) chemistry. In a part of the cases, the MW
accomplishment offers special advantages compared to the thermal variation.
Besidesthegeneralbenefitsofshorterreactiontimes,higheryields,andselectivity,
certainreactionstakeplaceonlyunderMWconditions.Anadditionaladvantageis
thatanumberofMW-assistedorganicchemicaltransformationsmaybeperformed
under solvent-free conditions.
In this publication, we tried to provide information that represents hot, but less
reviewedtopics.Aftertheoverviewofthedevelopmentsofthethreedecadesofthe
MW discipline, fashionable reactions, such as multicomponent reactions, conden-
sations, coupling reactions, and cycloadditions are surveyed. This chapter is fol-
lowed by a summary of the results attained in the field of organophosphorus
chemistry. Theoretical calculations allowed the interpretation of the results and
considerations on the scope and limitations of the possible use of the MW tech-
nique. Possible simplification of catalysts or catalytic systems under MW condi-
tions are also discussed.
The last part is on the interpretation of advantageous reaction outcomes
encounteredinMW-assistedorganicchemistryonthebasisofassumednonthermal
and thermal effects. The different explanations for the rate enhancing effects are
discussedcritically viawell-selected examples. Thecurrentlyacceptedtheoriesare
presented in a way to elucidate the adequate phenomena, and the most common
misconceptions. Modern experimental techniques in MW chemistry reveal the
fundamentalroleoftemperatureininterpretingtheMWeffects.Thermaleffectscan
be differentiated between macroscopic and microscopic effects, both of which are
discussed in detail with illustrative examples. The concept of nonthermal MW
effects is critically reviewed.
ix
Chapter 1
The Spread of the Application
of the Microwave Technique in Organic
Synthesis
Erika Bálint and György Keglevich
Abstract The first chapter summarizes the birth and spread of the application of
the microwave (MW) technique in organic syntheses placing the stress on the
developmentoftheMWequipment.Thesedaysprofessionalbatchandcontinuous
flow reactorsareavailable,andtheapplicationisknockingatthedoor ofindustry.
(cid:1) (cid:1)
Keywords Microwave Batch reactors Continuous reactors
These days, the protection of our environment and our health is becoming
increasingly importantduetotheworldwide spread ofgreen chemistry.According
to the 12 principles of green chemistry [1], preparation and development of
environmentally-friendly and harmless products and technologies are the main
tasks.Inthiscontext,theapplicationofthemicrowave(MW)techniqueinorganic,
inorganic, medicinal, analytical and polymer chemistry has spread fast [2–8].
Thefirstdomesticmicrowaveovenwasintroducedbyattheendof1955,butthe
widespreaduseoftheseovensinhouseholdsoccurredduringthe1970sand1980s.
From the middle of 1970s, engineers and researchers started to apply the MW
technique in food processing, in the drying industry, in waste remediation and in
analytical chemistry. In the latter case, this technique has been used for sample
preparation(e.g.digestion,extraction,dissolution,etc.)[9–12].Thefirstapplication
ofmicrowaveirradiationinchemicalsynthesiswaspublishedin1986bythegroups
ofGedyeandGiguere[13,14].Sincethen,thenumberofpublicationsinthisfield
has sharply increased (Fig. 1.1). Most of these publications describe important
acceleration of a wide range of organic chemical reactions, excellent repro-
E.Bálint(&)
MTA-BMEResearchGroupforOrganicChemicalTechnology,
1521Budapest,Hungary
e-mail:[email protected]
G.Keglevich
DepartmentofOrganicChemistryandTechnology,BudapestUniversity
ofTechnologyandEconomics,1521Budapest,Hungary
©SpringerInternationalPublishingSwitzerland2016 1
G.Keglevich(ed.),MilestonesinMicrowaveChemistry,
SpringerBriefsinGreenChemistryforSustainability,
DOI10.1007/978-3-319-30632-2_1
2 E.BálintandG.Keglevich
Fig. 1.1 The number of publication on MW-assisted synthesis (1986–2015). Web of Science
keywordsearchon“microwavesynthesis”
ducibility, improved yields and less side reactions compared to conventional
heating.
EarlypioneeringexperimentswereperformedindomesticMWovens,wherethe
irradiationpowerwascontrolledgenerallybyon-offcyclesofthemagnetron,andit
was not possible to monitor the inner temperature in a reliable way, thus the
reactions were not reproducible. The other problems were on the safety issues of
suchexperiments[15–17].Fromtheearly2000s,dedicatedMWinstrumentsstarted
appearing in market, which are indeed suitable for performing chemical reactions
under controlled conditions [2, 3, 18]. All commercially available dedicated MW
reactors consist of a MW cavity, magnetic stirrer, sensor probe (IR sensor or fiber
optic probe), and software that enables on-line temperature/pressure control by
regulating the MW power output.
The MW instruments are classified in two types, monomode (single mode) and
multimodeMWreactors.Themaindifferencebetweenthetwosystemsisthatwhile
in monomode reactors only one reaction vessel can be irradiated, multimode
reactors may accommodate several vessels simultaneously.
A monomode instrument has a small compact cavity, where the microwave
energy is generated by a single magnetron, and directed through a rectangular
waveguidetothereactionmixture,whichispositionedatamaximizedenergypoint
(Fig. 1.2). A highly homogenous energy field of high power intensity is provided,
resulting in exceedingly fast heating rates.
In addition, monomode instruments with a self-tuning circular waveguide are
also available (Fig. 1.3). This cavity features multiple entry points for introducing
the microwave energy into the vessel.
Multimode reactors have larger cavities, in which the microwaves are reflected
from the cavity walls, and distributed in a rather chaotic manner (Fig. 1.4). The
reaction vessels are continuously rotated within the cavity, to provide a steady