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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