Atmospheric pressure microwave assisted heterogeneous catalytic reactions

Article abstract of DOI:10.3390/12071399

The purpose of the study was to investigate microwave selective heating phenomena and their impact on heterogeneous chemical reactions. We also present a tool which will help microwave chemists to answer to such questions as "My reaction yields 90% after 7 days at reflux; is it possible to obtain the same yield after a few minutes under microwaves?" and to have an approximation of their reactions when conducted under microwaves with different heterogeneous procedures. This model predicting reaction kinetics and yields under microwave heating is based on the Arrhenius equation, in agreement with experimental data and procedures.

Full text of DOI:10.3390/12071399

Molecules 2007, 12, 1399-1409
molecules
ISSN 1420-3049
© 2007 by MDPI
www.mdpi.org/molecules
Full Paper
Atmospheric Pressure Microwave Assisted Heterogeneous
Catalytic Reactions
Zoubida Chemat-Djenni 1,2,*, Boudjema Hamada 1 and Farid Chemat 3
1 Laboratoire de Synthèse Pétrochimique, Faculté des Hydrocarbures et de la Chimie, Université
M’Hamed Bouguerra, 35000 Boumerdès, Algeria
2 Faculté de Médecine, Université Saad Dahlab, 09000 Blida, Algeria
3 Université d’Avignon et des Pays de Vaucluse, UMR A408 INRA-UAPV, 33 rue Louis Pasteur
84029 Avignon, France
* Author to whom correspondence should be addressed. E-mail: chemats@wanadoo.fr
Received: 15 June 2007; in revised form: 8 July 2007 / Accepted: 9 July 2007 / Published: 11 July
2007
Abstract: The purpose of the study was to investigate microwave selective heating
phenomena and their impact on heterogeneous chemical reactions. We also present a tool
which will help microwave chemists to answer to such questions as “My reaction yields
90% after 7 days at reflux; is it possible to obtain the same yield after a few minutes under
microwaves?” and to have an approximation of their reactions when conducted under
microwaves with different heterogeneous procedures. This model predicting reaction
kinetics and yields under microwave heating is based on the Arrhenius equation, in
agreement with experimental data and procedures.
Keywords: Microwaves, heterogeneous reactions, isomerisation, xylene.
Introduction
Nowadays, an important development in the chemical industry is that many traditional chemical
processing techniques are reaching their optimum performance, while consumer’s demands stretch and
governmental regulations tighten. Within the past 20 years, there has been a growing interest in new
reaction conditions and activation methods, including 'dry conditions' (reactions without solvent) and
reactions under extreme or non-conventional conditions (high pressure, ultrasound or microwave

Molecules 2007, 12
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activation). The effects usually expected are rate enhancements, yield and/or selectivity improvements,
easier work-ups or less polluting processes. Microwave heating makes it convenient to perform
reactions very efficiently in the absence of any organic solvents, under so-called dry media conditions.
The advantages of using dry media conditions go from faster reactions with different selectivity to
more economical conditions due to the absence of organic solvents [1].
The purpose of this study was to investigate microwave selective heating phenomena and the
impact on heterogeneous chemical reactions of using microwave heating. We felt that heterogeneous
catalytic reactions could be good candidates as model reactions, in order to compare not only the
reaction times, yields and ‘green’ procedures, but also energy consumption for microwave and
conventional technologies. Energy efficiency of microwave processes is rarely discussed in published
articles, but the energy consumption should also be considered since an organic synthesis process
consumes non-renewable resources and produces waste, and this could also influence in the near future
environmental acceptability and economic viability.
Results and Discussion
Original thermal 2.45 GHz microwave effect
Frequencies ranging from 3 MHz to 30 GHz i.e. from radio-frequencies to the infrared are being
used to process food. Depending on the chosen frequency and the particular design of the applicator,
treatment by electromagnetic energy at different wavelengths has distinct features. For example, in
microwave ovens electromagnetic waves with centimeter wavelengths freely propagate and are
absorbed by solid or liquid phase food products. The principle of microwave heating is that the
changing electrical field interacts with the molecular dipoles and charged ions. The heat generated by
the molecular rotation is due to friction of this motion.
The influence of microwave energy on chemical or biochemical reactions is strictly thermal. The
microwave energy quantum is given by the usual equation W = h ν. Within the frequency domain of
microwaves and hyper-frequencies (300 MHz - 300 GHz), the corresponding energies are 1.24 10-6 -
1.24 10-3 eV, respectively. These energies are much lower than the usual ionisation energies of
biological compounds (13.6 eV), of covalent bond energies like OH (5 eV), hydrogen bonds (2 eV),
Van der Waals intermolecular interactions (lower than 2 eV) and even lower than the energy
associated to Brownian motion at 370C (2.7 10-3eV). From this scientific point of view, direct
molecular activation of microwaves should be excluded. Some kind of stepwise accumulation of the
energy, giving rise to a high-activated state should be totally excluded due to fast relaxation [2]. Like
Peterson [3] wrote in many of his articles: “The question and the debate of the non thermal effect of
microwave give a lot of damage for the reputation of this technology and its application in industry”.
Microwaves are only absorbed by dipoles, transforming their energy into heat.
Heat transfer advantages of applying microwave power, a non contact energy source, into the bulk
of a material include: faster energy absorption, reduced thermal gradients, selective heating and
virtually unlimited final temperatures. For chemical production, the resultant value could include:
more effective heating, fast heating of catalysts, reduced equipment size, faster response to process
heating control, faster start-up, increased production, and elimination of process steps.

