Boron nitride nanoplatelets as a solid radical initiator for the aerobic oxidation of thiophenol to diphenyldisulfide

Article abstract of DOI:10.1002/cctc.201402876

Boron nitride (BN) nanoplatelets suspended in ethanol were obtained through the sonication of BN powders prepared through biopolymer-templated pyrolysis and air calcination of (NH₄)₃BO₃-chitosan powders. AFM measurements indicate that BN nanoplatelets have an average height of 1.5 nm and length and width dimensions between 30 and 100 nm. BN nanoplatelets exhibit higher catalytic activity for the molecular oxygen-mediated oxidation of aromatic thiols to the corresponding disulfides than do boron and nitrogen-codoped graphene or commercial bulk hexagonal BN. The reaction scope includes substituted aromatic and heteroaromatic thiols, whereas aliphatic thiols are considerably less reactive. The hot filtration test and radical quenching by N-tert-butyl-α-phenylnitrone support an autoxidation mechanism involving thiyl radicals. BN nanoplatelets are deactivated during the course of the reaction owing to aggregation. The present study uncovers the activity of BN nanoplatelets used as an insoluble radical initiator of S-H bonds. Aerobics is fun: Boron nitride nanoplatelets prepared through pyrolysis and sonication demonstrate higher catalytic activity for the aerobic oxidation of thiophenol.

Full text of DOI:10.1002/cctc.201402876

DOI: 10.1002/cctc.201402876
Full Papers
Boron Nitride Nanoplatelets as a Solid Radical Initiator for
the Aerobic Oxidation of Thiophenol to Diphenyldisulfide
[a, b]
[b]
[b]
[b]
Amarajothi Dhakshinamoorthy,*
Hermenegildo Garcia*
Ana Primo, Ivan Esteve-Adell, Mercedes Alvaro, and
[b, c]
Boron nitride (BN) nanoplatelets suspended in ethanol were
obtained through the sonication of BN powders prepared
through biopolymer-templated pyrolysis and air calcination of
commercial bulk hexagonal BN. The reaction scope includes
substituted aromatic and heteroaromatic thiols, whereas ali-
phatic thiols are considerably less reactive. The hot filtration
test and radical quenching by N-tert-butyl-a-phenylnitrone
support an autoxidation mechanism involving thiyl radicals. BN
nanoplatelets are deactivated during the course of the reaction
owing to aggregation. The present study uncovers the activity
of BN nanoplatelets used as an insoluble radical initiator of
SÀH bonds.
(
NH ) BO –chitosan powders. AFM measurements indicate that
4 3 3
BN nanoplatelets have an average height of 1.5 nm and length
and width dimensions between 30 and 100 nm. BN nanoplate-
lets exhibit higher catalytic activity for the molecular oxygen-
mediated oxidation of aromatic thiols to the corresponding di-
sulfides than do boron and nitrogen-codoped graphene or
Introduction
There is a considerable interest in finding alternatives to noble
and “critical” transition metals in catalysis. One of the possibili-
ties to avoid the use of transition-metal-containing catalysts is
carbocatalysis, in which the active sites are embedded in
same structure as graphene, but has different physical proper-
ties, such as the lack of electrical conductivity, complete trans-
parency, and emission in the deep UV region. BN is chemically
more robust than graphene, and this robustness is, in princi-
ple, advantageous for its use in catalysis.
[
1–4]
a carbon matrix.
Because graphene and related materials
have become widely available, carbocatalysis is experiencing
a considerable growth and it appears that many different
types of organic reactions, particularly oxidations, can be cata-
Perhaps the main reason why, in contrast to graphene, BN
has not yet been explored as a catalyst is that single- or few-
layer BN suspensions are still difficult to prepare, particularly in
[
5]
[8–11]
lysed by graphene. As a consequence, the use of single- or
few-layer graphene and related nanomaterials as catalysts is
becoming an active area of research aimed at exploring the
potential of this type of materials to compete with convention-
al transition-metal catalysts. In this context, one 2D nanomate-
rial that has not been reported as an insoluble radical initiator
till date is boron nitride (BN). Single-layer BN is composed of
conventional, not highly viscous solvents.
