Diphenyldiselenide-catalyzed selective oxidation of activated alcohols with tert-butyl hydroperoxide: New mechanistic insights

Article abstract of DOI:10.1021/jo900059y

Diselenides are known precatalysts for catalytic oxidations. The use of these widely available compounds as catalysts for the oxidation of alcohols was investigated, still leaving many mechanistic questions to be answered. By using a range of analytical t

Full text of DOI:10.1021/jo900059y

Diphenyldiselenide-Catalyzed Selective Oxidation of Activated
Alcohols with tert-Butyl Hydroperoxide: New Mechanistic Insights
John C. van der Toorn,†,‡ Gerjan Kemperman,‡ Roger A. Sheldon,† and
Isabel W. C. E. Arends*,†
Laboratory for Biocatalysis and Organic Chemistry, Delft UniVersity of Technology,
Julianalaan 136, 2628 BL Delft, The Netherlands, and Department of Process Chemistry, Schering-Plough,
Molenstraat 110, 5342 CC Oss, The Netherlands
i.w.c.e.arends@tudelft.nl
ReceiVed January 12, 2009
Diselenides are known precatalysts for catalytic oxidations. The use of these widely available compounds
as catalysts for the oxidation of alcohols was investigated, still leaving many mechanistic questions to be
answered. By using a range of analytical techniques, we found evidence for the unexpected involvement
of seleninic anhydride in the catalytic mechanism. The activation time of the diselenide and its influence
on the oxidation reaction itself was also investigated. On the basis of these findings, an improved protocol
for the selective oxidation of activated alcohols was devised resulting in significantly decreased catalyst
loadings (<1%).
Introduction
terminal oxidant.4,5 Major drawbacks of these systems are the
formation of halogenated side products and the use of halogen-
rich solvents. Even though the iodine(III) reagents can be used
chloride- and bromide-free, their use is accompanied by the
formation of 2 equiv of acid.
Alcohol oxidations are highly relevant reactions in synthetic
organic chemistry.1 The development of catalytic systems for
these types of transformations, affording sustainable and atom-
efficient methodologies, is still of great interest.2 Excellent
transition-metal catalysts, based on, e.g., Cu, Pd, Ru, and Pt,
have been developed which allow the use of molecular oxygen
as the terminal oxidant.3 However, these metal catalysts are often
unsuitable for highly functionalized molecules, which are used
as intermediates in the pharmaceutical industry. In these cases,
organocatalytic methodologies can offer a distinct advantage,
due to their high selectivities. A good example of an industrially
applied organocatalyst capable of alcohol oxidations is the
2,2,6,6-tetramethylpiperidinyloxy radical (TEMPO), using bleach
(sodium hypochlorite) or a hypervalent iodine(III) species as
In our search for other main group elements capable of
performing these types of redox reactions with benign oxidants,
our interest focused on the use of organoselenium compounds
as catalysts.6-8 Organoselenides are known to be highly
selective, mild, and reliable reagents for oxidative transforma-
tions.9 The classical organoselenium reagent for alcohol oxida-
tions is benzeneseleninic acid anhydride (BSA), which was
introduced by Barton and co-workers in the late 1970s.10 They
(4) Anelli, P. L.; Biffi, C.; Montanari, F.; Quici, S. J. Org. Chem. 1987, 52,
2559–2562.
(5) DeMico, A.; Margarita, R.; Parlanti, L.; Vescovi, A.; Piancatelli, G. J.
Org. Chem. 1997, 62, 6974–6977.
(6) ten Brink, G. J.; Vis, J. M.; Arends, I. W. C. E.; Sheldon, R. A.
Tetrahedron 2002, 58, 3977–3983.
(7) ten Brink, G. J.; Vis, J. M.; Arends, I. W. C. E.; Sheldon, R. A. J. Org.
Chem. 2001, 66, 2429–2433.
(8) ten Brink, G. J.; Fernandes, B. C. M.; van Vliet, M. C. A.; Arends,
I. W. C. E.; Sheldon, R. A. J. Chem. Soc., Perkin Trans. 1 2001, 224–228.
(9) Mlochowski, J.; Brzaszcz, M; Giurg, M.; Palus, J.; Wojtowicz, H. Eur.
J. Org. Chem. 2003, 4329–4339.
† Delft University of Technology.
‡ Schering-Plough.
(1) Ba¨ckvall, J.-E. Modern Oxidation methods; Wiley: New York, 2004.