Molecules 2007, 12
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Microwave assisted heterogeneous catalytic reactions
Most industrial chemical reactions are carried out in a solvent in the presence of solid catalysts.
When the reaction is conducted in a heterogeneous medium using a dissipative and/or catalytic solid
phase and under microwave heating, the reaction rate increases compared to classical heating under the
same conditions (pressure, temperature and reagent concentrations). In this paper, several reactions of
industrial interest have been studied: isomerisation of m-xylene to p-xylene in presence of aluminum
intercalated montmorillonite, Wacker oxidation of cyclohexene with PdCl2 in the presence of heptane
as solvent, hydrolysis of hexanenitrile to hexanoic acid and esterification of fatty acids. Aluminum
intercalated montmorillonite or granulated ceramics (diameter 5 mm) are used as a catalyst and
dissipative solid phase.
When the catalyst is introduced in solid granular form, the yield and the rate of the heterogeneous
isomerisation, oxidation, esterification and hydrolysis reactions increases with microwave heating as
compared to conventional heating under the same reaction. Table 1 shows an increase yield of 200%
for the oxidation and 150% for hydrolysis when the reaction is conducted in the microwave batch
reactor.
Table 1. Heterogeneous reactions under microwave and classical heating.
Chemical reaction
T(°C) time (min) MW Yield (%) Classical Yield (%)
Isomerization of m-xylene
Hydrolysis of hexanenitrile
Oxidation of cyclohexene
Esterification of stearic acid
400
100
80
30
60
25
40
26
97
16
26
12
83
60
140
120
The increase in reaction rate corresponds to a virtual difference in reaction temperature. Since the
bulk temperature is equal for both the conventional and microwave heated systems, there must be an
elevated temperature at the local reaction site; i.e. the catalytic surface. This is possible since the heat
transfer by microwaves depends on the specific loss factor of the different materials - the catalyst and
the solvent. Many metallic catalysts are semi-conductors and will readily absorb microwave energy,
especially at higher temperatures.
The apparent temperature of the catalytic site under microwave irradiation can be estimated from
the initial reaction rates. The reaction rate is connected to the temperature by the Arrhenius equation k
= A exp (-Eact/RT). For two temperatures, the ratio of the respective reaction rates is related to:
⎛ ⎞
⎛
⎜
⎝
⎞
⎟
⎠
k2
Eact
R
1
1
ln
=
−
(1)
⎜ ⎟
k
T
T
⎝ ⎠
1
1
2
From a kinetic analysis of the esterification reaction, the activation energy (Eact) for the hydrolysis
of hexanenitrile has been determined to be 70 ± 3 kJ/mole. From equation (1), it follows that the
apparent elevated temperature of the catalyst for the batch reactions was calculated to be 9 ± 1 K
higher than the measured bulk temperature.
In the steady state, the microwave heat transfer to the catalyst is equal to the heat loss of the
catalyst to its surroundings. The resulting ΔT will be linearly dependent on the difference in loss factor
and the radius of the catalyst.