This is due to the
difficulty in exfoliation of bulk hexagonal BN (h-BN) particles
that are chemically inert and, in contrast to graphite, cannot
be oxidised to promote exfoliation. Alternative procedures for
the preparation of thin-walled BN samples are based on the
synthesis of BN from aminoborane along with the generation
[12]
of bubbles through the evaporation of ethanol. We have re-
cently developed a new procedure that can be used to pre-
pare BN either as a film or as a type of powder that can be
2
a one-atom-thick sheet of alternating sp boron and nitrogen
[
5–10]
atoms in a hexagonal arrangement.
Single-layer BN has the
[13]
easily exfoliated, thus making available BN suspensions. This
methodology makes it possible to explore the catalytic activity
of few-layer BN nanoplatelets that up to now have remained
undisclosed. Although by now there are sufficient reports on
the catalytic activity of graphene and related carbon materi-
[
a] Dr. A. Dhakshinamoorthy
School of Chemistry
Madurai Kamaraj University
Tamil Nadu 625 021 (India)
E-mail: admguru@gmail.com
[5]
als, the catalytic activity of BN remains unknown. Herein, we
report that single- and few-layer BN nanoplatelets suspended
in ethanol promotes the oxidative coupling of thiophenol (1)
to diphenyldisulfide (2).
[b] Dr. A. Dhakshinamoorthy, Dr. A. Primo, I. Esteve-Adell, Prof. M. Alvaro,
Prof. H. Garcia
Instituto de Tecnologꢀa Quꢀmica,
and Chemistry Department CSIC-UPV
Av. De los Naranjos s/n, 46022 Valencia (Spain)
E-mail: hgarcia@qim.upv.es
Disulfides have been used extensively in chemical and bio-
[
14–17]
logical studies.
They are also often used as reagents in or-
[18,19]
[20]
[
c] Prof. H. Garcia
Centre of Excellence for Advanced Materials Research
King Abdulaziz University
ganic syntheses
and as a protecting group for thiols.
One of the most commonly used methods for the synthesis of
disulfides is the oxidative coupling of thiols with permanga-
Jeddah 80200 (Saudi Arabia)
[21]
[22]
[23]
[24]
nate, halogens, iron(III) chloride, and peroxides as re-
agents. Furthermore, transition-metal complexes have been
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402876.
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used as catalysts for the conver-
[
25–27]
sion of thiols to disulfides.
The aerobic oxidation of thiols
to disulfides is a green alterna-
tive to those using other oxidis-
ing reagents such as organic
peroxides
in
stoichiometric
amounts. In this context, the
aerobic oxidation of thiols to di-
sulfides has been reported with
heterogeneous catalysts such as
[
28]
metal–organic
frameworks,
[
29]
graphite oxide, neutral alumi-
[
30]
na, copper nanoparticles sup-
ported on diamond nanoparti-
[
31]
cles,
and gold supported on
[
32]
CeO2. The selection of this re-
action to check the catalytic ac-
tivity of BN was based on the
number of precedents showing
Figure 1. a and b) AFM images of BN platelets of two different samples obtained following the procedure indicat-
ed in Scheme 1, showing length and width dimensions ranging from 30 to 80 nm. c) Height of three representa-
that graphene can promote the tive BN nanoplatelets. d) Statistical distribution of the height of these platelets, showing that more than 80% of
the particles comprise less than four BN layers.
oxidation because of the pres-
[
33–35]
ence of defects,
such as
[
29]
thiols, and also because some
transition metals are deactivated in the process of thiol oxida-
tion owing to the strong interaction of the metal with thiolate
BN nanoplatelets were characterised by X-ray photoelectron
spectroscopy analysis, and the peaks of boron and nitrogen
present in a 1:1 atomic ratio at 190.75 and 398.20 eV binding
energy were recorded, which were consistent with the values
[
36]
groups. We anticipated that the chemical inertness of BN
would make the use of thiols as substrates possible.
