synchrotron or inverse Compton emission from
the jet already observed in the radio band (23).
Unfortunately, current knowledge of the jet at
radio wavelengths does not allow discriminating
between the two processes.
To have such a clear polarimetric signal, the
magnetic field has to be coherent over a large
fraction of the emission site (5). Such a coherent
magnetic-field structure may indicate a jet origin
for the gamma rays above 400 keV (24). In addition, because the gamma rays emitted in BH x-ray
binaries are generally thought to be emitted close
to the BH horizon (7, 25), and because the synchrotron photons we observed in the hard tail are
too energetic to be effectively self-Comptonized,
these observations might be evidence that the jet
structure is formed in the BH vicinity, possibly
in the Compton corona itself. Another possibility is that the gamma rays are produced in the
initial acceleration region in the jet, as observed
at higher energies by the Fermi Large Area Telescope from the microquasar Cygnus X-3 (26).
The spectrum observed above 400 keV is
consistent with a power law of photon index 1.6 T
0.2. This means that this spectrum, if due to synchrotron or inverse Compton emission, is caused
by electrons whose energy distribution is also a
power law with an index p of 2.2 T 0.4 (27),
consistent with the canonical value for shock-accelerated particles p = 2. Synchrotron radiation
at MeV energies implies also that the electron
energy, for a magnetic field of 10 mG, which is
reasonable for this kind of system (28), would
be around a few TeV (27, 29). Inverse Compton
scattering of photons off these high-energy TeV
electrons, whose lifetime due to synchrotron energy loss is about 1 month (27), could also be the
origin of the TeV photons detected from Cygnus
X-1 with the Major Atmospheric Gamma-ray
Imaging Cerenkov telescope experiment (30) and
possibly also the gamma rays claimed by Astro-rivelatore Gamma ad Immagini Leggero/Light
Imager for Gamma-Ray Astrophysics (31).
The position angle (PA) of the electric vector, which gives the direction of the electric field
lines projected onto the sky, is 140° T 15°. This
is at least 100° away from the compact radio jet,
which is observed at a PA of 21° to 24° (32). Such
deviations between the electric field vector and
jet direction are also found in other jet sources,
such as Active Galactic Nuclei (33) or the galactic source SS433 (34).
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5 million seconds, which is ~58 days.
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Acknowledgments: ISGRI has been realized and maintained
in flight by CEA-Saclay/IRFU with the support of Centre
National d’Etudes Spatiales. Based on observations with
INTEGRAL, a European Space Agency (ESA) project with
instruments and science data center funded by ESA
member states (especially the Principal Investigator
countries: Denmark, France, Germany, Italy, Switzerland,
and Spain), Czech Republic and Poland, and with the
participation of Russia and the United States. We
acknowledge partial funding from the European Commission under contract ITN 215212 “Black Hole
Universe” and from the Bundesministerium für Wirtschaft
und Technologie under Deutsches Zentrum für Luft-und Raumfahrt grant 50 OR 1007. K.P. acknowledges
support by NASA’s INTEGRAL Guest Observer grants
NNX08AE84G, NNX08AY24G, and NX09AT28G. We thank
S. Corbel for useful comments.
23 November 2010; accepted 3 March 2011
Published online 24 March 2011;
Hydrogenolysis of Aryl Ethers
Alexey G. Sergeev and John F. Hartwig*
Selective hydrogenolysis of the aromatic carbon-oxygen (C-O) bonds in aryl ethers is an unsolved
synthetic problem important for the generation of fuels and chemical feedstocks from biomass and for
the liquefaction of coal. Currently, the hydrogenolysis of aromatic C-O bonds requires heterogeneous
catalysts that operate at high temperature and pressure and lead to a mixture of products from
competing hydrogenolysis of aliphatic C-O bonds and hydrogenation of the arene. Here, we report
hydrogenolyses of aromatic C-O bonds in alkyl aryl and diaryl ethers that form exclusively arenes and alcohols.
This process is catalyzed by a soluble nickel carbene complex under just 1 bar of hydrogen at temperatures
of 80 to 120°C; the relative reactivity of ether substrates scale as Ar-OAr>>Ar-OMe>ArCH2-OMe (Ar, Aryl; Me,
Methyl). Hydrogenolysis of lignin model compounds highlights the potential of this approach
for the conversion of refractory aryl ether biopolymers to hydrocarbons.
References and Notes
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Astrophys. J. 547, 1024 (2001).
8. K. Ebisawa, Y. Ueda, H. Inoue, Y. Tanaka, N. E. White,
Astrophys. J. 467, 419 (1996).
Selective hydrogenolysis of aromatic carbon- oxygen (C-O) bonds (scission by reaction with hydrogen to form CH and OH bonds
in their place) is challenging because of the
strength and stability of these linkages (1); yet,
this process is important for the conversion of
oxygen-rich lignocellulosic plant biomass to de-
Department of Chemistry, University of Illinois, 600 South
Matthews Avenue, Urbana, IL 61801, USA.
*To whom correspondence should be addressed. E-mail:
oxygenated fuels and commercial chemicals (2–5).
Whereas the exclusively aliphatic C-O bonds in
cellulose can be cleaved with hydrolysis and
dehydration (3), the aromatic C-O bonds in lignin
cannot undergo these processes and have resisted selective cleavage by hydrogen (2, 4). In
addition, brown coal’s polymeric network contains aromatic C-O bonds inherited from lignocellulosic biomass, and the liquefaction of these
bonds could facilitate the liquification of this carbon source and its conversion to arene feedstocks
(6). A general, mild method for reductive cleav-