Molecules 2007, 12
1402
Figure 1. Microwave and classical continuous reactors [4].
catalyst
vessel
catalyst
catalyst
vessel
vessel
doubel
cover
microwaves
microwaves
Fig 1.a
Fig 1.b
Fig 1.c
pump
pump
pump
To prove the essential combination of microwave and catalyst, the continuous flow microwave
reactor (Figure 1) has been used in two different set-ups. In the first experimental set-up (Figure 1a)
the solid catalyst is submitted to microwave irradiation and the liquid is heated when it passes through
the catalyst. In the second experiment (Figure 1b), only the liquid is heated by microwaves when it
circulates in the cavity vessel and the catalyst is placed outside the microwave cavity. The temperature
was maintained and checked to be constant throughout the circuit, since the heat loss to the
surrounding occurs mainly in the cavity where it is compensated by microwave energy. In the third
experiment (Figure 1c), the reaction was conducted in a conventional continuous reactor operating
under the same conditions (temperature, concentration and pressure) as the microwave continuous
reactor.
Figure 2. Influence of the location of the catalyst in continuous microwave reactor
(ο) Fig 1.a (Δ) Fig 1.b (•) Fig 1.c.
100
90
80
70
60
50
40
30
20
10
0
0
20
40
60
80
100
120
time (min)
In Figure 2, the yield is plotted as a function of time for the three experiments at 80 °C and for a
flow rate of 1.33 mL/s. Only a direct heating of the catalyst by microwaves (Figure 1a) gave an
increase of initial esterification reaction rate of 150%. Conventional heating of the catalyst vessel
(Figure 1c) and microwave heating with the catalyst outside the cavity (Figure 1b) gave identical
results because the temperature at the catalytic surface was equal to the bulk temperature. Although the
bulk temperature in all experiments was the same, there will be a higher temperature at the surface of
the catalyst when it is directly heated by microwaves.

Molecules 2007, 12
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Prediction model: Arrhenius equation
The principal question which microwave chemists ask is why a category of reactions is accelerated
by microwaves, like esterification of fatty acids, acylation of aromatic ethers or Diels-Alder reaction,
and a second one is not accelerated by microwaves, like arylation of alkenes, hydrolysis of sugars or
cyclisation of citronellal [1].
In the field of microwave assisted organic synthesis, scientist report their results in terms of the
yield obtained after a certain time. In order to estimate the influence of the microwaves on the different
reaction times or yields obtained when either microwave or conventional heating is applied, it is useful
to have a numerical approximation for the processes involved [5-6].
We present a tool which will help microwave chemists estimate microwave reaction kinetics and
yield parameters related to the process setting for commercial microwave reactors. This model
predicting reaction kinetics and yields under microwave heating is based on the Arrhenius equation, in
agreement with experimental data and procedures. Chemists could answer to such questions as “my
reaction yields 90% after 7 days at reflux; is it possible to obtain the same yield after a few minutes
under microwaves?” or “my reaction is not activated by microwaves, what is the problem?” The
prediction tool is freely available from the authors and is hopefully helpful for the comprehension of
microwave chemistry, to rapidly explore the ‘chemistry space to increase the diversity of the
microwave accelerated reactions, or to compare results with scientists in the microwave chemistry
field.
For a homogeneous chemical reaction system, it is mainly the fast heating rate that accounts for the
differences observed. In comparison with classical heated systems, microwaves give us the opportunity
to reach process condition in time and/or temperatures that are not normally accessible. A high
temperature results in a fast reaction rate; thus a fast heating results in a quick completion of the
reaction without essentially changing the reaction kinetics. That is, if the reaction time is in the order
of magnitude of the heating time. Although classical heat transfer is often not considered to be a
limiting factor in laboratory scale experiments, the successful application of closed plastic reaction
vessels, proves that even at a small scale, the application of microwave heating makes a reduction in
reaction time practical. Heating rates can also influence the selectivity between two competing
processes. The reaction rate of one path might increase more with the temperature then the other.
Through analysis of the classical Arrhenius behaviour, it will be shown that the region in which we
can discriminate between two similar reactions is in practice quite limited. Rapid volumetric heating
was also found to improve the reaction in processes with a phase transfer.
The volumetric heating aspect is particularly beneficial in solvent free reaction systems, where the
concentrations are high and the conductive heat transfer limited. A heat transfer rate similar to that of
microwaves is often not feasible by conventional means at a larger scale. This is inherent to the severe
temperature gradient, which causes degradation at the surface of the reactor. The application of
volumetric heating and the fact that microwave can be directly regulated, make it feasible to work just
below the degradation limit temperature. In solvent reaction systems, the volumetric heating might
result in super heated boiling. The absence of nucleation sides in the bulk of the homogeneous liquid
results in a reverse thermal gradient. The liquid can only loose heat by boiling at the reactor surface or