[39]
reported in the literature for single-layer BN (Figure S1). In
Raman spectroscopy and XRD, the characteristic peaks of BN
Results and Discussion
À1
[39]
at 1380 cm and 278 were recorded (Figure S2). High-resolu-
tion TEM shows the structural ordering at the microscopic
scale of the material, and selected area electron diffraction
shows the hexagonal symmetry
Suspensions of BN nanoplatelets were obtained through the
pyrolysis of dry (NH ) BO –chitosan powders at 9008C under
4
3
3
of the layers. AFM (Figure 1)
shows that BN suspensions are
composed of BN nanoplatelets
with an average height of
1.5 nm (approximately three
layers) and length and width di-
mensions between 30 and
80 nm.
These BN nanoplatelets were
tested as catalysts for the oxida-
tion of thiols to disulfides. In the
Scheme 1. Procedure for the preparation of h-BN nanoplatelets: i) precipitation of the solution of H
3 3
BO +chitosan
first stage,
1 was used as
in NH OH (solution 25%), ii) pyrolysis at 9008C, iii) calcination at 10008C, and iv) exfoliation of BN nanoplatelets.
4
a model substrate to optimise
the reaction conditions. The
argon flow and subsequent air calcination at 10008C
Scheme 1). The rationale of this procedure is derived from the
reported formation of graphene through the pyrolysis of chito-
aerobic oxidation of 1 to 2 in the absence of a catalyst resulted
in 6% conversion. In contrast, the presence of BN nanoplate-
lets resulted in complete conversion of 1 after 8 h under at-
mospheric oxygen pressure with a selectivity towards 2 higher
than 99%. The time–conversion plot for the conversion of 1 to
2 with BN as a promoter is shown in Figure 2. To put the activi-
ty of BN nanoplatelets into context, a series of other related
materials such as bulk h-BN and doped graphenes were
screened under the same reaction conditions. Thus, boron and
(
[
37,38]
san
and the comparison of graphene and BN structures in
such a way that chitosan pyrolysis is templating BN forma-
tion. Subsequently, combustion of graphene in air results in
BN particles that can be easily exfoliated and suspended in
water, ethanol, dichloromethane, and other volatile organic
solvents.
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Figure 3. Effect of the amount of BN present in the system on the aerobic
oxidation of 1 to 2 in the presence of a) 10, b) 5, and c) 3 mg of BN.
Figure 2. Time–conversion plot for the aerobic oxidation of 1 to 2 with
a) BN, b) boron and nitrogen-codoped graphene, c) commercial h-BN, and
d) blank reaction without any catalyst.
[a]
Table 1. Aerobic oxidation of 1 to 2 promoted by various materials.
nitrogen-codoped graphene exhibited 51% conversion of
Entry
Promoter
T
Conversion
[%]
Selectivity
[%]
1
after 8 h under identical reaction conditions. In contrast, the
[
8C]
conversion of 1 was only 23% after 8 h with commercial h-BN
as a promoter under identical reaction conditions. The avail-
able kinetic data indicate that the initial reaction rate and the
final conversion of 1 with these materials were lower than
those achieved with BN nanoplatelets (Figure 2). These experi-
mental data reveal that BN lacking a transition metal can pro-
mote chemical reactions. The enhanced activity of BN as com-
pared with other catalysts is believed to be due to its platelet
morphology, a thin-layer structure with fine distribution of
boron and nitrogen atoms; the nitrogen atoms are preferen-
tially located at the periphery of the nanoplatelets. The lack of
such preferential location of nitrogen atoms at the periphery
and the larger sheet dimensions of boron and nitrogen-codop-
ed graphene can be responsible for its lower activity than that
of BN. As expected, replacing oxygen by nitrogen drastically
reduced the conversion of 1, which still undergoes some oxi-
dation owing to the incomplete removal of residual oxygen
from the reaction medium. Furthermore, the conversion of
1
2
3
4
5
6
7
8
–
BN
70
70
70
70
70
70
70
RT
6
100
23
51
29
27
31
12
99
99
99
99
97
99
99
99
commercial h-BN
(B,N)-G
BN
BN
BN
BN
[
b]
[
c]
[
d]
[e]
[
a] Reaction conditions: 1 (1 mmol), ethanol (3 mL), oxygen purged, pro-
moter (10 mg), t=8 h; [b] Boron and nitrogen-codoped graphene; [c] Re-
action performed in the presence of 100 mg of N-tert-butyl-a-phenyl-
nitrone; [d] Reaction under inert atmosphere; [e] Reaction under air at-
mosphere.
the system. Similarly, the conversion of 1 to 2 was found to
depend on the oxygen pressure in the system (cf. entries 2, 6,
and 7 in Table 1).