(2) Anastas, P. T.; Williamson, T. C. Green Chemistry; Oxford University
Press: Oxford, 1998.
(3) Sheldon, R. A.; Arends, I.; Dijksman, A. Catal. Today 2000, 57, 157–
166.
10.1021/jo900059y CCC: $40.75
Published on Web 03/26/2009
2009 American Chemical Society
J. Org. Chem. 2009, 74, 3085–3089 3085

van der Toorn et al.
SCHEME 1. Mechanism of Alcohol Oxidation by BSA
TABLE 1. Yields of Benzaldehyde (Aldehyde) and Benzoic Acid
(Acid) in Ph2Se2 (5%) Catalyzed Oxidation of Benzyl Alcohol with
1.1 equiv of TBHP (80 °C, 8 h)
SCHEME 2. Rearrangement of Benzeneselenate to
Benzeneseleninic Acid and Ph2Se2
TBHP in H2O
TBHP in decane
solvent
MeCN
xylene
EtOAc
trichloroethane
CCl4
heptane
toluene
aldehyde (%) acid (%) aldehyde (%) acid (%)
67
61
62
60
58
61
79
9
2
11
10
7
66
62
49
48
70
61
86
16
6
10
14
12
8
7
4
5
proposed a mechanism involving the selenenate ester (compound
2) as the intermediate species (Scheme 1).
The aim of the present study was to develop a catalytic
procedure based on aromatic diselenides as the catalysts and
using readily available and stable hydroperoxides as oxidants.
Herein, we report our investigation on the mechanism of Ph2Se2-
catalyzed alcohol oxidations which led to the development of a
new procedure for alcohol oxidations employing as little as 1
mol % of diphenyl diselenide as the catalyst and TBHP as the
terminal oxidant.
Interestingly, if one performs the oxidation of benzyl alcohol
with BSA, a yellow color immediately appears upon addition
of the alcohol which is attributed to the formation of Ph2Se2.10
The formation of Ph2Se2 can be explained by an equilibrium
between 3 equiv of benzeneselenate (4) which gives H2O and
Ph2Se2 and 1 equiv of benzeneseleninic acid (Scheme 2).11
We reasoned that diselenides could be introduced as precur-
sors for the active oxidant as several oxidants are known to
oxidize aromatic diselenides to the corresponding anhydrides.
If this could be done in situ, this would yield a new catalytic
process for the oxidation of alcohols.
Results and Discussion
Ph2Se2-Mediated Oxidation of Benzyl Alcohol: Cata-
lytic and Stoichiometric Reactions. Initially we repeated the
Ph2Se2-catalyzed oxidation of benzyl alcohol as described by
Kuwajima et al.12 This involved reactions in chlorobenzene at
80 °C, employing 10 mol % of Ph2Se2 and 1.5 equiv of aqueous
TBHP. In agreement with Kuwajima’s results, we found that
the use of less than 10 mol % of Ph2Se2 resulted in incomplete
conversion of benzyl alcohol and the formation of a significant
amount of benzoic acid. We also found that the use of TBHP
in decane rather than aqueous TBHP led to an increased yield
and selectivity of the reaction, depending on the solvent used.
In the older reports, chlorobenzene or benzene was the preferred
solvent. As we were not interested in these halogenated or
carcinogenic solvents, we tested various alternatives (Table 1).
The best results were obtained by using an apolar solvent
with a boiling point at or higher than 80 °C, such as heptane or
toluene. When using 5 mol % of catalyst and TBHP, an
induction period of ca. 1 h was observed, suggesting that a
preactivation of the Ph2Se2 catalyst was required. Therefore,
we performed a series of experiments under stoichiometric
conditions to investigate the origin of this induction period. We
found that premixing Ph2Se2 with 1 equiv of TBHP in toluene
for 2 h followed by the addition of 1 equiv of benzyl alcohol
resulted in complete conversion to benzaldehyde within 40 min
(Figure 1). When 2 or 3 equiv of TBHP was added, the rate of
benzyl alcohol oxidation increased only slightly.