Molecules 2007, 12
1404
top liquid surface. The super heated temperature of the bulk is very depended on the thermodynamic
and dielectric properties of the solvent. The phenomena can be applied to conduct homogeneous
reactions at 30 degrees higher temperature then classical possible under atmospheric pressure,
resulting in a corresponding reaction rate increase.
Volumetric heating does not imply a homogeneous temperature distribution. Especially in batch
processing, the result of a high standing wave ratio is local hot spots, which might be several 10 to 100
°C hotter than the average temperature. As the reaction rate increases non-linear with the temperature,
will the observed average reaction rate be somewhat higher than the reaction rate corresponding with
the average temperature.
The material selective nature of microwave heating results in more defined and localised hot spots
in a heterogeneous system because of the difference in loss between the two media. In heterogeneous
catalysis, the catalyst can have a steady state temperature well above the continuous medium.
Although the catalytic side might actually occupy a small fraction of the total systems volume, the
reaction only proceeds there. Consequently will the observed reaction rate be faster then what would
be expected on basis of the measured bulk temperature. From a simple two-compartment model it can
be concluded that in this case, the mass exchange and reactor cooling are crucial factors. The effect on
the overall kinetic as a function of the thermal energy flow will be discussed.
Figure 3: Experimental procedures generally used in microwave assisted organic synthesis.
Microwave assisted organic synthesis
Homogeneous medium
Heterogenous medium
High pressures
5 to 100 bars
Atmospheric
pressure
High pressure
5 to 100 bars
Increase of the
Boiling point
Selective heating
Increase of boiling point
Selective heating
Gains of ΔT = 10 – 50°C
Gains of ΔT = 10 – 100°C
Gains of ΔT = 10 – 100°C
Atmospheric
pressure
Gains of ΔT = 10 – 100°C
Gains of ΔT = 10 – 100°C
Rapid heating
containment
Over boiling
Gains of ΔT = 1 – 40°C
Adsorbent
(montmorillonite)
Convector
(graphite)
Absence of support
Presence of support
‘dry’ media
absence of solvant

Molecules 2007, 12
1405
According to the selected experimental procedure, a reaction conducted under microwaves gains
10 to 100°C in comparison with the maximum temperature reached by conventional heating (Figure
3). Advantages of applying microwave power, a no contact energy source, into the bulk of a material
include: faster energy absorption, reduced thermal gradients, selective heating and virtually unlimited
final temperature. For chemical synthesis, the resultant value could include: more effective heating,
fast heating of catalysts, reduced equipment size, faster response to process heating control, faster
start-up, increased production, and elimination of process steps.
The ideal model to which every researcher seeks is obviously the theoretical and explanatory
model which is built from fundamental laws. The simplest example of this type of model, in the field
of chemistry, is the Arrhenius equation:
k = A exp (- Eact/ RT)
where Eact : Activation energy ; k : rate constant ; T : reaction temperature ; A : frequency factor ; R :
constant of ideal gas. Another relation exists between activation energy and the temperature factor
which mesure the relative enhancement of reaction rate with the increase of reaction temperature ΔT:
Ln (kT) = Ln (A) - Eact / (R * T)
Ln (kT+ΔT) = Ln (A) - Eact / (R * (T+ΔT)
We deducted: Ln (kT+ΔT / kT) = ΔT * Eact / (R * T * (T+ΔT))
In general chemistry textbooks, it is usually assumed that the temperature factor kT+ΔT/kT doubles
when the reaction temperature is increased by a factor of ΔT = 10°C. This assumption could give
incorrect conclusions, because it is valid only for specific values of temperature and activation energy.
In this work, we have considered the temperature induced by microwaves as the major factor
influencing acceleration of organic synthesis. We have made a similarity between the temperature
factor and the microwave ’acceleration effect’ noted: M = kMW / kConv. = kT+ΔT / kT
This microwave factor M represents the ratio between the reaction rate under microwaves (at a
temperature of T + ΔT) and the reaction rate under conventional heating (at a temperature T). For first
order organic reactions, the microwave factor also represents the ratio between reaction times under
conventional heating and microwaves: M = treact. (Conv.)/ t react. (MW).
Table 1 is generated from the equation of the microwave factor in function of reaction temperature,
activation energy and elevated temperature induced by microwaves in function of the experimental
procedure used. The reactions could be divided into two categories according to the activation energy
and to the microwave ‘acceleration effect’ factor: a) Reactions accelerated by microwaves: high
activation energy > 100 kJ/mole. In this category, an increase of temperature by a few degrees could
enhance dramatically the organic reaction by dividing the reaction temperature by 100 to 1,000,000. b)
In the second category, we have reactions not accelerated by microwaves that have low activation
energy. They need a maximum of microwave energy to have a great increase in reaction temperature
of more than 100°C to see a minor effect in reaction yields and kinetics. To have the maximum
microwave ‘acceleration effect’ factor, the reaction has to possess high activation energy, conducted at
low temperature in the conventional procedure, and realized with a maximum temperature gradient
under appropriate microwave procedure.