The heterogeneity of the reaction was addressed by using
the hot filtration test. After achieving approximately 31% con-
version of 1, BN was removed from the reaction mixture
through filtration while it was hot and the resultant reaction
mixture was allowed to react further in the absence of solid
(Figure 4). Notably, the conversion of 1 reaches to 70% after
8 h. This result indicates that the process follows an autoxida-
tion mechanism with a radical chain involving thiyl radicals
generated by the promoter. Thus, these experiments clearly es-
tablish that BN platelets act as radical initiators rather than as
true catalysts. However, the effect of the amount of BN on the
conversion indicates that there is the population of thiyl radi-
cals generated that depends quasi-linearly on the amount of
BN present in the system.
1
was reduced if the reaction was performed in the presence
of air at atmospheric pressure instead of pure oxygen. These
data clearly indicate the active role of the molecular oxygen as
the oxidant in this reaction. In contrast, 12% conversion of
1
was observed if the aerobic oxidation was performed at
room temperature. In addition, a control experiment of the
aerobic oxidation of 1 to 2 with BN as a promoter was per-
formed in the presence of the radical scavenger N-tert-butyl-a-
phenylnitrone, and only 29% conversion of 1 was observed;
this result confirms that the process involves radicals as inter-
mediates that can be quenched by the phenylnitrone.
The effect of the amount of BN as a promoter under the
general reaction conditions was investigated. As shown in
Figure 3, the temporal profile of the reaction at 708C in etha-
nol depends on the amount of BN platelets, and the conver-
sion at a given time decreases as the amount of BN present in
the system decreases from 10 to 3 mg. The initial reaction rate
estimated at 2 h from the time–conversion plot follows
a quasi-linear relationship with the amount of BN present in
BN was reused for the aerobic oxidation of 1 to 2 under
identical conditions. Unfortunately, the sample showed a con-
siderable decrease in the conversion of 1 from 100 to 28% in
the second run. The recovered solid was further analysed by
using TEM. A comparison of the TEM images of the fresh and
used BN materials is shown in Figure 5. As shown in the figure,
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Table 2. Aerobic oxidation of various thiols (R-SH; see R in the table) to
[
a]
their corresponding disulfides promoted by BN platelets.
Entry
R
t
Conversion
[%]
Selectivity
[%]
[
h]
1
2
3
4
5
6
7
8
9
C
6
H
5
8
5
8
9
24
22
6
100
99
100
99
90
99
100
54
32
99
99
99
99
97
99
99
99
99
4-CH
4-Cl-C
4-OCH
4-F-C
2-pyridyl
2-naphthyl
benzyl
1-hexyl
3
-C
6
H
4
6
H
4
3
6 4
-C H
6
H
4
23
48
[
a] Reaction conditions: thiol (1 mmol), ethanol (3 mL), oxygen purged,
BN (10 mg), T=708C.
Figure 4. Time–conversion plot for the oxidation of 1 at 708C a) in the pres-
ence of BN and b) in the hot filtration test in which the reaction is initiated
in the presence of BN up to 3 h and then the solid removed while hot and
the reaction continued in the absence of BN.
under the general reaction conditions in only 6 h. As expected,
in view of the relative stability of the corresponding thiyl radi-
cals, aliphatic thiols were less reactive than aromatic thiols. For
example, benzyl mercaptan exhibited 54% conversion after
2
4
3 h; in contrast, 1-hexanethiol showed 32% conversion after
8 h.