In the 1970s and 1980s, much effort was directed toward the
use of organoselenides as catalysts, of which the work of
Kuwajima et al. is the best known. Their best results involved
the use of mesitylene diselenide (0.5 equiv) and aqueous tert-
butyl hydroperoxide (TBHP) (1.5 equiv). This combination was
applied to oxidize a variety of primary (benzylic and aliphatic)
alcohols to the corresponding aldehydes in high selectivity.12,13
Two possible mechanisms were proposed, but neither was
substantiated with experimental evidence. One possible mech-
anism involved a selenenate ester, and the other cycle was based
upon a seleninate ester as the active intermediate. The catalytic
use of simple diphenyl diselenide was also mentioned, but the
authors stated that in this case only benzylic (also secondary
benzylic) and primary allylic alcohols could be fully oxidized
and that using less than 10% mol of this (standard) diselenide
did not result in complete conversion of the alcohol. In the
literature, the use of different diselenides in combination with
sulfonamides as oxidants has been reported with reasonable
success.14,15 The major disadvantage of the use of these
sulfonamides is that they are expensive and not readily available.
(10) Barton, D. H. R.; Brewster, A. G.; Hui, A. H. F.; Lester, D. J.; Ley,
S. V.; Back, T. G. J. Chem. Soc., Chem. Commun. 1978, 952–954.
(11) Hori, T.; Sharpless, K. B. J. Org. Chem. 1978, 43, 1689–1697.
(12) Kuwajima, I.; Shimizu, M.; Urabe, H. J. Org. Chem. 1982, 47, 837–
842.
In theory, the use of 3 equiv of TBHP should result in the
formation of 1 equiv of BSA relative to benzyl alcohol. A further
increase of the amount of TBHP to 4 or 5 equiv resulted in
oxidation of toluene to a mixture of benzyl alcohol and
(13) Shimizu, M.; Kuwajima, I. Tetrahedron Lett. 1979, 2801–2804.
(14) Onami, T.; Ikeda, M.; Woodard, S. S. Bull. Chem. Soc. Jpn. 1996, 69,
3601–3605.
(15) Ehara, H.; Noguchi, M.; Sayama, S.; Onami, T. J. Chem. Soc., Perkin
Trans. 1 2000, 9, 1429–1431.
3086 J. Org. Chem. Vol. 74, No. 8, 2009

SelectiVe Oxidation of ActiVated Alcohols
FIGURE 3. Reaction calorimetry profile of the activation of 0.1 M
Ph2Se2 by 1 equiv of TBHP in toluene.
FIGURE 1. Oxidation of benzyl alcohol with Ph2Se2 preactivated with
different amounts of TBHP in toluene.
FIGURE 4. Reaction calorimetry of the activation of partially oxidized
Ph2Se2.
FIGURE 2. Influence of activation time length on the oxidation of
benzyl alcohol with Ph2Se2 and 2 equiv of TBHP in toluene.
of 196 kJ/mol could be made, based on a calculated heat of
formation of BSA and known gas-phase values for the other
compounds (see the Experimental Section). As there was a huge
acceleration in the last part of the reaction, the question arose
whether or not this could be attributed to the formed BSA.
Therefore, a mixture of Ph2Se2/BSA (95/5) was activated with
TBHP. This revealed that BSA indeed influences the oxidation
of Ph2Se2 to BSA as in this case the activation period was
virtually absent and the enthalpy had the same value (150 kJ/
mol). Presumably, mixing BSA with TBHP gives the intermedi-
ate tert-butyl perseleninic ester, which is possibly a stronger
oxidant than either TBHP or BSA.18 The synthesis of this
compound has so far not been successful in our hands, but we
were able to show that the oxidation of benzyl alcohol with a
mixture of BSA and TBHP proceeded at the same rate as with
BSA alone. However, there was a significant difference in
selectivity. BSA alone gave no overoxidation of benzaldehyde
to the benzoic acid. In contrast, the BSA-TBHP mixture
showed substantial conversion to the acid (5% in 20 min). Yet,
in the presence of Ph2Se2, the aldehyde was not overoxidized,
but the diselenide was converted to the anhydride, thereby
showing the selectivity of the oxygen transfer.
benzaldehyde, which was confirmed in blank experiments in
the absence of alcohol substrate. The oxidation of toluene has
been reported previously using BSA as the oxidant, but these
reactions are thought to occur at higher temperatures and with
longer reaction times.16 We assume that the excess of TBHP
could undergo (selenium-catalyzed) homolytic decomposition
to afford tert-butoxy and tert-butylperoxy radicals which initiate
the autoxidation of toluene. We conclude from these experiments
that it is important to keep the TBHP concentration low to avoid
competing homolytic decomposition of the TBHP and attending
autoxidation of toluene.17
To further understand the preactivation, Ph2Se2 was activated
with 2 equiv of TBHP at different time lengths, followed by
the addition of substrate (Figure 2). The oxidation of the
substrate was smooth and immediate when the preactivation was
performed for 30 min or longer. At shorter preactivation times,
an induction period was observed in conversion of the substrate,
comparable to results of the preliminary catalytic reactions. With
preactivation periods shorter than 15 min, this induction period
of the catalyst is even longer, indicating that the substrate
hampers the activation of Ph2Se2 by TBHP.