Molecules 2007, 12
1406
The table could be used also for yield and selectivity calculations by entering the appropriate
kinetic equations regarding the order of the reaction and the number of reagents used. For example, we
could calculate time and yield for a first order reaction by these equations.
Reagent
Product
t=0
t=t
a
0
a-x
x
The reaction rate for a first order reaction: v = k * (a-x). By integration, we could find the kinetic
equation: kT * t = Ln (a / (a-x)) for conventional heating; and kT+ΔT * t = Ln (a / (a-x)) for microwaves.
Table 2. Prediction of microwave assisted organic synthesis [7].
reaction temperature
T = 50 °C
reaction temperature
T = 100 °C
reaction temperature
T = 200 °C
reaction temperature
T = 400 °C
T = TMO - T Conv.
T = TMO - T Conv.
T = TMO - T Conv.
T = TMO - T Conv.
Δ
Δ
Δ
Δ
Eact. (J/mole)
20 000
T = 10
T = 50
3
T = 10
T = 50
2
T = 10
T = 50
2
T = 10
T = 50
Δ
Δ
ΔΤ = 100
6
Δ
Δ
ΔΤ = 100
4
Δ
Δ
ΔΤ = 100
2
Δ
Δ
ΔΤ = 100
1
2
2
2
3
4
5
6
1
1
2
2
2
3
3
4
1
1
1
2
2
2
2
2
1
1
1
1
1
1
1
2
1
2
2
3
3
4
6
7
2
3
40 000
7
34
5
15
3
6
60 000
20
197
10
60
4
14
4
80 000
54
1144
6656
38716
225182
1309730
21
234
7
35
6
100 000
120 000
140 000
160 000
147
399
1084
2942
45
914
11
18
30
49
85
10
16
25
40
97
3572
13966
54604
205
499
1213
208
445
Microwave 'acceleration' factor M = kMO / kConv. = kT+ΔT / kT = treact (Conv.) / treact (MW)
Time to yield 90% (x/a = 0.9) is equal to:
(t9/10 conv. = Ln (10) / kT for conventional heating.
(t9/10 MW = Ln (10) / kT+ΔT for microwaves.
)
)
The yield could be calculated by:
Y (%)conv. = x/a * 100= (1 – exp (-kT * t)) * 100
Y (%)MW = x/a * 100= (1 – exp (-kT+ΔT * t)) * 100
If an organic reaction (activation energy of 100 kJ/mole) is conducted in a conventional procedure
at 100°C for 7 days, it will be finished after 3 days in an homogeneous media with an over-boiling
phenomena (TMO=110°C; ΔT=10°C), or in 4 hours in microwave ‘dry media’ (TMO=150°C; ΔT=50°C),
or in 11 minutes in a microwave reactor under pressure or using a convector like graphite
(TMO=200°C ; ΔT=100°C).
The prediction model can be applied to organic reactions with high or low activation energies.
Hydrolysis of nitriles to carboxylic acids has an activation energy of 120 kJ/mole. This reaction yields
76% after heating conventionally at 140°C for 7 days. The prediction model shows that this reaction

Molecules 2007, 12
1407
could be finished with a yield of 99% after only 30 minutes when applying microwaves under high
pressure (in a Teflon bomb) at a reaction temperature of 240°C. This prediction is in accordance with
published results [8].
Cost, environmental friendliness and scale-up
The reduced cost of extraction is clearly advantageous for the proposed microwave heterogeneous
catalysis reactions (MHCR) in terms of time and energy. The energy required to perform isomerization
of m-xylene with the two reaction methods are 0.8 kWh for the conventional procedure and 0.04 kWh
for the microwave assisted heterogeneous catalysis reaction, respectively. The power consumption has
been determined with a watt meter at the microwave generator entrance and the electrical heater power
supply. The energy efficiency of the solvent free microwave method is considerably higher than the
conventional procedure if we take in account the short reaction times required and cleanliness of the
process.
Figure 4. Schematic of a 6kW continuous microwave heterogeneous-media reactor. Total
length 4 m.
Antenna
Waveguide
Pyrex Reaction
supports
6kW 2450 MHz
GENERATOR
Resonantie
cavity volume
Power
meters
Impedantie
adjustment
(stubs)
Entrance and
exit chokes
Adjustable cavity volumes
for optimal resonance
Teflon
shield
Regarding environmental impact, the calculated quantity of carbon dioxide injected into the
atmosphere is higher in the case of the conventional procedure (640 g CO2/experiment; 12,800 g CO2/
mole of product) than for the microwave solvent free procedure (32 g CO2/experiment; 640 g CO2/
mole of product). These calculations have been made according to literature: to obtain 1 kW h from