Conclusions
Boron nitride (BN) platelets of 30–80 nm in size are prepared
by using the pyrolytic preparation method based on the tem-
plating effect of chitosan; these BN nanoplatelets are readily
suspended in ethanol and conventional organic solvents,
which enables us to study their activity. Similarly to graphene
that has the same structure, BN platelets were found to pro-
mote the aerobic autoxidation of thiols to disulfides, a reaction
that typically leads to poisoning of transition-metal catalysts.
The evidence indicates that the activity of BN as an initiator
derives from the dispersion of BN as nanometric platelets and
is lost under the reaction conditions owing to massive agglom-
eration. As the activity of BN used to promote reactions re-
mains unexplored, our study can open new avenues to delin-
eate the potential of BN in catalysis and to determine the
nature of the active sites that can be present in this 2D nano-
material.
Figure 5. TEM images at two different magnifications of a and b) fresh and
c) used BN platelets in the reaction of 1 to 2.
fresh BN platelets show the expected layered morphology.
Upon the use of BN as a promoter, its morphology changes
drastically and the material becomes agglomerated, also show-
ing the appearance of some nanoparticles. This drastic change
in morphology explains the origin of the loss of the activity of
BN used as an oxidation promoter.
Experimental Section
Synthesis of h-BN nanoplatelets
h-BN powders were obtained through the precipitation of chitosan
The scope of BN as a radical initiator was studied by testing
the reactivity of different aromatic and aliphatic thiols under
optimal conditions (Table 2). 4-Fluoro-, 4-chloro-, 4-methyl-,
and 4-methoxythiophenol reached higher than 90% conver-
sion with 99% selectivity towards the corresponding disulfide.
Even heterocyclic 2-mercaptopyridine showed 99% conversion
to the corresponding disulfide with very high selectivity, al-
though it requires long time. 2-Napthylthiol showed complete
conversion and selectivity towards the corresponding disulfide
(1.12 g dissolved in 25 mL of 0.3m HAcO) and H BO (0.45 g) solu-
tion in a NH OH aqueous solution (25%). The resulting spheres
4
3
3
were pyrolysed under argon flow (increasing the temperature up
À1
to 9008C; heating rate: 0.98Cmin ) and subsequently calcined in
À1
air up to 10008C (heating rate: 88C min ). Then, h-BN powders
were subjected to exfoliation by sonication. Exfoliation was per-
formed by suspending h-BN powders in water and sonicating
them with an ultrasound source (400 W) for 3 h. The resulting dis-
persion was left to stand for approximately 24 h to allow any un-
stable aggregates to form and precipitate. Subsequently, the sus-
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pension was centrifuged at 1500 rpm for 30 min to obtain a homo-
geneous dispersion that was indefinitely persistent.
[1] J. Pyun, Angew. Chem. Int. Ed. 2011, 50, 46; Angew. Chem. 2011, 123, 46.
[
[
2] A. Schaetz, M. Zeltner, W. J. Stark, ACS Catal. 2012, 2, 1267.
3] C. Su, M. Acik, K. Takai, J. Lu, S.-J. Hao, Y. Zheng, P. Wu, Q. Bao, T. Enoki,
Y. J. Chabal, K. P. Loh, Nat. Commun. 2012, 3, 757–766.
4] D. R. Dreyer, C. W. Bielawski, Chem. Sci. 2011, 2, 1233.
5] S. Navalon, A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Chem. Rev. 2014,
114, 6179.
[
[
Characterisation techniques
The Raman spectra were recorded on a Renishaw in Via Raman
spectrometer equipped with a charge coupled device detector at
ambient temperature using a 514 nm laser excitation. The TEM
images were acquired with a Philips CM300 FEG system operating
at a voltage of 100 kV. The X-ray photoelectron spectra were re-
corded on a SPECS spectrometer equipped with a PHOIBOS 150
MCD-9 detector using a non-monochromatic X-ray source (Al and
Mg) operating at 200 W. The samples were evacuated in the pre-
[6] S. Z. Butler, S. M. Hollen, L. Cao, Y. Cui, J. A. Gupta, H. R. Gutierrez, T. F.