Reaction Calorimetry. The activation period was further
investigated by reaction calorimetry. First, the activation of
Ph2Se2 (0.1 M) in toluene with 1 equiv of TBHP was studied
(Figure 3).
Upon addition of the cold TBHP there was an expected drop
in temperature, but after 20-25 min a sudden increase in
reaction temperature was observed. This showed an exothermic
reaction with an enthalpy of approximately 150 kJ/mol, and
careful analysis of the mixture showed that it consisted of one-
third BSA. For the exotherm of this reaction a rough estimation
In order to investigate whether the in situ formed BSA could
be used for a shorter activation period in a second round of
diselenide activation, an experiment was performed in which
Ph2Se2 was activated with 1 equiv of TBHP and was subse-
2
quently reacted with /3 equiv of benzyl alcohol. In this case,
some of the BSA or other oxidized selenium intermediates
should remain in the reaction mixture. TBHP (2/3 equiv) was
subsequently added, and indeed, the preactivation of Ph2Se2 was
instantaneous as indicated by the exotherm (Figure 4).
In a subsequent experiment, the activation of Ph2Se2 by TBHP
was investigated in the presence of 1 equiv of substrate. As
(16) Barton, D. H. R.; Hui, R.; Lester, D. J.; Ley, S. V. Tetrahedron Lett.
1979, 3331–3334.
(17) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidations of Organic
Compounds; Academic Press: New York, 1981.
(18) Bloodworth, A. J.; Lapham, D. J. J. Chem. Soc., Perkin Trans. 1 1983,
471–473.
J. Org. Chem. Vol. 74, No. 8, 2009 3087

van der Toorn et al.
TABLE 2. Results of Optimized Reaction Conditions
substrate
product
TTNa
selectivity (%)
benzyl alcohol
cinnamyl alcohol
benzaldehyde
cinnamaldehyde
115
180
99.1
>99.9
a TTN ) mmol product/mmol catalyst.
SCHEME 4. Catalytic Cycle in the Oxidation of Alcohols
with TBHP as the Terminal Oxidant and Ph2Se2 as Catalyst
FIGURE 5. Reaction calorimetry of activation of 0.1 M Ph2Se2 in the
presence of 1 equiv of benzyl alcohol.
SCHEME 3. Experimental Set-up for the Oxidation of
Alcohols with Ph2Se2
can be deduced from Figure 5, in the presence of substrate the
activation of Ph2Se2 is significantly slower. This can be
explained by taking into account that in the presence of benzyl
alcohol BSA is immediately consumed by oxidation of benzyl
alcohol to benzaldehyde. Therefore, the perester formation is
inhibited, thus reducing or precluding its involvement in the
oxidation of Ph2Se2 by TBHP. The latter result also supports
the hypothesis that perester is involved in the formation of BSA
from Ph2Se2 and TBHP.
a deleterious effect on the reaction, which can be attributed to
the hydrolysis of BSA, thus competing with the alcohol
substrate. This was overcome by adding a drying agent to the
reaction mixture (anhydrous MgSO4 or MS 4 Å) enabling
substrate to catalyst ratios of more than 100 (Table 2).
Based on the above observations, we propose the following
tentative mechanism for the Ph2Se2-catalyzed oxidation of
alcohols with TBHP (Scheme 4).
In summary, a number of the above-mentioned findings are
of importance for the development of an effective Ph2Se2-
mediated oxidation of benzyl alcohol with TBHP as the terminal
oxidant. First, exposure of more than 3 equiv of TBHP relative
to the amount of Ph2Se2 causes overoxidation of benzaldehyde
to benzoic acid and the oxidation of toluene to benzyl alcohol.