Molecules 2007, 12
1408
coal or fuel, 800 g of CO2 will be injected into the atmosphere during the combustion of fossil fuel [9].
These results are in accordance with previous published articles claiming that microwave energy is
cleaner than conventional heating for promoting chemical reactions [10].
In this study, we present microwave heterogeneous catalytic reactions as an “environmentally
friendly” synthesis method suitable for preparation of xylene, nitriles, oxides, etc. It is a very clean
method, which avoids the use of large quantities of solvent and voluminous reactors for large scale
applications. It could also be used to produce larger quantities by using existing large scale microwave
reactors. These microwave reactors are suitable for the heterogeneous catalytic reactions of 10, 20 or
100 kg of products at a time (Figure 4) [11].
Safety considerations
Microwave chemistry and processing are simple and can be readily understood in terms of the
operating steps to be performed. However, the application of microwave energy can pose serious
hazards in inexperienced hands. A high level of safety and attention to details when planning and
performing experiments must be used by all the persons dealing with microwaves.
Conclusions
In perspective, we think that selective heating is one of the specific microwave effects that can be
exploited to improve chemical processes by reducing the energy consumption with higher yields and a
minimum of waste. A new prediction tool for microwave assisted organic synthesis has been
developed to facilitate the estimation of reaction rate, time, yield, conversion and selectivity. This
simple approach is based on the Arrhenius equation and need only a knowledge of the activation
energy of the reactions, which could be known from experimentation, bibliography (articles, books,
etc.) databases (Belstein) or chemical softwares (ChemDraw, HyperChem, etc). The prediction model
also allows determination of the optimum microwave procedure suitable for a studied reaction. The
results indicate also a significant gain in energy efficiency using microwaves: 20-fold reduction in
energy demand on switching from electrical heater power supply to microwave reactor. Microwave
provides highly focused energy, enabling rapid reaction, substantial savings of energy consumption,
and a reduced environmental burden (less CO2 injected into the atmosphere).
References and Notes
1. Loupy, A. Microwaves in organic synthesis, 2nd ed.; Wiley-VCH: Weinheim, 2006.
2. Metaxas, A.C.; Meredith, R.J. Industrial microwave heating; Peregrinus Ltd.: London, 1993.
3. Peterson, E.R. Microwave Chemical Processing. Res. Chem. Intermed. 1994, 1, 93-96.
4. Chemat, F.; Esveld, D.C.; Poux, M.; Dimartino, JL. The role of selective heating in the
microwave activation of heterogeneous catalysis reactions using a continuous microwave. J.
Microwave Power E. E. 1998, 33, 88-94.
5. Roberts, B.A.; Strauss, C.S. Toward rapid, "green", predictable microwave-assisted synthesis.
Acc. Chem. Res. 2005, 38, 653-661.

Molecules 2007, 12
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6. Roberts, B.A.; Strauss, C.S. Development of predictive tools for optimizing organic reactions.
Molecules 2004, 9, 459-465.
7. The prediction tool (in Excel table format) is available free of charge from the authors by e-mail.
8. Chemat, F. Towards the rehabilitation of the Mathews' “dry” hydrolysis reaction using microwave
technology. Tetrahedron Lett. 2002, 43, 5555-5557.
9. Bernard, J. Les centrales thermiques. Sci. Vie 2001, 214, 68-69.
10. Gronnow, M.J.; White, R.J.; Clark, J.H.; Macquarie, D.J. Energy Efficiency in Chemical
Reactions: A Comparative Study of Different Reaction Techniques. Org. Proc. Res. Dev. 2005, 9,
516-518.
11. Esveld, E.; Chemat, F.; Van Haverin, J. Design, modelling and performance of a pilot scale
continous microwave dry media reactor. Chem. Eng. Tech. 2000, 23, 279-283.
Sample Availability: Available from authors.
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