Heinz, S. S. Hong, J. Huang, A. F. Ismach, E. Johnston-Halperin, M. Kuno,
V. V. Plashnitsa, R. D. Robinson, R. S. Ruoff, S. Salahuddin, J. Shan, L. Shi,
M. G. Spencer, M. Terrones, W. Windl, J. E. Goldberger, ACS Nano 2013,
7, 2898.
[
[
7] A. Nag, K. Raidongia, K. P. S. S. Hembram, R. Datta, U. V. Waghmare,
C. N. R. Rao, ACS Nano 2010, 4, 1539.
8] C. N. R. Rao, H. S. S. R. Matte, U. Maitra, Angew. Chem. Int. Ed. 2013, 52,
13162; Angew. Chem. 2013, 125, 13400.
À9
chamber of the spectrometer at 1ꢁ10 mbar (1 mbar=0.1 kPa).
Some of the samples were activated in situ under N flow at 4508C
for 3 h followed by evacuation at 10 mbar. The measured intensi-
[9] C. N. R. Rao, A. Nag, Eur. J. Inorg. Chem. 2010, 4244.
[10] M. Xu, T. Liang, M. Shi, H. Chen, Chem. Rev. 2013, 113, 3766.
2
À8
[
[
[
[
11] C. Zhi, Y. Bando, C. Tang, H. Kuwahara, D. Golberg, Adv. Mater. 2009, 21,
889.
12] X. Wang, C. Zhi, L. Li, H. Zeng, C. Li, M. Mitome, D. Golberg, Y. Bando,
Adv. Mater. 2011, 23, 4072.
13] A. Primo, S. Navalon, A. M. Asiri, H. Garcia, Chem. Eur. J. DOI: 10.1002/
chem.201405469.
14] E. Zysman-Colman, D. N. Harpp, J. Org. Chem. 2005, 70, 5964.
ty ratios of components were obtained from the area of the corre-
sponding peaks after a non-linear Shirley-type background subtrac-
tion and corrected by the transmission function of the spectrome-
ter. The XRD patterns were obtained with a Philips X’Pert X-ray dif-
fractometer using CuKa radiation (l=1.541178 ꢂ). AFM measure-
ments were performed with a Veeco AFM apparatus operating in
contact mode in air at ambient temperature. Notably, AFM meas-
urements were not performed in a clean room and therefore films
on glass substrates might have contained dust that could be de-
tected by these techniques.
2
[15] R. J. Cremlyn in An Introduction to Organosulfur Chemistry, Wiley, New
York, 1996.
[16] G. H. Whitham in Organosulfur Chemistry, Oxford University Press,
Oxford, 1995.
[
[
17] S. Ghammamy, M. Tajbakhsh, J. Sulfur Chem. 2005, 26, 145.
18] L. Bischoff, C. David, L. Martin, H. Meudal, B.-P. Roques, M.-C. Fournie-Za-
luski, J. Org. Chem. 1997, 62, 4848.
19] J. Zhao, H. Fang, J. Han, Y. Yi Pan, G. Guigen Li, Adv. Synth. Catal. 2014,
DOI: 10.1002/adsc.201400032.
Reactivity tests
[
A 50 mL round bottom flask was charged with the solid (10 mg) in
ethanol (3 mL) and subjected to sonication (150 W) for 30 min.
Thereafter, the substrate (1 mmol) was added to the dispersion
and the flask immersed into an oil bath preheated at the reaction
temperature, 708C in most of the experiments. This reaction mix-
ture was purged with oxygen from an inflated balloon. Then, it
was continuously stirred magnetically. The reaction was monitored
periodically by analysing the sample using GC until the completion
of the reaction. The aliquots were filtered through a 0.2 mm nylon
filter and analysed immediately without delay. The mass balances
of the final reaction mixture accounted for more than 97% of the
initial substrate, as confirmed by GC using nitrobenzene as the ex-
ternal standard. The yields of the product were determined with
nitrobenzene as the external standard, considering the response
factors to be unity. In most of the cases, the expected disulfide
with an acceptable purity was obtained directly from the reaction
mixture without further purification.