We attribute this to the formation of the perseleninic ester, which
can oxidize benzaldehyde easily to benzoic acid. In addition, a
relatively high concentration of TBHP could undergo homolytic
cleavage, thereby promoting the latter two reactions via a
radical-autoxidation process. Therefore, the concentration of
TBHP should remain low throughout the process. Second, the
preactivation of Ph2Se2 by reaction with TBHP to afford BSA
is autocatalytic, that is, the BSA catalyzes its own formation
which we attribute to the formation of the perester, and thus,
regeneration of the active species is most effective when a small
amount of BSA remains present in the reaction mixture.
These findings have led us to the development of a protocol
(Scheme 3) in which first Ph2Se2 is pretreated with TBHP in
order to generate BSA. Next, an amount of an activated alcohol
(such as benzyl alcohol or cinnamyl alcohol) is added that is
insufficient to consume all of the BSA. Subsequently, after the
oxidation of the substrate, another portion of TBHP is added in
order to regenerate all of the BSA.
Conclusions
The Ph2Se2-catalyzed oxidation of activated alcohols with
TBHP as the terminal oxidant is a reaction that has been known
for a long time. The main problem of the methodology was the
high loading of catalyst required. We have shown that benzene-
seleninic anhydride (BSA) is the active oxidant and that it
catalyzes its own formation most likely via the in situ formation
of a perester. If the concentration of TBHP is too high,
homolytic decomposition of this perester results in the autoxi-
dation of solvents containing reactive C-H bonds, such as
toluene, and the autoxidation of benzaldehyde to benzoic acid.
Based upon these findings, we developed a new catalytic
protocol which included the in situ removal of water. A drying
agent could be added, but alternatively, the reaction can be
performed under Dean-Stark conditions, which is more con-
venient on a larger scale. Two activated alcohols, benzyl alcohol
and cinnamyl alcohol, were oxidized by TBHP to the corre-
sponding aldehydes employing <1% of Ph2Se2 as the catalyst.
Compared to other organocatalytic methods, our method is
advantageous in that all compounds are cheap and readily
available, and the method is completely halogen-free. However,
the use of Ph2Se2 as a catalyst precursor has the disadvantage
that only activated alcohols are oxidized smoothly, which was
already found previously.12 Preliminary experiments in the use
of this system in the oxidation of 1-decanol (an aliphatic alcohol)
Initial experiments according to this protocol showed that
substrate/catalyst ratios above 10 could be achieved. However,
the water formed in the oxidation during these cycles showed
3088 J. Org. Chem. Vol. 74, No. 8, 2009

SelectiVe Oxidation of ActiVated Alcohols
By using this sequence, cinnamyl alcohol could be oxidized to
cinammaldehyde (180 mmol was converted; 0.55% Ph2Se2) without
any byproduct formation. In this case, cinnamaldehyde was
dissolved in toluene as a standard solution (2.0 M).
Reaction Calorimetry. This was performed in a Multimax
apparatus: a programmable 4 parallel reactor box, reaction volume
from 25 to 70 mL with overhead stirring, temperature range from
-25 to +150 °C, reflux cooler and inter gas purging. Each reactor
can be set individually for temperature and stirring. Temperature
control modes: Jacket and reactor contents. Reaction calorimetry
is done by adding a known amount of heat to the reaction mixture
using a calibration probe (150 Ω, 24 V).
To a 100 mM solution of Ph2Se2 at 80 °C was added the
appropriate amount of TBHP in decane after which the temperature
difference between the internal sensor (Tr; temperature of the
reaction) and the external sensor (Tj; temperature of the jacket) was
monitored.
Calculation of Heat of Reaction of Oxidation of Diphenyl
Diselenide with tert-Butyl Hydroperoxide. The heat of reaction
for the oxidation of diphenyl diselenide into benzeneseleninic acid
anhydride (BSA) with tert-butyl hydroperoxide can be roughly
estimated from the respective heats of formation of the different
compounds involved, assuming that solvation enthalpies for
substrates and products are equal. For this calculation, the ∆Hf (g)
for BSA was calculated with MOPAC using the semiempirical AM1
theory as -117 kJ/mol (in a comparison of known and calculated
values for diphenyldiselenide, AM1 gave far better results than
PM3; the difference between known and calculation amounted to
an overestimation of only 42 kJ/mol in this case). Other values
were taken from the NIST Chemistry Webbook.19 Thus the ∆Hr
for the reaction: 1/3Ph2Se2 (∆Hf ) 237 kJ/mol) + 1C4H9OOH (∆Hf
) -235 kJ/mol) f 1/3PhSe(O)OSe(O)Ph (∆Hf,calc ) -117 kJ/mol)
+ 1C4H9OH (∆Hf ) -313 kJ/mol) can be estimated as -196 kJ/
mol. Taking the calculated value of Ph2Se2 instead of the true value
leads to -211 kJ/mol. Given the uncertainty in calculated and liquid
phase values, this is in good agreement with the observed heat of
reaction of 150 kJ/mol TBHP.