[
[
[
[
[
[
[
[
20] F. Hosseinpoor, H. Golchoubian, Catal. Lett. 2006, 111, 165.
21] N. A. Noureldin, M. Caldwell, J. Hendry, D. G. Lee, Synthesis 1998, 1587.
22] M. H. Ali, M. McDermott, Tetrahedron Lett. 2002, 43, 6271.
23] A. R. Ramesha, S. Chandrasekaran, J. Org. Chem. 1994, 59, 1354.
24] A. R. Hajipour, S. E. Mallakpour, H. Adibi, J. Org. Chem. 2002, 67, 8666.
25] H. Golchoubian, F. Hosseinpoor, Catal. Commun. 2007, 8, 697.
26] S. M. S. Chauhan, A. Kumar, K. A. Srinivas, Chem. Commun. 2003, 2348.
27] K. Tanaka, K. Ajiki, Tetrahedron Lett. 2004, 45, 25.
[28] A. Dhakshinamoorthy, M. Alvaro, H. Garcia, Chem. Commun. 2010, 46,
6476.
[
29] D. R. Dreyer, H.-P. Jia, A. D. Todd, J. Geng, C. W. Bielawski, Org. Biomol.
Chem. 2011, 9, 7292.
[
[
30] T. Chatterjee, B. C. Ranu, RSC Adv. 2013, 3, 10680.
31] A. Dhakshinamoorthy, S. Navalon, D. Sempere, M. Alvaro, H. Garcia,
ChemCatChem 2013, 5, 241.
[
[
32] A. Corma, T. Rodenas, M. J. Sabater, Chem. Sci. 2012, 3, 398.
33] D. R. Dreyer, H.-P. Jia, C. W. Bielawski, Angew. Chem. Int. Ed. 2010, 49,
6813; Angew. Chem. 2010, 122, 6965.
[
[
34] H.-P. Jia, D. R. Dreyer, C. W. Bielawski, Tetrahedron 2011, 67, 4431.
35] H.-P. Jia, D. R. Dreyer, C. W. Bielawski, Adv. Synth. Catal. 2011, 353, 528.
Acknowledgements
[36] A. Dhakshinamoorthy, M. Alvaro, P. Concepcion, H. Garcia, Catal.
Commun. 2011, 12, 1018.
[
37] A. Primo, P. Atienzar, E. Sanchez, J. Maria Delgado, H. Garcia, Chem.
Commun. 2012, 48, 9254.
38] A. Primo, E. Sanchez, J. M. Delgado, H. Garcia, Carbon 2014, 68, 777.
A.D. thanks the University Grants Commission, New Delhi, for the
award of Assistant Professorship under UGC-Faculty Recharge
Programme. We gratefully acknowledge financial support by the
Spanish Ministry of Economy and Competitiveness (grant no.
CTQ-2012-32315 and Severo Ochoa) and Generalidad Valenciana
[
[39] K. K. Kim, A. Hsu, X. Jia, S. M. Kim, Y. Shi, M. Hofmann, D. Nezich, J. F. Ro-
driguez-Nieva, M. Dresselhaus, T. Palacios, J. Kong, Nano Lett. 2012, 12,
161.
(
Prometeo 2012-014). This research has received partial funding
from the European Community’s Seventh Framework Programme
FP7/2007-2013) (grant agreement no. 228862).
(
Received: October 30, 2014
Revised: December 5, 2014
Published online on && &&, 0000
Keywords: autoxidation · boron · graphene · nanoparticles ·
transition metals
ChemCatChem 0000, 00, 0 – 0
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&
These are not the final page numbers! ÞÞ

FULL PAPERS
A. Dhakshinamoorthy,* A. Primo,
I. Esteve-Adell, M. Alvaro, H. Garcia*
Aerobics is fun: Boron nitride nano-
platelets prepared through pyrolysis
and sonication demonstrate higher cat-
alytic activity for the aerobic oxidation
of thiophenol.
&& – &&
Boron Nitride Nanoplatelets as a Solid
Radical Initiator for the Aerobic
Oxidation of Thiophenol to
Diphenyldisulfide
&
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www.chemcatchem.org
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ꢀ 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!