showed that the dehydrogenation step was slow and not
complete, thereby prohibiting the practical appliciation of the
above-described optimized system. Further investigations are
underway with regard to the substrate scope of the system and
the effect of electron-donating or -withdrawing groups in the
diselenide catalyst on the rate of the reaction.
Experimental Section
Materials. Ph2Se2 (99%), TBHP in decane (5.5 M), benzyl
alcohol (99+%), 1,2-dimethoxybenzene (99+%), molecular sieves
(4 Å), MgSO4 (anhydrous 97%), benzeneseleninic anhydride,
toluene (reagent grade, stored over molecular sieves 4 Å), and ethyl
acetate (p.a.) were all used as received.
Catalytic Reactions. To a stirred solution of benzyl alcohol (2
mmol, 216 mg), 1,2-dimethoxybenzene (0.5 mmol, 69 mg, internal
standard), and Ph2Se2 (0.1 mmol, 31 mg) in 10 mL of toluene was
added TBHP (2.2 mmol, 400 µL) at 80 °C. At several intervals, 50
µL aliquots were withdrawn and quenched with Na2SO3 (100 mg
in 1.5 mL of EtOAc), and the solids were filtered off. The mixture
was then analyzed by GC.
Stoichiometric Reactions. To a stirred solution of Ph2Se2 (1
mmol, 312 mg) and 1,2-dimethoxybenzene (0.5 mmol, 69 mg,
internal standard) in 10 mL of toluene at 80 °C was added TBHP
(5.5 M solution in decane), and after the appropriate amount of
time, benzyl alcohol was added. At several intervals, 50 µL aliquots
were withdrawn and quenched with Na2SO3 (100 mg in 1.5 mL
EtOAc), and the solids were filtered off. The mixture was then
analyzed by GC.
Catalytic Protocol for the Use of Low Concentrations of
Catalyst. To a solution of Ph2Se2 (1 mmol, 312 mg) and
1,2-dimethoxybenzene (5 mmol, 690 mg) in 15 mL of toluene at
80 °C was added first 2 mmol of TBHP (364 µL) with a pump
system (syringe pump equipped with a glass syringe and PFTE
1/16 in. tubing into the reaction), and the mixture was allowed to
stand for 1 h. After this, 1 mmol of benzyl alcohol (103 µL) was
added with a pump system (programmable syringe pump equipped
with a glass syringe and PFTE 1/16 in. tubing into the reaction)
which was allowed to react for 30 min. After this, 1 mmol of TBHP
(182 µL) was added with the pump system, and the mixture was
allowed to stand for 30 min after which benzyl alcohol was added,
and this sequence was allowed to loop 30 times. Anhydrous Na2SO4
was added to dry the reaction in case there were no molecular sieves
in the reaction. The solids were then filtered off, the solvent was
evaporated, and the residue was redissolved in 15 mL of toluene
after which the sequence was restarted. This allowed a total of 115
mmol of benzyl alcohol to be converted (0.86% Ph2Se2) into
benzaldehyde, after which benzoic acid formation could no longer
be suppressed. Another method of water elimination was to perform
a Dean-Stark reflux after 30 cycles of the reaction.
Acknowledgment. This project is financially supported by
The Netherlands Ministry of Economic Affairs and the B-Basic
partner organizations (www.b-basic.nl) through B-Basic, a
public-private NWO-ACTS programme (ACTS ) Advanced
Chemical Technologies for Sustainability). We thank Peter
Hilberink for the assistance in using the Multimax equipment
for the reaction calorimetry.
JO900059Y
(19) Afeefy, H. V.; Liebman, J. F.; Stein, S. E. In NIST Chemistry Webbook;
Linstrom, P. J., Mallard, W. G., Eds.; NIST Standard Reference Database No.
69; National Institute of Standards and Technology: Gaithersburg, MD, http://
webbook.nist.gov (retrieved Jan 7, 2009).
J. Org. Chem. Vol. 74, No. 8, 2009 3089